ENCYCLOPEDIA OF ENVIRONMENTAL SCIENCE AND ENGINEERING - SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR DOMESTIC AND SPECIAL APPLICATIONS docx

In this article the state of the art of small flow wastewater treatment systems developed for such special applications is presented.. Subsurface soil absorption systems trench and bed

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DOMESTIC AND SPECIAL APPLICATIONS

Recent concern regarding water pollution and general

worldwide public awareness of the problem associated with

pollution has resulted in increased pressures on all waste

dis-chargers to provide effective treatment and disposal of their

waste streams Small subdivisions, motels, resorts, mobile

homes, watercraft, railroads, and the like, have not escaped

these pressures, although in many respects their total waste

contribution to the environment may be small However, as

a result of the public awareness of pollution and

increas-ing regulatory pressures, there has been a rapid commercial

growth in recent years in plants designed and built

specifi-cally for such applications In this article the state of the art

of small flow wastewater treatment systems developed for

such special applications is presented

INDIVIDUAL HOMES

The 1990 census figures indicate that there are more than

25 million onsite residential wastewater treatment systems

in the United States, often because wastewater collection

sewers are not available. 1 These systems include a variety of

components and configurations Among the most common

systems are the anaerobic and aerobic biological treatment

In recent years constructed wetlands have also been

investi-gated for home application However, no treatment systems

as yet has been entirely satisfactory either to homeowners or

to health officials. 2,3

Anaerobic System

Septic Tank Septic tank is the most commonly used

individ-ual waste disposal system The US Environmental Protection

Agency estimates that there are approximately 18 million

housing units in the US that use on-site wastewater and

disposal systems This is about 25% of all housing units

Additionally, about one-half million new systems are being

installed each year. 2,3

A septic tank consists of a tank in which wastes are

accumulated and digested under anaerobic conditions The

effluent from septic tanks is malodorous, and the bacterial

count is often quite high Subsurface absorption field is

nec-essary to absorb the effluent from the septic tank Capacity,

hydraulic design and soil conditions are most important

fac-tors influencing the septic tank performance A detailed

dis-cussion on septic tank design, performance, and economics

is available in several publications. 1 – 7

A conventional septic tank removes about 40–50 percent TSS In recent years many improvements have been made

in the design of septic tank, gravel filter, and soil absorption trenches that enhance their performance significantly An important variation in conventional septic tank design is

cur-rently being manufactured The Ruck system requires wash

waters be separated from sanitary and kitchen wastes The san-itary and kitchen wastes are thus held in an upper compartment for a longer period of anaerobic digestion, providing more con-centrated treatment to the sanitary wastes. 3,8 The wash water

is treated in a lower compartment for shorter periods where effluent from the upper chamber is mixed The system is sold

as a package unit in a fiberglass housing A soil absorption system is also included in this package which is designed to make the system independent of the natural soil characteris-tics Andreadakis reviewed the performance of an on-site treat-ment and disposal system using a septic tank, gravel filter, and soil absorption trenches. 9 BOD 5 and TSS removal efficiencies averaged over 92 and 93 percent respectively, and up to 70 percent nitrogen was removed due to nitrification followed by denitrification. 9,10 Many researchers believe that the reduction

in hydraulic loading by water conserving devices will improve the performance of on-site treatment and disposal systems. 11

Intermittent Sand Filters The main purpose of the

inter-mittent sand filters is to reduce the BOD 5 and TSS prior to soil infiltration Currently, many intermittent sand filters are used throughout the United States to treat wastewater from indi-vidual homes The process is highly efficient, and requires a minimum of operation and maintenance Intermittent sand filters are beds of granular material underlain by graded gravel and collecting tiles. 2 Uniform distribution is normally obtained by dosing or flooding the entire surface of the bed

Recirculation has also been used The filters may be buried

or may have some free access

Disposal Methods Under favorable conditions the

efflu-ent from treatmefflu-ent devices are safely disposed of by (a) sub-surface absorption, (b) evaporation, and (c) discharge into surface waters The subsurface soil absorption is usually the best method of wastewater disposal from homes because

of its simplicity, stability and low cost Partially treated wastewater is discharged below ground surface where it

is absorbed and treated by the soil as it percolates into the ground Nearly one-third of the homes in the United States dispose of their wastewater in this way. 9

