Handbook of industrial and hazardous wastes treatment - Part 7 (end) potx

The rubber processing industry is divided into 11 subcategories based on raw waste loadsas a function of production levels, presence of the same or similar toxic pollutants resulting fro

Zorex Corporation, Newtonville, New York, U.S.A., and

Lenox Institute of Water Technology, Lenox, Massachusetts, U.S.A

Yung-Tse Hung

Cleveland State University,

Cleveland, Ohio, U.S.A

SIC 2822: Synthetic Rubber Manufacturing (vulcanizable elastomers);

SIC 3011: Tire and Inner Tube Manufacturing;

SIC 3021: Rubber Footwear;

SIC 3031: Reclaimed Rubber;

SIC 3041: Rubber Hose and Belting;

SIC 3069: Fabricated Rubber Products, Not Elsewhere Classified; and

SIC 3293: Rubber Gaskets, Packing, and Sealing Devices

Approximately 1650 plants exist in the United States and have production ranges from1.6  103kkg/year (3.5  106lb/year) to 3.7  108Kkg/year (8.2  108lb/year). Table 1presents a summary of the rubber processing industry regarding the number of subcategories andthe number and types of dischargers Table 2presents a subcategory profile of best practicalcontrol technology currently available (BPT) regulations (daily maximum and 30-day averages)[2] The effluent limitations are shown as kilogram of pollutants per 1000 kg of raw material

processed (kg/kkg).

1233

The rubber processing industry is divided into 11 subcategories based on raw waste loads

as a function of production levels, presence of the same or similar toxic pollutants resulting fromsimilar manufacturing operations, the nature of the wastewater discharges, frequency andvolume of discharges, and whether the discharge is composed of contact or noncontactwastewater Other primary considerations are treatment facilities and plant size, age, andlocation The 11 subcategories are listed below A brief description of each subcategory follows Subcategory 1: Tire and Inner Tube Manufacturing;

Subcategory 2: Emulsion Crumb Rubber Production;

Subcategory 3: Solution Crumb Rubber Production;

Subcategory 4: Latex Rubber Production;

Subcategory 5: Small-Sized General Molding, Extruding, and Fabricating Rubber

Subcategory 8: Wet Digestion Reclaimed Rubber;

Subcategory 9: Pan, Dry Digestion, and Mechanical Reclaimed Rubber;

Subcategory 10: Latex-Dipped, Latex-Extruded, and Latex Molded Goods;

Subcategory 11: Latex Foam

Subcategory 1 Tire and Inner Tube Manufacturing

The production of tires and inner tubes involves three general steps: mixing and preliminaryforming of the raw materials, formation of individual parts of the product, and constructing andcuring the final product In total, 73 plants use these general steps to produce tires in the UnitedStates

The initial step in tire construction is the preparation or compounding of the raw materials.The basic raw materials for the tire industry include synthetic and natural rubber, reinforcingagents, fillers, extenders, antitack agents, curing and accelerator agents, antioxidants, andpigments The fillers, extenders, reinforcing agents, pigments, and antioxidant agents are addedand mixed into the raw rubber stock This stock is nonreactive and can be stored for later use.When curing and accelerator agents are added, the mixer becomes reactive, which means it has ashort shelf-life and must be used immediately

Industry: Rubber processing

Total number of subcategories: 11

Number of subcategories studied: 3a

Number of dischargers in industry:

† Direct: 1054

† Indirect: 504

† Zero: 100

a

Wet digestion, although not a paragraph 8 exclusion, was

not studied because of the lack of plant-specific data.

Emulsion and solution crumb rubber, although candidates

for exclusion, were studied, because data were available

Source: USEPA.

Table 2 BPT Limitations for Subcategories of Rubber Processing Industry (kg/kkg of raw material)

Tire and innertube plantsb

Emulsion crumbrubber

Solution crumb

Pollutant

Dailymax

30-dayavg.a

Dailymax

30-dayavg.a

Dailymax

30-dayavg.a

Dailymax

30-dayavg.a

Dailymax

30-dayavg.a

Dailymax

30-dayavg.a

Pan, dry digestion,mechanical

Dailymax

30-dayavg.a

Dailymax

30-dayavg.a

Dailymax

30-dayavg.a

Dailymax

30-dayavg.a

Dailymax

30-dayavg.a

a Computed from average daily value taken over 30 consecutive days.

bOil and grease limitations for nonprocess wastewater from plants placed in operation before 1959: daily max ¼ 10 mg/L; 30-day avg ¼ 5 mg/L.

c General molded, extruded, and fabricated rubber.

d Limitation is 6 – 9 pH units for all subcategories.

e Latex-dipped, latex-extruded, and latex-molded goods.

After compounding, the stock is sheeted out in a roller mill and extruded into sheets orpelletized This new rubber stock is tacky and must be coated with an antitack solution, usually asoapstone solution or clay slurry, to prevent the sheets or pellets from sticking together duringstorage.

The rubber stock, once compounded and mixed, must be molded or transformed into theform of one of the final parts of the tire This consists of several parallel processes by which thesheeted rubber and other raw materials, such as cord and fabric, are made into the followingbasic tire components: tire beads, tire treads, tire cords, and the tire belts (fabric) Tire beads arecoated wires inserted in the pneumatic tire at the point where the tire meets the wheel rim (onwhich it is mounted); they ensure a seal between the rim and the tire The tire treads are the part

of the tire that meets the road surface; their design and composition depend on the use of the tire.Tire cords are woven synthetic fabrics (rayon, nylon, polyester) impregnated with rubber; theyare the body of the tire and supply it with most of its strength Tire belts stabilize the tires andprevent the lateral scrubbing or wiping action that causes tread wear

The processes used to produce the individual tire components usually involve similarsteps First, the raw stock is heated and subjected to a final mixing stage before going to a rollermill The material is then peeled off rollers and continuously extruded into the final componentshape Tire beads are directly extruded onto the reinforcing wire used for the seal, and tire belt isproduced by calendering rubber sheet onto the belt fabric

The various components of the tire are fitted together in a mold to build green, or uncured,tires which are then cured in an automatic press Curing times range from less than one hour forpassenger car tires to 24 hours for large, off-the-road tires After curing, the excess rubber on thetire is ground off (deflashed) to produce the final product

This subcategory is often subdivided into two groups of plants: (a) those startingoperations prior to 1959, (applies to 39 plants) and (b) those starting operations after 1959 Thissubdivision must be recognized in applying limitations on plant effluents of oil and greasebecause BPT limitations are different for the two groups of plants For plants placed in operation

after 1959, the 30-day average oil and grease limitation is 0.016 kg/kkg of product For plants placed in operation prior to 1959, the limitation is the same (0.016 kg/kkg) but only for process

wastewater Process wastewater for these pre-1959 plants comes from soapstone solutionapplications, steam cleaning operations, air pollution control equipment, unroofed process oilunloading areas, mold cleaning operations, latex applications, and air compressor receivers.Water used only for tread cooling and discharges from other areas of such plants is classified as

nonprocess wastewater, in which oil and grease levels are limited to 5 mg/L as a 30-day average and 10 mg/L as a daily maximum.

