Environmental engineers handbook - Chapter 8 pdf

Controlling Iron with Bacteria Removing Iron Salts Methylation of Inorganic Mercury Methods of Removal from Water Boiler Blowdown Water Spent Caustics from Refineries Phenolic Sulfid

Activated Carbon Adsorption Reverse Osmosis

Incineration Research Trends

Phenol

Solvent Extraction Biological Treatment Carbon Adsorption Chemical Oxidation

8.3REMOVING INORGANIC CONTAMINANTS Aluminum

Contaminants

I.M Abrams | D.B Aulenbach | E.C Bingham | L.J Bollyky | T.F.

| R.G Gantz | W.C Gardiner | L.C Gilde, Jr | E.G Kominek |

D.H.F Liu | A.F McClure, Jr | F.L Parker | R.S Robertson |

Controlling Iron with Bacteria

Removing Iron Salts

Methylation of Inorganic Mercury

Methods of Removal from Water

Boiler Blowdown Water

Spent Caustics from Refineries

Phenolic

Sulfidic

Steel Mill Pickle Liquor

The Pickling Process

Disposition of Spent Liquor

8.5OIL POLLUTION Effects on Plant and Animal Life

Toxicity Marine Organisms Plants and Oil

Sources and Prevention

Oily Materials Detection, Identification, and Surveys

Prevention

Methods of Control

Characteristics and Composition Mechanical Containment Mechanical Recovery Application of Agents

8.6PURIFICATION OF SALT WATER Conversion Processes

Desalination Plants Desalting Processes

Multieffect Evaporation Vapor Compression Evaporation Multiflash Evaporators

Freezing Processes

Vacuum-Freeze Vapor pression

Com-Reverse Osmosis Electrodialysis The Future of Desalination

8.7RADIOACTIVE LIQUID WASTETREATMENT

Low-Activity Wastes

Precipitation Ion Exchange Evaporators Dilution and Release Hydrofracture Bituminization

High-Activity Wastes

Generation Storage in Tanks Conversion to Solids Storage

Algae Control

The types of algae and the concentration in wastewater

depend on residence time, climate and weather, amount

of pollutants entering the pond, and dimensions of the

pond Normally, small unicellular types of algae develop

first, e.g., Chlorella Because of their physical dimensions

they are difficult to remove by the processes listed in Table

8.1.1 Longer residence times lead to the development of

larger algae and other plankton, which is more readily

moved The algae concentration affects the choice of

re-moval process and the rate of treatment Because of their

light density, the dried weight of suspended solids is not

an efficient measure of concentration Algae are normally

measured in volumetric or areal standard units (Anon

1971) In surface water supplies, concentrations may be

as high as 30,000 cells per milliliter (ml), this can be much

higher in nutrient-rich waste treatment effluents A

com-bination of processes may be the best treatment, e.g.,

cop-per sulfate addition and microstraining, as used on surface

water supplies in London, England

Carbon Particles

Carbon particulate matter suspended in waste effluent

must be either controlled or removed prior to discharge

Wastes associated with the carbon black and acetylene

in-dustries are of concern These wastes may contain up to

1000 milligrams per liter (mg/l) carbon particles in

sus-pension; in most cases this carbon concentration must be

reduced to less than 50 mg/l suspended solids Usually,these solids settle readily and are removed by gravity set-tling and/or flotation

Individual particle sizes range from a submicron tolarger than 100 micron (m) Larger particles settle, whereassmaller particles float Transition size particles remain sus-pended almost indefinitely unless forced out of suspension

by mechanical or chemical means Unless a highly fied effluent is required, suspended matter may not have

clari-to be removed as it amounts clari-to a small proportion of clari-tal solids concentration

to-GRAVITY SETTLINGTwo types of gravity systems are available: (1) settlingLagoons, which provide retention time for solid particles

to settle as sludge These must be cleaned periodically; and(2) mechanical Clarifiers, which remove suspended solidsand also rid bottom sludges mechanically

The settling lagoon requires a minimum capital ment Cleanout costs are high compared with the me-chanical clarifier operating costs

invest-Settling devices are usually designed on the basis of flow rate, gal per day (gpd) per sq ft of surface area.According to the Ten State Standards (Great Lakes-UpperMississippi River Board of State Sanitary Engineers 1968),this rate should be in the range of 600 to 1000 gpd/sq ft

over-In designing the carbon settling lagoon, frequency of goon cleaning must be considered, and the lagoon must

la-be sized accordingly Carbon sludge will settle to a sity of 5–20% solids

den-8.1

REMOVING SUSPENDED SOLID CONTAMINANTS

Algae Removal Process Advantages Limitations

Copper sulfate Simple and inex- Creates toxicity; only some algal

pensive forms attacked Chlorine Simple and inex- High doses needed; not all algae

pensive attacked Coagulation and Positive removal of High chemical doses needed; dif- settling all types of algae ficult sludges produced Sand filters Positive removal of Rapid filter clogging may occur

all types of algae Microstraining Simple and inex- Not all algal forms removed

pensive Air flotation Positive removal of Not all algal forms removed;

all types of algae sludges may be difficult to handle

As an example, a 5-acre lagoon, 5 ft deep, with an

in-fluent suspended solids concentration of 1000 mg/l and an

effluent concentration of 50 mg/l at a flowrate of 10 mgd

will retain almost 80,000 lb of solids per day If the solids

settle to a 5% sludge density, the lagoon will be filled with

sludge in less than two months, as indicated by the

calcu-lations in Table 8.1.2 A settling lagoon design for this

ap-plication would probably be based on cleaning frequency

rather than on overflow rates

The outfall structure of a settling system should retain

floating material and maintain laminar flow to prevent

solids from resuspending at discharge due to turbulence

An underflow-overflow weir (Figure 8.1.1) efficiently

pro-vides such an outfall According to the Ten State Standards

(Great Lakes–Upper Mississippi 1968), weir loading rates

should not exceed 10,000 gpd per linear ft of weir to

as-sume minimum resuspension of settled matter from

tur-bulent flow For the example in Table 8.1.2, a weir 1000

ft long would be required

SOLIDS DISPOSAL

Whether a mechanical clarifier, a settling lagoon or other

means of solids removal is utilized, concentrated carbon

slurry or sludge must be disposed of Disposal methods

in-clude incineration, landfill disposal, reuse, and dewatering

Removal and disposal of concentrated solids slurry is the

most difficult part of the carbon clarification system

Eliminating waste at the source is ideal Tightening

pro-duction controls and modifying the process can drastically

reduce waste losses and should be investigated before anyremoval system is developed No treatment system is jus-tifiable without assurance that waste production is mini-mized at the source Frequently, waste carbon is a prod-uct loss, and recovery is valuable Keeping carbon out ofwastewater prevents problems in waste treatment

Foundry SandFoundry melting emissions contain solid particles rangingfrom coarse dust to fines of submicron size Cupola emis-sions are much coarser than electric furnace emissions,which are generally less than 5 m

Foundry melting dusts include combustibles containing20–30% carbonaceous material Iron oxides account fornearly 60% of collected dusts; silica and miscellaneousmetallic oxides account for smaller quantities

CALCULATION

Settling Lagoon Data:

Area 5 5 acres Depth 5 5 ft Flow 5 10 million gal/day (mgd) Influent concentration 5 1000 mg/l Effluent concentration 5 50 mg/l Sludge density 5 5%

Carbon deposited per day:

(1000 2 50) 3 10 3 8.34 5 80,000 lb/day Lagoon volume:

V 5 5 acre 3 5 ft 5 25 acre-ft 5 8.3 3 10 6

gal Solids capacity of lagoon at 5% sludge density:

5% 5 50,000 mg/l 5 0.42 }

g

lb

al } Capacity 5 0.42 }

g

lb

al } 3 8.3 3 10 6 gal 5 3.5 3 10 6

lb solids Time required to fill lagoon with sludge:

8

3 3

.5 1

3

0 4

1 l

0 b

6

/d

lb ay } 5 44 days

FIG 8.1.1 Settling lagoon outfall structure.

Water curtains and scrubbers are used to remove solids

from foundry stack gases Wet scrubbers also remove

acidic compounds Scrubber water is treated to neutralize

acids and to remove solids prior to recirculation Settled

solids are vacuum filtered prior to disposal Most foundries

have a number of scrubbers working on different

opera-tions, and all effluents are combined and treated together

In grinding and shakeout areas, the scrubber may be

ei-ther cyclonic or water curtain, which tolerates dirty

feed-water However, abrasive materials of 1200 mesh should

be removed to avoid abrasion of circulating pumps

For complete solids removal—down to smoke particles

from cupola emission gas—high-energy scrubbers such as

Venturis are required, which need clean water Cupola

cooling water should also be clean to prevent heat

ex-change surface fouling If water is used for slag

quench-ing, a mass of porous particles up to 1 /4 in is produced

These usually float Casting washing produces a slurry

with 1150 mesh sand Most of these materials can be

sep-arated on a vibrating screen of approximately 50 mesh

Depending on the recirculation system, grit separators,

settling basins, or clarifiers are used A hydroseparator

re-moves fine sand down to approximately 50 m Removal

of finer solids requires chemical treatment with lime, alum,

and possibly a polyelectrolyte to produce clarified effluent

containing 10–20 mg/l of suspended solids Disc, drum, or

belt filters are used for dewatering foundry waste solids

Filter rates range from 25–40 lb of dry solids/hr/sq ft

Some foundries have sand scrubber wastes This differs

from dust collection water as it settles more slowly

Overflow rates of no more than 0.3–0.5 gpm/sq ft can be

used Filtration rates for sand scrubber wastes vary from

3–10 lb of solids/hr/sq ft

Laundry Wastes

THE PROBLEM OF COMMERCIAL

WASTE

Commercial coin-operated laundry installations pose

problems when sewers are not available, and septic tank

or leach field systems are utilized Because of the small

amount of land available for liquid waste discharge,

ad-ditional treatment is necessary Treated effluent reuse

should also be considered

Table 8.1.3 indicates typical waste flow (Flynn and

Andres 1963) from laundry installations on Long Island,

N.Y A typical installation of 20 machines produces 4,000

gpd Depending on soil conditions, this volume might

re-quire a much larger disposal area than is available Table

8.1.4 describes typical laundry waste properties and

com-position as resembling weak sewage with the exception of

high alkyl benzyl sulfonate (ABS) and phosphate contents

Large quantities of water are required for washing,

therefore alleviating both water supply and waste disposal

problems via partial or complete recycling of treated water effluents should be considered

waste-TREATMENT SYSTEMSSeptic Tanks

Septic tanks followed by leach field systems are often adequate to process the quantity and quality of water to

in-be disposed

Physical MethodsAll laundry waste should be strained in a removable bas-ket so that lint does not clog pumps and other equipment

in the treatment system

Plan settling of laundry waste removes the heavier gritparticles washed out of clothes Most biological oxygendemand (BOD) is soluble, therefore settling has little ef-fect on the BOD and chemical oxygen demand (COD) ofthe waste

Several types of filtration units are used to treat dromat wastes A sand filter efficiently removes particu-late matter Pressures and filters usually require less spacethan gravity sand filters The latter is used following othertreatment methods and is little different from filtrationthrough soil Filtration through diatomaceous earth filtercake is highly recommended, since it removes bacteria andsome viruses, and is particularly effective in separatingchemical sludges In diatomaceous earth filtration, priorsettling or sand filtration lengthens filter runs but will notresult in a better quality effluent

COIN-OPERATED WASHING MACHINE

Average wastewater flow 89–240 gal/day Maximum average flow 587 gal/day Minimum design basis for

treatment based on a 12–hr day 550 gal/machine

WASTES

Concentration, mg, per liter Parameter Average Range

pH 7.13 5.0–7.6 BOD 120 50–185 COD 315 136–455 ABS (methylene blue active 33 15–144 substance)

Total Dissolved Solids 700 390–1450

Chemical Methods

Coagulation or precipitation followed by settling and/or

filtration has proven effective in treating laundromat

wastes Alum alone at a pH of 4–5 may result in a 75%

reduction in ABS and an 85% reduction in phosphate

con-tent of the waste Iron salts effect a similar reduction,

whereas calcium chloride can reduce ABS by 85%, but

this results in only a 50% reduction in phosphate content

at high doses

In addition, ABS may be completely neutralized,

us-ing a cationic detergent Tests must be performed to

pro-vide exact equalization with no excess of either

deter-gent Substances to perform this are commercially

available Phosphates are effectively removed by

precip-itation techniques Alum, iron salts, and calcium salts at

high pH offer a high degree of phosphate removal Better

than 90% phosphate removal can be obtained by

cal-cium chloride combined with adjusting the pH to 10, or

by lime, both followed by filtration in a diatomaceous

earth filter

Physicochemical Methods

Considered a physicochemical process, ion exchange has

not been successful in producing high quality water for

reuse from laundry waste

Residual organic matter may be effectively removed by

contact with activated carbon Granular carbon in an

up-flow pressure tank seems to be most efficient, although

adding powdered activated carbon to other chemicals prior

to filtration can also be effective Activated carbon is also

effective in removing anionic detergents However, high

ABS concentration exhausts the capacity of activated

car-bon to remove other organic matter, therefore prior

treat-ment to reduce ABS should be applied

Biological MethodsWhen soluble organic material is present, it is difficult toreduce BOD by more than 60% through chemical pre-cipitation and filtration To achieve high degrees of BODremoval, biological treatment may be required Althoughthere is an adequate bacteria food supply of carbon andphosphorus in the waste, total nitrogen content may bedeficient for biological treatment

Solids DisposalChemical precipitation solids and diatomaceous earthsolids are amenable to landfill disposal Biological sludgesare treated similarly to septic tank sludges The sludgeholding tank should be conveniently located for periodicpumping by a local scavenging firm

Suggested Treatment System

A schematic flow diagram for a suggested laundromatwaste treatment system is shown in Figure 8.1.2 Afterscreening lint, waste is stored in a holding tank to equal-ize flow and provide sufficient volume for operating thetreatment system during normal daytime hours A pumpcan deliver waste to the chemical mixing tank where theappropriate chemicals are added A settling tank removesthe bulk of precipitated solids prior to diatomaceous earthfiltration A pump is required to provide pressure for fil-tration in the diatomaceous earth filter Recycling to thechemical mixing tank would be required during the filterprecoat operation

Following filtration, activated carbon adsorption may

be practiced as needed A final storage tank is providedfor adding chlorine if needed or for holding effluent forfuture use Settling tank sludges and diatomaceous earthfilter discharges should be collected in a sludge holding

FIG 8.1.2 Laundry waste treatment

tank and pumped out periodically by a scavenger system.