Evaporation systems utilize techniques to evaporate the effluent without infiltration The system utilize evaporation

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SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR DOMESTIC AND SPECIAL APPLICATIONS 1083

and evapotranspiration beds Direct discharge of onsite

treat-ment system effluent is also a disposal option if an

appropri-ate receiving wappropri-ater is available and if the regulatory agencies

permit such discharges Various onsite disposal methods are

listed below Detailed discussion may be found in Ref 2

Typical design of septic tank and intermittent filter are shown

in Figure 1 Typical trench, seepage pit and mound systems

are shown in Figure 2

Subsurface soil absorption systems

trench and bed

seepage pit

mound

fill

artificially drained systems

electro-osmosis *

Evaporation systems

evapotranspiration and evapotranspiration—

percolation

evaporation and evapopercolation ponds

Surface water disposal

outfall in stream

outfall in lake

Aerobic System

Several types of household treatment systems are available

which utilize aerobic stabilization of organic wastes Most

systems are designed for continuous flow

The raw wastewater enters an anaerobic tank where

solids are settled and partially digested The liquid enters an

aerobic compartment Air is supplied either by mechanical

aerators or by diffusers The bacterial action thus produced

is similar to that in an activated sludge plant The solids in

the aerated liquid are settled into a separate tank This tank

most commonly has a sloping bottom to return the settled

sludge into the aeration tank by gravity System components

of such units are schematically shown in Figure 3

Some of the manufacturers’ variations in the aerobic system

include (1) absence of anaerobic digestion tank, (2) different

methods of aeration, (3) packed bed media, (4) trickling filter,

(5) rotating biological contactor, and (6) use of tube settlers for

increasing the sedimentation rate. 2,12 Many of these variations

are shown in Figure 4

The effluent from an aerobic system is generally better

than that from a septic tank Manufacturers claim BOD and

suspended solids removal of about 90% The effluent from

aerobic systems has lower clogging effect on soil absorption

system If the system operates properly, the effluent is

suit-able for surface drainage The disadvantages of the aerobic

system are higher operating costs, susceptibility to shock

loading, and variation in effluent quality The design criteria,

operational characteristics and cost data on aerobic systems are extensively available in the literature. 2,3,13,14

Constructed Wetlands

Constructed and natural wetland rely solely on natural process to treat wastewater and are most often used for sec-ondary treatment In a single-residence system, for exam-ple, a septic tank generally provides partial treatment The effluent flows to the wetlands where it is distributed into the system Organic matter is stabilized by microorganisms attached to the plant roots Aquatic plants deliver oxygen, provide shade, metabolic nutrients and surface area for microbiological growth

Constructed wetlands are designed either as a “discharge”

system or as an “non-discharge” system. 1 Two basic design approaches exit for constructed wetlands These are developed

by (1) Tennessee Valley Authority (TVA) for systems less than 75,700 L/d, and (2) EPA for larger municipal wastewater treatment plants The design equations are based on hydraulic loading, organic loading, and Darcy’s equation The design procedure for constructed wetland can be found in Refs 1, 15–17 The suggested residential wetland design details are:

length ⫽ 12.7 m, width ⫽ 4.3m, depth ⫽ 0.3 m, detention time ⫽ 3d, and hydraulic loading criteria ⫽ 1.3 m 2 /L·d

The aquatic plants are generally chosen from

indig-enous species of Typhaceae (cattail family), Cyperaceae (sedge family), Gramineae (grass family), Scirpus validus (softstem bulrush), or Phragmites australis (giant reed)

Care should be taken to avoid plants that “choke out” each other, or those eaten by animals The choice of vegetation is dependent upon wastewater characteristics, solar radiation, temperature, aesthetics, wildlife desired, indigenous species, and the depth of constructed wetlands Vegetation harvesting may be necessary when it becomes too dense, cause obstruc-tion to the natural flow and create anaerobic condiobstruc-tions. 1

SMALL ESTABLISHMENTS Small establishments generally include motels, restau-rants, stores theatres, clubs, camps, rest areas, institutions, apartment houses, small factories, subdivisions, small communities, etc Disposal of wastewaters from these establishments in suburban areas certainly poses serious problems Construction of public sewer systems may not

be economically feasible to convey the wastewaters to an existing treatment plant Since the flows are relatively large, often septic tanks and subsurface absorption fields may not provide safe disposal, causing a very serious public health hazard or pollution of ground or surface waters

Package treatment plants were first introduced about thirty-five years ago to treat wastes from small establish-ments During this time, there has been a rapid commercial growth in package plant industry The package plants are prefabricated in the factory and, in most cases, completely assembled prior to delivery to the plant site Most of the plants are made of steel but many concrete plants are also

* Electro-osmosis is a technique used to drain and stabilize slowly

permeable soils during excavation A direct current is passed through

the soil which draws the free water in the soil pores to the cathode.