Emulsion polymerization, the traditional process for synthetic rubber production, is thebulk polymerization of droplets of monomers suspended in water Emulsion polymerization isoperated with sufficient emulsifier to maintain a stable emulsion and is usually initiated byagents that produce free radicals This process is used because of the high conversion and thehigh molecular weights that are possible Other advantages include a high rate of heat transferthrough the aqueous phase, easy removal of unreacted monomers, and high fluidity at highconcentrations of product polymer Over 90% of styrene butadiene rubber (SBR) is produced bythis method Approximately 17 plants use the emulsion crumb rubber process

Raw materials for this process include styrene, butadiene, catalyst, activator, modifier, andsoap solution

Polymerization proceeds stepwise through a train of reactors This reactor systemcontributes significantly to the high degree of flexibility of the overall plant in producingdifferent grades of rubber The reactor train is capable of producing either “cold” (277 – 280 K,

103 – 206 kPa) or “hot” (323 K, 380 – 517 kPa) rubber The cold SBR polymers, produced at the

lower temperature and stopped at 60% conversion, have improved properties when compared tohot SBRs The hot process is the older of the two For cold polymerization, the monomer –additive emulsion is cooled prior to entering the reactors Each reactor has its own set of coolingcoils and is agitated by a mixer The residence time in each reactor is approximately one hour.Any reactor in the train can be bypassed The overall polymerization reaction is ordinarilycarried to no greater than 60% conversion of monomer to rubber since the rate of reaction fallsoff beyond this point and product quality begins to deteriorate The product rubber is formed inthe milky white emulsion phase of the reaction mixture called latex Short stop solution is added

to the latex exiting the reactors to quench the polymerization at the desired conversion Thequench latex is held in blowdown tanks prior to the stripping operation

The stripping operation removes the excess butadiene by vacuum stripping, and thenremoves the excess styrene and water in a perforated plate stripping column The water andstyrene from the styrene stripper are separated by decanting and the water is discharged to thetreatment facility The recovered monomers are recycled to the monomer feed stage The latex isnow stabilized and is precipitated by an electrolyte and a dilute acid This coagulation impartsdifferent physical characteristics to the rubber depending on the type of coagulants used Carbon

black and oil can be added during this coagulation/precipitation step to improve the properties

of the rubber This coagulated crumb is separated from the liquor, resuspended and washed withwater, then dewatered, dried, and pressed into bales for shipment The underflow from thewashing is sent to the wastewater treatment facility

Subcategory 3: Solution Crumb Rubber Production

Solution polymerization is bulk polymerization in which excess monomer serves as the solvent.Solution polymerization, used at approximately 13 plants, is a newer, less conventional processthan emulsion polymerization for the commercial production of crumb rubber Polymerizationgenerally proceeds by ionic mechanisms This system permits the use of stereospecific catalysts

of the Ziegler – Natta or alkyl lithium types which make it possible to polymerize monomers into

a cis structure characteristic that is very similar to that of natural rubber This cis structure yields

a rubbery product, as opposed to a trans structure which produces a rigid product similar toplastics

The production of synthetic rubbers by solution polymerization processes is a stepwiseoperation very similar in many aspects to production by emulsion polymerization Thereare distinct differences in the two technologies, however For solution polymerization, themonomers must be extremely pure and the solvent should be completely anhydrous In contrast

to emulsion polymerization, where the monomer conversion is taken to approximately 60%,solution polymerization systems are polymerized to conversion levels typically in excess of90% The polymerization reaction is also more rapid, usually being completed in 1 to 2 hours.Fresh monomers often have inhibitors added to them while in storage to prevent prematurepolymerization These inhibitors and any water that is present in the raw materials must beremoved by caustic scrubbers and fractionating drying columns to provide the solution processwith the high purity and anhydrous materials needed The purified solvent and monomers arethen blended into what is termed the “mixed feed,” which may be further dried in a desiccantcolumn

The dried mixed feed is now ready for the polymerization step, and catalysts can be added

to the solution (solvent plus monomers) just prior to the polymerization stage or in the leadpolymerization reactor

The blend of solution and catalysts is polymerized in a series of reactors The reaction ishighly exothermic and heat is removed continuously by either an ammonia refrigerant or by

chilled brine or glycol solutions The reactors are similar in both design and operation to thoseused in emulsion polymerization The mixture leaves the reactor train as a rubber cement, that is,polymeric rubber solids dissolved in solvent A short stop solution is added to the cement afterthe desired conversion is reached.

The rubber cement is then sent to storage tanks where antioxidants and extenders aremixed in The rubber cement is pumped from the storage tank to the coagulator where the rubber

is precipitated with hot water under violent agitation The solvent and unreacted monomer arefirst steam stripped overhead and then condensed, decanted, and recycled to the feed stage.The bottom water layer is discharged to the wastewater treatment facility

The stripped crumb slurry is further washed with water, then dewatered, dried, and baled

as final product Part of the water from this final washing is recycled to the coagulation stage, andthe remainder is discharged for treatment

Subcategory 4: Latex Rubber Production

The emulsion polymerization process is used by 17 production facilities to produce latex rubberproducts as well as solid crumb rubber Latex production follows the same processing steps asemulsion crumb rubber production up to the finishing process Between 5 and 10% of emulsionpolymerized SBR and nearly 30% of nitrile rubber production (NBR) are sold as latex Latexrubber is used to manufacture dipped goods, paper coatings, paints, carpet backing, and manyother commodities

