Aerobic Treatment Units: An Alternative to Septic Systems
Contents
1. 7 AIR LINE INLET SETTLING AREA pie 0f a po Adapte e 0 om Pe ate eventually settle out as sludge Many aerobic units include a sec ondary chamber called a settling chamber or clarifier where excess solids can settle See Figure 1 Other designs allow the sludge to accumulate at the bottom of the tank See Figure 2 In aerobic units designed with a separate settling compartment the sludge returns to the aeration chamber either by gravity or by a pump ing device The sludge contains bacteria that also aid in the treatment process Although in theory the aerobic treatment process should eventually be able to consume the sludge complete ly in practice the sludge does build up and will need to be pumped out frequently so that solids don t clog the unit Flow Design The wastewater flow and quantity received by the aerobic unit differs from design to design Continuous flow designs simply allow the wastewater to flow through the OUTLET MIXING AREA SETTLING AREA RECIRCULATING TUBE 4 AIR DIFFUSER Die aerop ATG ollege of A e ensio unit at the same rate that it leaves the home Other designs employ devices such as pretreatment tanks surge chambers and baf fles to control the amount of the incoming flow Batch process designs use pumps or siphons to control the amount of wastewater in the aeration tank or to dis charge the treated wastewater2. require oxygen Bacteria that thrive in oxygen rich environ ments break down and digest the wastewater inside the aerobic treatment unit as they are sus pended in the liquid Like most onsite systems aerobic systems treat the wastewater in stages Sometimes the wastewater receives pretreatment before it enters the aerobic unit and the treated wastewater leaving the unit requires additional treat ment or disinfection before being returned to the environment Such a variety of designs exists for home aerobic units and systems that it is impossible to describe a typical system Instead it is more practical to discuss how some common design features of aerobic systems work and the dif ferent stages of aerobic treatment g AERATOR AERATION COMPARTMENT h SETTLING MIXING ROTOR SLUDGE RETURN i Figure 1 An example of a possible aerobic unit design Adapted with permission from Pennsylvania State University College of Agriculture Extension Service National Environmental Services Center 800 624 8301 or 304 293 4191 Pretreatment Some aerobic systems include a pretreatment step to reduce the amount of solids in the waste water going into the aerobic unit Solids include toilet paper and other materials that are put down the drain or flushed into the sys tem Too much solid material can clog the unit an
3. In some cases regulations allow ATUs to be installed in areas where the soils cannot handle septic tank effluent because they are less likely to cause soil clog ging Many states are requiring ATU effluent to be disinfected before direct discharge That is when the effluent is properly dis infected with a chlorinator for example it may be sent directly to a surface water body such as a stream This is a typical remedy for failing septic systems in many National Environmental a Services Center NESC Assistance Solutions Knowledge Pipeline is published quarterly by the National Environmental Services Center at West Virginia University P O Box 6064 Morgantown WV 26506 6064 Pipeline is funded through a grant from the U S Environmental Protection Agency Washington D C Steve Hogye Project Officer Municipal Support Division Office of Wastewater Management National Small Flows Clearinghouse West Virginia University Morgantown WV Rick Phalunas nterim Executive Director Marilyn Noah Editor Jennifer Hause Technical Advisor Clement Solomon Technical Advisor John Fekete Senior Graphic Designer Jamie Bouquot Graphic Designer Permission to quote from or reproduce articles in this publication is granted when due acknowledgement is given Please send a copy of the publication in which information was used to the Pipeline editor
4. Virginia counties were meeting health and environmental regulations Effluent samples from approximately 419 units were tested for biochemical oxygen demand BOD5 total sus pended solids TSS and fecal col iforms Data from the study guided state policy with regard to the monitoring of ATUs on existing sites and the permitting of aerobic units for use in new construction When 92 percent of 419 ATU sys tems were found to be discharging effluent of unacceptable quality poor maintenance practices were determined to be the main cause Researchers from West Virginia University concluded that ATUs require proper maintenance for the life of the system to operate reli ably and produce a high quality effluent contracts for ATU systems Conclusions were e ATUs with good maintenance histories exceeded the TSS and BOD5 limits Disinfection of effluent was inadequate and must be improved to avoid potential public health threats Inadequate maintenance was common The authors recommended safeguards be put in place to ensure effective continuous operation of these systems Mandatory lifetime maintenance should be required for ATU systems Source Sexstone Alan et al A Survey of Home Aerobic Treatment Systems Operating in Six West Virginia Counties Small Flows Quarterly Fall 2000 National Environmental Service Center Available for download at www nesc wvu edu nsfc sfgarchive frame html Aerobic wast
