Development, laboratory and pilot testing of an innovative single sludge step-feed anoxic–aerobic nitrogen removal process

A single-sludge step-feed anoxic–aerobic process (SSFAOP), characterized by enhanced nitrogen reduction performance, long solids retention time (SRT), and short aerobic hydraulic retention time (HRT), was designed to optimize nitrification and denitrification processes for ammonia and nitrogen removal. The favorable conditions for nitrifying bacteria were provided by using influent flow splitting and step feeding. The relative predominance of nitrifying bacteria resulted in an increase of nitrification rate and decrease of nitrification time. In addition, the SSFAOP process design and operation were optimized by computer simulation and laboratory testing. The optimum operating parameters were determined through laboratory and pilot testing by evaluating the effects of temperature, pH, and dissolved oxygen (DO) on ammonia reduction efficiencies and treatment performance. The laboratory and pilot testing results demonstrated that the SSFAOP was a cost-effective process for nitrogen reduction. It is, therefore, feasible to implement industrial full-scale applications in wastewater treatment plants.