Monomer conversion efficiencies for latex production range from 60% for temperature polymerization to 98% for high-temperature conversion

low-The monomers are piped from the tank farm to the caustic soda scrubbers where theinhibitors are removed Soap solution, catalysts, and modifiers are added to produce a feedemulsion which is fed to the reactor train Fewer reactors are normally used than the numberrequired for a crumb product line When polymerization is complete, the latex is sent to aholding tank where stabilizers are added

A vacuum stripper removes any unwanted butadiene, and the steam stripper following itremoves the excess styrene Neither the styrene nor butadiene is recycled Solids are removedfrom the latex by filters, and the latex may be concentrated to a higher solids level

Subcategories 5, 6, 7: Small-, Medium-, and Large-Sized General Molding,

Extruding, and Fabricating Plants

These three closely related subcategories are divided based on the volume of wastewateremanating from each These subcategories include a variety of processes such as compressionmolding, transfer molding, injection molding, extrusion, and calendering An estimated 1385plants participate in these subcategories

A common step for all of the above processes is the compounding and mixing of theelastomers and compounding ingredients The mixing operation is required to obtain a thoroughand uniform dispersion of the rubber and other ingredients Wastewater sources from the mixingoperation generally derive from leakage of oil and grease from the mixers

Compression molding is one of the oldest and most commonly used manufacturingprocesses in the rubber fabrication industry General steps for the processes include warming theraw materials, preforming the warm stock into the approximate shape, cooling and treating withantitack solution, molding by heat and pressure, and finally deflashing Major products from thisprocess include automotive parts, medical supplies, and rubber heels and soles

Transfer molding involves the forced shifting of the uncured rubber stock from one part

of the mold to another The prepared rubber stock is placed in a transfer cavity where a ram

forces the material into a heated mold The applied force combined with the heat from the moldsoftens the rubber and allows it to flow freely into the entire mold The molded item is cured,then removed and deflashed Final products include V-belts, tool handles, and bushings withmetal inserts.

Injection molding is a sophisticated, continuous, and essentially automatic process thatuses molds mounted on a revolving turret The turret moves the molds through a cyclic processthat includes rubber injection, curing, release agent treatment, and removal Deflashing occursafter the product has been removed A wide range of products is made by this process, includingautomotive parts, diaphragms, hot-water bottles, and wheelbarrow tires

The extrusion process takes unvulcanized rubber and forces it trough a die, which results

in long lengths of rubber of a definite cross-section There are two general subdivisions of thistechnique; one extrudes simple products and the other builds products by extruding the rubberonto metal or fabric reinforcement Products from these techniques include tire tread, cablecoating, and rubber hose

Calendering involves passing unformed or extruded rubber through a set or sets of rolls toform sheets or rolls of rubber product The thickness of the material is controlled by the spacebetween the rolls The calender may also produce patterns, double the product thickness bycombining sheets, or add a sheet of rubber to a textile material The temperature of the calenderrolls is controlled by water and steam Products produced by this process include hospitalsheeting and sheet stock for other product fabrication

This subcategory represents a process that is used to recover rubber from fiber-bearingscrap Scrap rubber, water, reclaiming and defibering agents, and plasticizers are placed in asteam-jacketed, agitator-equipped autoclave Reclaiming agents used to speed up depolymer-ization include petroleum and coal tar-base oils and resins as well as various chemical softenerssuch as phenol alkyl sulfides and disulfides, thiols, and amino acids Defibering agentschemically do the work of the hammer mill by hydrolyzing the fiber; they include caustic soda,zinc chloride, and calcium chloride

A scrap rubber batch is cooked for up to 24 hours and then discharged into a blowdowntank where water is added to facilitate subsequent washing operations Digester liquor isremoved by a series of screen washings The washed rubber is dewatered by a press and thendried in an oven Two major sources of wastewater are the digester liquor and the washwaterfrom the screen washings

Two rubber reclaiming plants use the wet digestion method for reclamation of rubber

Subcategory 9: Pan, Dry Digestion, and Mechanical Reclaimed Rubber

This subcategory combines processes that involve scrap size reduction before continuing thereclaiming process The pan digestion process involves scrap rubber size reduction on steel rolls,followed by the addition of reclaiming oils in an open mixer The mixture is discharged intoopen pans, which are stacked on cars and rolled into a single-cell pressure vessel where livesteam is used to heat the mixture Depolymerization occurs in 2 to 18 hours The pans are thendischarged and the cakes of rubber are sent on for further processing The steam condensate ishighly contaminated and is not recycled

The mechanical rubber reclaiming process, unlike pan digestion, is continuous andinvolves fiber-free scrap being fed into a horizontal cylinder containing a screw that works thescrap against the heated chamber wall Reclaiming agents and catalysts are used fordepolymerization As the depolymerized rubber is extruded through an adjustable orifice, it isquenched The quench vaporizes and is captured by air pollution control equipment Thecaptured liquid cannot be reused and is discharged for treatment

Subcategory 10: Latex-Dipped, Latex-Extruded, and Latex-Molded Goods

These three processes involve the use of latex in its liquid form to manufacture products Latexdipping consists of immersing an impervious male mold or article into the latex compound,withdrawing it, cleaning it, and allowing the adhering film to air dry The straight dip process isreplaced by a coagulant dip process when heavier films are desired Fabric or other items may bedipped in latex to produce gloves and other articles When it has the required coating, the mold isleached in pure water to improve physical and electrical properties After air drying, the itemsare talc-dusted or treated with chlorine to reduce tackiness Water is often used in severalprocesses, for makeup, cooling, and stripping Products from dipping include gloves, footwear,transparent goods, and unsupported mechanical goods

Latex molding employs casts made of unglazed porcelain or plaster of paris The molds aredusted with talc to prevent sticking The latex compound is then poured into the mold andallowed to develop the required thickness The mold is emptied of excess rubber and then ovendried The mold is removed and the product is again dried in an oven Casting is used tomanufacture dolls, prosthetics, printing matrices, and relief maps

Subcategory 11: Latex Foam

No latex foam facilities are known to be in operation at this time

30.1.2 Wastewater Characterization

The raw wastewater emanating from rubber manufacturing plants contains toxic pollutants thatare present due to impurities in the monomers, solvents, or the actual raw materials, or areassociated with wastewater treatment steps Both inorganic and organic pollutants are found inthe raw wastewater, and classical pollutants may be present in significant concentrations

Wastewater from reclaimed rubber manufacturing had 16,800 – 63,400 mg/L total solids,

1000 – 24,000 mg/L suspended solids, 3500 – 12,500 mg/L BOD (biochemical oxygen demand), 130 – 2000 mg/L chlorides, pH of 10.9 – 12,2, wile wastewaters from synthetic rubber manufacturing had 1900 – 9600 mg/L total solid, 60 – 3700 mg/L suspended solids,

75 – 1600 mg/L BOD, and pH of 3.2 – 7.9 [3].

