Pilot-scale studies on biological treatment of hypersaline wastewater at low temperature were conducted and results showed that seawater salinity had a strong negative effect on notrouomonas and nitrobaeter growth, but much more on the nitrobaeter. The nitrification action was mainly accomplished by nitrosomonas. Bench-scale experiments using two SBRs were carried out for further investigation under different conditions of salinities, ammonia loadings and temperatures. Biological nitrogen removal via nitrite pathway from wastewater containing 30 percent seawater was achieved, but the ammonia removal efficiency was strongly related not only to the influent ammonia loading at different salinities but also to temperatures. When the ratio of seawater to wastewater was 30 percent, and the ammonia loading was below the critical value of 0. 15 kgNH4 ^＋ -N/（ kgMLSS · d） , the ammonia removal efficiency via nitrite pathway was above 90 %. The critical level of ammonia loading was 0. 15, 0. 08 and 0. 03 kgNH4 ^＋ -N/（ kgMLSS · d） respectively at different temperatures of 30℃, 25℃ and 20℃ when the influent ammonia concentration was 60 - 80 mg/L and pH was 7.5 - 8.0.