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FIGURE 1 Typical design of septic tank and intermittent filter (Adapted from Ref 2.)

Access Manholes

Sanitary Tee

Inlet

Vent

Graded Gravel 3/4" to 2 1/2"

Graded Gravel 1/4" to 1 1/2"

Marsh Hay or Drainage Fabric

Top Soil Fill Drainage

Filter Media

Peforated or Open Joint Distributors

Perforated or Open Joint Pipe, Tarpaper Over Open Joints

> 8 in

24–36 in

> 6 in

6"

Distribution Box House Sewer Septic

Tank

Vent Pipe

A

Vent Pipe

Discharge Inspection Manhole and Disinfection Contact Tank (If Required) Profile

Plan

Section A-A Longitudinal Section

(a) Typical design of two-compartment

septic tank

(b) Typical design of buried intermittent

filter installation

Pea Gravel

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SMALL FLO

FIGURE 2 Subsurface absorption system (Adapted from Ref 2.)

Backfill

Barrier Material

3/4 –2 -1/2 in Rock

Water Table or Creviced Bedrock

Perforated Distribution Pipe 6-12 in.

1-3 ft

1-5 ft

2-4 ft Min.

(a) Typical trench system

4" Inspection Pipe

Reinforced Concrete Cover Extended to Solid Earth Effluent

Brick, Block, Ring, or Precast Chamber with Open Joints

6" to 12" of 3/4 –2 1/2"

Clean Rock Influent

Water Table 4' min Unsaturated Soil Impervious Layer

(b) Typical seepage pit system

Straw, Hay or Fabric

Fill Topsoil

Straw, Hay or Fabric Fill Topsoil

Cap

Distribution Lateral

Absorption Bed

Plowed Layer of Top Soil Slope

Rock Strata or Impermeable Soil Layer

(c) Typical mound for a slowly permeable soil

on sloping site

3 1

Plowed Layer of Top Soil Permeable Soil

Water Table or Creviced Bedrock (d) Typical mound system for a permeable soil with high groundwater or shellow creviced bedrock

3 1

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available During earlier years of package plant usage, the

plant size was usually limited to the maximum size that

could be shipped by truck This was about 190–228 m 3 /d

(50,000 to 60,000 gallons per day (gpd)) maximum plant

size Currently the manufacturers fabricate the plants in the

field Thus package plants with capacities over 3800 m 3 /d

(one million gallons a day (mgd)) can be obtained

The earlier package plants were designed as extended

aeration plants Currently available package plants utilize

many treatment processes Some of these processes are

listed below

Biological

Extended aeration

Contact stabilization

Completely mixed

Step aeration

Trickling filter

Rotating biological contractor Sequencing batch reactor (SBR)

Chemical

Chemical precipitation Electrochemical flotation Ultrafiltration

Detailed discussions on package plants including manu-facturers, process alternatives, size, weight, design criteria, and cost is extensively available in the literature. 18 – 22 These plants have been successfully applied in the treatment of wastewaters in the suburban areas The range of these plants has expanded from small establishments to large municipal and industrial applications Manufacturers broadly group the models or design series into flow capacity, BOD loading, dimensions, air supply, motor horse power, etc., which has simplified the job of unit selection

Influent

Blower

Effluent

Settling Chamber

Settling Chamber Sludge

Sludge

Aeration

Trash Trap

Scum

Scum Sludge

Sludge

Diffuser

Mechanical or Diffused Aeration (a) Diffused aeration

(b) Mechanical aeration FIGURE 3 System components of aerobic suspended growth biological treatment pro-cess (Adapted from Ref 2.)

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SMALL FLO

FIGURE 4 System components of aerobic attached growth biological treatment process (Adapted from Ref 2.)