Table 3presents an industry-wide profile of the concentration of toxic pollutants found atfacilities in each subcategory (no data are available for Subcategories 9, 10, and 11).Table 4gives a subcategory profile of the pollutant loadings (no data are available for Subcategories 8,

10, and 11) These tables were prepared from available screening and verification sampling data

The minimum detection limit for toxic pollutants is 10 mg/L and any value below 10 mg/L is

presented in the following tables as BDL, below detection limit

In-plant management practices may often control the volume and quality of the treatmentsystem influent Volume reduction can be attained by process wastewater segregation fromnoncontact water, by recycling or reuse of noncontact water, and by the modification of plantprocesses Control of spills, leakage, washdown, and storm runoff can also reduce the treatmentsystem load Modifications may include the use of vacuum pumps instead of steam ejectors,recycling caustic soda solution rather than discharging it to the treatment system, andincorporation of a more efficient solvent recovery system

30.1.3 Tire and Inner Tube Manufacturing

The tire and inner tube manufacturing industry has several potential areas for wastewaterproduction, but water recycle is used extensively The major area for water use is in processes

Table 3 Concentrations of Toxic Pollutants Found in the Rubber Processing Industry by Subcategory, Verification, and Screening

Toxic pollutants (mg/L)

Tire and inner tube manufacturing

Number of

Number of

Metals and Inorganics

Table 3 Continued

Toxic pollutants (mg/L)

Tire and inner tube manufacturing

Table 3 Continued

Toxic pollutants (mg/L)

Tire and inner tube manufacturing

Analytic methods: V.7.3.29, Data sets 1,2.

BDL, below detection limit.

a

40 mg/L of trichloroethylene also measured in city water.

b

Detection limit of acrylonitrile by direct aqueous injection was 2300 mg/L.

c This value believed to be a glassware contaminant.

d These pollutants appear to be attributed to tire operation.

e Wastewater is from both tire and reclaiming processes.

Table 4 Industry Profile of Toxic and Classical Pollutant Loadings, Verification, and Screening Data (Toxic Pollutants Kg/kkg)

Tire and inner tube manufacturing

Table 4 Continued

Tire and inner tube manufacturing

Latex rubber manufacturingMetals and Inorganics

Metals and Inorganics

Table 4 Continued

Tire and inner tube manufacturing

Analytic methods: V.7.3.29, Data sets 1,2.

BDL, below detection limit.

requiring noncontact cooling The general practice of the industry is to recirculate the majority

of this water with a minimal blowdown to maintain acceptable concentrations of dissolvedsolids Another water use area is contact water used in cooling tire components and in airpollution control devices This water is also recirculated Steam condensate and hot andcold water are used in the molding and curing areas The majority of the water is recycled back

to the boiler or hot water tank for use in the next recycle Soapstone areas and plant andequipment cleanup are the final water use areas Most facilities try to recycle soapstone solutionbecause of its high solids content Plant and equipment cleanup water is generally sent to thetreatment system Table 5 presents a summary of the potential wastewater sources for thissubcategory

Grease, oils, and suspended solids are the major pollutants within this industry Organicpollutants, pH, and temperature may also require treatment The organics present are duegenerally to poor housekeeping procedures

30.1.4 Emulsion Crumb Rubber Production

In-process controls for the reduction of wastewater flows and loads for emulsion crumb rubberplants include recycling of finishing line wastewaters and steam stripping of heavy monomerdecanter wastewater Recycling of finishing line wastewater occurs at nearly all emulsion crumbplants with the percent recycle depending primarily upon the desired final properties of thecrumb Approximately 75% recycle is an achievable rate, with recycle for white masterbatchcrumb below this level and that for black masterbatch crumb exceeding it

Organic toxic pollutants found at emulsion crumb rubber plants come from the rawmaterials, impurities in the raw materials, and additives to noncontact cooling water BOD,COD, and TSS levels may also reach high loadings

Tube Industry

Nature and origin ofwastewater contaminants

discharges from wet airpollution equipment

Solids from soapstone dip tanks; oil from seals

in roller mills; oil from solids from Banburyseals; solids from air pollution equipmentdischarge

Bead, tread, tube

formation

cementing operation; oil from seals in rollermills

Cord and belt

formation

oil from seals, in roller mills, calenders, etc

pollution equipment

Organics and solids from spray-paintingoperation; soluble organics and solids fromair pollution equipment discharge

pollution equipment

Solids and soluble organics from paintingoperations; solids from air pollutionequipment discharge

Source: USEPA.

Table 6 lists potential wastewater sources and general wastewater contaminants for theemulsion crumb rubber industry.

30.1.5 Solution Crumb Rubber Production

Solution crumb rubber production plants have lower raw wastewater loads than emulsion crumbplants because of the thorough steam stripping of product cement to remove solvent and permiteffective coagulation Recycling in this industry is comparable to that in the emulsion crumbindustry, with about 75% of the wastewater being recirculated

Toxic pollutants found in the wastewater streams are normally related to solvents andsolvent impurities, product additives, and cooling water treatment chemicals.Table 7presents alisting of the potential wastewater sources and the associated contaminants for this industry

30.1.6 Latex Rubber Production

No in-process contact water is currently used by the latex rubber industry No raw materialrecycling is practised because of poor control of monomer feeds and the buildup of impurities inthe water

Organic toxic pollutants and chromium are present in the raw wastewater and normallyconsist of raw materials, impurities, and metals used as cooling water corrosion inhibitors.Table 8presents potential wastewater sources and general contaminants for this industry

30.1.7 General Molding, Extruding, and Fabricating Rubber Plants

Toxic pollutants resulting from production processes within this industry are generally the result

of leaks, spills, and poor housekeeping procedures Pollutants include organics associated withthe raw materials and lead from the rubber curing process

Caustic soda

scrubber

Spent causticsolution

High pH, alkalinity, and color Extremely low averageflow rate

and COD discharges

overflow

Acidity, dissolved organics, suspended and high dissolvedsolids, and color High wastewater flow rates relative toother sources

overflow

Dissolved organics, and suspended and dissolved solids.Source of highest wastewater volume from emulsioncrumb rubber production

30.1.8 Rubber Reclamation

Wastewater effluents from this subcategory contain high levels of toxic organic and inorganicpollutants These pollutants generally result from impurities in the tires and tubes used in thereclamation process The wastewater from the pan process is of low volume [0.46 m3/kkg (56 gal/

1000 lb)], but is highly contaminated, requiring treatment before discharge The mechanicalreclaiming process uses water only to quench the reclaimed rubber, but it uses a much higher quantity(1.1 m3/kkg) Steam generated from the quenching process is captured in a scrubber and sent to the

treatment system Wet digestion uses 5.1 m3of water per kkg (610 gal/1000 lb) of product in

processing, of which 3.4 m3/kkg (407 gal/1000 lb) of product is used in air pollution control.

