An 80 m(3) pilot-scale gas-liquid-solid three-phase flow airlift loop bioreactor (ALR) with a low ratio of height to diameter, in which a biological membrane replaced the activated sludge, was used in the nitrifying treatment of a real effluent from a fertilizer plant. The influences of pH value, air influx (Q(g)) and hydraulic residence time (HRT) on the reductions in chemical oxygen demand (COD) and ammonia nitrogen (NH4-N) were investigated and are discussed herein. The optimum operating conditions were obtained at a pH value of 7.0-8.0, air influx of 500 m(3) h(-1) and an HRT of 10 h. Under these optimum conditions, the effluent COD and NH4-N were less than 50 mg L-1 and 10 mg L-1 for a 40-day run, which were far below the primary discharge standard for the chemical fertilizer industry in the People's Republic of China (COD <= 100 mg L-1 and NH4-N <= 40 mg L-1). Furthermore, this pilot-scale airlift loop bioreactor generated only one-quarter of the sludge waste compared with the traditional activated sludge process. (c) 2006 Society of Chemical Industry.