Motor

Effluent

Packed Media Influent

(a) Uptlow filter

Influent Distributor

Fixed Media

(c) Tricking filter Effluent to Clarifier or Septic Tank

(b) Rotating Biological contactor

Tank

Influent

Timer Control Valve Clarifier Motor

Effluent

Sludge

Under Drain

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In recent years natural systems are also used for

waste-water treatment from small establishments and sub-divisions

Among these are land treatment, and natural and constructed

wetland Information on natural system may be found in

Refs 1, 4, 15–17, 23 and 24

POLAR REGIONS

Waste handling in polar regions is a complex problem

Conventional wastewater collection and treatment systems

have severe limitations due to cold weather Sewers

con-structed through snow, ice or permafrost 2 must be insulated

to transport the wastes without freezing Waste treatment by

chemical or biological methods may not be possible due to

retarded reaction rates

The predominant sanitary facility used in small Alaskan

villages is manual collection of human fecal waste and their

disposal to ground, snow or ice In many cases, pit

priv-ies, vaults, bored holes, straddle trenches, box and can, and

crude chemical toilets are also used Problems with these

systems are: inconvenient to use especially in cold climates,

unaesthetic features such as odor and unsightly conditions,

and health hazards. 25,26

Perhaps the most comprehensive analysis of waste

prob-lems in arctic areas was conducted by the Federal Housing

Administration about 50 years ago. 27,28 Subsequently, a

number of research programs were conducted by the US

Public Health Service, National Research Council, US Navy,

US Air Force, and US Army in developing suitable systems for

use in Greenland, Alaska and most recently in the Antarctic. 29

Prime requirements for a system suitable for installation in

these areas were: (1) minimum water use as year-round water

supply in these areas may be lacking, (2) non-electric

opera-tion, (3) freeze-free, (4) minimum final disposal problems,

(5) odor-free, and (6) minimum of maintenance Systems

investigated in these research programs included: (1)

incin-erating toilets, (2) chemical toilets, and (3) chemical and

bio-logical toilets with recirculation

Incinerating Toilets

Incinerating toilets have been designed to destroy human

body wastes The thermal energy required may be obtained

from electricity, fuel, oil, or liquified petroleum gas (LPG)

Several designs of incinerating toilets are now

commer-cially available Although these toilets provide complete

prevention of pollution from human wastes, they are

rela-tively inefficient in terms of fuel consumption and often

fail to provide complete burning which may result in a

nox-ious odors or excessive smoke. 28 Two incinerating toilets

Incinolet and Stornburn are manufactured for application

in Alaska. 26

Chemical and Composting Toilets

Chemical toilets require addition of chemicals into the waste

storage tank These chemicals liquify the fecal wastes, produce

bactericidal effect and suppress fecal odors Most commonly used chemicals are: (1) halogens and their compounds, (2) coal-tar distillate (phenols and cresols), (3) heavy metals and their salts (zinc, copper and silver salts), (4) quaternary ammonium compounds, and (5) alkaline substances such as sodium and potassium hydroxide and lime Various chemi-cals are sold in the market under different trade names

One mechanical-flush chemical toilet was developed by Naval Engineering Laboratory, Port Huneme, California (US Patent No 3,460,165) for use at remote Antarctic stations

This toilet was extensively tested by the military personnel and found satisfactory for polar applications

A variety of composting toilets are on the market for application in cold region These toilets use no water, and eventually produce compost that can be used on home garden Three composting toilets named in the literature are

AlasCan, the Phoenix, and the Sun-Mar 26,29,30

Chemical and Biological Toilets with Recirculation

A special application of waste treatment unit for polar use

is a unit where treated effluent could be recirculated as a flush fluid Such concepts with both chemical and biologi-cal treatment systems were investigated Walters developed

a recirculating chlorinator toilet which used standard toilet fittings. 31 The heavily chlorinated effluent from the storage tank was reused for flushing the toilet bowl The system was tested in Alaskan single homes and results were found esthetically acceptable

Another study evaluated three extended aeration plants

in which the effluent was recirculated for toilet flushing. 32 The findings of this investigation showed that the flushing fluid turned brown during the first week and remained that color for the entire test period of several months However,

no odors were detected

Both the chemical and biological treatment system with effluent recirculation have great promise in developing toilets for use in polar regions These toilets have unique features such as: no water requirement, non-electrical (with hand pump), non-freezing, no odor, conventional toilet design, and a minimum of maintenance

