SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR 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 dischargers 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 increasing regulatory pressures, there has been a rapid commercial growth in recent years in plants designed and built specifically 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 investigated 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 individual 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 necessary to absorb the effluent from the septic tank Capacity, hydraulic design and soil conditions are most important factors influencing the septic tank performance A detailed discussion 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 currently being manufactured The Ruck system requires wash waters be separated from sanitary and kitchen wastes The sanitary and kitchen wastes are thus held in an upper compartment for a longer period of anaerobic digestion, providing more concentrated 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 characteristics Andreadakis reviewed the performance of an on-site treatment and disposal system using a septic tank, gravel filter, and soil absorption trenches.9 BOD5 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 intermittent sand filters is to reduce the BOD5 and TSS prior to soil infiltration Currently, many intermittent sand filters are used throughout the United States to treat wastewater from individual 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 effluent from treatment devices are safely disposed of by (a) subsurface 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 1082 © 2006 by Taylor & Francis Group, LLC C019_002_r03.indd 1082 11/18/2005 11:06:45 AM SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR DOMESTIC AND SPECIAL APPLICATIONS and evapotranspiration beds Direct discharge of onsite treatment system effluent is also a disposal option if an appropriate receiving water is available and if the regulatory agencies permit such discharges Various onsite disposal methods are listed below Detailed discussion may be found in Ref Typical design of septic tank and intermittent filter are shown in Figure Typical trench, seepage pit and mound systems are shown in Figure 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 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 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 suitable 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, * 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 1083 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 secondary treatment In a single-residence system, for example, 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 ϭ 12.7 m, width ϭ 4.3m, depth ϭ 0.3 m, detention time ϭ 3d, and hydraulic loading criteria ϭ 1.3 m2/L·d The aquatic plants are generally chosen from indigenous 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 obstruction to the natural flow and create anaerobic conditions.1 SMALL ESTABLISHMENTS Small establishments generally include motels, restaurants, 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 establishments 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 © 2006 by Taylor & Francis Group, LLC C019_002_r03.indd 1083 11/18/2005 11:06:45 AM 1084 C019_002_r03.indd 1084 A Distribution Box Vent Pipe Discharge Inspection Manhole and Disinfection Contact Tank (If Required) A Access Manholes Profile Plan Top Soil Fill Drainage Sanitary Tee Vent Liquid Level Inlet 6" > in Marsh Hay or Drainage Fabric Outlet > in Graded Gravel 3/4" to 1/2" Peforated or Open Joint Distributors 24–36 in Filter Media Pea Gravel > in Perforated or Open Joint Pipe, Tarpaper Over Open Joints Graded Gravel 1/4" to 1/2" Longitudinal Section (a) Typical design of two-compartment septic tank FIGURE Typical design of septic tank and intermittent filter (Adapted from Ref 2.) 11/18/2005 11:06:45 AM © 2006 by Taylor & Francis Group, LLC Section A-A (b) Typical design of buried intermittent filter installation SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR DOMESTIC AND SPECIAL APPLICATIONS Vent Pipe House Sewer Septic Tank Barrier Material Straw, Hay or Fabric Cap Distribution Lateral Fill Absorption Bed Topsoil 3/4–2-1/2 1-5 ft in Rock Plowed Layer of Top Soil Slope 2-4 ft Min Perforated Distribution Pipe 1-3 ft Rock Strata or Impermeable Soil Layer (c) Typical mound for a slowly permeable soil on sloping site Water Table or Creviced Bedrock 6-12 in (a) Typical trench system 4" Inspection Pipe Reinforced Concrete Cover Extended to Solid Earth Effluent Influent Brick, Block, Ring, or Precast Chamber with Open Joints Straw, Hay or Fabric Cap Absorption Bed Topsoil Plowed Layer of Top Soil 6" to 12" of 3/4–2 1/2" Clean Rock 4' Unsaturated Soil Water Table Impervious Layer (b) Typical seepage pit system Subsurface absorption system (Adapted from Ref 2.) © 2006 by Taylor & Francis Group, LLC Permeable Soil Water Table or Creviced Bedrock (d) Typical mound system for a permeable soil with high groundwater or shellow creviced bedrock 1085 11/18/2005 11:06:46 AM FIGURE Distribution Lateral Fill SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR DOMESTIC AND SPECIAL APPLICATIONS C019_002_r03.indd 1085 Backfill 1086 SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR DOMESTIC AND SPECIAL APPLICATIONS Blower Influent Effluent Scum Trash Trap Settling Chamber Aeration Sludge Sludge Diffuser (a) Diffused aeration Mechanical or Diffused Aeration Influent Effluent Scum Trash Trap Settling Chamber Aeration Sludge Sludge (b) Mechanical aeration FIGURE System components of aerobic suspended growth biological treatment process (Adapted from Ref 2.) 