Information to help you better understand your onsite wastewater system

• BOD5 - Quantitative measure of the amount of O2 consumed by bacteria while stabilizing, digesting, or treating biodegradable organic matter under aerobic conditions over a 5 day incubation period; expressed in milligrams per liter
• Effluent - Liquid flowing from a component or device. In our case a septic tank to a drainfield.
• Aerobic - Having molecular oxygen as a part of the environment, or a biological process that occurs only in the presence of molecular O2.
• ATU - Aerobic treatment Unit that utilizes O2 to degrade or decompose wastewater, with or without mechanical means.
• Anaerobic - Absence of molecular O2 as part of the environment, or a biological process that occurs in the absence of molecular oxygen.
• FOG - (Fats, Oils, and Grease) - Constituent of sewage typically originating from foodstuffs or consisting of compounds of alcohol or glycerol w/ fatty acids (soaps).
• Ponding - Accumulation of liquid on an infiltrative surface. Ie. Liquid accumulating on top of a drainfield.
• Sludge - Accumulated solids and associated entrained water within a pretreatment component, generated during the biological, physical, or chemical treatment; coagulation; or clarification of wastewater.
• High-Strength Wastewater - Influent having BOD5 greater than 300 mg/L and/or TSS greater than 200 mg/L, & or fats, oils and grease greater than 50 mg/L entering a pretreatment component.
• Residential Wastewater Strength - Effluent from a septic tank with a BOD5 of less than or equal to 170 mg/L; TSS less than or equal to 60 mg/L, and fats, oils, and grease less than or equal to 25 mg/L.

Aerobic bacteria live and multiply in the presence of free oxygen. Facultative bacteria always achieve an aerobic state when oxygen is present. While the name “aerobic” implies breathing air, dissolved oxygen is the primary source of energy for aerobic bacteria. The metabolism of aerobes is much higher than for anaerobes. This increase means that 90% fewer organisms are needed compared to the anaerobic process, or that treatment is accomplished in 90% less time. This provides a number of advantages including a higher percentage of organic removal. The by-products of aerobic bacteria are carbon dioxide and water. Aerobic bacteria live in colonial structures called floc and are kept in suspension by the mechanical action used to introduce oxygen into the wastewater. This mechanical action exposes the floc to the organic material while treatment takes place. Following digestion, a gravity clarifier separates and settles out the floc. Because of the mechanical nature of the aerobic digestion process, maintenance and operator oversight are required.