Nitrifying treatment of wastewater from fertilizer production in a multiple airlift loop bioreactor

An 80 m3 gas-liquid-solid three-phase flow multiple airlift loop bioreactor (ALR) with a low ratio of height to diameter s, in which biofilm replaced the activated sludge, was used in the nitrifying treatment of the effluent from Tengfei Chemical Fertilizer Plant, Tianjin, PR China. The influences of the ratio of bed (settled) volume to bioreactor volume Vb/VR, superficial air velocity Ug, hydraulic residence time HRT and pH value on ammonia nitrogen reduction were investigated and discussed. The optimum operating conditions were obtained as pH value of 7.0-8.0, Vb/VR of 0.65, Ug of 0.01 m s−1 and HRT of 6 h were found. Under the optimum operating conditions, the effluent COD and NH4N were less than 50 and 10 mg l−1, which was far below the primary discharge standard for chemical fertilizer industry of PR China: COD < 100 mg l−1 and NH4-N < 40 mg l−1 (GWPB4-1999).