| It is difficult to achieve large-scale centralized processing for treating decentralized sewage because of its small quantity and relatively decentralized. At present the common treatment technology all have problem with long-term stability, the economic costs and practicability, etc. Based on the characteristics of the decentralized sewage our team developed airlift-reflux combined process. The process could run normally with just one blower. Also it featured no discharge sludge for a long term, low maintenance frequency, save energy consumption, water shock resistant and small footprint, etc. The reactor consisted of anoxic area, aerobic area, sedimentation area and airlift area. It collected residual gas from aeration tank to achieve mixed liquid reflux by airlift action. Through the pilot scale reactor the de-nitrification factors were investigated to seek to optimize control conditions on the de-nitrification and eventually reduced the effluent TN concentration and ensured other pollutants removal efficiency. The best operation parameters of the reactor could provide reference for the optimization of reactor and facilitate its popularization and application in engineering practice.The research was carried on a 10.31m3 (effective volume) airlift-reflux combined reactor with municipal pipe network sewage to investigate the removal of CODcr, NH4+-N, TN and turbidity to get the best operating control parameters. The research results of 12 months were:(1) When the influent COD load was 1.5kg/(m3·d), ammonia nitrogen was 0.2 kg/ (m3·d), dissolved oxygen in the aerobic zone was 0.5-1.5mg/L, the water temperature was higher than 20 ? and reflux ratio was controlled to 2.9, the system had a good pollutant removal. CODcr removal rate could reach more than 85%, NH4+-N and TN removal rates were 90% and 75% respectively and the effluent SS maintained at 10 about mg/L. The effluent targets could meet an A standard.(2) Nitrification performance was mainly affected by ammonia nitrogen load, hydraulic retention time and dissolved oxygen. When the ammonia nitrogen load was 0.2 kg/(m3·d), hydraulic retention time was over 16 h and dissolved oxygen was above 0.5 mg/L, effluent NH4+-n could be less than 5 mg/L.(3) When at low DO concentration (the DO concentration was between 0.5 mg/L-1.5 mg/L), system could maintain high removal efficiency. It was conducive to improve de-nitrification performance and energy consumption reduction.(4) The increase of reflux achieved denitrification and optimization and total nitrogen removal rate increased significantly. When the average reflux ratio was 1.4, the average effluent nitrate concentration was 21 mg/L and total nitrogen removal rate was 64%. When average reflux ratio was 2.1, the average effluent nitrate concentration was 18.5 mg/L and the total nitrogen removal rate was 71%. When average reflux ratio was 2.8, the average effluent nitrate concentration was 15 mg/L and total nitrogen removal rate was 75%. The effluent met the requirements of the level of A standard of total nitrogen and the optimization of effluent total nitrogen was successful.(5) When aeration rate was 20 m3/h, influent COD load was 1.75 kg/(m3·d), ammonia nitrogen load was 0.2 kg/(m3·d) and dissolved oxygen of aerobic zone was higher than 0.5 mg/L, effluent ammonia nitrogen was lower than 5 mg/L and effluent COD was about 60 mg/L. The effluent met the urban sewage treatment plant pollutant discharge standard (A standard of level 1) and effluent total nitrogen was 21 mg/L.(6)Because the system didn't discharge sludge for a long time, the lowest sludge activity of aerobic area in the reactor was 0.71 which was lower than the sludge activity of CASS process. The existence sludge digestion in anoxic area could realize sludge reduction to make reactor not discharge sludge for a long time. Sludge digestion rate was associated with temperature:the higher of the temperature, the faster of digestion rate. |
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