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 m3/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 m3/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 manufacturers, 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 © 2006 by Taylor & Francis Group, LLC C019_002_r03.indd 1086 11/18/2005 11:06:46 AM Motor Influent Effluent Packed Media Clarifier Timer Control Valve Influent Effluent Sludge Pump Septic Tank (a) Uptlow filter Sludge Influent Distributor (b) Rotating Biological contactor Fixed Media Under Drain Effluent to Clarifier or Septic Tank System components of aerobic attached growth biological treatment process (Adapted from Ref 2.) © 2006 by Taylor & Francis Group, LLC 1087 11/18/2005 11:06:46 AM (c) Tricking filter FIGURE SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR DOMESTIC AND SPECIAL APPLICATIONS C019_002_r03.indd 1087 Motor 1088 SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR DOMESTIC AND SPECIAL APPLICATIONS In recent years natural systems are also used for wastewater 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 constructed through snow, ice or permafrost2 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 privies, 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 problems 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 operation, (3) freeze-free, (4) minimum final disposal problems, (5) odor-free, and (6) minimum of maintenance Systems investigated in these research programs included: (1) incinerating toilets, (2) chemical toilets, and (3) chemical and biological 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 commercially available Although these toilets provide complete prevention of pollution from human wastes, they are relatively inefficient in terms of fuel consumption and often fail to provide complete burning which may result in a noxious 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 chemicals 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 biological 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, treatment, 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 pollution resulting from this source Many recreational watercraft and commercial and government vessels discharge wastes into the water.34 Recreational watercraft are highly mobile, © 2006 by Taylor & Francis Group, LLC C019_002_r03.indd 1088 11/18/2005 11:06:46 AM SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR DOMESTIC AND SPECIAL APPLICATIONS 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 specifies 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 facilities 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 macerator to grind the human fecal wastes, mix a disinfecting chemical (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 performance 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, usually 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 retention 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 fraction 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 support facilities for emptying and cleaning Low flush and vacuum flush toilets are desirable because they minimize storage and treatment requirement.34 1089 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 incinerator devices with watercraft include the difficulty of supplying electrical power as most small craft not have the generating 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 systems for increased biological activity Trickling filter-type biological treatment systems with forced air aeration have also been adopted to shipboard applications.18 These systems, which provide treatment to all waste streams generated 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 floatation 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 subsequent disposal to shore facility or into unrestricted waters COMMERCIAL AIRCRAFT Until about 1940, waste management problems aboard aircraft were considered minor; human wastes were simply discharged overboard In January of 1943, the US Public Health Service published the “Sanitation Manual for Land and Air Conveyance Operating in Interstate Traffic,” which formulated policy regarding “Discharge of Wastes from Conveyance En Route.”54 Following this publication, the International Sanitary Convention for Aerial Navigation issued a publication in February, 1945, forbidding aircraft to throw or let fall matter capable of producing an outbreak of infectious diseases.