This system should provide effluent satisfactory for

dis-charge or partial reuse

QUALITY OF EFFLUENT

Chemically precipitated and filtered wastes can be disposed

in a subsurface system, provided that there is adequate

land to accommodate the hydraulic load Biological

treat-ment may be necessary to improve water quality before

discharge into a small stream

Water reuse should be considered because of the large

volume Since chemical coagulants increase total dissolved

solids in water, complete reuse and recycle would

contin-uously increase total dissolved solids Thus, chemicals

should be limited to prevent excess Because the water is

still warm, heat energy can be saved by recycling treated

effluent To control total solids buildup, an ion exchange

system is theoretically applicable However, experience

shows that this system is not effective in treating laundry

waste effluents Other uses for the treated water may be

found, depending on the water requirements of nearby

in-dustries Recharging water into the soil uses the soil’s

nat-ural treatment ability and maintains a high water level in

the aquifer, providing water for the laundromat

Mill Scale

This is a case history of the design, construction, and

op-eration of a wastewater treatment system established to

remove mill scale from water contaminated by steel mill

scale removal operation and to provide a closed system

enabling reuse of water for the mill scale removal

opera-tion

The installed cost of the total system was

approxi-mately $600,000, including two parallel treatment

sys-tems assuring continuous 24-hr operation via available ternate flow patterns for necessary equipment repair ormaintenance

al-DESIGN PARAMETERS

To define the problem, existing system elements were viewed (Figure 8.1.3) The original design specified a once-through system capable of processing an existing flow of

re-3500 gpm with the capability to handle 7000 gpm in thefuture Effluent quality was to meet stringent state re-quirements for discharge to the waterway Applyingknowledge of stream quality to the original design re-quirements raised question about the once-through con-cept It was noted that if process utilization of this waterdid not require a higher quality supply than the pollutedraw river water presently used, the need for a once-throughsystem was questionable

A system to treat this wastewater to meet stage charge standards would be very expensive However, itcost much less to treat this wastewater only to the extentrequired by the process Historically, this requirement wasmet by the quality of a badly polluted stream The costdifference between a reuse system and a once-through dis-charge system is substantial Water quality design stan-dards were key factors in system cost

dis-Table 8.1.5 lists the design parameters Provisions werealso made for sludge and recovered oil handling with min-imal expense and minimal personnel time required Theoriginal process flowsheet is shown in Figure 8.1.4 Aclosed system of this type is susceptible to three primaryproblems: algal accumulation, dissolved solids buildup,and heat buildup

Solving these problems requires bactericide and/or gicide additives, blowdown and addition of makeup wa-ter, and a system cooling tower The original design in-cluded a cooling tower hookup, if required, together with

al-a chemical-al feed system However, mal-akeup wal-ater from the

FIG 8.1.3 Original water supply layout A Original plant

wa-ter supply line (Raw river wawa-ter was used without pretreatment

for mill scale removal process.)

SCALE WATER TREATMENT PLANT a

Wastewater Flow 3500 gpm existing

7000 gpm design capability Primary Pollutants Iron solids (fines)

Oil Heat Treated Effluent Quality Continuous 24-hr reuse Required capability

Acceptable Pollutant Content Iron (suspended solids)

in Effluent 600 ppm

Oil 150 ppm (plus freefloating oil)

a System to be as fully automatic as possible.

river was thought sufficient to compensate for evaporative

losses and to control dissolved solids buildup Dissolved

solids presented no serious problem

OPERATIONAL HISTORY

In operation, the system is entirely satisfactory The

cool-ing tower was not installed originally because heat loss

through the system—due to the length of the lines and the

surface area of the tanks—was considered sufficient

During most of the operating time, this was true However,

during summer when ambient surface air temperatures

oc-casionally reach 110° to 115°F in this region, Joliet, Ill.,

heat loss was not enough to maintain comfort for

per-sonnel manning the spray nozzles in the plant During such

periods, return water temperature rose to 114°F for a few

days Therefore, a cooling tower was installed

The sludge averages 50 to 60% solids, about the

min-imum water content for the sludge to slide easily from the

discharge chutes into catch buckets

Oil-skimming devices are rotary cylinder units mounted

at the water surface level in the tanks These units requireheat protection to prevent freezing in the winter Thesludge is recovered; since it consists primarily of mill scale,

it can be sold as blast furnace charging material

Strainers are 0.005 in units with 5,000 gpm capacityeach These are in the system for insurance in the event ofheavy overloading of the settling tanks This might occur

if one of the two parallel systems was shut down for pump

or ejection mechanism repairs when the mill is operating

at peak capacity

Until now, the system has performed well, except forminor startup and training problems Mill operating per-sonnel are pleased, because return water quality is far bet-ter than the raw river water they were using

Mineral TailingsWastewater from mining or ore beneficiation contains sus-pended particles of fine sand, silt, clay, and possible lime-stone A large percentage of solids may be colloidal due

to their nature or as a result of milling and flotation

pro-FIG 8.1.4 Reuse system on steel plant water (P 5 pump; F

5 filter)

TABLE 8.1.6 SETTLING VELOCITY OF SILT AND

SAND PARTICLES IN TERMS OF APPLICABLE OVERFLOW RATES

cessing with reagents added to disperse the solids Table

8.1.6 shows the velocities at which particles of sand and

silt subside in still water (American Water Works

Asso-ciation 1969) at 50°F

Collodial particles cannot be removed by settling

with-out chemical treatment Because of the chemicals added

in milling and during flotation, it is virtually impossible

to economically clarify mineral tailings, and mineral

tail-ing overflows from thickener clarifiers are usually

re-tained indefinitely Figure 8.1.5 illustrates thickener

de-sign used in alumina, steel, coal, copper, and potash

processing

—E.W.J Diaper, T.F Brown, Jr.,

E.G Kominek, D.B Aulenbach, C.A Caswell

laun-Purdue University, Lafayette, Ind (May 5–7).

Aulenbach, D.B., M Chilson, and P.C Town 1971 Treatment of Laundromat Wastes, Part II Proceedings, 26th Industrial Waste

Conference Purdue University, Lafayette, Inc (May 4–6).

Burns and Roe, Inc 1971 Process design manual for suspensed solids removal Environmental Protection Agency Technology Transfer.

Flynn, J.M and B Andres 1963 Launderette waste treatment processes.

J.W.P.C.F., 35:783.

Great Lakes–Upper Mississippi River Board of State Sanitary Engineers.

1968 Recommended standards for sewage works.

8.2

REMOVING ORGANIC CONTAMINANTS

Aldehydes

Aldehydes have several properties important to water

pol-lution control Saturated aldehydes are readily biodegraded

and represent a rapid oxygen demand on the ecosystem,

whereas unsaturated aldehydes can inhibit biological

treat-ment systems at low concentrations Aldehyde volatility

makes losses through air stripping an important

consider-ation

BIOLOGICAL OXIDATION

Aldehyde amenability to biodegradation is indicated by

high biochemical oxygen demand (BOD) levels reported

by several investigators At a low test concentration,

formaldehyde, acetaldehyde, butyraldehyde,

crotonalde-hyde, furfural, and benzaldehyde all exhibited substantial

biooxidation (Heukelekian and Rand 1955; Lamb and

Jenkins 1952) An olefinic linkage in the a,b position

usu-ally renders the material inhibitory (Stack 1957) The

lev-els inhibitory to unacclimated microorganisms for acrolein,

methacrolein and crotonaldehyde were 1.5, 3.5, and 14

mg per liter (mg/l), respectively, whereas levels for

ac-etaldehyde, propionaldehyde and butyraldehyde were 500

mg/l or above Formaldehyde was inhibitory at 85 mg/l

Bacteria can develop adaptive enzymes to allow

bio-logical oxidation of many potentially inhibitory aldehydes

to proceed at high influent levels Stabilization by

accli-mated organisms of several organic compounds typical of

petrochemical wastes has been investigated (Hatfield

1957) For organisms acclimated to 500 mg/l hyde, approximately 3 hr aeration time was required tobring the effluent concentration to zero However, efflu-ent organic concentration after this interval was still high,indicating oxidation to formic acid or Cannizzaro dismu-tation to methanol and formic acid Eight to ten hr of aer-ation were required for the effluent BOD to approach zero.Removals of acetaldehyde (measured as BOD) were from

formalde-an initial concentration of 430 to 35 mg/l after a 5 hr ation time Propionaldehyde removals were from 410–25mg/l after five hr The oxidation pattern of paraformalde-hyde, the polymer of formaldehyde, resembled its precur-sor

aer-Data collected through Warburg respirometer studiesusing seed sludges from three waste treatment plants(Gerhold and Malaney 1966) showed that aldehydes wereoxidized to an extent second only to corresponding pri-mary alcohols Only formaldehyde exhibited toxicity to allthree sludges Branching in the carbon chain increased re-sistance to biooxidation

AIR STRIPPINGKinetic data for air stripping of propionaldehyde, bu-tyraldehyde, and valeraldehyde have been presented(Gaudy, Engelbrecht and Turner 1961) Removal of pro-pionaldehyde in model units at 25°C followed first-orderreaction kinetics; removals calculated from residual alde-hyde and residual chemical oxygen demand (COD) analy-ses were parallel, indicating that no oxidation of the acid

occurred However, at 40°C stripping was not described

by first-order kinetics, and propionaldehyde oxidation to

less volatile propionic acid was apparent when removals

measured as COD were less than those measured as

alde-hyde

Stripping of butyraldehyde and valeraldehyde at 25°C

did not follow first-order kinetics, indicating oxidation of

aldehyde to acid may also be occurring Removals after

an 8 hr aeration time at 25°C and an air flow of 900

ml/min/l, were 85% for propionaldehyde and

butyralde-hyde, and 98% for valeraldehyde In a biological system

all three removal mechanisms would exist: biological

ox-idation and synthesis, air stripping, and air oxox-idation The

magnitude of each means would depend primarily on the

activity of the bacterial culture and the degree of

gas-liq-uid contact

CARBON ADSORPTIONAldehydes, due to their low molecular weight and hy-drophilic nature, are not readily adsorbed onto activatedcarbon Typical data from Freudlich isotherm tests of ad-sorbability at various carbon dosage levels are presented

in Table 8.2.1 On a relative basis, aldehydes were lessamenable to adsorption than comparable undissociated or-ganic acids but were more amenable than alcohols (Giusti1971) However, none of the low molecular weight, po-lar, highly volatile materials were readily adsorbed

Cellulose PulpAll pulp mill effluents contain wood extractives, a highlydiverse, ill-defined chemical group that varies widely ac-cording to wood species and origin Chemical pulpingwastes also contain hydrolyzed hemicelluloses and lignin,solubilized during cooking Since various pulp processesvary considerably in mill design and operation, effluentsare extremely diverse

WASTEWATER VOLUMEProblems arise due to the tremendous volumes discharged(Table 8.2.2) Newer installations recycle process waters.Much market pulp is bleached, with bleach plant dis-charges as large as those from pulping Since mills with500–1000 ton/day capacity are not uncommon, volumesdischarged at a single point may be abnormally high

EFFLUENT CHARACTERISTICSPulp effluents usually have an abnormal pH, a variableloading of suspended fibrous solids, and an appreciableoxygen demand (Table 8.2.2) Older mills may have evenheavier loadings Kraft pulping produces alkaline wastes,

ALDEHYDES

Aldehyde Removal from 1000 mg/l Solution at 5 gm/l Carbon Dose Equilibrium

Loading mg/g Removal Carbon Level, %

TABLE 8.2.2 EFFLUENT CHARACTERISTICS OF CELLULOSE PULPING WASTES a

Unit Process U.S gal/ton pH lb/ton lb/ton

Hydraulic debarking 500–10,000 4.6–8.0 5–20 30–50 Groundwood 6,500–10,000 6.0–6.5 10–40 15–80 Neutral sulfite

semichemical pulping

Kraft pulping 6,000–20,000 7.5–10.0 10–50 ,20 Sulfite pulping

(no recovery) 20,000–30,000 2.5–3.5 550–750 150–200 Sulfite pulping

(with recovery) 20,000–30,000 2.5–4.0 50–100 40–60 Bleaching 20,000–40,000 2.0–5.0 10–25 14–25

a Oxygen consumed at 20°C during a 5-day incubation with acclimated microorganisms.

whereas sulfite pulping and bleaching plant wastes are

acidic Chemical recovery is essential in keeping

oxygen-depleting materials low Large calcium bisulfite mill

efflu-ents may have oxygen demands equivalent to 2,000,000

or 3,000,000 people Effluents display some toxicity to

aquatic fauna, albeit of a low order Neutral and higher

pH value effluents are darkly colored, which is

aestheti-cally undesirable and inhibits photosynthesis In smaller

streams, fish downstream from pulp mill outfalls can have

tainted flesh Odor and taste imparted to receiving waters

can also interfere with the subsequent use of the stream

for drinking water Wind and wave action can create foam

on receiving waters, and inorganic salt content may

pre-vent use in irrigation

METHODS OF TREATMENT

No process can alleviate all pulping effluent problems

Abnormal pH is neutralized with slaked lime, calcium

car-bonate or sodium hydroxide, since integrated pulping

ef-fluents are usually acidic (Laws and Burns 1960; Charles

and Decker 1970) Settling removes suspended solids

ex-cept for some mechanically ground “fines.”