5. at the address above MM West Virginia v University an equal opportunity affirmative action institution SSN 1060 0043 The contents of this newsletter do not necessarily reflect the views and policies of the U S Environmental Protection Agency nor does the mention of trade names or commercial products constitute endorsement or recommendation for use PIPELINE Summer 2005 Vol 16 No 3 Aerobic Treatment Units areas Additionally aerated efflu ent has been shown to renovate a clogged drainfield Upgrading a septic tank to an ATU can rejuve nate an existing drainfield and extend its life There are of course some draw backs to ATUs The basic unit is more expensive to own and oper ate than a septic tank and requires more maintenance The solids must be pumped out at much more frequent intervals and the electrical mechanical parts must be maintained Most ATUs are sold with a two year service con tract covering inspections and maintenance Manufacturers and regulators recommend that such a contract be extended for the life of the unit ATUs are not the solution for every situation but they do offer a reasonable alternative for diffi cult sites that require onsite wastewater treatment This issue of Pipeline focuses on individual home aerobic units as one alternative for onsite waste water treatment How Aerobic Treatment Works Aerobic systems treat wastewater using natural processes that
6. copy of Standard 40 may be purchased for 90 00 NSF ANSI Standard 46 Standard 46 relating to compo nents of wastewater treatment systems applies to any waste water treatment product not covered by Standards 40 and 41 Standard 46 was developed to replace NSF Criteria C 9 which was withdrawn in 2000 Standard 46 currently includes perform ance evaluations for grinder pumps septic tank effluent filters chlorination devices and UV dis infection devices As product users regulatory officials and manufacturers identify the need for additional performance evalu ations for other classes of waste water treatment products the NSF Joint Committee on Wastewater Technology will develop the eval uations and add them to Standard 46 A copy of Standard 46 may be purchased for 75 00 NSF also produces a complete list ing of approved systems titled NSF Listings of Wastewater Treatment Units This listing may be down loaded at www nsf org Certified Wastewater Listings asp You may search the listing by product name manufacturer or product standard For more information or to order these products contact NSF International at 800 NSF MARK or 800 673 6275 5 NESC WESC Products SFPLN27 Disinfection is generally required with onsite treatment systems where the effluent is to be surface discharged to prior to some other immediate reuse of effluent This issue titled The Disinfection Question Answers
7. cost of construction of the drainfield or cost of other method of additional treatment if required cost of electricity per year maintenance service contract fee per year and cost of disinfection if applicable The price of some of these factors such as unit price may be adversely affected by the lack of demand for aer obic systems in certain areas Installation costs may be higher for aerobic units than for septic tanks because of the electrical work required All of these factors need to be carefully considered when determining the cost effectiveness of aerobic treatment ver sus other treatment methods Your local health official can help you evalu ate your options The maintenance contract may include at least two service visits per year for the next two years The number of visits and service performed will differ from unit to unit and location to location depending on manufacturers recommendations and local regulations During a typical visit the service provider will remove the unit s cover and check its general appearance He or she will check pipes and the inside of the aera tion chamber and will note the National Environmental Services Center 800 624 8301 or 304 293 4191 Aerobic Treatment Units Six county survey recommends mandatory lifetime maintenance In 1998 a survey was conducted to et determine if the ATU systems in six West
8. if nobody is home where to find a key to the system and the schedule for serv ice visits Homeowners should keep their own copies of all records and per mits A convenient record keep ing folder is available from the National Environmental Services Center Details about how to obtain this homeowner s packet may be found on page 8 Readers are encouraged to reprint Pipeline articles in local newspapers or include them in flyers newsletters or educational presenta tions Please include the name and phone number of the National Environmental Service Center NESC on the reprinted information and send us a copy for our files If you have any questions about rinting articles or about any of the top discussed in this newsletter please contact the NESC at 800 624 8301 PIPELINE Summer 2005 Vol 16 No 3 Aerobic Treatment Units NSFI provides industry standards Aerobic treatment systems are not accepted in all areas Regulations for onsite systems can vary from state to state and from one local government to the next One possible reason that the acceptance of aerobic systems has been slow in some communi ties may be that local regulators don t have much experience with them Unless aerobic systems are already in use locally there is lit tle opportunity for officials to become familiar with their per formance in different situations A major reason that aerobic sys tems are