A number of innovative wastewater collection, treat-ment, reuse and disposal system have also been applied for community and individual home applications in polar region Among these are pressurized and vacuum collection systems, low flush, ultra-low flush, micro-flush toilets, and mineral oil flush systems. 26,33 – 38

WATERCRAFT Use of the waterways for pleasure boating has increased enormously in this country Because of a substantial increase

in the number of recreational vessels, the public has become aware of the potential seriousness of the waterborne pollu-tion resulting from this source Many recreapollu-tional watercraft and commercial and government vessels discharge wastes into the water. 34 Recreational watercraft are highly mobile,

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and may reach beaches, commercial fisheries, shell-fish

growing areas and may seriously contaminate the waters,

thereby rendering them dangerous for public water supplies

and water contact sports Contamination may also seriously

affect the commercial fisheries and the shellfish industry

The discharge in territorial waters of the United States

is regulated by the Clean Water Act. 40 This Act also

speci-fies allowable types of marine sanitation devices (MSD), and

mandates, that the US Coast Guard test the various types of

MSD and certify them for use aboard water craft These tests

are found in 33CFR 159, page 492, 500 and 501. 41,42 Type

I MSD utilize macerator and disinfection Both commercial

disinfectants and onsite electrochemical devices are included

Type II MSD include biological treatment or fiber filtration

(microscreening) Type III MSD consists of storage tank

Sewage equipment for use aboard watercraft is already

available in the form of (1) maceration-disinfection devices,

(2) holding tanks and recirculating toilets, (3) incinerator

devices, and (4) chemical and biological treatment

facili-ties A brief discussion of these systems is given below For

details on manufacturers, cost and unit variations, readers

are referred to several sources in the literature. 43 – 49

Maceration-Disinfection Devices

Maceration-disinfection devices utilize a mechanical

macera-tor to grind the human fecal wastes, mix a disinfecting

chemi-cal (usually hypochlorite) and retain the disinfected sewage

mixture for a brief period before discharging it into the water

A number of companies manufacture such units for installation

aboard virtually every type of watercraft Such units are small,

lightweight, and relatively easy to install However, their

per-formance in terms of BOD and suspended solids reduction,

and degree of disinfection achieved may be questionable

Holding Tanks and Recirculating Toilet

A holding tank is a closed container for retaining sewage

onboard a watercraft until it can be properly emptied,

usu-ally into an onshore sewage receiving facility Holding tanks

include chemical toilets, recirculating flush toilets, classic

holding tanks, and any variation which simply retains the

sewage for later disposal at an appropriate site

One potentially useful variation of the holding tank is

the recirculating flush toilet This device requires a small

amount of precharge of chemically treated water in the

reten-tion tank integrated into the toilet design Waste deposited in

this toilet accumulates in the retention tank For subsequent

flushing, an internal separation mechanism recovers a

frac-tion of this precharge/waste mixture for continued reuse as

flushing fluid The tank retains sewage from 80 to 100 toilet

usages before it must be emptied It uses minimum space

and requires no water for flushing

Although holding tanks completely prevent the discharge

of sewage from watercraft, they require extensive shore

sup-port facilities for emptying and cleaning Low flush and

vacuum flush toilets are desirable because they minimize

storage and treatment requirement. 34

Incinerator Devices

As described earlier, several types of incinerating toilets have been developed to reduce human waste to a small amount of ash The most common problems encountered with incinera-tor devices with watercraft include the difficulty of supplying electrical power as most small craft do not have the generat-ing equipment required If gas or oil burner type incinerators are used, space is also required Such burners also provide fire hazards if improperly designed Regardless of the type

of fuel used, however, burning of human wastes may result

in emission of odor from the venting stack

Chemical and Biological Treatment Plants

Wastewater treatment plants similar to those frequently used for land-base sewage treatment have been adopted for vessel use The mot successful of the biological treatment systems are the extended aeration activated sludge process. 48 Attempts have been made also to adapt thermally heated aeration sys-tems for increased biological activity Trickling filter-type biological treatment systems with forced air aeration have also been adopted to shipboard applications. 18 These sys-tems, which provide treatment to all waste streams gener-ated aboard the watercraft, are relatively large and heavy, and easily upset due to change in salinity of flush water