All microbiological oxidation systems reduce pulp

ef-fluent oxygen demand, but concurrent removal of acute

toxicity is not related to operating parameters for these

systems Microbiological treatment may not completely

remove substances responsible for tainting fish flesh or

causing odor, foam, and taste in drinking water

Microbiological treatment does not remove color,

how-ever color bodies can be precipitated by massive lime

treat-ment (EPA 1970)

RESEARCH PROBLEMS

Originally, pulping waste treatments were the same as

those used in domestic sewage treatment Problems arise

with pulping effluents because of their variable nature In

short-term microbiological oxidation systems, sludge

re-cycling difficulties may occur Biologists emphasize the

need to remove sublethal toxicity, however the

responsi-ble chemical entities are largely unknown, and means of

measurement are lacking Massive lime treatment has

tech-nical and economic limitations, and specific information

concerning unresolved problems is lacking Thus, a

con-siderable impetus exists for in-process changes or new

processes to minimize current wastewater problems

Food Processing Wastes

Water is absolutely necessary in food processing Through

conservation and reuse, liquid waste is reduced, cutting the

pollution load The National Canners Association has set

four conditions governing the use of reclaimed waters in

contact with food products:

1 the water must be free of microorganisms of publichealth significance

2 the water must contain no chemicals in concentrationstoxic or otherwise harmful to man

3 the water must be free of any materials or compoundsthat could impart discoloration, off-flavor or odors tothe product or otherwise adversely affect quality

4 the water appearance and content must be aesthicallyacceptable

WATER REUSEHistorically, water reuse was given little consideration.Water is relatively abundant in nature and reuse was con-sidered hazardous due to bacterial contamination.Contamination potential (Figure 8.2.1) shows that, inwashing fruit, unless 40% of the water is exchanged eachhour, the growth rate of bacteriological organisms be-comes extremely high To overcome this, other means ofcontrol such as chlorination must be used The importance

of chlorination in maintaining satisfactory sanitary tions is graphically shown in Figure 8.2.2 When chlori-nation was discontinued, the bacterial count more thandoubled As soon as chlorination resumed, bacterial countswere again brought under control

condi-Water conservation can be achieved through flow reuse systems Figure 8.2.3 outlines a counterflow sys-tem for reuse of water in a pea cannery At the upper right,fresh water is used for the final product wash before thepeas are canned From this point, the water is reused andcarried back in successive stages for each preceding wash-ing and fluming (the transport of the fruits by flowing wa-ter in an open channel) operation As the water flows coun-

counter-FIG 8.2.1 Effect of rate of water replacement on growth of mesophilic bacteria at 90°F.

tercurrent to the product, the washing and fluming water

becomes more contaminated; therefore, it is extremely

im-portant to add chlorine At each stage, sufficient chlorine

should be added to satisfy the chlorine demand of the

or-ganic matter in the water

WATER CONSERVATION

Recently, it was determined that adding citric acid to

con-trol the pH of fruit fluming waters reduced water use

with-out increasing bacteria A pH of 4 (Figure 8.2.4) will

main-tain optimum conditions with cut fruit, such as peaches

The system not only reduces the total water volume and

therefore the amount of wastewater discharged, but also

increases product yield due to decreased solids loss from

sugar and acids leaching Consequently, total organic

pol-lutants in the wastewater are reduced Flavor and color of

the canned fruit are also improved because of better

solu-ble solid retention

Closed loop systems, such as the hydrostatic

cooker-cooler for canned product, are another conservation

method The water is reused continuously, with freshmakeup water added only to offset minor losses from evap-oration Closed loop systems not only conserve water butalso reclaim much heat and can result in significant eco-nomic savings

It is not the intent of this section to describe the mous array of concepts and ramifications used in the foodprocessing industry to reduce water and waste loads whilemaintaining product quality Many factors determine thefinal effectiveness of proper water use For example, toma-toes spray-washed on a roller belt where they are turnedare almost twice as clean as the same tomatoes washed on

enor-a belt of wire mesh construction In enor-another exenor-ample,warm water is approximately 40% more effective in re-moving contaminants than the same volume of cold wa-ter

There is a delicate balance between water conservationand sanitation, with no straightforward or simple formulafor the least water use Each process must be evaluatedwith the equipment used to arrive at a satisfactory proce-dure for water use, chlorination, and other factors, such

as detergents

ELIMINATION OF WATER USEEliminating water in certain operations eliminates atten-dant wastewater treatment problems Wherever possible,food should be handled by either a mechanical belt orpneumatic dry conveying system If possible, the foodshould be cooled in an air system Recent studies by theNational Canners Association in comparing hot airblanching of vegetables with conventional hot waterblanching show that both product and environmentalquality were improved by using air Blanching, used to de-activate enzymes, produces a very strong liquid waste For

FIG 8.2.2 Effect of chlorine concentration on bacterial counts

in reused water A Chlorine concentration; B Bacterial counts.

FIG 8.2.3 Four-stage counterflow system in a pea cannery A.

First use of water; B Second use of water; C Third use of

wa-ter; D Fourth use of wawa-ter; E Concentrated chlorine water.

FIG 8.2.4 Effect of pH control on bacterial cell growth.

pea processing, this small volume of wastewater is

esti-mated to be responsible for 50% of the entire wasteload

BOD; for corn, 60%; and for beets with peelings, 80%

Preliminary results show a reduced pollution load (Table

8.2.3), while improving product nutrients, vitamins, and

mineral content

WASTEWATER TREATMENT

Preprocessing

Proper management of food processing wastes requires

consideration of individual operations from harvest

through waste disposal as integrated subunits of the total

process Every effort should be made to eliminate wastes

and to avoid bringing wastes from the farm into the

pro-cessing plant Where possible, prepropro-cessing should occur

in the field, returning the organic materials to the land In

the processing plant, wastewater volume and strength

should be reduced at each step This principle applies to

all food processing wastes, including fruit, vegetables, meat

and poultry, and dairy

Waste segregation within a plant is important in

opti-mizing the least-cost approach to treatment In a typical

brewery (Figure 8.2.5), where 3% of the flow contains

59% of the BOD, it is less expensive to treat this smallflow separately than to mix it with the entire plant wasteflow This is effective when a plant treats its own wastes

or releases waste to a municipality with surcharges forhigh-strength waste

Food processing wastes are amenable to biologicaltreatment, and they frequently provide nutrients essential

to efficient biological treatment Although various wastetreatment methods are available to the food processor(Figure 8.2.6) there is no simple guide for the most prac-tical and economical method

Lagoons and Land Disposal SystemsSince food wastes contain suspended and soluble organiccontaminants, they are readily treated in lagoons and landdisposal systems The lagoons may be complete storageponds, frequently used by seasonal processors for wastecontainment In four to six months, the waste is stabilized,with up to 90% BOD reduction If large lagoon acreage

is available, aerobic conditions are maintained by limitingorganic loadings to less than 100 lb of BOD per acre perday When extremely strong wastes are encountered, acombination of anaerobic and aerobic lagoons provides anexcellent means of treatment on less land, since the anaer-obic system may reduce BOD from 60% to 90%, reduc-ing the aerobic lagoon acreage required to achieve desiredeffluent quality

Anaerobic lagoons are odorous and require an artificial

or natural cover In meat products, the high grease tent forms a natural cover Aerobic lagoons can also causeodors if overloaded and lacking sufficient dissolved oxy-gen Various mechanical aeration methods have reducedrequired lagoon acreage, but these increase power costs.Land disposal can be achieved by flooding; however,the most efficient means is conventional farm spray irri-gation equipment Sandy soil with a high infiltration rateoffers no surface runoff, and no discharge to a receivingstream Recently, an overland flow technique has been de-veloped as an equivalent of tertiary treatment

Blanching Wastewater COD Produced SS Produced Product System gal/ton lb/ton lb/ton

Green peas Hot water 1,000.0 32.70 1.42

Green peas Hot air 0.018 Not measured Not measured Green beans Hot water 1,710.0 4.70 0.11

Green beans Hot air 0.25 0.002 0.0002 Corn on the cob Hot water 1,223.0 4.70 0.041

Red beets Hot water 1,333.0 4.11 0.16

FIG 8.2.5 Source and relative strength of brewery wastes

Canning Wastes

The canning industry uses an estimated 50 billion gal of

water per year to process one billion cases of food Liquid

waste is normally screened as a first step in any treatment

process Solids from these screens can be trucked away as

garbage or collected in a by-products recovery program

Food product washing is the greatest source of liquid

waste The water used is normally reclaimed in a

coun-terflow system, with a final discharge high in soluble

or-ganic matter and containing suspended solids—much of it

inorganic—from the soil Other wastes come from peeling

operations The amount of suspended matter varies with

the type of peeling The type of peeler—steam, lye, or

abra-sive—has an effect on the nature of the waste generated

Normal practices utilize large volumes of water to washaway loosened peelings, creating tremendous suspendedand organic loads in the waste stream Lye peeling alsogenerates wastewater with markedly high caustic alkalineconcentrations Equipment for dry lye peeling of fruits andvegetables removes the lye peelings in a semidry state sothat solids can be handled separately without liquid con-tamination

Raw foods are blanched to expel air and gases fromvegetables; to whiten, soften, and precook beans and rice;

to inactivate enzymes that cause undesirable flavor andcolor changes; and to prepare products for easy filling intocans Little fresh water is added during blanching (8-hrshift), therefore the organic material concentration be-

FIG 8.2.6 Wastewater treatment maze (for organic waste from food processing industries) The diagram illustrates the many tions open to solving waste treatment problems The best route through the maze is suggested by an engineering study and report Such a report discloses possible treatment methods, anticipated influent properties, effluent requirements and costs Most important, the report serves as a mutually agreed-upon criterion with regulatory agencies Designing a waste treatment system should not be considered without such a study and report.

op-comes high due to leaching of sugars, starches, and other

soluble materials Although low in volume, blanch water

is highly concentrated and frequently represents the largest

load of soluble wastes in the entire food processing

oper-ation The amount of dissolved and colloidal organic

mat-ter varies, depending on the equipment used

The last major source of liquid wastes is the washing

of equipment, utensils, and cookers, as well as washing of

floors and food preparation areas This wastewater may

contain a large concentration of caustic, increasing the pH

above the level experienced during food processing

After cooking, the cans are cooled, which requires a

large volume of water The cooling water is clean and

warm and should be reused for washing

Meat and Poultry Wastes

Feed lot, stockyard, and poultry receiving area wastes

con-sist primarily of manure, unconsumed feed, feathers, and

straw, together with common dirt and drain water

Pollution can be reduced if solid wastes are not diluted by

water

In killing operations blood must be collected separately

and prevented from entering sewer or waste treatment

sys-tems, since blood has an extremely high waste strength of

about 100,000 ppm BOD In poultry plants, various

processes must be isolated to avoid cross-contamination

from live birds or wastes of previous operations As the

bird goes through the plant on shackles, feathers are

re-moved and flumed away A major incision is made,

en-trails and major organs are pulled out, and inedible

vis-cera are discarded in a flowaway flume system The lungs

and other material remaining in the carcass are removed

by vacuum suction

Flowaway systems (for feathers, entrails and offal)

cre-ate an increased organic load, and it is desirable to use a

dry conveying system Most plants use the flowaway

sys-tem as a more convenient and nuisance-free operation

After the offal flowaway leaves the area, it must be

screened in order to remove solids These solids and wastes

from other operations are then sent to a rendering plant

where they are utilized in making chicken feed

Meat packing houses generate a strong waste These

wastes are amenable to treatment, as are poultry wastes

Before releasing processing wastewaters into city sewers or

private waste treatment systems, screening and grease

re-moval should be provided to recover solids for

by-prod-uct use Removal of large solids and free floating grease is

also important to avoid clogging sewer lines and fouling

biological treatment systems

Dairy Wastes

Among waste generating operations in the dairy industry

are receiving stations, bottling plants, creameries, ice cream

plants, cheese plants, and condensed and dried milk

prod-uct plants Wastes include separated milk, buttermilk, orwhey, as well as occasional batches of sour milk Diversemethods are being explored for reclamation and concen-tration of materials, such as reverse osmosis for whey.Unfortunately, there is no simple economical method toreclaim and utilize these materials as byproducts.Indiscriminate dumping of these materials into sewersshould be avoided, and where possible these extremelystrong wastes should be treated separately or eliminated

by hauling

Milk wastes are normally treated in municipal plants,since most dairies are located in communities The wastesare amenable to biological treatment, and screening is com-monly provided; grit removal is sometimes necessary, aswell

Solid Waste DisposalMost solid wastes from food processing are generated inprocessing raw materials Some materials, such as pack-aging, faulty or damaged containers, office or warehousepapers, and refuse from laboratories, should be kept sep-arate from the food solids Solid food waste is produced

in growing and harvesting raw crops, in food processing,and by the retailer and consumer

Many food processing operations are seasonal and erate large quantities of organic solid wastes in a shorttime The putrescible nature of the wastes requires quickhandling in utilization or disposal Land disposal opera-tions—by far the most common method of disposal—must

gen-be rigidly controlled to prevent odor production and flybreeding It is apparent that the food processing industrymust recycle and recover more of its by-products.Utilization of food processing waste as animal feed is awidely used method of disposal In some areas, seafoodcanning waste is pressed into fish meal for animal feed orinto fertilizer material Tomatoes are pressed and dehy-drated for use as dog food and cattle food Pea vines, corn-cobs, and corn husks are also used as feed Citrus peelwaste may be pressed for molasses, which may then beprocessed, dried, and sold as cattle feed Certain types ofpits and nutshells have been converted to charcoal.Other possibilities exist, such as producing alcohol fromfruit wastes and composting fruit waste solids, but usually

it is much cheaper to dump, landfill, spread on the land,

or discharge at sea than to attempt reclamation There doesnot appear to be much chance of a change in this area un-less prevailing economic conditions can be altered throughnew legal restrictions or some form of subsidy program

Hydrocarbons

A bulk oil handling terminal stores and tranships leum products, petrochemicals, animal fats, greases andfood grade vegetable oils In addition they often acceptand dispose of ballast wastewaters from marine tankers

petro-that deliver to the terminal or pick up cargo for

tranship-ment A biological treatment system is appropriate because

of the wide range of physical and chemical characteristics

of the various types of oils and petrochemicals;

mechani-cal and/or chemimechani-cal means of separation and

neutraliza-tion are too expensive to install and operate

The equipment used in the system includes (1) a

col-lection system for the wastewater flow; (2) an API

sepa-rator; (3) a high-rate oxidation pond (or “aerated lagoon”)

with a 150,000 gal capacity; (4) a secondary settling or

“polishing pond” with a capacity of 450,000 gal; (5) a

re-circulation system; and (6) an 800,000 gal storage tank

for ship ballast holding and for surge flow equalization

DESIGN BASIS

Biological treatment was chosen because some oils float,

some sink, some are “soluble,” and some saponifiable

Thus, a broad-spectrum treatment was required No

mu-nicipal sewerage system was available, therefore the

efflu-ent had to meet waterway discharge requiremefflu-ents This

specified effluent concentration limits (mg/l): including

bi-ological oxygen demand (BOD) of 20 or less; hexane

sol-ubles of 15 or less; suspended solids of not over 25; and

a pH range of 6 to 10 In addition, effluent had to be

sub-stantially color free Influent characteristics were as

fol-lows:

Average daily flow 20 gpm

Average BOD 400 ppm

Average hexane solubles 300 ppm

Average suspended solids 100 ppm

Average pH range 5 to 12

Maximum aeration requirements were calculated to

pro-vide (1) sufficient flexibility to vary input air in response

to extreme pollutant load variations; and (2) excess

hy-draulic mixing capacity to increase suspended solids

oxi-dation and reduce the volume of sludge accumulating in

the system

The use of 3–5 hp floating aerators provides a total

available oxygen transfer rate of 7.5 lb oxygen per lb of

BOD, according to the manufacturer Under most nal operating conditions, only two aerators were required

termi-to provide 95% BOD removal Sludge accumulation wasbelow 350 lb wet sludge (7 lb dry) per day The systemhas never had an odor problem

A recirculating system was established for peak wasteloads in oil handling terminal operations (Figure 8.2.7).The 800,000 gal ballast tank gives an additional ten days

of holding time for recirculation when pollutant loadingsfar exceed design capacity

OPERATIONAL HISTORYThe BOD of the high-rate oxidation pond (“small pond”)

at startup was 2420 ppm (mg/l), and the hexane solublecontent was 2040 mg/l Both ponds were covered withabout 6 in of floating oil and grease (see Figure 8.2.8 forthe rate of stabilization)

The system was set on a recirculation rate of 50 gpm.Three days later, when the pH showed no further erraticswings, dried bacterial cultures (special species of sapro-phytic and facultative bacteria that consume oil) wereadded to create a biomass specifically for oil and greasereduction The initial dosage was 5 lb, followed by 1 lb/dayaddition for 14 days After this initiation, the system wasFIG 8.2.7 Bulk oil-handling terminal waste treatment system.

