Guide to Aerobic Septic Systems - A Design Alternative for Difficult Sites InspectAPedia® -
AEROBIC Septic systems guide - ATUs aerobic treatment units
Design, installation, and maintenance of aerobic septic systems
Aerobic treatment unit ATU tank size, 2, 3, and 4-chamber aerobic septic tank designs
Aerobic treatment unit ATU final treatment of septic effluent
Aerobic treatment unit ATU certifications, Aerobic treatment unit ATU problems and solutions
Aerobic treatment unit ATU maintenance procedures, Aerobic treatment unit ATU disinfectant choices and use
Aerobic treatment unit ATU continuous flow suspended growth design
Aerobic treatment unit ATU effluent spray head maintenance and replacement
Questions & answers about aerobic treatment units (ATUs) and aerobic septic systems: design, installation, inspection, maintenance, & repair
ATUs - Aerobic Septic Systems: this article series explains the designs and products, installation, maintenance, and repair of aerobic septic treatment units (ATUs) for onsite waste disposal, also called fine bubble aeration systems.
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AEROBIC Septic systems add oxygen using any of several types aeration or "fine air bubble" systems to increase the level of
effluent treatment in the septic tank by encouraging
aerobic bacteria. Aerobic systems produce a better-quality wastewater effluent for discharge into the absorption system for final
treatment and disposal.
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What is an Aerobic Treatment Unit for Septic Effluent?
In residential use, aerobic treatment units (ATUs, also called "home aeration systems" or "septic tank aeration systems")
are pre-packaged septic treatment systems which are in essence a mini-wastewater treatment plant for home use. "Aerobic" refers to the
use of an air pump to add oxygen to the treatment tank to increase the level of treatment by
the system.
AEROBIC Septic systems thus require electrical power and cost more to install
and operate (more frequent tank pumping) than a traditional gravity septic tank and drainfield.
Aerobic treatment, which can produce very high quality treated effluent, is used at sites where a conventional septic drainfield simply wont' work, perhaps
because of wet soils or very rocky conditions.
ATUs are also used to restore a working septic system where a traditional
septic system has failed and is difficult to repair. Other common reasons for installing aerobic septic treatment units include
lots close to lakes and streams or lots which are too small to fit a conventional septic system.
Aerobic treatment may not entirely eliminate the
requirement for a drainfield, but it can substantially reduce the drainfield area and capacity
required. This is not a "new" idea. Aeration of wastewater as a
means of septic effluent treatment has been in use for more than 100 years (using media filters
according to Jantrania).
How do Aerobic Septic Treatment Units Work?
An aerobic treatment unit is basically an "oxidizer" which uses extra oxygen dissolved in the wastewater to
support aerobic microorganisms which in turn decompose dissolved organic and nitrogen compounds into simple CO2 or into inorganic compounds.
As microorganisms die off they accumulate as a sludge of biological material, some of which supports the development of new cells or microorganisms
to keep the system working.
ATU's separate solid waste first in the "trash tank" and
later, additional solids are separated in the clarifier or settlement tank from which they may be
returned to the primary tank for more treatment. (See the sketch at the top of this page.)
"Typical organic materials that are found in residential strength wastewater include
carbohydrates, fats, proteins, urea, soaps and detergents. All of these compounds contain
carbon, hydrogen, and oxygen. Domestic wastewater also includes organically bound
nitrogen, sulfur and phosphorus.
During biochemical degradation, these three elements
are biologically transformed from organic forms to mineralized forms (i.e., NH3, NH4,
NO3, SO4, and PO4)." -- Reference #3 at page bottom. In contrast, an example of an anaerobic process
involved in the breakdown of wastewater would be
fermentation, the exothermic, enzymatic breakdown of soluble
organic compounds which does not depend on the presence of dissolved oxygen. Methane and CO2 are both
products of wastewater fermentation.