Among the chemical systems, an electrochemical floata-tion plant for shipboard waste treatment was designed and built. 49,50 This system utilized chlorine gas for disinfection, and partial oxidation and flotation of organic matter Another chemical process oriented system utilized a comprehensive approach to the management of wastewater on board ship and is concerned not only with an improved treatment but also with an innovation and improved collection system

The system employs two main elements: (1) a recirculating chemical toilet, and (2) an evaporation system for solid/liquid separation. 31,51 – 53 Condensed liquid is discharged overboard after chlorination Concentrated sludge is stored for subse-quent disposal to shore facility or into unrestricted waters

COMMERCIAL AIRCRAFT Until about 1940, waste management problems aboard air-craft were considered minor; human wastes were simply dis-charged overboard In January of 1943, the US Public Health Service published the “Sanitation Manual for Land and Air Conveyance Operating in Interstate Traffic,” which formu-lated policy regarding “Discharge of Wastes from Conveyance

En Route.” 54 Following this publication, the International Sanitary Convention for Aerial Navigation issued a publica-tion in February, 1945, forbidding aircraft to throw or let fall matter capable of producing an outbreak of infectious dis-eases. 55 Federal laws and regulations now prohibit air-planes indiscriminately discharging untreated human wastes. 56 Early waste management practices for aircraft included carry-out pail methods of waste collection within aircraft and hand-carrying them to the ground servicing facilities

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Subsequently, this system was replaced by built-in retention

tanks These retention tanks utilized wash and galley water

for toilet flushing purposes The system posed several

opera-tional problems, including the fact that the flushing water

taxed the capacity of the retention tanks on longer flights,

and was later replaced by recirculating chemical toilets

Recirculating chemical toilets currently being used aboard

commercial aircraft have highly improved features to fulfill

the requirements of the modern planes Reinforced

fiber-glass retention tanks for lightness, teflon coated toilet bowls

for cleanliness, timer assemblies to control the flush cycle,

improved reversible-motor-operated pumps, and a number of

filter and filter-cleaning devices have all been developed to

provide trouble-free operation and an aesthetic facility

The recirculating chemical toilets provide efficient

oper-ation but, depending on the capacity of the water tank, the

system requires frequent ground servicing Furthermore, the

amount of space and weight available for waste storage in

aircraft is quite limited Therefore, a system to concentrate

the wastes during the flight is considered highly desirable

To achieve this, several waste-volume-reduction techniques

have been investigated for use aboard commercial aircraft

These include:

1) Evaporation of the liquid to yield dry or highly

concentrated solids to reduce the waste-storage space in the aircraft and eliminate the frequent ground servicing need

2) Incineration devices which utilize electrical

and fuel energy for waste incineration Several improved incineration systems for aircraft appli-cation have been built and evaluated. 57 – 59

3) Evapo-combustion system to burn the macerated

waste into a combustion chamber of the jet en-gine Vacuum toilets have also been successively installed on large commercial aircraft These toi-lets reduce the waste accumulation. 34, 60 – 64

RAILROAD TRAINS

Historically, wastes from railroad trains have been discharged

into the environment without benefit of any treatment This

primitive practice poses a threat to the public health Although

passenger traffic on trains in the US has declined in recent

years, large numbers of persons, including railroad employees

still use toilet facilities on trains According to Food and Drug

Administration (FDA), about 23 million pounds of human

excrement or 16 million gallons of wastewater are discharged

annually from locomotives and cabooses, and about 9.5

mil-lion gallons of “untreated human wastes” were discharged in

1968 from intercity and commuter passenger train cars. 56 A

history of some of waste disposal practices of Amtrak was

presented in a hearing before Congress in 1988. 65

Federal laws and regulations now prohibit buses

(42 CFR 72.156) from discharging untreated human

waste. 56,57 As a result, the passenger buses are equipped with

suitable types of chemical or recirculating toilets

Currently, several types of waste treatment and disposal systems are being marketed which are designed and built for railroad trains These include incinerating toilets, retention tanks, and recirculating toilets