FIG 8.2.8 BOD reduction in ponds as a function of time after startup (BOD is usually 50% of ODI.)

maintained by the addition of Aslb of the dried culture

three times a week Figure 8.2.9 illustrates initial

reduc-tion of the hexane soluble content and continuing control

since the beginning of plant operation

The effectiveness of a biological treatment to control

oily wastewater is also shown in Figure 8.2.10 where

the-oretical and actual performances are compared

Pesticides

Since pesticides enter the aquatic environment in runoff

from agricultural areas as well as from point sources,

con-trol must be based on a multiphased approach:

1 Controlled application in minimum quantities over

ar-eas where specifically needed

2 Degradation in soil and watercourses

3 Removal at plants producing potable water

4 Treatment of wastes from pesticide handling facilities

and sewered areas

The various mechanisms for removing pesticides entering

the environment are discussed in this section as outlined

in Table 8.2.4, and the chemical structures of the

pesti-cides are shown in Figure 8.2.11

PESTICIDE REMOVAL IN NATURALAQUATIC SYSTEMS

Pesticide occurrence in surface waters can be traced to eral sources: agricultural runoff, industrial discharge, pur-poseful application, cleaning of contaminated equipment,and accidental spillage Chlorinated hydrocarbons in aque-ous solutions are readily adsorbed by clay materials Afteradsorption, small fractions of some pesticides are gradu-ally desorbed into the overlying water where the pesticideconcentration is maintained at a dynamic equilibrium level.Drainage of clay-bearing waters from agricultural areasrepresents a continuous supply of pesticides to the aque-ous solution Desorption rates are not significantly affected

sev-by pH, temperature, salt and organic levels (Huang 1971).The introduction of many new pesticides in recent yearshas created the need for reliable evaluation of the effects

on the aquatic biota The model ecosystem for these uations consists of glass aquaria arranged in a sloping soil-air-water interface (Metcalf, Sangha and Kapoor 1971) Afood chain of plant and animal organisms, compatible withthe environmental conditions simulated in the aquarium,

eval-is chosen for following radiolabeled DDT (labeled in thearyl rings with C14) and methoxychlor Average data pre-sented in Table 8.2.5 show a 13,000-fold increase in con-

FIG 8.2.9 Polishing pond performance from startup A 5

ini-tial BOD of 2420 ppm (at startup ODI roughly equals BOD;

later BOD is stabilized at 50 percent ODI for this waste); B 5

FIG 8.2.10 Theoretical vs actual performance A Rate of lutant addition reducers; B Standard theoretical curve for rate of pollutant reduction by biological treatment systems; C Curve dis- tortion due to exceptional load condition System gave 97% re- duction in 30 days.

pol-centration of carbon-14 in the fish over the conpol-centration

in water The DDE metabolite of DDT was largely

re-sponsible for the undesirable accumulations in animal

tis-sue noted

In studies with tritium-labeled methoxychlor,

accumu-lations of the pure compound and its degradation

prod-ucts in fish were of the order of 0.01 those for DDT

(Metcalf, Sangha and Kapoor 1971) The presence of

sev-eral degradation products and the relatively low

accumu-lations in most organisms revealed the environmentallydegradable nature of methoxychlor

The organophosphate insecticides were less persistent

in the aquatic environment than were the organochloridecompounds (Graetz, et al 1970) Depending on environ-mental conditions, degradation is by chemical or microbi-ological means, or both Chemical degradation involveshydrolysis of the ester linkages Hydrolysis can be eitheracid-catalyzed, e.g., ciodrin, or base-catalyzed, e.g.,malathion Microbial degradation can be by hydrolysis oroxidation Partial degradation is often the case, althoughfor diazinon, chemical hydrolysis of the thiophosphatelinkage attached to the heterocyclic ring results in 2-iso-propyl-4-methyl-6-hydroxypyrimidine, which is degradedrapidly by soil microorganisms Among the orthophos-phates, parathion is one of the most resistant to chemicalhydrolysis, but microbial degradation to aminoparathioncan proceed

Adsorption onto clay and precipitates Soils and clay-bearing watercourses

Water treatment coagulation processes Controlled self-destruction Soil and watercourses

Degradation by biological systems Soil at point of pesticide application

Watercourses receiving runoff containing pesticides Waste treatment system at pesticide handling facility

systems Activated carbon adsorption Water and wastewater treatment

systems

systems

FIG 8.2.11 Chemical structures of key pesticides A.

Chlordane; B 2,4-D; C DDT; D Dieldrin; E DNOCHP: F.

DNOSBP; G Endrin; H Heptachlor; I Lindane; J Parathion;

K Sevin; L Silvex; M 2,4,5-T; N Toxaphene.

ECOSYSTEM

Distribution

Total Carbon-14 Content, mg per

Standard biochemical oxygen demand tests involving

glucose incubation with a carbaryl insecticide, Sevin,

indi-cate no inhibition of bacterial oxidation of glucose up to

a Sevin concentration of 100 mg/l In fact, Sevin was

bioox-idized to a considerable extent at this level; oxidation was

enhanced after a period of acclimatization

BIODEGRADABLE REPLACEMENT AND

CONTROLLED SELF-DESTRUCTION

Biodegradable substitutes have been developed for some

hard pesticides One approach is to substitute aromatic

chlorine atoms in the DDT molecule (Anon., Chemical

Week 109:36 1971) The new compounds reportedly do

not build up in animal tissue and concentrate at higher

levels in the food chain

A mildly acid reduction by zinc will speed degradation

of DDT and other pesticides in natural systems (EPA

1970) A copper catalyst speeds up the reduction Effective

degradation of DDT to bis(p-chlorophenyl) ethane appears

possible in soil by using micron-sized particles of the

re-ductant in close proximity to the DDT Thin, slowly

sol-uble wax or silyl coatings on the reductant can delay the

reaction A second technique for delayed reaction involves

controlled air oxidation to sulfur to produce the required

acidity Effective degradation of DDT in aqueous systems

was also achieved using reduction techniques The

proce-dure was reported effective in substantially degrading

dieldrin, endrin, aldrin, chlordane, toxaphene, Kelthane,

methoxychlor, Perthane and lindane

BIOLOGICAL TREATMENT PROCESSES

The waste flow from a parathion production unit

under-goes activated sludge treatment (Coley and Stutz 1966)

with a residence time of 7–10 days, providing nearly

com-plete breakdown of parathion and paranitrophenol as well

as over 95% reduction in organic matter as measured by

chemical oxygen demand (COD)

Studies were also conducted in designing a wastewater

treatment facility for production of organic phosphorus

pesticides (Lue-Hing and Brady 1968) Although

treata-bility studies showed the waste to be biodegradable, shock

loads caused stresses at up to 6000 mg/l solids

Consequently, a two-stage activated sludge system was

chosen in which the first stage is a dispensable, low-solids,

detoxification unit Removal of dissolved organic matter

measured as biochemical oxygen demand was 90–98% in

the pilot plant

The oxidation of Sevin carbaryl insecticide by an

acti-vated sludge culture is depicted in Figure 8.2.12 No

ad-verse effects on bacteria, protozoa and rotifers were noted

Biological degradation studies (Leigh 1969) of lindane

in-dicated no significant removal of this pesticide from

mi-crobial activity following 28 days of acclimatization in

sta-tically aerated cultures Removals in unseeded controls(reference samples) were approximately 46% while bio-logical removals averaged only 41% The biodegradabil-ity of heptachlor could not be deduced from similar stud-ies because analyses of aqueous solutions of this pesticideindicated partial degradation to 1-hydroxyl chlordene and

an undetermined compound Removals of as high as99.4% were attained within four days for heptachlor, butvolatilization losses were considered significant

The degradation of chlorinated hydrocarbon pesticideswas studied under anaerobic conditions (Hill and McCarty1966) such as lake and stream bottoms, lagoon treatmentsystems, and digestion systems Lindane and DDT wererapidly decomposed, the latter to DDE which degradedmore slowly Heptachlor and endrin also formed inter-mediate degradation products within short periods Therate of decomposition of aldrin was similar to that forDDD; only slight degradation of heptachlor epoxide oc-curred, and dieldrin remained unchanged Anaerobic con-ditions were more favorable than aerobic conditions forpesticide degradation Sorption of chlorinated hydrocar-bon pesticides was found to be greater on algae than onbentonite or fine sand; the process was partially reversibleand the degree of sorption was inversely related to the sol-ubility of the pesticide

Lindane was degraded anaerobically in pure culture;only 0.5% of the lindane present after 1 hr incubation wasfound in the reaction mixture after 27 hr incubation(MacRae, Raghu and Bautista 1969) The covalentlylinked chlorine of the lindane molecule was released A de-tected intermediate product reached a maximum level af-ter about 4 hr incubation and diminished to undetectablelevels after 27 hr incubation

FIG 8.2.12 Oxidation of Sevin carbaryl insecticide by mated bacteria.

accli-CHEMICAL FLOCCULATION AND

OXIDATION

Since pesticides are used mainly in unsewered agricultural

areas, they reach lakes and streams without passing

through treatment facilities Consequently, ease of removal

in conventional water supply treatment processes (when

water is withdrawn for processing to produce potable

wa-ter) is important A study used pilot water supply

ment plants to evaluate conventional and auxilliary

treat-ment process effectiveness in removing pesticides from

natural surface water (Robeck, Dostal, Cohen and Kreiss

1965) The results showed that each part of the water

treatment plant had some potential for reducing certain

pesticides The effectiveness of the standard process of

co-agulation and filtration is shown in Table 8.2.6 Removals

ranged from 98% for DDT to less than 10% for lindane

The only pesticide affected significantly by the application

of chlorine or potassium permanganate (1–5 mg/l) was

parathion, 75% of which was oxidized to paroxon, a more

toxic material At high dosages, ozone (10–38 mg/l)

re-duced chlorinated hydrocarbons; by-products of unknown

toxicity were formed

In full-scale evaluations (Nicholson, Grzenda and

Teasley 1968), the standard processing steps of

coagula-tion, settling, rapid sand filtracoagula-tion, and chlorination were

successful in reducing DDT and DDE levels but not

toxaphene and lindane levels Side tests with a 25-m filter

removed DDT and DDE more effectively than toxaphene

and lindane, indicating that the latter materials were

trans-ported in solution

Chemical degradability of frequently used chlorinated

hydrocarbon insecticides has also been investigated (Leigh

1969) Lindane and endrin were not removed by either

chlorine or potassium permanganate at oxidant dosages

ranging from 48 to 61 mg/l, contact times of 48 hr and a

wide range of pH values Heptachlor was removed by

KMnO4to the extent of 88% with only slight variation

due to pH adjustment Heptachlor and DDT were both

partially removed by chlorine, and DDT was partially

re-moved by KMnO4with slightly higher removals at lower

pH levels Maximum removals by potassium persulfate,attained only for lindane and DDT, were 9.4% and18.5%, respectively, at higher pH values

Several physical and chemical treatments for removingthe herbicide 2,4-D and its ester derivatives from naturalwaters have also been investigated (Aly and Faust 1965).Chemical coagulation of 1 mg/l solutions by 100 mg/l alu-minum sulfate showed no promise with the herbicides andderivatives studied Activated carbon studies indicated car-bon requirements for reducing 2,4-D concentrations from

1 to 0.1 mg/l were 31 mg/l for sodium salt, 14 mg/l forisopropyl ester, 15 mg/l for butyl ester and 16 mg/l forisooctyl ester Potassium permanganate dosed at 3 mg/ldid not oxidize 1 mg/l of these same compounds However,0.98 mg/l of 2,4-DCP was completely oxidized by 1.25mg/l KMnO4 in 15 min Ion exchange studies indicatedthat strongly basic anion-exchange resins more effectivelyremoved the compounds studied than cation exchangeresins

Strong oxidants to degrade chlorinated hydrocarbonpesticides (Buescher, Dougherty and Skrinde 1964) havealso been studied Preliminary studies with lindane andaldrin showed negligible removals with hydrogen perox-ide and sodium peroxide at 40 mg/l dosages and four-hrcontact times Chlorination had negligible effects on lin-dane, but completely oxidized aldrin, while potassium per-manganate (KMnO4) oxidized lindane to approximately12% and aldrin, fully Further studies of potassium per-manganate added in varying doses from 6 to 40 mg/l tolindane solution indicated that the excessive time and ox-idant dosages required for removals greater than 40%made this treatment unfeasible Complete removal foraldrin could be attained in 15 min at 1 mg/l dosage ofKMnO4

Due to the relatively small fraction of ozone in the airstream used for ozonation, pesticide removals from airstripping were measured, as well as removals from oxida-tion Up to 75% of lindane was removed by ozonation,whereas aeration alone had no measurable effect Dieldrinand aldrin were completely removed almost at once, butaeration studies also showed fairly rapid removals

ACTIVATED CARBON ADSORPTIONConsiderable data on the adsorption of several pesticidesand related nitrophenols on activated carbon have beenreported (Weber and Gould 1966) Carbon loadings of40–53% indicate economic feasibility for removal of tracequantities of these persistent compounds Rate andLangmuir equilibrium constants for the pesticides areshown in Table 8.2.7 The quantity of pesticide adsorbedper gm of carbon at complete monolayer coverage of thecarbon surface (Xmvalues) indicates high ultimate carbonloadings B21values, which relate to energies of adsorp-tion, indicate that relatively high residual concentrations