Simplest Two-Chamber Aerobic Treatment Unit Design
Waste from the occupied building is fed into a septic tank primary treatment chamber where it
is kept agitated and aerated (oxygenated) by an air pump and rotor or mixer. By increasing the oxygen level in the
effluent, we increase activity by the tank's aerobic bacteria and other naturally occurring
microorganisms such as fungi, protozoa, rotifers, and other microbes.
Effluent passes out of the primary treatment tank into a settlement chamber where sludge settles out
for recycling into the primary treatment tank. Clarified effluent passes to an absorption or further
treatment system. An alarm system is usually installed to
tell the building owner if the equipment has stopped working.
Three-Chamber Aerobic Septic System ATU Design
AEROBIC Septic Trash Tank: Waste from the occupied building is fed into a "trash tank" (similar to a septic tank);
septic solid waste and scum are retained in the "trash tank" and as with a conventional septic tank, must be periodically
removed by a septic pumping company. (ATU's require more frequent septic tank pumping than a conventional
septic system.)
The ATU tank works like a septic tank but can be smaller because
the system does not depend on a long "settlement time" to remove solids and grease as occurs in a conventional
septic tank.
AEROBIC Septic System Aeration Chamber & Aeration Pump: An aerator or air pump, normally installed
in a chamber atop or close to the septic tank, pumps air into the septic tank's aeration compartment using any of
several methods to aerate the wastewater.
A mixing device or rotor may be used to further agitate the wastewater in the
aerobic treatment tank to increase the oxygen level in the effluent
and to support treatment by aerobic bacteria in the tank. Speaking slightly more technically,
the aerobic process in the treatment tank provides for biochemical
oxidation of the soluble organic compounds found in domestic wastewater.
AEROBIC Septic Aeration Chamber: Septic effluent moves out of the "trash tank"
to a separate aeration chamber.
In the aeration chamber air (oxygen) is pumped through the system to provide oxidation and waste treatment using a variety
of designs.
The added level of oxygen permits a variety of microbial life forms (bacteria, fungi, protozoa,
and others) to oxidize or otherwise process pathogens and nitrogen compounds in the discharged septic effluent.
The aerated, or oxygenated wastewater is called the "mixed liquor".
AEROBIC Septic System Clarification Chamber: After having been aerated and mixed in the aeration chamber, the effluent flows to a clarification chamber.
Solids settle out of the effluent and stay inside the ATU. In some designs the sludge is recycled to the
aeration chamber.
The settled sludge and solids support
the formation of additional microbial growth which in turn is used to process pathogens as we just described.
The ATU may, depending on its design, also remove
nutrients, solids which were not retained in the trash tank, and pathogens.
Suspended Growth vs. Attached Growth Septic Systems: Oxygen-supported (aerobic) bacteria in the mixed liquor perform the primary treatment in the system. As the bacteria themselves
die off they remain suspended in the mixed liquor - a "suspended growth aerobic treatment system". Alternatively, a media, such as synthetic
fabrics, may be suspended in the treatment tank, permitting the bacteria to attach to the media surfaces - an "attached growth
aerobic treatment system".
Saturated vs. Non-Saturated Wastewater Treatment Systems: An aerobic treatment unit (ATU), because it involves
a tank filled with wastewater and forced oxygenation of that wastewater, is a type of saturated wastewater treatment system.
Other non-saturated wastewater treatment systems such as
trickling filter beds use passively-infused air to support their oxygen-supported microorganisms. Unlike ATUs,
non-saturated systems allow passive air contact with
effluent as it moves through the media. Air is not being pumped. Both types of systems make use of aerobic microorganisms.
Four-Chamber Aerobic Systems - 4-chamber ATU Design
Four-chamber Aerobic Treatment Units are also designed for and used in some areas, though how we count chambers
may be confusing - some designers may not design or count a separate aeration chamber. A four-chamber aerobic tank
uses
AEROBIC Septic Tank Sewage receiver: a compartment to receive sewage and collect sludge;
Aerobic Treatment Unit Aeration Chamber: an aerobic chamber to pump air and thus oxygen
through wastewater to assist in the aerobic treatment process;
AEROBIC Septic Effluent Settling Chamber: a clarifying or settling chamber which permits
remaining solids to settle out of the wastewater; disinfection may take place in this chamber;
AEROBIC Septic Effluent Pumping Chamber: a pumping chamber
to receive treated effluent for discharge to an absorption system or other destination.