9. in controlled amounts after a certain period of time Controlling the flow of waste water helps to protect the treat ment process When too much wastewater is flushed into the system all at once it can become overburdened and the quality of treatment can suffer The disad vantages to mechanical flow con trol devices are that like all mechanical components they need maintenance and run the risk of malfunctioning Homeowners can help their sys tem s performance by conserving water Leaking faucets and run 5i s NESC National Environmental Services Center 800 624 8301 or 304 293 4191 WARNING SIGNS of Aerobic System Problems Any changes in the system s normal operating sound Excessive solids foam or scum in the unit Sewage odors in the house or yard ning toilets should be repaired and washing machines and dish washers should be used only when full Installing water saving devices in toilets faucets and showers can reduce water use by up to 50 percent Homeowners should try to space out activities requiring heavy water use like laundry to avoid overloading their systems Final Treatment and Dispersal Although properly operated and maintained aerobic units are very effective the wastewater leaving the units is not ready to be returned to the environment and must receive final treatment PIPELINE Summer 2005 Vol 16 No 3 Aerobic Treatment Units or disinfection Methods f
10. in the sand Disinfection is another method of treatment commonly used with surface discharged aerobic units Some units have the disinfection process incorporated into the unit design In some cases disinfec tion may be the only treatment required of the wastewater from an aerobic unit before the water National Environmental Services Center 800 624 8301 or 304 293 4191 is released into the environment One disadvantage of this method is the added cost of the disinfec tants and maintenance Chlorination is the most com mon method of disinfection However ultra violet UV disin fection is gaining prominence The use of UV light is often preferable since it does not have any unwanted residual effect as the use of chlorine can The Spring 2004 issue of Pipeline pro vides a complete description of the disinfection treatment process and the various technologies available Other Design Considerations Controls and Alarms Most aerobic units have controls that can be switched on and off by the homeowner in case of emergency Aerobic units also are required to have alarms to alert the homeowner of malfunctions Depending on the design of the system controls and alarms can be located either inside or outside the home and alarms can be vis ible audible or both Homeowners should make sure that controls and alarms are always protected from corrosion and that the aerobic unit is turned back on if there is a power
11. outage or if it is turned off temporarily Size Aerobic units should be large enough to allow enough time for the solids to settle and for the wastewater to be treated The size of most units range from 300 to 1 500 gallons per day but local regulations often require that the unit be at least large enough to handle 500 gallons of wastewater per day The needed size of an aerobic unit is often estimated the same way the size of a septic tank is estimated by the number of bed rooms not bathrooms in the house It is assumed that each person will use approximately 50 to 100 gallons of water per day and that each bedroom can accommodate two people When calculated this way a three bed room house will require a unit with a capacity of 300 to 600 gal lons per day Some health departments require that aerobic units be sized at least as large as a septic tank in case the aerobic unit malfunc tions and oxygen doesn t mix with the wastewater In such cases the aerobic unit will work as a septic tank which will at least provide partial treatment for the wastewater Temperature Lower temperatures tend to slow down most biological processes and higher temperatures tend to speed them up The aerobic process itself creates heat which along with the temperature of the wastewater may help to keep the treatment process active However cold weather can have adverse ef
12. d prevent effective treatment Some pretreatment methods include a septic tank a primary settling compartment in the treatment unit or a trash tank The trash tank removes solid materials that the bacteria can not breakdown Pretreatment greatly improves a unit s per formance Treatment The main function of the aerobic unit is to collect and treat house hold wastewater which includes all water from toilets bathtubs showers sinks and laundry Aerobic units themselves come in many sizes and shapes The process most aerobic units use to treat wastewater is referred to as suspended growth These units include a main compart ment called an aeration chamber in which air is mixed with the wastewater Because most home aerobic units are buried under ground like septic tanks the air must be forced into the aeration chamber by an air blower or a compressor The forced air mixes with waste water in the aeration chamber and the oxygen supports the growth of aerobic bacteria that digest the solids in the wastewater This mixture of wastewater and oxygen is called the mixed liquor The treatment occurring in the mixed liquor is referred to as sus pended growth because the bac teria grow and die as they are suspended in the liquid unat tached to any surface Unfortunately the bacteria can not digest all of the solids in the mixed liquor and these solids PIPELINE Summer 2005 Vol 16 No 3
13. ewater treatment may be a good option when A septic system has failed The soil quality is not appropriate for a septic system There is high groundwater or shallow bedrock A higher level of wastewater treatment is required There is not enough land available for a septic system appearance of the wastewater inside the unit and its color and odor If the unit includes a chlori nator this too will be checked and may be cleaned Samples may be taken of the mixed liquor from the aeration chamber as well as the final treated wastewater The operator will also check to see that all mechanical parts alarms and controls are in working order and that solids are pumped from the system if needed The service provide will inspect the soil absorption field sand fil ter or other method of final treatment Recordkeeping It is a good idea for the homeown er or the service provider to keep detailed records about the system and service visits NSF approved units are required to include a user s manual that describes such things as the manufacturer s rec ommendations for the unit the system design how to operate and maintain it as well as how to tell if it is working properly The state permitting license the date the system was installed the type of disinfection used and any modifi cations made to the system should also be recorded Other important information to keep on hand includes where to contact the owner
