Aerobic Treatment Units: An Alternative To Septic Systems
SUMMER 2005Vol. 16, No. 3Small Community Wastewater Issues Explained to the PublicAerobic Treatment Units: An Alternative to Septic SystemsMany homes in the U.S. are locatedin small or rural communities wherehouses are spaced widely apart. Inthese communities, central seweragesystems are often not cost-effective,so many homeowners rely on septicsystems or other systems that treatand dispose of household wastewater onsite. Some homes for whichseptic systems are not a good option,becauseof site or soil conditions, rely on individual aerobic systems for wastewatertreatment.Aerobic systems are similar to septicsystems in that they both use natural processes to treat wastewater.But unlike septic (anaerobic) treatment, the aerobic treatment processrequires oxygen. Aerobic treatmentunits (ATUs), therefore, use a mechanism to inject and circulate air insidethe treatment tank. This mechanismrequires electricity to operate.For this reason, ATUs cost more tooperate and need more routine maintenance than most septic systems.However, when properly operatedand maintained, aerobic systems canprovide a high-quality wastewatertreatment alternative to septic systems. (Aerobic treatment units arealso known as ATUs, home aerationsystems, and aeration systems.)Why choose aerobic treatment?Septic tank-soil absorption systemsare relatively inexpensive and areeasy to maintain. They are the mostcommon onsite wastewater treatment systems used in rural areas.However, there are many householdsfor which a traditional septic systemmay not be the best wastewatertreatment option. Regulationsare changing to accept aerobic treatment systems as part of the normalapproval process.For example, septic systems are notsuitable for every lot. In fact, approximately two-thirds of all the landarea in the U.S. is estimated to beunsuitable for the installation of septicsystems. Some homes may not haveenough land area or appropriate soilconditions to accommodate a conventional soil absorption drainfield. Insome communities, the water table istoo high to allow the drainfield to giveadequate treatment to the wastewater before it reaches groundwater.Other site-related concerns includehomes located on small lots or on lotsclose to a body of water. The wastewa-This issue of Pipeline is anupdate to the Winter 1996issue, Vol. 7, No. 1.ter treated by a septic system is oftennot of high enough quality to be discharged very close to a body of water.But one of the most common reasonsthat aerobic wastewater treatmentunits are chosen by communities is toreplace failing septic systems. Failingseptic systems are a major source ofgroundwater pollution in some areas.If a failed septic system needs to bereplaced, or if a site is inappropriatefor conventional systems, aerobicwastewater treatment becomes aviable option. Installation of aerobicunits in new construction has alsobecome a common practice.In some cases, regulations allow ATUsto be installed in areas where the soilscannot handle septic tank effluent,
Aerobic Treatmentbecause they are less likely to causesoil clogging. Many states are requiring ATU effluent to be disinfectedbefore direct discharge. That is, whenthe effluent is properly disinfectedwith a chlorinator for example, it maybe sent directly to a surface waterbody, such as a stream. This is a typical remedy for failing septic systemsin many areas. Additionally, aeratedeffluent has been shown to renovatea clogged drainfield. Upgrading aseptic tank to an ATU can rejuvenatean existing drainfield and extend itslife.with a two-year service contract, 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 everysituation, but they do offer a reasonable alternative for difficult sites thatrequire onsite wastewater treatment.This issue of Pipeline focuses onindividual home aerobic units as onealternative for onsite wastewatertreatment.There are, of course, some drawbacksto ATUs. The basic unit is more expensive to own and operate than a septictank and requires more maintenance.The solids must be pumped out atmuch more frequent intervals, andthe electrical-mechanical parts mustbe maintained. Most ATUs are soldHow AerobicTreatment WorksAerobic systems treat wastewaterusing natural processes that requireoxygen. Bacteria that thrive in oxygen-rich environments break downand digest the wastewater inside theaerobic treatment unit as they aresuspended in the liquid.Like most onsite systems, aerobic systems treat the wastewater in stages.Sometimes the wastewater receivespretreatment before it enters the aerobic unit, and the treated wastewaterleaving the unit requires additionaltreatment or disinfection beforebeing returned to the environment.Such a variety of designs exists forhome aerobic units andsystems that it is impossible todescribe a typical system. Instead, it ismore practical to discuss how somecommon design features of aerobicsystems work and the different