30.1.9 Latex-Dipped, Latex-Extruded, and Latex-Molded Goods

Wastewater sources in this subcategory are the leaching process, makeup water, cooling water, andstripping water Toxic pollutants are present at insignificant levels in the wastewater discharges

average flow rateMonomer and solvent

overflow

Dissolved organics, and suspended anddissolved solids Source of highest volumewastewater flow

suspended and dissolved solids

Source: USEPA.

low average flow rate

latex concentration

Dissolved organics, suspended anddissolved solids Relatively highwastewater flow rates

dissolved solids High quantities ofuncoagulated latex

dissolved solids High quantities ofuncoagulated latex

suspended and dissolved solids

Source: USEPA.

Plant 000012 produces 3.9  104kkg/year (8.7  107lb/year) of emulsion crumb

rubber, primarily neoprene The contact wastewater flow rate is approximately 8.45 m3/day

(2.25  103gpd) and includes all air pollution control equipment, sanitary waste, maintenanceand equipment cleanup, and direct contact wastewater The treatment process consists ofactivated sludge, secondary clarification, sludge thickening, and aerobic sludge digestion.Noncontact wastewater, with a flow rate of approximately 1.31  105m3/day (3.46  107gpd),

is used on a once-through basis and is returned directly to the river source Contact wastewater isalso returned to the surface stream after treatment

Plant 000033 produces three types of emulsion crumb rubber in varying quantities.Styrene butadiene rubber (SBR) forms the bulk of production, at nearly 3.7  105kkg/year

(8.2  108lb/year), with nitrile butadiene rubber (NBR) and polybutadiene rubber (PBR)

making up the remainder of production [4.5  103kkg/year (1.0  107lb/year) and

4.5  103kkg/year, respectively] Wastewater consists of direct contact process water,

noncontact blowdown, and noncontact ancillary water The total flow of contact water isapproximately 1.27  104m3/day (3.355  106gpd), and the total flow of noncontact water is340.4 m3/day (9  104gpd) Treatment of the wastewater consists of coagulation, sedimen-tation, and biological treatment with extended aeration Treated wastewater is discharged to asurface stream

Tables 9 and 10 present plant-specific toxic pollutant data for the selected plants.Table 11gives plant-specific classical pollutant data, including BPT regulations set for eachspecific plant

30.2.1 Solution Crumb Rubber Production

Plant 000005 produces approximately 3.2  104kkg/year (7.0  107lb/year) of isobutene –

isopropene rubber Wastewater generally consists of direct processes and MEC water Contactwastewater flow rate is approximately 1040 m3/day (2.75  105gpd), and noncontact waterflows at about 327 m3/day (8.64  104gpd) Treatment consists of coagulation, flocculation,and dissolved air flotation, and the treated effluent becomes part of the noncontact coolingstream of the onsite refinery

Plant 000027 produces polyisoprene crumb rubber [4.5  104kkg/year (1.0  108lb/

year)] polybutadiene crumb rubber, and ethylene-propylene-diene-terpolymer rubber [EPDM;4.5  104kkg/year (1.0  108lb/year)] Wastewater consists of contact process water,

MEC, cooling tower blowdown, boiler blowdown, and air pollution control Wastewater isproduced at about 12,100 m3/day (3.2  106gpd) Treatment consists of API separators,sedimentation, stabilization, and lagooning, followed by discharge to a surface stream

Tables 12and13show plant specific toxic pollutant data for the above plants Classicalpollutant data and BPT regulations are presented inTable 14.

30.2.2 Dry Digestion Reclaimed Rubber

A data summary for plant 000134 is given in Table 15 Production, wastewater flow, andtreatment data are currently not available for a plant within this subcategory

In this industry, numerous organic compounds, BOD, and COD are typically found in plantwastewater effluent Industrywide flow and production data show that these pollutants can bereduced by biological treatment In emulsion crumb and latex plants, uncoagulated latexcontributes to high suspended solids Suspended solids are produced by rubber crumb fines andinclude both organic and inorganic materials Removal of such solids is possible using a

combination of coagulation/flocculation and dissolved air flotation.

Solvents, extender oils, and insoluble monomers are used throughout the rubber industry

In addition, miscellaneous oils are used to lubricate machinery Laboratory analysis indicatesthe presence of oil and grease in the raw wastewater of these plants Oil and grease entering thewastewater streams are removed by chemical coagulation, dissolved air flotation, and, to someextent, biological oxidation

Table 9 Plant-Specific Verification Data for Emulsion Production Plant 000012

Local in process line

Pollutant

Stripperdecant

Spray washwater

Treatmentinfluent

Treatmenteffluent

Raw intakewater

Analytic methods: V.7.3.29, Data set 2.

Flow rate (cu m/day): contact ¼ 8.45; noncontact ¼ 131,000.

Source: USEPA.

Table 10 Plant-Specific Verification Data for Emulsion Crumb Rubber Production Plant 000033

Location in process line

Pollutant (mg/L)

SBRstripper

Finishingcomp

NBRfinishing

Treatmentinfluent

Treatmenteffluent

NBRdecant

Raw intake,well

Raw intake,river

Analytic methods: V.7.3.29, Data set 2.

Flow rate (cu.m/day): SBR – contact ¼ 10,200, noncontact ¼ 190; NBR – contact ¼ 1,250, noncontact ¼ 75.7; PBR – contact ¼ 1,250, noncontact ¼ 75.7; Total – contact ¼ 12,700,

Wastewater sampling indicates that toxic pollutants found in the raw wastewater can beremoved Biological oxidation (activated sludge) adequately treats all of the organic toxicpollutants identified in rubber industry wastewater streams Significant removal of metals wasalso observed across biological treatment The metals are probably absorbed by the sludge massand removed with the settled sludge Treatment technologies currently in use are described in thefollowing subcategory descriptions.