14. fects on the perform ance of aerobic units In one study of aerobic units there were problems when the temperature of the wastewater inside some of the units fell below 15 degrees Celsius 59 degrees Fahrenheit Insulating around the units avoids these problems Your health department should know whether aerobic systems are suitable for your area Aerobic System Maintenance It is important that mechanical components in aerobic systems receive regular inspection and maintenance For example mechanical aerators sometimes need to be oiled and vanes fil ters and seals may need to be replaced In most cases home owners do not have the expertise to inspect repair and maintain their own systems PIPELINE Summer 2005 Vol 16 No 3 Aerobic Treatment Units If your unit carries the NSF International approval it will include the first two years of serv ice visits with the purchase price and an option to renew the serv ice contract after two years Refer to page 7 for more information about NSF It is a good idea for homeowners to renew their serv ice agreements after two years or to find another service organiza tion to take over the job In addition to routine mainte nance NSF requires service con tractors to stock replacement parts for mechanical components and to be available for emer gency servicing Under the origi nal two year agreement failed equipment is replaced a
15. for Onsite Systems describes two of the most common methods of disinfection used with onsite systems chlorine and ultraviolet light Pros and cons of the use of these methods are discussed Information about the dosage and design parameters of each type of disinfection process are presented May be downloaded as a pdf file at www nesc wvu edu nsfc plarchiveframe html SFPLN26 The Summer issue of Pipeline presents an overview of gravelless and contour drainfield systems for onsite wastewater treatment and dis persal The issue compares the two technologies with conventional drainfields It also explains their operation and maintenance and advantages and disadvantages A case study about a chamber system used in a West Virginia School is included May be downloaded as a pdf file at www nesc wvu edu nsfc plarchivetrame html NESC ENCEN Olona ee les AM NMOLNVSYOW ve ON LINYAd Wd ANVLSOd S N NOILLVZINVDYO LISQOYdNON Ultraviolet Disinfection AWWFSGN98 1998 Chlorine Disinfection WWFSGN99 1998 Ozone Disinfection WWFSGN100 1998 WBLPE37 WWPKPE28 WWFSGN160 WWFSGN170 To order call 800 624 8301 for prices and availability CaLSANDAY AOIAUAS SSAYCAV JSJN 7909 S0S9Z AM umojuebioy v909 xog Od g Aysi nuN eIUIBIIA S9M uoneiodiog yoseasay NAM J9 UBD SEdIMIAS ezju wuou JeuOIeN
16. ice contract is carried out by the dealer selling the aerobic unit representing the manufacturer Standard 40 details what type of service is to be performed and what records need to be kept Both the manu facturers and their distributors are inspected annually by NSF to ensure continued compliance with the requirements Some state and local govern ments that allow aerobic treat ment require that units carry the NSF approval Your local health department will be familiar with the regulations and permit requirements for your area as well as which onsite options are best for your particular property NSF ANSI Standard 40 Residential Wastewater Treatment Systems Standard 40 relating to residen tial wastewater treatment sys tems requires six months of per formance testing incorporating stress tests to simulate wash day working parent power outage and vacation conditions National Environmental Services Center 800 624 8301 or 304 293 4191 Although the U S EPA permit program does not apply to onsite discharge Class I listed units have been shown to produce an equivalent quality effluent when tested for six months at their design rated capacities This Standard contains minimum requirements for residential wastewater treatment systems having single defined discharge points and rated treatment capacities between 1514 liters per day 400 gallons per day and 5678 liters per day 1500 gallons per day A
17. ms used in rural areas However there are many households for which a traditional septic system may not be the best wastewater treatment option Regulations are changing to accept aerobic treatment systems as part of the normal approval process For example septic systems are not suitable for every lot In fact approximately two thirds of all the land area in the U S is esti mated to be unsuitable for the installation of septic systems Some homes may not have enough land area or appropriate soil conditions to accommodate a conventional soil absorption drainfield In some communities the water table is too high to allow the drainfield to give ade quate treatment to the wastewater before it reaches groundwater Other site related concerns include homes located on small lots or on lots close to a body of water The wastewater treated by a septic sys tem is often not of high enough quality to be discharged very close to a body of water But one of the most common rea sons that aerobic wastewater treatment units are chosen by communities is to replace failing septic systems Failing septic sys tems are a major source of groundwater pollution in some areas If a failed septic system needs to be replaced or if a site is inappropriate for conventional systems aerobic wastewater treatment becomes a viable option Installation of aerobic units in new construction has also become a common practice