stagesof aerobic treatment.PretreatmentPipeline is published quarterly by theNational Environmental Services Centerat West Virginia University,P.O. Box 6064, Morgantown, WV 26506-6064Some aerobic systems include a pretreatment step to reduce the amountof solids in the wastewater going intoPipeline is funded through a grant from theU.S. Environmental Protection Agency, Washington, D.C.Steve Hogye — Project OfficerMunicipal Support Division,Office of Wastewater ManagementNational Small Flows ClearinghouseWest Virginia University, Morgantown, WVRick Phalunas — Interim Executive DirectorMarilyn Noah — EditorJennifer Hause — Technical AdvisorClement Solomon — Technical AdvisorJohn Fekete — Senior Graphic DesignerJamie Bouquot — Graphic DesignerPermission to quote from or reproduce articles in thispublication is granted when due acknowledgement is given.Please send a copy of the publication in which informationwas used to the Pipeline editor at the address above.an equal opportunity/affirmative action institutionISSN 1060-0043The contents of this newsletter do not necessarily reflect theviews and policies of the U.S. Environmental Protection Agency,Printed onnor does the mention of trade names or commercial productsrecycled paperconstitute endorsement or recommendation for use.Figure 1 An example of a possible aerobic unit design2Adapted with permission from Pennsylvania State University College of Agriculture Extension ServicePIPELINE – Summer 2005; Vol.16, No. 3National Environmental Services Center (800) 624-8301 or (304) 293-4191
Aerobic Treatmentthe aerobic unit. Solids include toiletpaper and other materials that are putdown the drain or flushed into thesystem. Too much solid material canclog the unit and prevent effectivetreatment.Some pretreatment methods includea septic tank, a primary settling compartment in the treatment unit, or atrash tank. The trash tank removessolid materials that the bacteria cannot breakdown. Pretreatment greatlyimproves a unit’s performance.TreatmentThe main function of the aerobicunit is to collect and treat householdwastewater, which includes all waterfrom toilets, bathtubs, showers, sinks,and laundry. Aerobic units themselvescome in many sizes and shapes.The process most aerobic units use totreat wastewater is referred to as suspended growth. These units include amain compartment called an aerationchamber in which air is mixed withthe wastewater. Because most homeaerobic units are buried undergroundlike septic tanks, the air must beforced into the aeration chamber byan air blower or a compressor.The forced air mixes with wastewaterin the aeration chamber, and the oxygen supports the growth of aerobicbacteria that digest the solids in thewastewater. This mixture of wastewater and oxygen is called the mixedliquor.The treatment occurring in the mixedliquor is referred to as suspendedgrowth because the bacteria growand die as they are suspended in theliquid unattached to any surface.Unfortunately, the bacteria cannotdigest all of the solids in the mixedliquor, and these solids eventually settle out as sludge. Many aerobic unitsinclude a secondary chamber calleda settling chamber or clarifier whereexcess solids can settle. (See Figure1.) Other designs allow the sludgeto accumulate at the bottom of thetank. (See Figure 2.) In aerobic unitsdesigned with a separate settlingcompartment, the sludge returnsto the aeration chamber (either bygravity or by a pumping device). TheTINGFigure 2 Another example of a possible aerobic unit designAdapted with permission from Pennsylvania State University College of Agriculture Extension Servicesludge contains bacteria that also aidin the treatment process. Although, intheory, the aerobic treatment processshould eventually be able to consumethe sludge completely, in practice,the sludge does build up and willneed to be pumped out frequently sothat solids don’t clog the unit.Flow DesignThe wastewater flow and quantityreceived by the aerobic unit differsfrom design to design. Continuousflow designs simply allow the wastewater to flow through the unit at thesame rate that it leaves the home.Other designs employ devices (such aspretreatment tanks, surge chambers,and baffles) to control the amountof the incoming flow. Batch processdesigns use pumps or siphons to control the amount of wastewater in theaeration tank or to discharge the treated wastewater in controlled amountsafter a certain period of time.Controlling the flow of wastewaterhelps to protect the treatment process. When too much wastewater isflushed into the system all at once,PIPELINE – Summer 2005; Vol.16, No. 3it can become overburdened, andthe quality of treatment can suffer.The disadvantages to mechanicalflow control devices are that, like allmechanical components, they needmaintenance and run the risk of malfunctioning.Homeowners can help their system’sperformance by conserving water.Leaking faucets and running toiletsshould be repaired, and washingmachines and dishwashers should beused only when full. Installing watersaving devices in toilets, faucets, andshowers can reduce water use by upto 50 percent. Homeowners shouldtry to space out activities requiringheavy water use (like laundry) toavoid overloading their systems.Final Treatment and DispersalAlthough properly operated andmaintained aerobic units are veryeffective, the wastewater leaving theunits is not ready to be returned tothe environment and must receivefinal treatment or disinfection.Methods for final treatment include3National Environmental Services Center (800) 624-8301 or (304) 293-4191