30.3.1 Emulsion Crumb Rubber Plants

There are a total of 17 plants in the United States producing emulsion-polymerized crumbrubber Five of these plants discharge to POTWs; 10 discharge to surface streams; one plantdischarges to an evaporation pond; and one plant employs land application with hauling ofsettled solids Of the five plants discharging to POTWs, four pretreat using coagulation andprimary treatment and one employs equalization with pH adjustment All 10 of the plantsdischarging to surface streams employ biological waste treatment ranging from conventionalactivated sludge to nonaerated wastewater stabilization lagoons

Organic pollutants are generally found to be reduced to insignificant levels (,10 mg/L)

by biological treatment Most metals are also found to be reduced across biological treatment;they are generally at very low levels in the treated effluent However, significant metalconcentrations may be found in some treated effluent

At emulsion crumb rubber facilities, a well-operated biological treatment facility permitscompliance with BPT limitations and reduces organic toxic pollutant levels Toxic metals thatmay not be reduced include chromium, cadmium, copper, selenium, and mercury Tables 16and 17 show pollutant removal efficiencies at two emulsion crumb plants

Table 11 Plant-Specific Classical Pollutant Data for Selected Emulsion Crumb Rubber ProductionPlants, Verification Data

Waste load, plant 000012

Analytic methods: V.7.3.29, Data set 2.

Blanks indicate data not available.

Source: USEPA.

30.3.2 Solution Crumb Rubber Plants

There are 13 solution crumb rubber plants in the United States Twelve of these plants dischargetreated wastewater to surface streams; the other plant discharges its treated wastewater into aneighboring oil refinery’s noncontact cooling water system

Table 12 Plant-Specific Verification Data for Solution Crumb Rubber Production Plant 000005

Location in process line

Boilerfeedwater (a)

Boilerblowdown

Ten of the plants discharging to surface streams employ some form of biological treatmentfor waste load reduction Two of the plants discharging to surface streams use in-processcontrols, oil removal, and primary treatment prior to discharge In-process control employed atone plant consists of steam stripping of wastewaters, while in-process control at the second plantwas not disclosed The plant discharging to the oil refinery noncontact cooling water system usedcoagulation, flocculation, and dissolved air flotation prior to discharge.

The results of the verification program showed that all organic toxic pollutants werereduced across biological treatment Chloromethane, used as a solvent at plant 000005, waspresent at significant levels in treated effluent

Tables 18 and 19 show pollutant removal efficiencies at two selected solution crumbrubber plants

30.3.3 Latex Rubber Plants

There are 17 latex rubber production facilities in the United States Of these, nine plantsdischarge to POTWs; seven discharge to surface streams; and one employs land application withcontractor disposal of solids All seven plants discharging to surface streams employ biologicaltreatment before discharge Pretreatment for the POTW dischargers consists of coagulation,flocculation, and primary treatment for seven of the nine dischargers, equalization for onedischarger, and biological treatment for the other plant

30.3.4 Tire and Inner Tube Manufacturing

There are a total of 73 tire and inner tube manufacturing facilities in the United States, of which

39 were placed in operation prior to 1959 Twenty-three of the pre-1959 plants do not treat theirwastewaters, and six of these plants discharge to POTWs A total of 17 plants placed in operationsince 1959 provide no treatment of their wastewaters, and 10 of these plants discharge intoPOTWs

Table 13 Plant-Specific Verification Data for Solution Crumb Rubber Production Plant 000027

Pollutant (mg/L)

SN/CB

process

EPDMprocess

Treatmentinfluent

Treatmenteffluent

Wellwater

Boilerblowdown

Analytic methods: V.7.3.29, Data set 2.

Total flow rate: 12,100 cu m/day.

Source: USEPA.

Table 14 Plant-Specific Classical Pollutant Data for Solution Crumb Rubber Production Plant

Analytic methods: V.7.3.29, Data set 2.

Parameter data: kg/day (lb/day).

Table 15 Plant-Specific Verification Data for Pan, Dry Rubber Digestion, and Mechanical Reclaiming Plant 000134

Location in process line

Pollutant (mg/L)

Treatment influent,automatic sampler

Treatment effluent,grab composite

Treatment effluent,automatic samples

Boilerblowdown

Intakewater

Table 15 Continued

Location in process line

Pollutant (mg/L)

Treatment influent,automatic sampler

Treatment effluent,grab composite

Treatment effluent,automatic samples

Analytic methods: V.7.3.29, Data set 2.

Blanks indicate data not available.

The toxic pollutants present in raw wastewaters from tire and inner tube manufacturingoperations are volatile organic pollutants that are used as degreasing agents in tire production.These toxic pollutants (methylene chloride, toluene, trichloroethylene) were found to be reduced

to insignificant levels across sedimentation ponds

30.3.5 Rubber Reclamation Plants

There are nine rubber reclaiming plants in the United States Two of these use wet digestion, andall nine use pan, mechanical, and dry digestion Eight of the plants discharge to POTWs Theother plant employs cartridge filtration and activated carbon for oil removal, followed byactivated sludge.Table 20shows the pollutant removal efficiency at a dry digestion reclaimingplant

30.3.6 Rubber Fabricating Operations

Rubber fabricating operations include latex-dipped, extruded, and molded goods (LDEM), andgeneral molded, extruded, and fabricated rubber (GMEF) There are an estimated 1385 rubberfabricating plants in the United States

No treatment method descriptions are currently available for this subcategory Wastewatertreatment technology consistent with equalization and sedimentation may permit compliancewith BPT regulations

Verification Data (Treatment Technology: Activated Sludge, Discharge Point: Surface

Intake measured at 1.5 mg/L, making plant’s contribution minimal.

b Analytical methodology for phthalates is questionable Therefore, significance of values reported is

unknown.

Source: USEPA.

30.4 TREATMENT METHODS

The treatment methods for ruber wastewaters consist of various biological processes, andphysico-chemical processes including coagulation, ozonation, activated carbon adsorption,aeration, sulfonation, chlorination, and aeration, and biological nutrient removal processes Thepurpose of the treatment is to meet USEPA effluent limitations [4]

Suspected contaminant from glassware cleaning procedures or analytical methods.

