Wastewater treatment

Claim 1

In a process of nitrogen removal from wastewater comprising: a. mixing wastewater containing reduced nitrogenous compounds with active nitrifying organisms and an oxygen-containing gas for a sufficient length of time to convert substantially all of the nitrogenous material to the nitrate form and thereby produce a nitrified wastewater stream and accumulated biomass; b. separating said nitrifying organisms and accumulated biomass from said nitrified wastewater stream, recycling the separated nitrifying organisms and accumulated biomass to the nitrification contacting step, and periodically or continuously removing a portion of the accumulated biomass from the nitrifying step; c. contacting said nitrified wastewater stream with heterotrophic denitrifying organisms and an organic carbon source for a length of time sufficient to reduce the nitrate nitrogen to elemental nitrogen; d. separating said denitrifying organisms and accumulated biomass from the denitrified wastewater stream, recycling the separated denitrifying organisms and accumulated biomass to the denitrification step, and periodically or continuously removing a portion of the accumulated biomass from the denitrifying step; and e. removing a final effluent with nitrogen removed therefrom; the improvement which comprises heating the biomass removed from the nitrifying and denitrifying steps in the presence of an oxygen-containing gas at a temperature of 175°C. to 315°C. at an oxygen partial pressure of 5 to 250 psi to partially oxidize the biomass and convert substantially all of the organic nitrogen to ammonia nitrogen, separating the resulting oxidized mixture into a solid phase and a liquid phase, removing ammonia from the liquid phase and directing said liquid phase to the denitrifying contact step to provide a source of organic carbon for the denitrifying organisms.