Questions & Answers regarding this article
Questions & answers about aerobic treatment units (ATUs) and aerobic septic systems: design, installation, inspection, maintenance, & repair.
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Additional technical contributors & reference sources for this article are listed below.
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Continuous-Flow, Suspended-Growth Aerobic Systems References
Ayres Associates. 1998. Florida Keys Onsite Wastewater Nutrient Reduction Systems Demonstration Project. Contract no. LP 988. Florida Department of Health Onsite Sewage Program, Tallahassee, FL.
Brewer, W.S., J. Lucas, and G. Prascak. 1978. An evaluation of the performance of household aerobic sewage treatment units. Journal of Environmental Health 41(2):82-84.
Converse, J.C., and M.M. Converse. 1998. Pump Chamber Effluent Quality Following Aerobic Units and Sand Filters Serving Residences. In Proceedings of the Eighth National Symposium on Individual and Small Community Sewage Systems. American Society of Agricultural Engineers, Orlando, FL.
Englehardt, J.D., and R.C. Ward. 1986. Operation and maintenance requirements for small flow treatment systems. Journal of the Water Pollution Control Federation 58(10).
Hutzler, N.L., L. Waldorf, and J. Fancy. 1978. Performance of Aerobic Treatment Units. In Proceedings of the Second National Home Sewage Treatment Symposium. American Society of Agricultural Engineers, Chicago, IL.
Kellam, J.G., et al. 1993. Evaluation of Performance of Five Aerated Package Treatment Systems. Bull. 178. Virginia Water Resources Research Center, Blacksburg, VA.
Mason, D.G. 1977. A Unique Biological Treatment System for Small Plants. Paper presented at the 50th Water Pollution Control Federation Conference, Philadelphia, PA.
Midwest Plan Service. 1982. On-site Domestic Sewage Disposal Handbook. Midwest Plan Service, University of Minnesota, St. Paul, MN.
Otis, R.J., and W.C Boyle. 1976. Performance of single household treatment units. Journal of Environmental Engineering Division, ASCE, 102, EE1, 175.
Otis R.J., et al. 1975. The Performance of Household Wastewater Treatment Units under Field Conditions. In Proceedings of the Third National Home Sewage Disposal Symposium. American Society of Agricultural Engineers, Chicago, IL.
Rogella, F., J. Sibony, G. Boisseau, and M. Benhomme. 1988. Fixed Biomass to Upgrade Activated Sludge. Paper presented at 61st Annual Water Pollution Control Federation Conference, Philadelphia, PA.
Rusten, B., M.J. Tetreault, and J.F. Kreissl. 1987. Assessment of Phased Isolation Ditch Technologies for Nitrogen Control. In Proceedings of the Seventh European Sewage and Refuse Symposium, pp. 279-291, Munich, Germany.
Tchobanoglous, G., and F. Burton. 1991. Wastewater Engineering. 3rd ed. McGraw-Hill, Inc., New York.
U.S. Environmental Protection Agency (USEPA). 1978. Management of Small Waste Flows. Small Scale Waste Management Project. EPA/600/2-78-173. National Technical Information Service PB 286 474.
U.S. Environmental Protection Agency (USEPA). 1980. Design Manual: Onsite Wastewater Treatment and Disposal Systems. EPA 625/1-80-012. U.S. Environmental Protection Agency, Office of Water Programs, Washington, DC
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Advanced Onsite Wastewater Systems Technologies, Anish R. Jantrania, Mark A. Gross. Anish Jantrania, Ph.D., P.E., M.B.A., is a Consulting Engineer, in Mechanicsville VA, 804-550-0389
(2006), Advanced Onsite Wastewater Systems Technologies.