Treatment technology: Primary flocculation/separation, aerated lagoons.

Discharge point: Surface stream.

Source: USEPA.

Table 18 Toxic Pollutant Removal Efficiency at Solution Crumb Rubber Plant 000005

Found at significant levels in treatment effluent.

Treatment technology: Primary flocculation/clarification (DAF).

Discharge point: Treated effluent is discharged to a nearly oil refinery’s cooling water system.

Analytical methodology for phthalates is questionable; therefore, significance of values reported is unknown.

Treatment technology: Sedimentation, waste stabilization lagoons.

Discharge point: Surface stream.

Source: USEPA.

Table 20 Toxic Pollutant Removal Efficiency at Dry Digestion Reclaiming Plant 000134, Verification Data

Treatment technology: Cartridge filtration, activated carbon (oil removal), activated sludge sedimentation.

Discharge point: Noncontact cooling water system, blowdown of this system to surface stress.

concentration of 4100 reduced odor to 250 and 500 using 100 ppm Na2SO3 and Na2Srespectively after 17 days of treatment For styrene wastewaters of initial odor concentration of

128, it was reduced to 4 after 9 days treatment with 100 ppm Na2SO3 and for the samewastewaters with initial odor concentration of 65 ppm, it was reduced to 4 ppm using Na2S usingthe same dosage and same duration of treatment [6]

30.4.3 Biological Treatment

A trickling filter has been used to treat neutralized rubber wastewaters with initial BOD of

445 mg/L It removed 92.1% BOD with a 24-hour detention time [5] The activated

sludge process has removed 85% BOD from combined rubber and domestic wastewaterwastewaters [7]

30.4.4 Nutrient Removal

Attached-growth waste stabilization ponds have been used to remove 65 – 70% TKN (totalKjeldahl nitrogen), and 70 – 83% NH3-N from concentrated latex and rubber sheet plantwastewaters [8] A combined algae and water hyacinth system has been used to remove 96.41%COD, 98.93% TKN, 99.28% NH3-N, 100% NO2-N, and 100% NO3-N [9]

The investment cost, operating, and maintenance costs, and energy costs for the application

of control technologies to the wastewaters of the rubber processing industry have beenanalyzed These costs were developed to reflect the conventional use of technologies in this

industry Several unit operation/unit process configurations have been analyzed for the cost

of application of technologies and to select BPT and BAT level of treatment The able tretment technologies, cost methodology, and cost data are available in a detailedpresentation [10]

Standards for the Tire and Synthetic Segment of the Rubber Processing Point Source Category, US

5 Morzycki, J Effluents from sewage contaminated with latex Chem Abs 1966, 64, 3192

6 Black, O.R Study of wastes from rubber industry Sewage Works J 1946, 18, 1169

7 Mills, R.E Progress report on the bio-oxidation of phenolic and 2,4-D waste waters In Proceedings

of 4th Ontario Industrial Waste Conference, June 1957; 30

8 Rakkoed, A.; Danteravanich, S.; Puetpaiboon, U Nitrogen removal in attached growthwaste stabilization ponds of wastewater from a rubber factory Water Sci Technol 1999,40(1), 45 – 52.

9 Bich, N.N.; Yaziz, M.I.; Bakti, N.A.K Combination of Chlorella vulgaris and Eichhornia crassipesfor wastewater nitrogen removal Water Res 1999, 33 (10), 2357 – 2362

Processing Point Source Category, Technical Report No 68-01-4673; US Environmental ProtectionAgency: Washington, DC, 1978

Treatment of Timber Industry Wastes

Lawrence K Wang

Zorex Corporation, Newtonville, New York, U.S.A., and

Lenox Institute of Water Technology, Lenox, Massachusetts, U.S.A

31.1 INTRODUCTION

The timber products processing industry encompasses manufacturers and processors who useforest materials to produce their goods and merchandise Fifteen distinct subcategories of

manufacturers and/or processors are engaged in the utilization of timber This chapter addresses

three major subsections of the entire industry: (a) wood preserving, both steaming and Boultonprocesses; (b) insulation board manufacturing; and (c) both wet – wet (S1S or smooth one side)and wet – dry (S2S or smooth two side) hardboard manufacturing

The number of dischargers in the timber products processing industry in the United Statescan be broken down as follows: (a) 19 direct dischargers; (b) 55 indirect dischargers; and (c) 172zero dischargers

31.1.1 Water Pollution

The timber industry treats timber and wood products with chemical preservatives to protect thewood from degradation due to various organisms including fungi, and insects such as borers andtermites This treatment extends the range of applications and the service life of the wood Bydesign, the chemicals used to protect wood must be toxic to the target organisms, but they mayalso affect nontarget organisms and the environment [1]

The following groups of preservatives are commonly used for wood preservation: (a)copper chrome arsenate (CCA); (b) copper-based alternatives to CCA [ammoniacal copperquaternary (ACQ) and copper azole]; (c) boron; (d) creosote; and (e) pyrethroid- and metal-based light organic solvent preservatives (LOSPs) Section 31.2.1 presents a complete list oftoxic chemicals used in wood preservation in the United States

Copper chrome arsenate (also known as CCA or chromated copper arsenate) consists ofthree metals: copper, chromium, and arsenic All three metals pose a risk to the environment.Both hexavalent chromium and arsenic can cause cancer in humans The CCA concentrate isdiluted with water to create a working solution that is used in the pressure treatment of timber.CCA-treated timber is commonly a greenish color, but this is also often the case with theother copper-based preservatives CCA-treated timber is registered for use by the industrialcountries under their laws The registered uses include internal building uses and external usessuch as decks, walkways, fences, playground equipment and retaining walls, and some marinewater applications such as wharfs and jetty piles

1269

31.1.2 Air Pollution and Health Hazards

Published results of scientific studies indicate that copper, chromium, and arsenic slowly leachfrom CCA-treated timber products All three metals pose a risk to human health and theenvironment, but also exist naturally in the environment in varying concentrations

Based on currently available evidence, CCA-treated wood does not pose any significantrisk to the public However, as arsenic is a known human carcinogen, it would be prudent toavoid unnecessary exposure to it Some common sense tips to minimize unnecessary exposure toCCA-treated timber are: (a) treated wood should never be burned in open fires, stoves, fireplaces,

or residential boilers; (b) hands should always be washed thoroughly after contact with anytreated wood, especially before eating and drinking; (c) food should not come into direct contactwith any treated wood; and (d) precautions should be taken to wear protective gear whenworking with CCA-treated wood