TREATMENT PLANT OPERATIONS

are required for all but parathion to attain saturation

ca-pacity

Additional studies (Dedrick and Beckman 1967)

indi-cate that adsorption of 2,4-dichlorophenoxyacetic acid

(2,4-D) can be correlated by both the Freundlich and the

Langmuir isotherms; however, two sets of correlating

con-stants are required for each of the low and high

concen-tration ranges No significant differences in carbon

ca-pacities were noted between granular and powdered

carbon Carbon loadings of approximately 60% by weight

of the herbicide were attained at liquid concentrations

95% of saturation, or about 740 mg/l

Carbon adsorption studies using a slurry approach

showed parathion to be most amenable and lindane least

amenable (Table 8.2.6) to removal by activated carbon

Use of a granular bed at 0.5 gpm/cu ft resulted in almost

complete removal of all pesticides

REVERSE OSMOSIS

Specific chemical permeation through a cellulose acetate

membrane has also been reported (Hindin, Bennett and

Narayanan 1969) The membranes were immersed in

wa-ter at 82°C for 30 min prior to use At a pressure

differ-ential of 100 atm, a temperature of 25°C, flux rates on

the order of 15 gal/sq ft/day, and feed concentrations of

about 500 mg/l, reduction of lindane was 73% while DDT

and TDE (DDD) were rejected above 99% High

reduc-tions were obtained for those chemical species existing

primarily in the colloidal, aggregate, micelle, or

macro-molecular form If the chemical species existed both as an

aggregate in dispersion and as a discrete molecule in true

solution where vapor pressure of the discrete molecule in

true solution was appreciably greater than that of water,

the range of reduction was 50–80% Where discrete

mol-ecules more volatile than water were tested, range of

re-ductions was 14–40%

INCINERATIONAlong with deep-well injection, incineration of concen-trated pesticide waste is an alternative to treatment anddisposal in surface waters Solid wastes are burned in a ro-tary kiln or other incinerator at 1600°–2200°F (Anon.Chemical Week 108:37 1971) Afterburners can be used

to reach temperatures of 2800°F A scrubber is used toclean exhaust gases

RESEARCH TRENDSSince outlawing DDT and other pesticides that build up

in the foodchain seems imminent in many developed eas, replacements must be found, or there will be a re-crudescence of health problems For example, malaria andVenezuelan equine encephalomyelitis resurge in areaswhere mosquito control is lax or mosquitos become re-sistant to the pesticides used In the case of mosquito con-trol, malathion and propoxur are recommended as re-placements for DDT as resistance grows (Anon ChemicalWeek 109:36 1971) Although fenitrothion, iodofenphos,phenothoate and Landrin show promise, all are more ex-pensive and less effective than DDT

ar-Until suitable replacements are developed, much mains to be done in the realm of pesticide removal fromwaters—both prior to discharge of wastewater and intreating water for human use Although the literature onthe effects and measurement of pesticides is voluminous,articles on removal techniques for pesticides are relativelyfew

re-PhenolAlthough phenol (C6H5OH) has been detected in decay-ing organic matter and animal urine, its presence in a sur-face stream is attributed to industrial pollution Petroleumrefineries, coke plants, and resin plants are major indus-

Relative Rate

m b b

C C }

(Reprinted with permission, from I.C MacRae, K Raghu, and E.M Bautista, 1969, Nature 221:859.

trial phenolic waste sources Phenolic compounds and their

derivatives are used in coatings, solvents, plastics,

explo-sives, fertilizer, textiles, pharmaceuticals, soap, and dyes

Treatment methods for phenol removal include

bio-logical (activated sludge, trickling filter, oxidation pond,

and lagoon); chemical oxidation (air, chlorine, chlorine

dioxide, ozone, and hydrogen peroxide); physical

(acti-vated carbon adsorption, solvent extraction, and ion

ex-change); and physicochemical (incineration and electrolytic

oxidation)

SOLVENT EXTRACTION

For wastewaters containing high phenol concentrations,

solvent extraction reduces the phenol to acceptable levels

Occasionally, recovered phenol is reused in the

manufac-turing process or solid as a by-product In solvent

extrac-tion, two immiscible or partially soluble liquids are

brought into contact for transfer of one or more

compo-nents Using a solvent such as benzene, phenol can be

ex-tracted from the wastewater The exex-tracted phenol is then

washed out with caustic to form the sodium salt, and the

benzene is reused In the petroleum industry, light catalytic

cracking oils are used as extractors, and in the coking

in-dustry, coke oven light oils are used as extractors Process

efficiency depends on solvent choice and system design

BIOLOGICAL TREATMENT

The microorganisms capable of degrading phenol are

highly specialized and require a controlled, stable

envi-ronment Under ideal conditions several weeks are required

to develop the proper biological sludge The efficiency of

an acclimated biological system treating phenolic wastes

depends strongly on temperature, pH, nutrients (nitrogen,

phosphorus, minerals), oxygen concentration, phenol

con-centration, and other organics concentrations in the

waste-water

To degrade phenol, the microorganism population must

be stable Fluctuation in any of the preceding variables

shifts the balance of this population, reducing system

effi-ciency and possibly killing the biological organisms

Optimum phenol removal occurs at neutral pH (7.0), 70°F

and constant phenol concentration

Biological methods of phenol removal include activated

sludge, trickling filters, oxidation ponds, and lagoons

Efficiency ranges from 65–90% removal, depending on the

ability of the particular wastewater treatment system to

control the process variables listed Activated sludge,

trick-ling filters, and oxidation ponds are all capable of high

phenol removal if properly designed and operated;

how-ever, the trickling filter process is regarded as being more

capable of withstanding slug loads without loss of

perfor-mance Lagoons for treating phenolic wastes are designed

to avoid overflow, with evaporation and seepage used to

balance the influent flow This method is less desirable,due to the possibility of ground water pollution, odor, andoverflows from rainfall

Frequently, phenolic wastes are diluted with sanitarywastes and treated at the local municipal plant (Mullerand Covertry 1968) Combined municipal-industrial treat-ment buffers the dilution and provides an ample supply ofnutrients and microorganisms should the system be upset.Phenolic wastewaters should be neutralized prior to dis-charge to the municipal sewer system

CARBON ADSORPTIONActivated carbon in the powdered and granular forms isused to remove phenolic tastes and odors from drinkingwater supplies In wastewater treatment applications,where phenol content is considerably greater than inpotable water applications and the flow is continuous,granular carbon systems are more economical

Depending on the concentration of phenol and otherorganic compounds in the wastewater, activated carbonwill adsorb from 10 to 25 lb of phenol per 100 lb of car-bon This capacity can be determined from isotherm andcolumn test data In general, phenol adsorption improves

as the pH decreases

Adsorption at high pH is poor, since phenolate saltforms and is difficult to adsorb This is an advantage inapplications where phenol recovery is worthwhile Thephenol is adsorbed at the low pH and reclaimed as sodiumsalt by chemical regeneration, using hot caustic If the phe-nolate cannot be reused, regenerant disposal is a problem.Also, if quantities of other organic substances are present

in the waste stream, they too will be adsorbed These ganic compounds may not be desorbed during caustic re-generation, which will decrease the phenol capacity of thecarbon upon subsequent regeneration If chemical regen-eration does not sufficiently recover the phenol capacity

or-of the carbon, thermal reactivation will be required.Figure 8.2.13 is a flow diagram of a granular carbonsystem for phenol removal employing chemical regenera-tion and phenol recovery Pretreatment consists of acidifi-cation to pH 4.2 to precipitate the suspended solids andclarify the overflow The phenol content of the feedstreamranges from 400 to 2500 mg/l, and the effluent objective

is less than 1 mg/l phenol (Gould and Taylor 1969)

CHEMICAL OXIDATIONAir, chlorine, ozone, and other chemical oxidizing agentsare used to destroy phenol, which is first converted to hy-droquinone and then to quinone Additional oxidation de-stroys the aromatic ring, forming organic acids and even-tually carbon dioxide and water (Eisenhauer 1968).Air is an inexpensive oxidizing agent but reactions areslow Phenol can be completely decomposed by chlorina-

tion at pH 7.7, provided that the stoichiometric amount

of chlorine is added This is accomplished in water

treat-ment plants by superchlorination The major portion of

the chlorine applied consumes other organic compounds

and destroys ammonia Approximately 42 parts of

chlo-rine per part of phenol are required (Ohio River Valley

Sanitation Commission 1951)

Ozonation effectively oxidizes phenol However, the

initial cost of producing ozone is high Ammonia does not

interfere in ozonation, and approximately 5.8 parts of

ozone are required per part of phenol (Ohio River Valley

Sanitation Commission 1951)

Starch

Starch wastes are produced by food processing operations,

including starch manufacturing from corn, potatoes, and

wheat The wastes are essentially carbohydrates with a

high oxygen demand

BIOLOGICAL TREATMENTStarch wastes respond to biological treatment using trick-ling filters, aerated lagoons, or activated sludge processes.Waste pH should be adjusted to between 6.0 and 9.0, sus-pended solids should be removed and, if necessary, nutri-ents should be added to maintain a BOD-nitrogen-phos-phorous ratio of 100 to 5 to 1

Starch is almost completely oxidized biologically, vided that the loading is maintained within the limits ofthe biological activity If an activated sludge process is used,

pro-it is important to maintain an F to M (BOD to mixedliquor suspended solids) ratio of less than 0.3 (per day) tominimize propagation of filamentous organisms that in-terfere with solids separation

Oxygen Requirements

In activated sludge operations it is necessary to supply gen to sustain the process and to provide intimate mixingand contact of activated sludge with the organic matterand nutrients (A low-speed turbine-type surface aerator isshown in Figure 8.2.14.) Oxygen requirements depend onBOD removal and on process loading The oxygen re-quirement is expressed by equation 8.2(1):

oxy-lb of oxygen required per oxy-lb BOD removed

8.2(1)

In equation 8.2(1), “A” is related to the oxygen ment for synthesis of new cells, and “B” is related to theoxygen requirement for respiration The value of “A”ranges from 0.35 to 0.55, and “B” ranges from 0.05 to

require-lb mixed liquor volatile suspended solids }}}}}

lb BOD applied per day FIG 8.2.13 Granular carbon systems for phenol removal

FIG 8.2.14 Low-speed surface aerator installation

TABLE 8.2.8 COMPOSITION OF WASTES FROM A SYNTHETIC FIBER FINISH MILL

BOD

peroxide Nylon processing

phenylmethylcarbinol (30%

monochlorobenzene (40%

From Masselli, Masselli, and Burford A simplification of textile waste survey and treatment New England Interstate Water Pollution Control Commission.

a % on weight of fiber, a weight percentage based on dried cloth weight.

b OWF, weight percentage based on dried cloth.

0.10 As a general rule, one lb of oxygen is required per

lb of BOD removed under conventional activated sludge

operations with an F to M ratio of 0.3 to 0.5 For

aero-bic digestion with an F to M ratio of 0.1, approximately

1.5 lb of oxygen are required per pound of BOD removed

Sludge Production

In the activated sludge process, soluble organic matter is

converted to suspended solids in the form of bacterial cells

The amount of sludge produced is a function of processloading and of BOD removal Sludge production can beexpressed within practical limits by equation 8.2(2):

8.2(2)

lb mixed liquor volatile suspended solids }}}}}

lb BOD applied per day

lb of volatile suspended solids produced }}}}}

lb BOD removed

The value of “A” varies from 0.4 to 0.9, and the value of

“B” from 0.01 to 0.1, depending on the waste being

treated An approximate expression for sludge production

in many treatment applications is given in equation 8.2(3):

8.2(3)

Based on conventional activated sludge operations,

be-tween 0.5 and 0.6 lb of excess sludge are produced per lb

of BOD removed With aerobic digestion, approximately

0.2 lb of excess sludge are produced per lb of BOD

re-moved

Aerobically digested sludge can be dewatered on

vac-uum filters with loadings of approximately 1 lb/sq ft/hr

Dewatering excess sludge from conventional activated

sludge operations requires a heat treatment for sludge

con-ditioning or a heavy dosage of concon-ditioning chemicals to

form a filter cake that will dewater and separate from a

filter cloth

Textile Industry Wastes

Textile industry wastes are categorized by their source

Man-made fibers constitute approximately 80% of the

lb mixed liquor volatile suspended solids }}}}}

lb BOD applied per day

lb volatile suspended solids produced

}}}}

lb BOD removed

fibers used Table 8.2.8 lists wastewater compositions fromsynthetic fiber finish mills, and Table 8.2.9 reflects per-formance data of the various treatment methods in re-ducing BOD, SS, color, grease, and alkalinity

In textile wastes the suspended solids concentration isminute, the BOD range can attain 3000 ppm, and colorcan sometimes reach as high as 3000 APHA color units.Electroflocculation removes most color by electrolyticallyinducing flotation and collection of foam Thereafter, bi-ological or chemical oxidation can be utilized to polish theeffluent and reduce the BOD to 25—virtually eliminatingcolor Such textile mill effluent is of sufficient quality to

be recycled and reused

Viruses and BacteriaBacteria and viruses are removed or killed by disinfectionand sterilization Disinfection destroys all harmful mi-croorganisms, while sterilization kills all living organisms.Disinfection of drinking water protects public health bypreventing microorganism growth in the pipelines.Disinfection of wastewater treatment effluents protectsmarine life Sterilization provides water suitable for med-ical and pharmaceutical use Numerous disinfection andsterilization techniques are available, and Tables 8.2.10and 8.2.11 compare the effectiveness, advantages, and dis-advantages

Normal reduction % Treatment Suspended method BOD Grease Color Alkalinity Solids

Grease recovery Acid cracking 20–30 40–50 0 0 0–50 Centrifuge 20–30 24–45 0 0 40–50 Evaporation 95 95 0 0

Screening 0–10 0 0 0 20 Sedimentation 30–50 80–90 10–50 10–20 50–65 Flotation 30–50 95–98 10–20 10–20 50–65 Chemical coagulation

Alum 20–56 — 75 Copperas 20

Reprinted, from FWPCA 1967 The cost of clean water, vol III Industrial Waste Profile, No 4 Textile Mill Products September.

TABLE 8.2.10 DISINFECTION TREATMENT METHODS

Advantages Inexpensive and well- Rapid method of removing Fast method Requires no Similar to chlo- Has long-lasting

developed technology, color, taste and odor while which requires special equip- rine except less bactericidal which provides lasting destroying viruses and no chemicals ment irritating to the effect.

oxidation products are non-toxic.