Aerobic TreatmentWARNINGSIGNSof AerobicSystem ProblemsAlarms or lights going offAny changes in the system’snormal operating soundAny changes in the normal colorof the wastewater in the aerationchamber (for example, if the color isgreyish brown rather than chocolatebrown, this can sometimes indicateproblems)Excessive solids, foam, or scumin the unitPlumbing backupsSewage odors in the houseor yarddischarge to a soil absorption field,a sand filter, an evapotranspirationbed, or drip irrigation. Sometimes,the wastewater receives disinfectionbefore being discharged to the soilor directly to a body of water. Yourhealth department is familiar withlocal regulations and the treatmentoptions that are best in your area andfor your property.Soil absorption fields (or drainfields)are the most common method of finaltreatment used for septic systems. Anaerobic unit can sometimes help toprolong the life of a drainfield.The amount of dissolved oxygencontained in wastewater from anaerobic unit can help the growth of4microorganisms that treat the wastewater in the soil and can help preventthe pores in the soil from clogging.However, when aerobic units malfunction, they can release solids thatcan clog the drainfield, which maycancel out any potential benefits.Evapotranspiration beds are a lesscommon method of final treatmentand use vegetation and evaporationto naturally treat the wastewater. Dripirrigation is another less commonlyused method to treat and disperse ofwastewater.Sand filters are sometimes used totreat the wastewater from aerobicunits. The wastewater is pumpedevenly over several layers of sand andgravel, which are located either aboveor below ground. As with soil treatment systems, the purification process is aided by bacteria that occurnaturally in the sand.Disinfection is another method oftreatment commonly used with surface-discharged aerobic units. Someunits have the disinfection processincorporated into the unit design.In some cases, disinfection may bethe only treatment required of thewastewater from an aerobic unitbefore the water is released into theenvironment. One disadvantage ofthis method is the added cost of thedisinfectants and maintenance.Chlorination is the most commonmethod of disinfection. However,ultra-violet (UV) disinfection is gaining prominence. The use of UV lightis often preferable since it does nothave any unwanted residual effect asthe use of chlorine can. The Spring2004 issue of Pipeline provides acomplete description of the disinfection treatment process and the various technologies availableOther Design ConsiderationsControls and AlarmsMost aerobic units have controls thatcan be switched on and off by thehomeowner in case of emergency.Aerobic units also are required tohave alarms to alert the homeownerof malfunctions. Depending on thedesign of the system, controls andalarms can be located either inside orPIPELINE – Summer 2005; Vol.16, No. 3outside the home, and alarms can bevisible, audible, or both.Homeowners should make sure thatcontrols and alarms are always protected from corrosion, and that theaerobic unit is turned back on if thereis a power outage or if it is turned offtemporarily.SizeAerobic units should be large enoughto allow enough time for the solids tosettle and for the wastewater to betreated. The size of most units rangefrom 300 to 1,500 gallons per day, butlocal regulations often require thatthe unit be at least large enough tohandle 500 gallons of wastewater perday.The needed size of an aerobic unitis often estimated the same way thesize of a septic tank is estimated, bythe number of bedrooms (not bathrooms) in the house. It is assumedthat each person will use approximately 50 to 100 gallons of waterper day, and that each bedroom canaccommodate two people. Whencalculated this way, a three-bedroomhouse will require a unit with a capacity of 300 to 600 gallons per day.Some health departments requirethat aerobic units be sized at leastas large as a septic tank in case theaerobic unit malfunctions and oxygendoesn’t mix with the wastewater. Insuch cases, the aerobic unit will workas a septic tank—which will, at least,provide partial treatment for thewastewater.TemperatureLower temperatures tend to slowdown most biological processes, andhigher temperatures tend to speedthem up. The aerobic process itselfcreates heat, which, along with thetemperature of the wastewater, mayhelp to keep the treatment processactive. However, cold weather canhave adverse effects on the performance of aerobic units.In one study of aerobic units, therewere problems when the temperatureof the wastewater inside some of theunits fell below 15 degrees Celsius(59 degrees Fahrenheit). InsulatingNational Environmental Services Center (800) 624-8301 or (304) 293-4191