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 © 2006 by Taylor & Francis Group, LLC C019_002_r03.indd 1089 11/18/2005 11:06:46 AM 1090 SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR DOMESTIC AND SPECIAL APPLICATIONS 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 operational 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 fiberglass 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 operation 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 application have been built and evaluated.57–59 3) Evapo-combustion system to burn the macerated waste into a combustion chamber of the jet engine Vacuum toilets have also been successively installed on large commercial aircraft These toilets 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 million 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 temperature, 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 CO2 removal, O2 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 performance specifications.67–73 Table provides a list of ECLSS technologies used or evaluated The space systems have grown in complexity and comprehensiveness as both the duration of the missions and the size of the crew have increased With the possibility of long duration 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 © 2006 by Taylor & Francis Group, LLC C019_002_r03.indd 1090 11/18/2005 11:06:46 AM SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR DOMESTIC AND SPECIAL APPLICATIONS 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 hyperbaric 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- 1091 ing CO2 and regenerating O2, 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 TABLE ECLSS technologies used or evaluated ECLSS subsystem category Atmosphere revitalisation Used/Evaluated Technology Used LiOH Used Molecular sieve Used Sabatier reactor Used Static feed water electrolysis Evaluated Solid amine fixed bed Evaluated Liquid sorbent closed loop Evaluated Algal bioreactor Evaluated Trace contaminant removal Bosch system Evaluated Growing green plants Activated charcoal Used Catalytic oxidiser Used Water recovery and management Used Particulate filters 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 Temperature and humidity control Used Plant transpiration and water recovery Water cooled suits Used Compressed gas storage Used Waste management Condensing heat exchangers Used Atmosphere control and supply Used Cryogenic gas storage 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 © 2006 by Taylor & Francis Group, LLC C019_002_r03.indd 1091 11/18/2005 11:06:47 AM 1092 SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR DOMESTIC AND SPECIAL APPLICATIONS TABLE Possible terrestrial applications of spacecraft environmental systems ECLS systems Possible earthbound uses Water reclamation Submarines, arid area operations, supply of filtered and sterile water for medical, experimental uses Cleaning industrial effluent Oxygen generation Submarines, medical use in oxygen enriched atmosphere, hyperbaric chambers, under water habitats and deep undergroundwork locations CO2 removal Submarines, rescue and scuba equipment, under water habitats, hyperbaric chambers Cleaning industrial emmissions Revitalising atmosphere in deep underground work locations Trace contaminant removal Submarines, under water habitats, hyperbaric chambers Temperature, humidity control Passive systems developed for the control of the space station temperature gain and loss from and to space itself may have some terrestrial applications Active systems used in controlling temperature in locations where there are localised sources of heat may be useful for cooling dense electronics, in satellites, possibly in aircraft, and perhaps in advanced super computers A joint NASA and NSF life support system utilizing some of the water recovery, waste treatment, plant growth, and energy efficiency technologies is to be installed at the US research station at the South Pole This will provide a real world opportunity to use the planned technologies on a realistic scale.78 16 17 REFERENCES 18 Sauter, G and K Leonard, Natural Home Remedy, Water Environment & Technology, Water Environment Federation, 7, No 8, pp 48–52 (August 1995) US Environmental Protection Agency, Design manual, Onsite wastewater treatment and disposal systems, Office of water Program Operations, Municipal Environmental Research Laboratory, Cincinnati, Ohio, EPA 625/1-800-012, October 1980 US Environmental Protection Agency, Handbook of Septage Treatment and Disposal, USEPA 625/6-84-009, Center for Environmental Research Information, Cincinnati, OH, October 1984 Qasim, S.R., Wastewater Treatment Plants: Planning, Design and Operation, Technomic Publishing Co., Lancaster, PA (1994) Manual of septic-tank practice, USPHA, Publication No 526, US Department of the Interior, Washington D.C (1967) Coulter, J.B., The septic tank system in suburbia, Pub Health Rept., 73, 488 (1958) Winneberger, J.H., et al., Biological aspects of failure of septic 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