Disadvantages Not effective against some More expensive and less Leaves no protective Slow and Slower and more Slow and

expen-spores and viruses; can, in developed than chlorine residue, expensive, expensive expensive than sive Amines and high concentrations, produce and it does not leave a not applicable on chlorine other pollutants

re-moval.

Other Remarks Most frequently utilized Frequently used in Europe; Mostly used on Excellent house- Sometimes used as

method in the United States combined with chlorina- special laboratory hold emergency swimming pool —

tion, it can produce high- and small industrial method disinfectant.

quality drinking water applications

Note: A 5 requirements for drinking water disinfection.

B 5 requirements for the disinfection of secondary (activated) wastewaters treatment effluent.

Disinfection should kill or inactivate all

disease-pro-ducing (pathogenic) organisms, bacteria, and viruses of

in-testinal origin (enteric)

Pathogenic organisms include (1) bacteria of the

col-iform group, both fecal and nonfecal, such as Escherichia

coli, Aerobacter aerogenes, and Escherichia freundii; (2)

bacteria of the fecal streptococcus group; (3) other

mi-croorganisms such as Salmonella, Shigella, and the cyst

Endamoeba histolytica; and (4) enteric viruses such as the

etiologic agents of polio and infectious hepatitis Test

pro-cedures, developed for their identification, are usually

in-volved and time consuming Therefore, the identifications

(Metcalf, Wallis and Melmick 1972) of one group of

bac-teria (coliform) is usually taken as an indication of water

quality and a measure of effectiveness of bacteria

disin-fection It is assumed that the absence of coliform

bacte-ria indicates the absence of all pathogenic bactebacte-ria

Enteric viruses in the drinking water are reported to be

responsible for hepatitis, poliomyelitis, and other epidemic

diseases Viruses are substantially more resistant to

chlo-rine than bacteria, and the absence of coliform bacteria

does not necessarily indicate the absence of viruses

Virology is not developed to the point that routine

iden-tification and assay tests are possible The development of

a portable virus concentrator, making routine

identifica-tion and assay of viruses in water and wastewater more

practical, has been reported The concentrator first

re-moves suspended solids through filtration and absorbs

viruses on a cellulose adsorption column The viruses are

then eluted from the adsorption column and subjected to

standard laboratory assay (1972)

The probability of disease (D) when a pathogenic

or-ganism is brought into contact with a human water

con-sumer (host) is proportional to the number of organisms

(N) and their virulence (V) and inversely proportional to

the resistance (R) of the host The purpose of disinfection

is to minimize N and V in equation 8.2(4)

D 5 }NR

V

Disinfection treatments utilize oxidation, surface activechemicals, acids and bases, metal ions, ultraviolet radia-tion, and physical treatment

CHLORINATIONChlorination is by far the most frequently used disinfec-tion method in United States municipal drinking watertreatment plants The acting disinfectant may be chlorine

or a chlorine derivative, such as hypochlorous acid (mostcommonly), chloramines, or chlorine dioxide Several

treatment methods have been developed Simple tion involves adding chlorine after filtration or as the only treatment Chlorine-ammonia treatment utilizes the addi-

chlorina-tion of both ammonia and chlorine and the germicidal

ac-tion of chloramines Residual chlorinaac-tion is applied to provide residual chlorine in the water Breakpoint chlori- nation adds sufficient chlorine to react with ammonia and

all other chemicals present as well as to assure a free rine residue

chlo-Liquid chlorine is the least expensive form of chlorine

It was used in most large municipal water works until eral large cities restricted or prohibited transportation andstorage of large volumes of liquid chlorine to prevent ac-cidental release into the atmosphere Chlorine can be usedand stored more safely in its solid form as Ca(OCl)2.However, the cost is substantially higher

sev-Bactericidal and Viricidal ActionThe bactericidal action of chlorine is the result of its strongoxidizing power The formation of hypochlorous acid, thestrongest disinfecting agent among the chlorine derivatives,

is shown by equation 8.2(5) The bacteria-killing nism is believed to involve diffusion of hypochlorous acidthrough the cell membrane and oxidation of the cell en-zymes

The viricidal action of hypochlorous acid is

Operating Treatment Conditions Advantages Disadvantages

micro-organisms

tially slower and less effective than its bactericidal action.

The killing mechanism is believed to involve attacking

many protein sites rather than one critical site of the virus

The chlorine treatment, designed to kill bacteria, does not

necessarily kill viruses Chlorine is not effective in normal

concentrations to kill the cyst Endamoeba histolytica, the

cause of amoebic dysentery, a protozoan disease that

vades the body by a parasitic organism through the

in-testinal tract Fortunately, it is a relatively rare disease

Chlorine is also ineffective against nematodes, a

free-living microorganism present in surface water supplies

Nematodes, although nonpathogenic, are capable of

in-gesting and harboring potentially dangerous organisms

Minimum bactericidal chlorine residual was determined

by the Public Health Service in terms of free available

chlo-rine, using a 10-min contact time, and in terms of

com-bined available chlorine (free chlorine and chloramines),

using a 60-min contact time The free available chlorine

necessary for disinfection is 0.2 ppm at pH 6–8 and 0.4

ppm at pH 8–9 The corresponding concentrations with

combined available chlorine are 1.5 and 1.8 ppm

OZONATION

Ozone, a triatomic allotrope of oxygen, is produced

in-dustrially in an electric discharge field generator from dry

air or oxygen at the site of use The ozone generator

pro-duces an ozone-air or ozone-oxygen mixture containing 1

and 2% ozone by weight This gas mixture is introduced

into the water by injection or diffusion into a well-baffled

mixing chamber or scrubber, or by spraying the water into

an ozone atmosphere

Ozone is a powerful oxidizing agent The mechanism

of its bactericidal action is believed to be diffusion through

the cell membrane followed by the irreversible oxidation

of cell enzymes Disinfection is unusually rapid and

re-quires only low ozone concentrations

The viricidal action of ozone is even faster than its

bac-tericidal effect The mechanism by which the virus is

de-stroyed is not yet understood Ozone is also more

effec-tive than chlorine against spores and cysts such as

Endamoeba histolytica.

Disinfection, color, taste, and odor control can be

ac-complished in a single treatment step by ozonation Ozone

reacts rapidly with all oxidizable organic and inorganic

materials present in the water

The ozone dosage necessary for disinfection depends on

pollutant concentration in the raw water An ozone dose

of 0.2 to 0.3 ppm is usually sufficient for bactericidal

ac-tion only The ozone dosage necessary for secondary

acti-vated wastewater treatment effluent disinfection is 6 or

more ppm Ozonation leaves no disinfection residue, and

therefore ozonation should be followed by chlorination in

drinking water supply treatment applications To obtain

optimum drinking water, raw water should first be

ozonated to remove color, odor, and taste and to destroy

bacteria, viruses and other organisms Then the watershould be chlorinated lightly to prevent recontamination

Aquarium and Fish Farm WaterDisinfection

Ozonation should be selected as a disinfection treatmentfor marine applications where residual disinfecting agents

or toxic oxidation products (chlorinated amines) cannot

be tolerated Ozone is unstable in water and decomposesslowly, with a half-life of approximately 30 min at 25°C.The decomposition rate is dependent on water quality Thehalf-life of the ozone at 25°C is 50 min in distilled waterand 20 min in tap water Decomposition is substantiallyaccelerated by hydroxyl ions, transition metals and freeradicals The oxidation products of ozonation are usuallynontoxic and biodegradable Furthermore, ozonationleaves the water saturated with dissolved oxygen, impor-tant in fish hatcheries or fish farms

Ozonation disinfects water and saturates it with solved oxygen Ozonation can reduce organic contami-nants and waste in fish farm water, allowing water recy-cling Ozone concentrations higher than 0.1 ppm should

dis-be avoided dis-because they can harm the fish Research fromthe National Marine Fisheries Service demonstrates thatozonation destroys undesirable microorganisms with noharmful effects to the fish

Other Disinfectants For a discussion of the merits and

drawbacks of ultraviolet irradiation, heating, chemical idants and metal ions, see Table 8.2.10

ox-—R.A Conway, C.C Walden, L.C Gilde, Jr., C.A Caswell, R.H Zanitsch, E.G.

Kominek, J.W T Ferretti, L.J Bollyky

ReferencesAly, O.M., and S.D Faust 1965 Removal of 2,4-dichlorophenoxyacetic

acid derivatives from natural waters J Am Water Works Assoc.

Buescher, C.A., J.H Dougherty, and R.T Skrinde 1964 Chemical

ox-idation of selected organic pesticides J Water Pollution Control Fed.

36(8):1005.

Charles, G.E., and G Decker 1970 Biological treatment of bleach plant

wastes J Water Poll Contr Fed 42:1725.

Coley, G., and C.N Stutz 1966 Treatment of parathion wastes and

other organics J Water Pollution Control Fed 38(8):1345.

Dedrick, R.L., and R.B Beckman 1967 Kinetics of adsorption by

acti-vated carbon from dilute aqueous solution Chem Engr Prog Symp Ser 63(74):68.

Eisenhauer, H.R 1968 Dephenolization of water and wastewater Water and Pollution Control 106(9) (September) p 34.

Gaudy, A.F., R.S Engelbrecht, and B.G Turner 1961 Stripping

kinet-ics of volatile components of petrochemical wastes J Water Pollution

Control Fed 33(4):383.

Gerhold, R.M., and G.W Malaney 1966 Structural determinations in

the oxidation of aliphatic compounds by activated sludge J Water

Pollution Control Fed 38(4):562.

Giusti, D.M 1971 Amenability of petrochemical waste constituents to

activated carbon adsorption Master’s Thesis, West Virginia

University Morgantown, W.Va.

Gould, M., and J Taylor 1969 Temporary water clarification system.

Chemical Engineering Progress 65(12) (December) p 47.

Graetz, D.A., G Chesters, T.C Daniel, L.W Newland, and G.B Lee.

1970 Parathion degradation in lake sediments J Water Pollution

Control Fed 42(2):R 76.

Hatfield, R 1957 Biological oxidation of some organic compounds.

Industrial and Engineering Chemistry 49(2):192.

Heukelekian, H., and M.C Rand 1955 Biochemical oxygen demand of

pure organic compounds J Water Pollution Control Federation

27(9):1040.

Hill, D.W., and P.C McCarty 1966 The anaerobic degradation of

se-lected chlorinated hydrocarbon pesticides Paper presented at Annual

Meeting of Water Pollution Control Federation Kansas City, Kansas.

(September).

Hindin, E., P.J Bennett, and S.S Narayanan 1969 Organic compounds

removed by reverse osmosis Water & Sewage Works 116(12):466.

Huang, J 1971 Effect of selected factors on pesticide sorption and

de-sorption in the aquatic environment J Water Pollution Control Fed.

43(8):1739.

Lamb, C.R., and G.F Jenkins 1952 BOD of Synthetic Organic

Chemicals Proc 7th Ind Waste Conference Purdue University.

Lafayette, Ind.

Laws, R.L., and O.B Burns, Jr 1960 Recent developments in the

ap-plication of the activated sludge process for the treatment of pulp and

paper mill wastes Pulp and Paper Magazine of Canada

61:T507–T513.

Leigh, G.M 1969 Degradation of selected chlorinated hydrocarbon

in-secticides J Water Pollution Control Fed 41(11):R 450.

Lue-Hing, C., and S.D Brady 1968 Biological Treatment of Organic

Phosphorus Pesticide Wastewaters Proc 23rd Purdue Industrial

Waste Conference, Purdue Univ Eng Extension Series, No 132, 1166 MacRae, I.C., K Raghu, and E.M Bautista 1969 Nature 221:859.

Metcalf, R.L., G.K Sangha, and I.P Kapoor 1971 Model ecosystem for the evaluation of pesticide biodegradability and ecological mag-

nification Environmental Sci Tech 5(8):709.

Metcalf, C.J., C Wallis, and J.L Melmick 1972 Concentrations of viruses from sea water Proceedings from the 6th International

Conference on Water Pollution Research Jerusalem, Israel (June) Muller, J.M., and F.L Covertry 1968 Disposal of coke plant waste in

the sanitary water system Blast Furnace and Steel Plant 56(5) (May).

wastes—treat-Robeck, G.C., K.A Dostal, J.M Cohen, and J.F Kreissl 1965.

Effectiveness of water treatment processes in pesticide removal J Am Water Works Assoc 57(2):181.

Stack, V.T., Jr 1957 Toxicity of alpha, beta-unsaturated carbonyl

com-pounds to microorganisms Industrial and Engineering Chemistry

49(5):913.

U.S Environmental Protection Agency (EPA) 1970 Investigation of means for controlled self-destruction of pesticides Aerojet-General

Corporation Report for the Water Quality Office 16040 ELO (June).

U.S Environmental Protection Agency (EPA) 1971 Research, ment and demonstration projects: 1970 grant and contract awards.

develop-Environmental Protection Agency, Water Quality Office, Office of Research and Development Washington, D.C.

Wallis, C., and J.L Melmick 1972 A portable virus concentrator for use in the field Proceedings of the 6th International Conference on

Water Pollution Research Jerusalem, Israel (June).

Wallis, C., A Homma, and J.L Melmick Development of an

appara-tus for concentration of viruses from large volumes of water J Amer Water Works Assoc.

Weber, W.J., Jr., and J.P Gould 1966 Sorption of Organic Pesticides from Aqueous Solution In Gould, R.F (ed.) Organic Pesticides in

the Environment Advances in Chemistry Series, 60 Washington,

D.C.: ACS Publication 280.