Aerobic Treatmentaround the units avoids these problems. Your health department shouldknow whether aerobic systems aresuitable for your area.Aerobic SystemMaintenanceIt is important that mechanical components in aerobic systems receiveregular inspection and maintenance.For example, mechanical aeratorssometimes need to be oiled, andvanes, filters, and seals may need tobe replaced. In most cases, homeowners do not have the expertise toinspect, repair, and maintain theirown systems.If your unit carries the NSFInternational approval, it will includethe first two years of service visitswith the purchase price and anoption to renew the service contractafter two years (Refer to page 7 formore information about NSF.) It is agood idea for homeowners to renewtheir service agreements after twoyears, or to find another service organization to take over the job.In addition to routine maintenance,NSF requires service contractors tostock replacement parts for mechanical components and to be availablefor emergency servicing. Under theoriginal two-year agreement, failedequipment is replaced at no additional cost to the homeowner.The service contract may or may notcover such problems as damage frompower failures, breaking or crushingof pipes leading to and from the system, flooding, fires, homeowner misuse, and other catastrophes beyondthe control of the manufacturer.The dealer or other independentservice organization that has anagreement with the manufacturerwill carry out the service visit. In somecases, health departments will havemanagement programs, such as sanitary districts, for aerobic systems andother onsite systems in their area.What To Expect at a TypicalService VisitThe first service visit should be scheduled immediately after the system isinstalled to make sure that everythingis working correctly. The service contractor may also arrange a meetingwith the homeowner to go overissues, such as proper operation, whatto do in case of emergency, etc. Forseasonal properties, homeowners willneed to know how to shut the systemdown in the off season and start itagain when needed. After the firstvisit, the maintenance service contract is issued to the homeowner.The maintenance contract mayinclude at least two service visits peryear for the next two years. The number of visits and service performedwill differ from unit to unit and location to location depending on manufacturers’ recommendations and localregulations.During a typical visit, the serviceprovider will remove the unit’s coverand check its general appearance.He or she will check pipes and theinside of the aeration chamber, andwill note the appearance of the wastewater inside the unit and its color andodor. If the unit includes a chlorinator,this too will be checked and may becleaned. Samples may be taken of themixed liquor from the aeration chamber, as well as the final treated wastewater. The operator will also check tosee that all mechanical parts, alarms,and controls are in working order, andthat solids are pumped from the system if needed.The service provide will inspect thesoil absorption field, sand filter, orother method of final treatment.RecordkeepingIt is a good idea for the homeowner orthe service provider to keep detailedrecords about the system and servicevisits. NSF-approved units are requiredto include a user’s manual thatdescribes such things as the manufacturer’s recommendations for the unit,the system design, how to operate andmaintain it, as well as how to tell if itis working properly. The state permitting license, the date the system wasinstalled, the type of disinfection used,and any modifications made to thePIPELINE – Summer 2005; Vol.16, No. 3Cost ConsiderationsThe cost of aerobic treatment varies depending on factors, such asdesign, size, location, and operationand maintenance requirements.Some of the factors affecting the costof aerobic treatment are as follows: unit price, cost of unit installation andelectricians’ fees, cost of construction of thedrainfield or cost of othermethodof 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 adverselyaffected by the lack of demand foraerobic systems in certain areas.Installation costs may be higherfor aerobic units than for septictanks because of the electrical workrequired. All of these factors needto be carefully considered whendetermining the cost-effectivenessof aerobic treatment versus othertreatment methods. Your local healthofficial can help you evaluate youroptions.systemshould also be recorded.Other important information to keepon hand includes where to contactthe owner if nobody is home, whereto find a key to the system, and theschedule for service visits.Homeowners should keep theirown copies of all records and permits. A convenient record-keepingfolder is available from the NationalEnvironmental Services Center.Details about how to obtain thishomeowner’s packet may be foundon page 8.5National Environmental Services Center (800) 624-8301 or (304) 293-4191