Incinerating toilets built for railroad cars operate on natural gas, propane, diesel fuel, or electricity These toilets operate without the use of water or chemicals and require no holding tanks or plumbing fixtures

Recirculating toilets of various types are also available for railroad use One system built for locomotives, cabooses and crew cars uses a vacuum system In this system air, rather than water, is used to carry waste from the toilets to a centrally located tank. 56,61 This system enables locating the holding tank elsewhere in the railroad car and two or more toilets can be connected to this tank

PICKUP CAMPERS, TRAVEL-TRAILERS, TENT CAMPING

Various types of portable recirculating toilets are currently manufactured These units have suitcase-style handles molded into their cases for easy carrying; can be used in tents or in camper. 66 A small family can get a few day’s use before the facility must be emptied and recharged

A unique system for reducing the volume of wastes from recirculating toilets was developed In this system, the fecal wastes were liquefied by adding chemicals The liquid mixture is pumped to a sanitizer which is a short, stainless steel tank connected to the exhaust pipe of the vehicle The sanitizer operates at about 500°F At this operating tempera-ture, the waste is concentrated and the microorganisms are destroyed. 66 The operating temperature of the sanitizer is reached at a vehicle speed of about 35 mph

ENVIRONMENTAL CONTROL AND LIFE SUPPORT SYSTEMS (ECLSS) FOR SPACE STATION

NASA has sponsored programs to develop efficient, compact equipment to handle the various aspect of environmental life support for spacecraft and for the planned space station The tasks include CO 2 removal, O 2 regeneration, temperature and humidity control, the purification of water recovered from the dehumidifier condensate, hygiene uses, and in the future, from urine Also the removal of trace contaminants from the air, the maintenance of the air composition and pressure, and the storage of solid wastes pending their return to earth are included A wide variety of techniques have been evaluated depending upon their prospects for meeting the desired per-formance specifications. 67 – 73 Table 1 provides a list of ECLSS technologies used or evaluated

The space systems have grown in complexity and compre-hensiveness as both the duration of the missions and the size

of the crew have increased With the possibility of long dura-tion space missions to other planets, and also the establishment

of bases on the moon, NASA is in the early stages of testing technologies for solid waste treatment and recycling, and the

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intensive agricultural technique necessary to grow and process

food in very confined spaces under low or zero gravity

Some of the technologies developed for the space

program have possible application on earth Many of the

applications will only be relevant to submarines and

hyper-baric chambers In some cases there may be more widespread

uses, such as the recovery and reuse of dehumidification and

hygiene water in arid areas or in very cold climates,

remov-ing CO 2 and regenerating O 2 , and controlling temperature and humidity in deep mines or while drilling long tunnels

Certain technologies may be applicable to the treatment of industrial emissions and/or effluents It is likely that the basic technological knowledge will be applied to terrestrial problems, rather than the actual hardware developed for the space program. 74 – 77 Possible terrestrial application of space craft environmental systems are presented in Table 2

TABLE 1 ECLSS technologies used or evaluated

Atmosphere revitalisation Used LiOH

Used Molecular sieve Used Sabatier reactor Used Static feed water electrolysis Evaluated Solid amine fixed bed Evaluated Liquid sorbent closed loop Evaluated Bosch system

Evaluated Algal bioreactor Evaluated Growing green plants Trace contaminant removal Used Activated charcoal

Used Catalytic oxidiser Used Particulate filters Water recovery and management Used Vapor compression distillation

Used Chlorine Used Sodium hypochlorite injection Used Iodine injection

Used Heat sterilisation Used Fuel cell byproduct water Evaluated Unibed filter

Evaluated TIMES membrane filter Evaluated Reverse osmosis Evaluated Electrodialysis Evaluated Electrooxidation Evaluated Supercritical water oxidation Evaluated Electrodeionisation Evaluated Air evaporation Evaluated Vapor phase catalytic

ammonia removal Evaluated Immobilised cell or enzyme bioreactors Evaluated Plant transpiration and water recovery Temperature and humidity control Used Condensing heat exchangers

Used Water cooled suits Atmosphere control and supply Used Compressed gas storage

Used Cryogenic gas storage Waste management Used Urine stored in bags

Used Feces stored in bags Used Urine vented Used Feces stored in bags and vacuum dried Used Urine stored in tank and vented Used Feces stored in bags and compacted

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