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: Methods and systems for utilizing biological wastewater treatment processes to remove nutrients from wastewater containing reduced sulfide compounds may include treating the wastewater in an anaerobic zone, an anoxic zone, and an aerobic zone. The wastewater is first treated in the anaerobic zone to uptake residual biodegradable organic material using specialized bacteria known as phosphorus accumulating organisms (“PAOs”) and glycogen accumulating organisms (“GAOs”). After treatment in the anaerobic zone, the wastewater is treated in an anoxic zone to convert nitrates to nitrogen gas and sulfur to sulfates. Following treatment in the anoxic zone, the wastewater is treated in the aerobic zone to oxidize ammonia to nitrate and to complete removal of phosphorus. After treatment in the aerobic zone, the wastewater may be treated in other zones, or may be delivered to a liquid-solids treatment stage.

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: Methods and systems for utilizing biological wastewater treatment processes to remove nutrients from wastewater containing reduced sulfide compounds may include treating the wastewater in an anaerobic zone, an anoxic zone, and an aerobic zone. The wastewater is first treated in the anaerobic zone to uptake residual biodegradable organic material using specialized bacteria known as phosphorus accumulating organisms (“PAOs”) and glycogen accumulating organisms (“GAOs”). After treatment in the anaerobic zone, the wastewater is treated in an anoxic zone to convert nitrates to nitrogen gas and sulfur to sulfates. Following treatment in the anoxic zone, the wastewater is treated in the aerobic zone to oxidize ammonia to nitrate and to complete removal of phosphorus. After treatment in the aerobic zone, the wastewater may be treated in other zones, or may be delivered to a liquid-solids treatment stage.

Abstract: An apparatus using activated sludge for the removal of biological nutrients from a wastewater includes a bioreactor for containing a mixture of wastewater under treatment and activated sludge. The bioreactor is divided into a plurality of serially connected treatment zones and includes a wastewater inlet, a downstream aerobic zone and an upstream aerobic zone between the wastewater inlet and the downstream aerobic zone, the upstream and downstream aerobic zones being separated by an anoxic zone. A membrane filter is provided in the downstream aerobic zone so that it functions as an immersed membrane filter with a bioreactor containing an operative volume of wastewater and activated sludge. The immersed membrane filter filters treated water flowing from the bioreactor through a first outlet. An aerator is operative associated with the membrane filter for purging solids from the membrane filter.

Abstract: An apparatus using activated sludge for the removal of biological nutrients from a wastewater includes a bioreactor for containing a mixture of wastewater under treatment and activated sludge. The bioreactor is divided into a plurality of serially connected treatment zones and includes a wastewater inlet, a downstream aerobic zone and an upstream aerobic zone between the wastewater inlet and the downstream aerobic zone. A membrane filter is provided in the downstream aerobic zone so that it functions as an immersed membrane filter with a bioreactor containing an operative volume of wastewater and activated sludge. The immersed membrane filter filters treated water flowing from the bioreactor through a first outlet. An aerator is operative associated with the membrane filter for purging solids from the membrane filter.