Aerobic TreatmentSix-county survey recommendsmandatory lifetime maintenancecontracts for ATU systemsIn 1998, a surveywas conducted todetermine if theATU systems in six WestVirginia counties were meetinghealth and environmental regulations. Effluent samples fromapproximately 419 units weretested for biochemical oxygendemand (BOD5), total suspendedsolids (TSS), and fecal coliforms.Data from the study guided statepolicy with regard to the monitoring of ATUs on existing sitesand the permitting of aerobicunits for use in new construction.When 92 percent of 419 ATU systems were found to be discharging effluent of unacceptablequality, poor maintenance practices were determined to be themain cause. Researchers fromWest Virginia University concluded that ATUs require propermaintenance for the life of thesystem to operate reliably andproduce a high quality effluent.Conclusions were: ATUs with good maintenance histories exceeded the TSS and BOD5limits. Disinfection of effluent was inadequate and must be improvedto avoid potential public healththreats. Inadequate maintenance wascommon. The authors recommended safeguards be put inplace to ensure effective continuous operation of these systems. Mandatory lifetime maintenanceshould be required for ATU systems.Source: Sexstone, Alan, et. al.“ASurvey of Home Aerobic TreatmentSystems Operating in Six WestVirginia Counties,” Small FlowsQuarterly, Fall 2000, NationalEnvironmental Service Center.Aerobic wastewater treatment may be a good option when. 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. A septic system has failed. There is not enough land available for a septic system.6PIPELINE – Summer 2005; Vol.16, No. 3
How Aerobic Treatment Works Aerobic systems treat wastewater using natural processes that require oxygen. Bacteria that thrive in oxy-gen-rich environments break down and digest the wastewater inside the aerobic treatment unit as they are suspended in the liquid. Like most onsite systems, aerobic sys-tems treat the wastewater in stages.
Aerobic Digestion is a biological process similar to Activated Sludge. Activated Sludge Growth Aerobic Digestion Decay. Aerobic Digestion Processes vs Activated sludge processes Practical Approach To Help Understand the Difference! Activated Sludge Aerobic Digestion . Aerobic Digestion Chemistry 1. Digestion: C 5H 7NO 2 5O
Aerobic treatment units can remove substantial amounts of contaminants that are not eliminated by the simple sedimentation that occurs in a septic tank. The aerobic process also breaks down dis-solved solids and ammonia and reduces the number of pathogens in the waste. Aerobic system processes In onsite wastewater treatment systems, micro-
The 3M Petrifilm Aerobic Count Plate is a ready-made culture medium system that contains modified Standard Methods nutrients, a cold-water-soluble gelling agent and an indicator that facilitates colony enumeration. 3M Petrifilm Aerobic Count Plates are used for the enumeration of aerobic bacteria. AC Aerobic Count Plate .File Size: 2MB
and aerobic digester is optimized for effective nitrogen removal. 12minutes aerobic and 12 minutes anoxic phase gave better nitrogen removal compared to all the cycles. Over all the aerobic digester gave about 92% ammonia removal, 70% VS destruction and 70% COD removal. The oxygen uptake rates (OUR's) in the aerobic digester are measured
aerobic exercise and a control session, in random order and on separate days. After the short-term sessions, all the patients will be randomly allocated into four groups and followed up for 8 weeks (between design): mild aerobic ex-ercise group, moderate aerobic exercise group, high-intensity aerobic exercise group and the control group.
aerobic exercise approaches is considered and has a place in mental health practice. According to many studies aerobic exercise is the preferred form of exercise for patients with MDD. Moreover, Aerobic exercise has been proven as an effective treatment for MDD, and there are sufficient studies to help health
wastewater treatment. These include aerobic, anaerobic, and facultative ponds. 2. Aerobic Ponds contain dissolved oxygen (DO) throughout the entire depth of the pond all the time. Treatment is accomplished through the stabilization of organic wastes by aerobic bacteria and algae. Dissolved oxygen can be introduced into a pond through several means.
2 CHAPTER1. INTRODUCTION 1.1.3 Differences between financial ac-countancy and management ac-counting Management accounting information differs from
