1056 results about "Biochemical oxygen demand" patented technology

A wastewater treatment process providing nitrogen, phosphorus, biochemical oxygen demand (BOD) and suspended solids removal comprises the steps of: passing wastewater containing ammonia nitrogen, phosphate, BOD and suspended solids, said wastewater mixed with recycled activated sludge from a subsequent step, into a first anoxic zone therein reducing nitrate nitrogen from the recycled sludge to molecular nitrogen; passing effluent from the first anoxic zone to a first aerobic zone therein oxidizing at least a portion of the BOD and oxidizing at least a portion of the ammonia nitrogen to nitrate nitrogen; recycling a portion of the contents at the end of the first aerobic zone back to the first anoxic zone; passing the effluent of the first aerobic zone to a second anoxic zone; introducing volatile fatty acid such as acetic acid into the second anoxic zone therein releasing phosphorus into a liquid phase; passing effluent from the second anoxic zone including the volatile fatty acid to a second aerobic zone therein substantially absorbing phosphorus into biomass and removing and/or oxidizing ammonia nitrogen; passing effluent from the second anoxic zone to a final settling zone therein separating: (i) a purified wastewater having decreased nitrogen, phosphorus, BOD and suspended solids and (ii) a sludge containing suspended solids, phosphate and BOD; and recycling at least a portion of the sludge (ii) to the first anoxic zone. In another embodiment, at least a portion of the sludge (ii) is also recycled to the second anoxic zone. In yet another embodiment, the second anoxic zone is divided into a first section and a second section. In the first section, anoxic conditions are established and in the second section, volatile fatty acid is added after anoxic conditions have been established.