8.3

REMOVING INORGANIC CONTAMINANTS

Aluminum

Aluminum may be present in acid wastes as the trivalent

aluminum ion or in alkaline wastes as an aluminate ion

Aluminum is precipitated as the hydroxide or hydrolysis

species of polymeric aluminum The precipitation and

con-ditioning of precipitated solids has an important effect on

the separation rate and on the settling and dewatering

char-acteristics of the precipitate Precipitation in the presence

of previously formed solids produces denser and more

rapidly settling floc particles The addition of a

polyelec-trolyte also improves settling characteristics Low velocity

gradients, with agitator peripheral speeds as low as 5 ft/sec,

are desirable to avoid shearing the floc into small particles

that settle slowly

Depending on the method of precipitation and solidsseparation, aluminum hydroxide can be concentrated to1.0 to 2.0% by weight Adding suitable polyelectrolytes,

it can be further dewatered by centrifugation or vacuumfiltration However, without preconditioning of the alu-minum hydroxide sludge, either precoat vacuum filtration

or filter presses are required for sludge dewatering

BicarbonateBicarbonate is the principal alkaline form in natural (un-treated) water, although carbonate and hydroxide arefound in lime or lime-soda treated waters, and phosphates

and silicates may also contribute to alkalinity in

waste-waters Adverse effects of high alkalinity in boiler

feed-water include corrosion from liberated carbon dioxide and

foaming—with resultant carry-over of contaminants

Scaling can also occur in cooling water systems due to the

formation of insoluble calcium carbonate For drinking

water, the U.S Public Health Service Standards limit

al-kalinity to 35 ppm over the hardness level

REMOVING BICARBONATE ALKALINITY

Methods for reducing bicarbonate alkalinity (Table 8.3.1)

are divided into chemical addition and ion exchange

tech-niques Chemical methods include cold lime process and

acidification Ion exchange methods involve strong-acid

cation exchange, weak-acid cation exchange, or

strong-base anion exchange in the chloride cycle

Cold Lime Process

Bicarbonate is removed by lime addition in accordance

with the following reactions:

Ca(HCO 3 ) 2 1 Ca(OH) 2 ® 2 CaCO 3 ¯ 1 2 H 2O 8.3(1)

as-Acidification

By adding sulfuric acid to water, calcium bicarbonate isconverted to calcium sulfate, minimizing scaling by the lesssoluble calcium carbonate The reaction may be repre-sented as follows:

Ca(HCO 3 ) 2 1 H 2 SO 4 ® CaSO 4 1 2 CO 2 - 1 2 H 2 O

8.3(4)

Carbon dioxide formed is removed by aeration Care must

be exercised in adding acid to avoid corrosive conditions.With waters already high in sulfate, the solubility product

of calcium sulfate may be exceeded, and unwanted cipitation is likely to occur

pre-Strong Acid Cation Exchange

By passing water through a sulfonic acid cation exchanger

in the hydrogen form, the following reaction occurs:

RSO 3 H 1 NaHCO 3 ® RSO 3 Na 1 CO 2 - 1 H 2O 8.3(5)

(where R represents the resin matrix) Neutral salts areconverted to free mineral acids, and the cation exchanger

is regenerated with an excess of acid The process may be

Relative Relative Capital Operating Process Results, Comments Cost Cost Indicated Application

Cold Lime Process Reduces bicarbonate, calcium and mag- High Low Municipal-large scale, where

hardness 35–90 ppm; supersaturated 250 gpm and up.

CaCO 3 may form unless recarbonated.

preven-Aeration excess to prevent corrosion; easily tion.

automated; use HCl or HNO 3 on high-sulfate waters.

Split Stream Process Partial or complete hardness removal; High Moderate Industrial; low-pressure boiler-feed (Strong-Acid Cation alkalinity controlled by proportioning water, especially where ion-exchange

Aeration) disposal; excess salt if softener used.

Weak-Acid Cation Effluent alkalinity from 0–20% of in- Moderate Low Industrial; process and boiler-feed water;

Aeration pletely removed; high acid efficiency,

minimum disposal; may be combined with salt-regenerated softener.

Chloride-Cycle Anion Exchange of bicarbonate, sulfate, phos- Low Moderate Small industrial for low-pressure Exchange phate and nitrate for chloride; no re- feed water; 50 gpm; also municipal—

boiler-duction in dissolved solids; regener- where removal of nitrate, phosphate

used in tandem with a conventional sodium cycle

(salt-re-generated) cation exchange softener Either the raw or

soft-ened water is blended with the acidified effluent to give a

split-stream which controls alkalinity.

Weak Acid Cation Exchange

Weak acid resins also remove both alkalinity and

hard-ness, as illustrated by the following reaction:

2 RCOOH 1 Ca(HCO 3 ) 2 ®

(RCOO) 2 Ca 1 2 CO 2 - 1 2 H 2O 8.3(6)

In contrast to the strong acid resin, the weak acid

ex-changer converts little, if any, of the neutral salts

(chlo-rides and sulfates) to free mineral acidity Neutralization

is not required, although degasification or aeration is

prac-ticed Regeneration of the weak acid resin is more efficient

than with strong acid cation exchangers, minimizing acid

waste disposal Combining a salt-regenerated softener with

an acid-regenerated weak acid resin provides complete

softening and dealkalization with a single column

Chloride Cycle Anion Exchange

Strong base anion exchangers remove bicarbonate, as

il-lustrated by the following reaction:

The principal regenerant is sodium chloride Capacities can

be increased by adding a small proportion of caustic soda

to the salt This process eliminates the need for acid-proof

equipment and offers convenience, low cost, and a

rela-tively small space requirement In addition to bicarbonate

removal, reductions in sulfate, nitrate, phosphate, anionic

surfactants and color are also achieved However, the

ef-fluent chloride level increases in the exchange

Cadmium

Cadmium, a relatively rare element, is extensively used not

only in protecting other metals, but also in manufacturing

primary batteries and standard electrochemical cells; in

producing pigments with outstanding properties; and in

production of phosphors, semiconductors, electrical

con-tactors, and special purpose low-temperature alloys

SOURCES OF CADMIUM-BEARING

WASTEWATERS

Because the largest consumption of cadmium (60%) is for

plating, performed in aqueous baths, there is a drag-out

of plating chemicals from the plating bath to the

follow-ing rinse bath The amount of drag-out is a function of

the size of the article being plated, its intricacy, the

pres-ence of blind holes, and the duration of pause to drip over

the plating tank

Cadmium is a by-product of zinc production and is avaluable source of revenue for the zinc smelter Duringzinc smelting, evolved cadmium fumes are collected.Consequently, if the gases from electric furnaces, autobodyincineration, and certain domestic products are waterscrubbed, cadmium is found in the scrubbing water.Whenever zinc or brass is electroplated, the drag-out alsocontains cadmium, as these plating tanks serve as cadmiumconcentrators

In the manufacture, incineration, and careless disposal

of primary cells, there is cadmium loss

The 1962 USPHS Drinking Water Standards set a mium limit of 0.01 mg/l The toxicity of cadmium and cer-tain disease manifestations necessitate treatment of waste-waters containing cadmium to reduce treated effluentconcentration to the level of 0.01 mg/l

cad-TREATMENT METHODSThe solubility product of cadmium sulfide is 3.6 3 10229.Its solubility is 8.6 3 10210 mg/l As cadmium electro-plating is performed in cyanide baths, the drag-out is al-kaline Therefore, alkaline carbonates and sulfides can re-move cadmium as an insoluble salt The hydroxide is toosoluble, resulting in cadmium concentrations of 5 to 10mg/l If carbon dioxide is subsequently absorbed beforeneutralization, additional cadmium will be removed.Cadmium, even when present in trace concentrations, isstrongly coprecipitated with calcium carbonate

Removal to concentration levels around 0.01 mg/l quires the removal of particulate carbonates or sulfides,since residual soluble cadimum can be expected to bewithin limits The particulates are very small and settlevery slowly, requiring digestion to increase particle size fol-lowed by settling or filtration to remove the fines

re-A treatment solution containing NaOH, Na2CO3, Na2Sand CaO will effect satisfactory treatment, but sulfide re-lease may result in disagreeable odors when final effluent

pH is reduced to low values, if the sulfide is not destroyed(e.g., by sodium hypochlorite, which is used for cyanidedestruction)

Ion exchange, reverse osmosis, electrodialysis, tion, and flotation processes can all remove cadmium fromwastewaters

distilla-Calcium

Calcium may be present in water solution as bicarbonate,sulfate, chloride, or nitrate It may also be produced in wa-ter solution when lime is used to neutralize waste acid.With the exception of calcium carbonate and calciumsulfate, most calcium compounds are very soluble The sol-ubility of calcium sulfate compounds varies with temper-ature Gypsum (CaSO4z 2H2O) has a solublity, in mg/l,

of about 1800 at 32°F, 2100 at 100°F, and about 1700

at 212°F The solublity of calcium carbonate in pure

wa-ter is small—about 15 mg/l However, when precipitated,

it produces supersaturated solutions that are relatively

sta-ble at water tempertures below 200°F

Precipitation in the presence of a common ion—either

calcium or carbonate—reduces solubility Precipitation in

the presence of about 5% by weight of calcium carbonate

virtually eliminates supersaturation This same

phenome-non is noted when calcium fluoride is precipitated

Precipitated calcium compounds are crystalline and

rela-tively easy to dewater by vacuum filtration at rates from

20 to 50 lb/sq ft/hr

Chromium

Hexavalent chromium salts occur as pollutants in

indus-trial effluents from leather, aluminum anodizing, and metal

plating Chemical plant effluents contain these from

ex-tensive use of chromium salts as corrosion inhibitors in

cooling systems

In industrial effluents, chromium wastes are treated by

reduction and precipitation, removing the pollutant, or by

ion exchange in which chromate salt is recovered and the

deionized water is reused The latter treatment recovers

the pollutant chromium for economical reuse

REDUCTION AND PRECIPITATION

Hexavalent chromium is first reduced to the trivalent state

by adding a reducing agent, with proper adjustment for

acidity This is followed by precipitation of the reduced

chromium as the hydroxide, which is then physically

re-moved from the system by settling The reactions are:

Reaction 8.3(8) proceeds almost instantaneously at a pH

of 2.0 or less Each reducing agent shown in the reaction

is effective; Fe2 1, however, requires an excess of about 21/2

times the stoichiometric quantity, resulting in an excess of

Fe(OH)3 sludge from neutralization In small treatment

systems, sodium metabisulfite (Na2S2O5) is usually the

pre-ferred reagent In water it hydrolyzes to sodium bisulfite,

and sulfuric acid must be added to lower the pH for the

reducing reaction Excess reagent must be added if

dis-solved oxygen is present in the wastewater Larger

sys-tems, on a batch or continuous basis, use sulfur dioxide,

which hydrolyzes to sulfurous acid Additional acid for pH

adjustment is not always required

ION EXCHANGE

Hexavalent chromium is recovered by ion exchange for

reuse as a chromate-rich solution This solution can be

re-cycled into the cooling tower water treatment system, andthe resulting chromate-free water may be disposed of orfurther demineralized and reused

A successful process contacts the chromate-ladenwastewater after proper pH adjustment, with a weak-baseanion exchange resin in the sulfate form The chromate(CrO42) ion exchanges with the sulfate (SO42) ion and isincorporated in the resin The chromate is recovered as amixture of sodium chromate (Na2CrO4) and sodiumdichromate (Na2Cr2O7) upon regeneration of the resin.The regenerant is a 5% (by weight) solution of causticsoda (NaOH) added in an overall quantity equivalent to10% in excess of the stoichiometric amount

Sodium hydroxide restores the chromate as sodium saltsand temporarily places the resin in the hydroxyl form Thesodium hydroxide on the resin is neutralized by adding thestoichiometric quantity of 0.1N sulfuric acid This neu-tralization step also restores the resin to the sulfate form.The reactions are as follows:

8.3(12)

where:

R° 5 R 3 N, a weakly basic macroporous resin

A typical flow diagram using the Higgins-type, ous, countercurrent ion exchange system is shown in

continu-Figure 8.3.1

Cyanides

The major portion of cyanide-containing wastewatercomes from metal finishing and metal plating plants.Photo-processing plants also contribute significantly.Cyanides are extremely poisonous, especially at acidic pHlevels, where they are present as hydrocyanic acid, a pow-erful poison Cyanide-containing wastewater should betreated prior to discharge into sewer lines, streams, orrivers Treatment processes usually involve either partialoxidation of the cyanide to the substantially less toxiccyanate or complete oxidation to carbon dioxide and ni-trogen Frequently used oxidizing agents include chlorine,ozone, and electrolytic oxidation The cyanide concentra-

tion in the effluent should be less than 0.2–1.0 ppm when

the receiving body is a sewer line, stream, or river

CHLORINATION

Oxidation of cyanide to cyanate occurs in the pH range

of 8–9 and requires only minutes (equation 8.3[13])

Further oxidation to carbon dioxide and nitrogen is much

slower, requiring hours (equation 8.3[14])

8.3(13)

N 2 1 2Na 2 CO 3 1 6NaCl 1 4H 2O 8.3(14)

Chlorine is added as gaseous chlorine or as a

hypochlo-rite solution Special equipment is required for safe and

ef-ficient addition of chlorine gas For smaller plants,

hypochlorite solution is recommended since metering and

handling is simpler and less hazardous Sludge formation

usually accompanies chlorination The sludge consists of

hydroxides of metal ions, always present in plating

solu-tion

OZONATION

Ozone oxidation of cyanides is best carried out in the pH

range of 9–10, and the oxidation of cyanide to cyanate is

extremely rapid (equation 8.3[15]) Further reaction of

cyanates is much slower The addition of copper (21) salt

catalysts accelerates the reaction A typical ozone control

system is shown in Figure 8.3.2

Cyanide oxidation can also be carried out electrolytically

The more toxic sodium and potassium cyanides can also

be converted to substantially less toxic ferrocyanide plexes by adding ferrous sulfate This process is not rec-ommended, however, because ferrocyanide releasescyanide when exposed to sunlight

com-Chlorination is the most frequently used and best veloped process The addition of chlorine gas is hazardousand requires storage of large quantities of chlorine Ozone

de-is a faster, more powerful oxidizing agent, requiringsmaller holding and reaction tanks The relative amountsrequired for each process are shown in Table 8.3.2

Fluoride

Fluoride occurs naturally in some U.S waters Dischargesfrom some industrial plants also contain fluoride The level

FIG 8.3.1 Chromate recovery by ion exchange.

