[Half-nitrosofication of dewatering liquid of digested sludge with high ammonia].

The affecting factors and controlling methods of how realizing and maintaining half-nitrosofication of dewatering liquid of digested sludge were investigated in an A/O process. The experimental results showed that the nitritation was obtained in 29 d under bulk liquid temperature of 9-20 degrees C, average DO of 5.4 mg/L, SRT of about 30 d and influent ammonia loading rate of 0.64 kg/(m3 x d). The nitritation with 70% nitrite accumulation efficiency was maintained during 65 d when average FA concentration in A/O reactor was more than 4 mg/L. Furthermore, the half-nitrosofication with effluent ammonia and nitrite ratio of 1:1.32 was obtained. When the ammonia loading rate reduced to 0.19 kg/(m3 x d) (FA < 1 mg/L), the nitritation disappeared, and the high FA as a main factor of maintaining half-nitrosofication was proved again with FISH under the condition of different FA. TN removal concentration was about 91 mg/L under influent COD of 282 mg/L and raw C/N ratio of 0.85 in the A/O system, which due to nitritation saving much carbon sources. The study showed that the half-nitrosofication of the dewatering liquid was obtained and stably maintained when FA was more than 4 mg/L in the A/O reactor by dynamic controlling influent ammonia loading rate and pH value in the system under middle or low temperature, high DO, long SRT.