Outstanding technical reference especially on alternative septic system design alternatives. Written for designers and engineers, this book is not at all easy going
for homeowners but is a text we recommend for professionals--DF.
AEROBIC SEPTIC SYSTEMS
Builder's Guide to Wells and Septic Systems, Woodson, R. Dodge: $ 24.95; MCGRAW HILL B; TP;
Quoting from Amazon's description: For the homebuilder, one mistake in estimating or installing wells and septic systems can cost thousands of dollars. This comprehensive guide filled with case studies can prevent that. Master plumber R. Dodge Woodson packs this reader-friendly guide with guidance and information, including details on new techniques and materials that can economize and expedite jobs and advice on how to avoid mistakes in both estimating and construction. Chapters cover virtually every aspect of wells and septic systems, including on-site evaluations; site limitations; bidding; soil studies, septic designs, and code-related issues; drilled and dug wells, gravel and pipe, chamber-type, and gravity septic systems; pump stations; common problems with well installation; and remedies for poor septic situations. Woodson also discusses ways to increase profits by avoiding cost overruns.
Country Plumbing: Living with a Septic System, Hartigan, Gerry: $ 9.95; ALAN C HOOD & TP;
Quoting an Amazon reviewer's comment, with which we agree--DF:This book is informative as far as it goes and might be most useful for someone with an older system. But it was written in the early 1980s. A lot has changed since then. In particular, the book doesn't cover any of the newer systems that are used more and more nowadays in some parts of the country -- sand mounds, aeration systems, lagoons, etc.
Design Manuals for Septic Systems
US EPA Onsite Wastewater Treatment Systems Manua [online copy, free] Top Reference: US EPA's Design Manual for Onsite Wastewater Treatment and Disposal, 1980, available from the US EPA, the US GPO Superintendent of Documents (Pueblo CO), and from the National Small Flows Clearinghouse. Original source http://www.epa.gov/ORD/NRMRL/Pubs/625R00008/625R00008.htm Onsite wastewater treatment and disposal systems,
Richard J Otis, published by the US EPA. Although it's more than 20 years old, this book remains a useful reference for septic system designers.
U.S. Environmental Protection Agency, Office of Water Program Operations; Office of Research and Development, Municipal Environmental Research Laboratory; (1980)
"International Private Sewage Disposal Code," 1995, BOCA-708-799-2300, ICBO-310-699-0541, SBCCI 205-591-1853, available from those code associations.
"Manual of Policy, Procedures, and Guidelines for Onsite Sewage Systems," Ontario Reg. 374/81, Part VII of the Environmental
Protection Act (Canada), ISBN 0-7743-7303-2, Ministry of the Environment,135 St. Clair Ave. West, Toronto Ontario M4V 1P5 Canada $24. CDN.
Manual of Septic Tank Practice, US Public Health Service's 1959.
Onsite Wastewater Disposal Books
Onsite Wastewater Disposal, R. J. Perkins;
Quoting from Amazon: This practical book, co-published with the National Environmental Health Association,
describes the step-by-step procedures needed to avoid common pitfalls in septic system technology.
Valuable in matching the septic system to the site-specific conditions, this useful book will help you install a reliable system in
both suitable and difficult environments. Septic tank installers, planners, state and local regulators, civil and sanitary engineers,
consulting engineers, architects, homeowners, academics, and land developers will find this publication valuable.
Onsite Wastewater Treatment Systems, Bennette D. Burks, Mary Margaret Minnis, Hogarth House 1994 - one of the best septic system books around, suffering a bit from small fonts and a weak index. (DF volunteers to serve as indexer if Burks/Minnis re-publish this very useful volume.)While it contains some material more technical than needed by homeowners, Burks/Minnis book on onsite wastewater treatment systems a very useful reference
for both property owners and septic system designers. We refer to it often.