FIG 8.3.2 Cyanide waste oxidation control systems utilizing ozone as the oxidant Key: pHRC 5 pH recording controller; ORPR 5 ORP recorder; PC 5 pressure controller; LLC 5 low- level control; AMP 5 amplifier

OF CYANIDE REMOVAL

Pound Chemical Required per lb Chemical of Cyanide Removed

Chlorine gas 2.7–6.8 Sodium hypochlorite 2.9–7.2 Calcium hypochlorite 2.8–6.9 Ozone 1.8–4.6

of fluoride is primarily of concern in domestic water

sup-plies Data indicate that an average of 1 mg/l of fluoride

is beneficial for the prevention of dental caries (the

allow-able level of fluoride is determined by the annual average

of the maximum daily air temperature) (U.S Public Health

Service 1962) Higher fluoride levels have been

responsi-ble for mottling of teeth The level of fluoride must also

be controlled for other uses, such as industrial water

sup-ply, irrigation water, stock watering, and aquatic life The

limits for these uses in mg/l (McKee and Wolf 1963) are

industrial water (1.0), stock watering (1.0), irrigation (10),

and aquatic life (1.5)

Wastewater effluents may contain some fluoride, as

long as adequate dilution is assured in the receiving stream

However, fluoride concentration in effluent is frequently

too great to be decreased by diluting waters, requiring

treatment of the waste stream prior to discharge

Principal flouride removal methods are precipitation by

lime, absorption on activated alumina, or removal by an

ion exchange process The addition of lime results in the

precipitation of fluoride as calcium fluoride:

2 HF 1 Ca(OH) 2 ® CaF 2 ¯ 1 2 H 2O 8.3(16)

Precipitated calcium fluoride can be settled out of solution

by thickening and clarification The settled chemical sludge

can then be treated as other sludges and dewatered

utiliz-ing vacuum filtration or centrifugation The limitutiliz-ing

fac-tor for this process is the solubility of calcium fluoride,

which is 7.8 mg/l (as F) There are indications that lime

high in magnesium can further reduce the fluoride

solu-bility concentration (Rohrer 1971)

Another method of fluoride removal is the use of an

aluminum compound to bind the aluminum and fluoride

as a complex While filter alum (aluminum sulfate) has

been investigated, it has not been effective, as other anions

in the water tend to reduce effectiveness Activated

alu-mina can be used to reduce fluoride concentration to the

1–2 mg/l range The capacity of activated alumina for

stor-ing fluoride is about 0.1 lb/cu ft Flowrates on the order

of 3–5 gpm/sq ft are possible The activated alumina can

be regenerated with caustic soda, aluminum sulfate, or

sul-furic acid with little apparent loss of capacity or activated

alumina volume

Ion exchange materials have also been investigated for

defluoridation of water Anion exchange materials

regen-erated with a caustic soda solution have been utilized, but

this is an expensive process if fluoride removal is the only

requirement

Hardness

Hardness is caused by divalent cations (ions with a

posi-tive charge of 21) Usually the offending cations are

cal-cium (Ca2 1) and magnesium (Mg2 1) These and similar

cations react with compounds containing monovalent

cations (usually sodium, Na1) to form insoluble products.Along with several lesser problems, these precipitants formencrustations and deposits in hot water pipes, heat ex-changers, and boilers (insolubility and precipitation in-crease with temperature) and also form scum when usingsoap for cleaning

The effect of soap added to water containing a calciumcompound is most striking Soap and many calcium com-pounds such as bicarbonate are normally soluble in wa-ter When the monovalent sodium ion in soap is replaced

by calcium, an insoluble end product is formed:

2C 17 H 35 COONa 1 Ca (HCO 3 ) 2 ® Soap Calcium

bicarbonate (C 17 H 35 COO) 2 Ca¯1 2NaHCO 3 8.3(16)

Insoluble scum Sodium

bicarbonate

Two types of hardness exist: carbonate hardness and carbonate hardness For the former, the cations are com-bined with either bicarbonate or carbonate For noncar-bonate hardness, the cations are combined with chlorides,sulfates, and other anions

non-ION EXCHANGE

To eliminate hardness, various resins known as zeolites

(Ze) are used These resins usually contain monovalentcations (usually Na1), but since they prefer divalent cationsfor stability, they exchange the Na1for calcium or mag-nesium

Ca 2 1 1 Na 2 Ze ® CaZe 1 2Na 1 8.3(17)

Sodium zeolite

The reaction may be reversed by adding a large quantity

of monovalent ions (Na1)

LIME AND LIME–SODA ASH SOFTENING

To reduce hardness to 80 or 100 mg/l, the lime or lime–soda ash softening processes may be used These processesare used when some hardness can be tolerated, as in do-mestic water supplies The operational cost of theseprocesses is much less than for the ion exchange process

In lime softening, calcium is removed as follows:

Ca (HCO 3 ) 2 1 Ca(OH) 2 ® 2CaCO3¯ 1 2H 2O 8.3(18)

Calcium Lime Calcium bicarbonate carbonate

The calcium carbonate is insoluble and precipitates out Ifnoncarbonate hardness such as calcium sulfate is also pre-sent, soda ash must be added:

Since lime is used in excess, the softened water still

con-tains Ca21and OH2ions that must be stabilized (Figure

8.3.3) This can be done by bubbling carbon dioxide

through the water (recarbonation) Water softening

oper-ations are usually followed by flocculation, settling, and

filtration

Iron

Iron usually occurs with manganese in groundwater The

presence of these metals in excess of 0.1 ppm and 0.05

ppm, respectively, is unacceptable for public water

sup-plies and for most industrial uses Above these

concentra-tions, precipitates are formed on contact with air; residuesstain fixtures and interfere with clothes washing and mostmanufacturing processes The iron may be a water solu-ble ferrous salt or iron bacteria, i.e., hydrated iron oxideenclosed in the cell structure of filamentous microorgan-

isms, such as Crenothrix polyspora Dissolved inorganic

iron is usually removed by aeration, chemical tion, or ion exchange Iron bacteria removal requires de-struction of cell membranes by strong oxidizing agentssuch as ozone or chlorine (Table 8.3.3)

precipita-The oxygen-poor, carbon dioxide–rich lower layers ofwater reservoirs reduce and dissolve iron salts in the soil

as ferrous salts Similarly, the relatively oxygen-free acidicFIG 8.3.3 Summary of hardness removal processes.

Treatment Nature of Contaminants Operating

pH Oxidation Remarks

Iron—no organic matter A-ST-SF 6.5 Yes Easy to operate

Iron and manganese; little organic matter A cat -ST-SF 6.5 Yes Easy to operate; requires double pumping Iron and manganese bound to organic A-F cat 6.5 Yes Easy to control; requires double pumping matter; no excessive organic acids “sniffler” valve

Iron and manganese bound to organic matter; F cat 6.5 Yes No aeration but filter reactivated by

no excessive organic acid or carbon dioxide chlorination or by permanganate Iron and manganese loosely bound to A-Cl-ST-SF 7.0–8.0 Yes Aeration reduces chlorine requirement organic matter

Iron and manganese in combination with A-L-ST-SF 8.5–9.6 Yes pH control required

organic matter and organic acids

Iron and manganese in colored turbid A-Co-L-ST-SF 8.5–9.6 Yes Laboratory control required

surface water containing organic matter

Iron and manganese in oxygen-free well water Cation exchange 6.5 No Periodic regeneration with salt

containing about 1.5 to 2.0 ppm iron and solution

groundwater dissolves iron deposits.

CONTROLLING IRON WITH BACTERIA

Filamentous microorganisms (C polyspora, Gallinella

fer-ruginea and Leptothrix ochracea) thrive in waters

con-taining traces of iron and/or manganese The actively

growing bacteria precipitate hydrated iron oxide in their

cell structures These bacteria grow in clumps of slime

at-tached to pipe walls or other submerged surfaces, causing

slow corrosion and dissolution of the iron, thereby

plug-ging the pipe Bacterial growth is controlled by careful

re-moval of iron and manganese from the water and by

pe-riodic disinfection with chlorine, ozone, or copper sulfate

REMOVING IRON SALTS

The treatment for removing dissolved iron salts usually

in-volves (1) oxidation by air, chlorine, or ozone followed by

filtration; (2) chemical precipitation followed by filtration;

or (3) ion exchange The capacity of the treatment plant,

the pH of the water, and the presence of other

contami-nants determine which process is the most economical

Iron is usually removed more readily than iron and

man-ganese together The removal of dissolved iron chelated to

organic compounds is usually accomplished by

coagula-tion followed by settling and filtracoagula-tion

Oxidation is accomplished most economically by

aera-tion Aeration also purges carbon dioxide from water,

which keeps iron dissolved as ferrous carbonate Iron

ox-ides may be removed by settling, filtration often is

neces-sary If the iron is loosely bound to organic matter, the

aeration process is slow and must be accelerated by iron

oxide or manganese dioxide catalysts deposited on sand,

crushed stone, or coke Chlorine and ozone effectively

ox-idize iron at low pH in the presence of a high organic

con-tent

Chemical precipitation by lime is usually effective if the

iron is present as ferric humates Above a pH of 9.6, most

iron is removed as ferric hydroxide Treatment is followed

by coagulation, settling, and filtration Ion exchange

ef-fectively removes ferrous and manganous salts using

sodium zeolite Air (oxygen) must be excluded in this

op-eration to prevent oxidation to iron and manganese

ox-ides, which can form precipitates and plug the ion

ex-change column This process also removes other salts in

the water and decreases hardness

Aeration is the most economical iron removal method

in large-capacity municipal treatment plants Chemical

precipitation is frequently used in beverage and food

pro-cessing plants Ozonation can selectively remove iron and

manganese and preserve the mineral taste of water

Lead

Lead is used mainly in various solid forms, as pure metaland in several compounds Major uses are storage batter-ies, bearings, solder, waste pipelines, radiation shielding,sound and vibration insulation, cable covering, ammuni-tion, printer’s type, surface protection, and weights andballasts

Wastewaters containing lead originate from only a few

of the processes that produce lead-containing products,such as plating, textile dyeing and printing, photography,and storage battery manufacturing and recycling

Lead is a toxic, heavy metal limited to 0.05 mg/l byUSPHS Drinking Water Standards, and to 0.10 mg/l byother standards Discharge standards in sewer use ordi-nances usually limit lead to 0.5 mg/l

TREATMENT METHODSChemical methods of treatment include batch, continuousflow, or integrated with the production process Table8.3.4 lists several insoluble lead compounds and their cor-responding solubilities at room temperature The anions

in these compounds and their sources are listed in Table8.3.5

Aluminum hydroxide from alum use aids in settling thelead sulfate formed A combination of hydroxide, car-bonate, and sulfide results in a buffered treatment solu-tion, allowing a check on the effectiveness of clarificationdue to the formation of black lead sulfide Hypochloritecan also be used to prepare the insoluble quadrivalent ox-ide:

Pb(OH) 2 1 ClO 2 ® PbO 2 1 H 2 O 1 Cl 2 8.3(21)

At high pH, lead exists as the plumbate ion, PbO22whichcan also be oxidized by hypochlorite

PbO 2 2 1 ClO 2 1 H 2 O ® PbO 2 1 Cl 2 1 2OH 2 8.3(22)

In reality, wastewaters contain other substances that also

require removal Therefore, a given treatment method may

also remove other substances, and a treatability study is

needed before selecting a treatment method

Expected effluent quality in terms of lead concentration

for batch or continuous flowthrough treatment is reported

to be 0.5 mg/l, whereas that for integrated treatment is

0.01 mg/l

The amphoteric nature of lead compounds requires

careful control of pH for both precipitation and handling

(dewatering) of sludges resulting from treatment Each

stage requires a different operating pH control range As

with all precipitation reactions, nucleation and crystal

growth are important, although the high molecular weight

of lead aids in particulate settling

Physical methods such as electrodialysis, ion exchange,

and reverse osmosis can also remove lead from

waste-waters Lead may also be removed by deliberately

intro-ducing the wastewater to acclimated biological treatment

plants for complexing with biologically formed organic

substances A combination of chemical and biological

methods, the in process treatment, can be used, with the

lead chemically complexed and removed from the

biolog-ical process

Magnesium

Magnesium is usually present in water or brine as

bicar-bonate, sulfate, or chloride It may also be produced in

water solutions, when dolomitic lime is used to neutralize

waste acid With the exception of magnesium hydroxide,

magnesium compounds are very soluble The solubility of

magnesium hydroxide is about 8 mg/l at ambient water

temperatures However, when precipitated without an

ex-cess of hydrogen ion, solubility, including supersaturated

mangesium hydroxide, rises to about 20 mg/l

If precipitation is carried out in the presence of a high

concentration—up to 5% by weight of previously

precip-itated hydroxide—supersaturation is reduced Magnesium

hydroxide usually precipitates as a flocculant material,

which settles slowly and will only concentrate to about

1% by weight However, when precipitated in the

pres-ence of previously precipitated solids, the settling rate anddensity of the settled sludge increase considerably.Magnesium is not considered a contaminant in waste-water unless it is present in a brine (saltwater) However,concentrations in excess of 125 mg/l can exert a catharticand diuretic effect In addition, magnesium salts breakdown on heating to form boiler scale

ManganeseThe limit for manganese in drinking water is 0.05 ppm.Above that concentration it stains fixtures and interfereswith laundering and chemical processing Manganese usu-ally occurs with iron in ground and surface waters, andmany iron-removing processes (Table 8.3.3) will also re-move manganese The treatment process usually oxidizesthe water-soluble manganous salts to insoluble manganesedioxide by catalytic air oxidation in the pH range of8.5–10, by chlorination at a pH of 9–10, or by ozonation

at neutral pH Ion exchange is also effective, but it removesother salts that may or may not be desirable

Manganese, like iron, is extracted from the bottom ofdeep reservoirs or from the ground by carbon dioxide–rich,oxygen-poor water as manganous bicarbonate

Catalytic air oxidation at an alkaline pH is the mosteconomical method for large treatment plants Aerationoccurs on contact beds of coke or stone coated with man-ganese dioxide or on beds of pyrolusite Oxidation is morerapid when the pH is adjusted between 8.5 and 10.0 bylime or caustic (Table 8.3.6) One ppm dissolved oxygenoxidizes approximately 7 ppm manganese The insolublemanganese dioxide is usually removed by settling and fil-tration

Oxidation of manganese can also be carried out at aneutral pH using ozone as oxidant, and excessive ozonedosages can oxidize the manganese to pink permanganate.Chlorine oxidation of manganese requires no catalyst.Ion exchange processes using sodium or hydrogen ex-change resin remove manganous salts effectively, togetherwith other salts The exchange resin has to be regenerated

COMPOUNDS

Anion Source of Anion

Chromate (CrO 4 2 ) Spent chrome plating bath

or chrome plating rinse

IRON AS A FUNCTION OF PH

Manganese Iron Residue Precipitated Residue Precipitated

pH (ppm) (ppm) (%) (ppm) (ppm) (%)

8.0 5.49 0.0 0.0 1.53 4.06 72.6 8.8 5.49 0.0 0.0 0.47 5.12 91.6 9.0 1.90 3.59 65.4

9.2 1.00 4.49 81.7 9.4 0.11 5.38 98.0 0.06 5.53 98.9 9.6 0.03 5.46 99.4 0.00 5.59 100.0