18. not more widely used is concern about improper operation and maintenance by homeowners Aerobic systems require regular maintenance and abuse or neglect can easily lead to system failure In answer to these concerns NSF International formerly the National Sanitation Foundation has tested aerobic units accord ing to the requirements of ANSI NSF Standard 40 NSF International is a nonprofit organization devoted to the pro tection of public health and the environment through the devel opment of product standards product evaluations research education and training The American National Standards Institute ANSI is the recognized accreditor in the U S for organi zations that develop consumer standards and for those that pro vide independent product evalua tions NSF is accredited by ANSI for both of these areas of service Aerobic units that satisfy the requirements of ANSI NSF Standard 40 may carry the NSF mark see mark above In addition to testing their units NSF requires manufacturers to include the cost of the first two years of service in the price of pur chase During this initial service contract each piece of equipment must be serviced a minimum of two times per year and emer gency service must be available to PIPELINE Summer 2005 Vol 16 No 3 the homeowner Manufacturers must also offer the homeowner the option of renewing the service contract after the two years In most cases the serv
19. or final treatment include discharge to a soil absorption field a sand filter an evapotranspiration bed or drip irrigation Sometimes the wastewater receives disinfection before being discharged to the soil or directly to a body of water Your health department is famil iar with local regulations and the treatment options that are best in your area and for your property Soil absorption fields or drain fields are the most common method of final treatment used for septic systems An aerobic unit can sometimes help to pro long the life of a drainfield The amount of dissolved oxygen contained in wastewater from an aerobic unit can help the growth of microorganisms that treat the wastewater in the soil and can help prevent the pores in the soil from clogging However when aerobic units malfunction they can release solids that can clog the drainfield which may cancel out any potential benefits Evapotranspiration beds are a less common method of final treatment and use vegetation and evaporation to naturally treat the wastewater Drip irriga tion is another less commonly used method to treat and dis perse of wastewater Sand filters are sometimes used to treat the wastewater from aer obic units The wastewater is pumped evenly over several lay ers of sand and gravel which are located either above or below ground As with soil treatment systems the purification process is aided by bacteria that occur naturally
20. pi NESC any homes in the U S are located in small or rural communities where houses are spaced widely apart In these communities central sewerage systems are often not cost effective so many homeowners rely on septic systems or other systems that treat and dispose of house hold wastewater onsite Some homes for which septic systems are not a good option because of site or soil conditions rely on individual aerobic systems for wastewater treatment Aerobic systems are similar to septic systems in that they both use natural processes to treat wastewater But unlike septic anaerobic treatment the aerobic treatment process requires Oxy gen Aerobic treatment units ATUs therefore use a mecha nism to inject and circulate air inside the treatment tank This mechanism requires electricity to operate For this reason ATUs cost more to operate and need more routine maintenance than most septic systems However when properly operated and maintained aero bic systems can provide a high quality wastewater treatment alternative to septic systems Aerobic treatment units are also known as ATUs home aeration systems and aeration systems j Small Community Wastewater Issues Explained to the Public Aerobic Treatment Units An Alternative to Septic Systems Septic tank soil absorption sys tems are relatively inexpensive and are easy to maintain They are the most common onsite wastewater treatment syste
21. t no addi tional cost to the homeowner The service contract may or may not cover such problems as dam age from power failures break ing or crushing of pipes leading to and from the system flooding fires homeowner misuse and other catastrophes beyond the control of the manufacturer The dealer or other independent service organization that has an agreement with the manufactur er will carry out the service visit In some cases health depart ments will have management programs such as sanitary dis tricts for aerobic systems and other onsite systems in their area What To Expect at a Typical Service Visit The first service visit should be scheduled immediately after the system is installed to make sure that everything is working cor rectly The service contractor may also arrange a meeting with the homeowner to go over issues such as proper operation what to do in case of emergency etc For seasonal properties homeowners will need to know how to shut the system down in the off sea son and start it again when needed After the first visit the maintenance service contract is issued to the homeowner Cost Considerations The cost of aerobic treatment varies depending on factors such as design size location and operation and main tenance requirements Some of the fac tors affecting the cost of aerobic treat ment are as follows unit price cost of unit installation and electricians fees
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