Abstract: The present invention relates to a process for treating wastewater utilizing a step feed return activated sludge process. The wastewater is directed via one or more step feed points through a mainstream process. The step feed point includes at least one aerobic zone and at least one anoxic zone, in repeating or alternating sequence. A portion of effluent from the one or more anoxic zones are fed through at least one anaerobic zone to which raw or pretreated wastewater is fed and returned to the upstream portion of the anoxic zone. Additionally, return activated sludge may be recycled to one or more of the anoxic zones.

Abstract: A water or wastewater treatment system to reduce phosphorus or other pollutant concentrations in water or wastewater may include an optional primary treatment stage in fluid communication with a biological secondary treatment stage. The secondary treatment stage may, in turn, be fluidly connected with a tertiary treatment stage, which may include a chemical treatment portion for reducing phosphorus or other pollutants to desired levels. The precipitated phosphorus and other solids or sludge produced from the chemical treatment portion may be recycled upstream for reuse in the primary, secondary, and/or tertiary treatment stages. Such recycle may reduce the amount of added chemicals required in the tertiary treatment stage to phosphorus or other pollutants to desired amounts.

Abstract: Removal of biological nutrients from a wastewater yielding a low phosphorous (e.g., less than 0.25 mg/L) output includes providing a serial multistage bioreactor containing activated sludge having in hydraulic series an anaerobic zone and a downstream aerobic zone, with each zone having an upstream inlet and a downstream outlet. The wastewater is provided to the anaerobic zone inlet. A quantity of chemical sufficient to precipitate soluble and particulate phosphorous is added to the downstream aerobic zone in an amount sufficient to yield a low phosphorous output. Treated water is separated from the activated sludge and precipitated phosphorous and a return activated sludge separated from the treated water is recycled to the anaerobic zone.

Abstract: A water or wastewater treatment system to reduce phosphorus or other pollutant concentrations in water or wastewater may include an optional primary treatment stage in fluid communication with a biological secondary treatment stage. The secondary treatment stage may, in turn, be fluidly connected with a tertiary treatment stage, which may include a chemical treatment portion for reducing phosphorus or other pollutants to desired levels. The precipitated phosphorus and other solids or sludge produced from the chemical treatment portion may be recycled upstream for reuse in the primary, secondary, and/or tertiary treatment stages. Such recycle may reduce the amount of added chemicals required in the tertiary treatment stage to phosphorus or other pollutants to desired amounts.

Abstract: A method of treating wastewater to increase effluent volatile fatty acid content consisting of providing wastewater to a primary treatment vessel and adding a select quantity of a chemical, typically an aluminum or iron salt, to the wastewater, enhancing the separation of organic matter. Separated organic matter is then removed from the chemically treated wastewater forming a primary sludge and a primary effluent. A portion of the primary sludge is fermented to form a volatile fatty acid rich liquor. The volatile fatty acid rich liquor may then be used with the primary effluent, directed to a bioreactor, thereby forming a volatile fatty acid enriched bioreactor feed. The volatile fatty acid enriched influent may be further treated through known biological phosphorous and nitrogen removal methods.