1 SUMMER 2005. Vol. 16, No. 3. Small Community Wastewater Issues Explained to the Public Aerobic Treatment Units: An Alternative to Septic Systems any homes in the Why choose Aerobic Treatment ? This issue of Pipeline is an M are located in small or rural communities where houses are spaced widely apart. In these Septic tank-soil absorption sys- tems are relatively inexpensive and are easy to maintain. They are the most common onsite update to the Winter 1996. issue, Vol. 7, No. 1. communities, central sewerage wastewater Treatment Systems drainfield. In some communities, Systems are often not cost-effective, used in rural areas. However, the water table is too high to so many homeowners rely on there are many households for allow the drainfield to give ade- Septic Systems or other Systems which a traditional Septic system quate Treatment to the wastewater that treat and dispose of house- may not be the best wastewater before it reaches groundwater.
2 Hold wastewater onsite. Some Treatment option. Regulations Other site-related concerns include homes for which Septic Systems are changing to accept Aerobic homes located on small lots or on are not a good option, because Treatment Systems as part of the lots close to a body of water. The of site or soil conditions, rely on normal approval process. wastewater treated by a Septic sys- individual Aerobic Systems for tem is often not of high enough For example, Septic Systems are wastewater Treatment . quality to be discharged very close not suitable for every lot. In fact, Aerobic Systems are similar to approximately two-thirds of all to a body of water. Septic Systems in that they both the land area in the is esti- But one of the most common rea- use natural processes to treat mated to be unsuitable for the sons that Aerobic wastewater wastewater. But unlike Septic installation of Septic Systems .
3 Treatment units are chosen by (anaerobic) Treatment , the Aerobic Some homes may not have communities is to replace failing Treatment process requires oxy- enough land area or appropriate Septic Systems . Failing Septic sys- gen. Aerobic Treatment units soil conditions to accommodate a tems are a major source of (ATUs), therefore, use a mecha- conventional soil absorption groundwater pollution in some 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 .). Aerobic Treatment Units areas.
4 If a failed Septic system needs to be replaced, or if a site is areas. Additionally, aerated efflu- ent has been shown to renovate How Aerobic inappropriate for conventional Systems , Aerobic wastewater a clogged drainfield. Upgrading a Septic tank to an ATU can rejuve- Treatment Treatment becomes a viable option. Installation of Aerobic nate an existing drainfield and extend its life. Works Aerobic Systems treat wastewater units in new construction has using natural processes that There are, of course, some draw- also become a common practice. require oxygen. Bacteria that backs to ATUs. The basic unit is In some cases, regulations allow more expensive to own and oper- thrive in oxygen-rich environ- ATUs to be installed in areas ate than a Septic tank and requires ments break down and digest the where the soils cannot handle more maintenance. The solids wastewater inside the Aerobic Septic tank effluent, because they must be pumped out at much Treatment unit as they are sus- are less likely to cause soil clog- more frequent intervals, and the pended in the liquid.
5 Ging. Many states are requiring electrical-mechanical parts must Like most onsite Systems , Aerobic ATU effluent to be disinfected be maintained. Most ATUs are Systems treat the wastewater in before direct discharge. That is, sold with a two-year service con- stages. Sometimes the wastewater when the effluent is properly dis- tract, covering inspections and receives pretreatment before it infected with a chlorinator for maintenance. Manufacturers and enters the Aerobic unit , and the example, it may be sent directly regulators recommend that such treated wastewater leaving the to a surface water body, such as a contract be extended for the life unit requires additional treat- a stream. This is a typical remedy of the unit . ment or disinfection before being for failing Septic Systems in many returned to the environment. ATUs are not the solution for every situation, but they do offer Such a variety of designs exists a reasonable Alternative for diffi- for home Aerobic units and cult sites that require onsite Systems that it is impossible to wastewater Treatment .
6 Describe a typical system. Instead, This issue of Pipeline focuses on it is more practical to discuss how individual home Aerobic units as some common design features of Pipeline is published quarterly by the Aerobic Systems work and the dif- National Environmental Services Center one Alternative for onsite waste- at West Virginia University, water Treatment . ferent stages of Aerobic Treatment . Box 6064, Morgantown, WV 26506-6064. Pipeline is funded through a grant from the Environmental Protection Agency, Washington, Steve Hogye Project Officer Municipal Support Division, Office of Wastewater Management National Small Flows Clearinghouse West Virginia University, Morgantown, WV. Rick Phalunas Interim 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.
7 Please send a copy of the publication in which information was used to the Pipeline editor at the address above. an equal opportunity/affirmative action institution ISSN 1060-0043. The contents of this newsletter do not necessarily reflect the views and policies of the Environmental Protection Agency, Printed on recycled paper nor does the mention of trade names or commercial products constitute endorsement or recommendation for use. Figure 1 An example of a possible Aerobic unit design Adapted with permission from Pennsylvania State University College of Agriculture Extension Service 2. PIPELINE Summer 2005; , No. 3 National Environmental Services Center (800) 624-8301 or (304) 293-4191. Aerobic Treatment Units 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.
8 Too much solid material can clog the unit and 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- TING. 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. Figure 2 Another example of a possible Aerobic unit design Aerobic units themselves come in Adapted with permission from Pennsylvania State University College of Agriculture Extension Service many sizes and shapes. The process most Aerobic units eventually settle out as sludge. unit at the same rate that it leaves use to treat wastewater is referred Many Aerobic units include a sec- the home.
9 Other designs employ to as suspended growth. These ondary chamber called a settling devices (such as pretreatment units include a main compart- chamber or clarifier where excess tanks, surge chambers, and baf- ment called an aeration chamber solids can settle. (See Figure 1.) fles) to control the amount of the in which air is mixed with the Other designs allow the sludge to incoming flow. Batch process wastewater. Because most home accumulate at the bottom of the designs use pumps or siphons to Aerobic units are buried under- tank. (See Figure 2.) In Aerobic control the amount of wastewater ground like Septic tanks, the air units designed with a separate in the aeration tank or to dis- must be forced into the aeration settling compartment, the sludge charge the treated wastewater in chamber by an air blower or a returns to the aeration chamber controlled amounts after a certain compressor.
10 (either by gravity or by a pump- period of time. ing device). The sludge contains The forced air mixes with waste- Controlling the flow of waste- bacteria that also aid in the water in the aeration chamber, water helps to protect the treat- Treatment process. Although, in and the oxygen supports the ment process. When too much theory, the Aerobic Treatment growth of Aerobic bacteria that wastewater is flushed into the process should eventually be able digest the solids in the wastewater. system all at once, it can become to consume the sludge complete- This mixture of wastewater and overburdened, and the quality of ly, in practice, the sludge does oxygen is called the mixed liquor. Treatment can suffer. The disad- build up and will need to be vantages to mechanical flow con- The Treatment occurring in the pumped out frequently so that trol devices are that, like all mixed liquor is referred to as sus- solids don't clog the unit .