31.1.3 Solid Wastes Disposal

Small quantities of household CCA-treated timber waste (e.g., offcuts from a small job) could beplaced in the owner’s rubbish bin, with the rest of owner’s household waste CCA-treated timberwaste from larger household building and demolition jobs is classified as inert waste, and can bedisposed of to most suburban landfills

CCA-treated timber waste from industrial sources should only be disposed of to certainlandfills CCA-treated timber waste must not be burned or used as such

31.1.4 Global Trends

The timber industry is moving away from using pesticides such as CCA and creosote TheUnited States and Canada have moved to phase out the use of CCA to treat timbers intended forresidential uses after December 2003 and Europe after June 2004 This trend appears to bedriven by recent European risk assessments of arsenic, the application of the “precautionaryprinciple”, and by perceived consumer demand shifts in North America [1]

The United States Environmental Protection Agency (USEPA) granted the cancellation ofCCA registration for most residential uses of treated timber following an application to do sofrom the wood preservation industry From January 1, 2004, the USEPA will not allow CCAproducts to be used to treat timber intended for most residential uses The USEPA is continuing

an assessment of the risks posed to children by arsenic leaching from CCA-treated timber TheEuropean Commission has announced a partial prohibition on the use of CCA-treated timber, totake effect after June 2004 In addition to the residential uses being restricted in the United Statesand Canada, CCA preservatives will also not be used in the EU for timber destined for marineand most agricultural uses

The New Zealand Environmental Risk Management Authority (ERMANZ) has decidednot to change the registration of CCA following a recent review of the potential publichealth risks arising from the continuing use of CCA-treated timber ERMANZ found thatthe extent of any risk to public health arising from CCA remains unclear but is consideringfurther investigation into the possible environmental and occupational health risks arisingfrom CCA

The Ministry of Environment and the Ministry of Health of Manatu Hauora [2] announcedtheir Guidelines for Selected Timber Treatment Chemicals in 1997

31.1.5 Cleaner Production and Economy

Cleaner production aims at avoiding the generation of waste and emissions, by making moreefficient use of materials and energy, through modifications in the production processes, input

materials, operating practices, and/or products and services [3,4] Van Berkel [4] illustrates how

the timber industry and other industries were able to implement cleaner production practices andtechnologies

Aruna and Mercer [5] state the timber economy of the Mid-Atlantic Region in the UnitedStates Specifically, the health and sustainability of ecosystems in an eight state region for theforest industries (including the timber industry) have been assessed Wang and colleagues [6],meanwhile, present the costs of various wastewater treatment systems

General descriptions and process descriptions for the major subcategories of the timber productsprocessing point source category are introduced in this section

31.2.1 Wood Preserving

Creosote, pentachlorophenol (PCP), and formulations of water-soluble inorganic chemicals arethe three most prevalent types of preservatives used in wood preserving The most common ofinorganic chemicals are the salts of copper, chromium, and arsenic Fire retardants areformulations of salts, the principal ones being borates, phosphates, and ammonium compounds

Of plants in the United States, 80% use at least two of the three types of preservatives Manyplants treat with one or two preservatives plus a fire retardant

There are two basic steps in the wood preserving process: (a) preconditioning the wood toreduce its natural moisture content and to increase permeability; and (b) impregnating the woodwith the desired preservatives

The preconditioning step may be performed by one of several methods including (a)seasoning or drying wood in large, open yards; (b) kiln drying; (c) steaming the wood at elevatedpressure in a retort followed by application of a vacuum; (d) heating the stock in a preservativebath under reduced pressure in a retort (Boulton process); or (e) vapor drying, heating ofthe unseasoned wood in a solvent to prepare it for preservative treatment All of thesepreconditioning methods have, as their objective, the reduction of the moisture content inthe unseasoned stock to a point where the requisite amount of preservative can be retained in thewood

Conventional steam conditioning (open steaming) is a process in which unseasoned orpartially seasoned stock is subjected to direct steam impingement at an elevated pressure in aretort The maximum permissible temperature is set by industry standards at 1188C and theduration of the steaming cycle is limited by these standards to no more than 20 hours Steamcondensate formed in the retort exits through traps The condensate is discharged to oil – waterseparators for removal of free oils Removal of emulsified oils requires further treatment

In closed steaming, a widely used variation of conventional steam conditioning, the steamneeded for conditioning is generated in situ by covering the coils in the retort with water from areservoir and heating the water by passing process steam through the coils The water is returned

to the reservoir after oil separation and reused during the next steaming cycle There is a slightincrease in volume of water in the storage tank after each cycle due to water exuded from the

wood A small blowdown from the storage tank is necessary to remove this excess water and tocontrol the level of wood sugars in the water.

Modified closed steaming is a steam conditioning process variation in which steamcondensate is allowed to accumulate in the retort during the steaming operation until it coversthe heating coils At that point, direct steaming is discontinued and the remaining steam requiredfor the cycle is generated within the retort by utilizing the heating coils Upon completion of thesteaming cycle, and after recovery of oils, the water in the cylinder is discarded

Preconditioning is accomplished in the Boulton process by heating the stock in apreservative bath under reduced pressure in the retort The preservative serves as a heat transfermedium After the cylinder temperature has been raised to operating temperature, a vacuum isdrawn, and water, which is removed in vapor form from the wood, passes through a condenser to

an oil – water separator At this point low-boiling fractions of the preservative are removed TheBoulton cycle may have a duration of 48 hours or longer for large poles and piling This factaccounts for the lower production per retort day as compared to plants that steam condition.The vapor-drying process consists of exposing wood in a closed vessel to vapors from anyone of the many organic chemicals that are immiscible with water and have a narrow boilingrange

The following is a summary of toxic pollutants found in significant quantities in the woodpreserving category [7,8]:

31.2.2 Insulation Board Manufacturing

Insulation board is a form of fiberboard, which in turn is a broad generic term applied to sheetmaterials constructed from ligno-cellulosic fibers Insulation board is a “noncompressed”fiberboard, which is differentiated from “compressed” fiberboards, such as hardboard, on the basis

of density Densities of insulation board range from about 0.15 to 0.50 g/cm3(9.5– 31 lb/ft3)