While Minnis says the best place to buy this book is at Amazon (our link at left), you can also see this book at Minnis' website at http://web page .pace.edu/MMinnisbook
Septic Tank/Soil-Absorption Systems: How to Operate & Maintain [ copy on file as /septic/Septic_Operation_USDA.pdf ] - , Equipment Tips, U.S. Department of Agriculture, 8271 1302, 7100 Engineering, 2300 Recreation, September 1982, web search 08/28/2010, original source: http://www.fs.fed.us/t-d/pubs/pdfimage/82711302.pdf
Planting Over Septic System Component", Daniel Friedman (author/editor, InspectAPedia.com), The Innovator, Winter/Spring 2008, BCOSSA, British Columbia OnSite Sewage Association, 201-3542 Blansard St., Victoria BC V8X 1W3 Canada
Septic System Owner's Manual, Lloyd Kahn, Blair Allen, Julie Jones, Shelter Publications, 2000 $14.95 U.S. - easy to understand, well illustrated, one of the best practical references around on septic design basics including some advanced systems; a little short on safety and maintenance. Both new and used (low priced copies are available, and we think the authors are working on an updated edition--DF.
Quoting from one of several Amazon reviews: The basics of septic systems, from underground systems and failures to what the owner can do to promote and maintain a healthy system, is revealed in an excellent guide essential for any who reside on a septic system. Rural residents receive a primer on not only the basics; but how to conduct period inspections and what to do when things go wrong. History also figures into the fine coverage.
Test Pit Preparation for Onsite Sewage Evaluations, State of Oregon Department of Environmental Quality, Portland OR, 800 452-4011. PDF document. We recommend this excellent document that offers detail about soil perc tests, deep hole tests, safety, and septic design. Readers should also see Soil Percolation Tests and for testing an existing septic system, also see Dye Tests
Grass is Always Greener Over the Septic Tank, Bombeck, Erma: $ 5.99; FAWCETT; MM;
This septic system classic whose title helps avoid intimidating readers new to septic systems, is available new or used at very low prices.
It's more entertainment than a serious "how to" book on septic systems design, maintenance, or repair. Not recommended -- DF.
US EPA Onsite Wastewater Treatment Systems Manual Top Reference: US EPA's Design Manual for Onsite Wastewater Treatment and Disposal, 1980, available from the US EPA, the US GPO Superintendent of Documents (Pueblo CO), and from the National Small Flows Clearinghouse. Original source http://www.epa.gov/ORD/NRMRL/Pubs/625R00008/625R00008.htm
Water Wells and Septic Systems Handbook, R. Dodge Woodson. This book is in the upper price range, but is worth the cost for serious septic installers and designers.
Quoting Amazon: Each year, thousands upon thousands of Americans install water wells and septic systems on their properties. But with a maze of codes governing their use along with a host of design requirements that ensure their functionality where can someone turn for comprehensive, one-stop guidance? Enter the Water Wells and Septic Systems Handbook from McGraw-Hill. Written in language any property owner can understand yet detailed enough for professionals and technical students this easy-to-use volume delivers the latest techniques and code requirements for designing, building, rehabilitating, and maintaining private water wells and septic systems. Bolstered by a wealth of informative charts, tables, and illustrations, this book delivers: * Current construction, maintenance, and repair methods
* New International Private Sewage Disposal Code
* Up-to-date standards from the American Water Works Association
Wells and Septic Systems, Alth, Max and Charlet, Rev. by S. Blackwell Duncan, $ 18.95; Tab Books 1992. We have found this text very useful for conventional well and septic systems design and maintenance --DF.
Quoting an Amazon description:Here's all the information you need to build a well or septic system yourself - and save a lot of time, money, and frustration. S. Blackwell Duncan has thoroughly revised and updated this second edition of Wells and Septic Systems to conform to current codes and requirements. He also has expanded this national bestseller to include new material on well and septic installation, water storage and distribution, water treatment, ecological considerations, and septic systems for problem building sites.
The NSFC Products List has an excellent list of design manuals/modules available from their website or by telephone 800-624-8301
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