Research Of An Airlift-Reflux Combined Reactor Treating On-site Domestic Sewage

Although decentralized wastewater treatment process has been applied in many areas in recent years, but its disadvantages such as large floor space, hard to maintain have restricted its further application. Aimed at such problems of decentralized wastewater treatment process, an airlifting-reflux combined reactor was invented mainly treating domestic sewage in decentralized areas. The study was aimed at finding out the best working condition of the reactor and the optimized options of the design for the practical engineering application in the future.An reactor with 140L total effective volume was used to treat campus domestic sewage, and the study lasted for 8 months. The major study aiming at the treating capacity and the optimized working conditions was conducted on the test of the remove effects of COD, NH₃-N, NO₃-N, TN, turbidity and the character of the activated sludge under different influent loads and aeration volumes. The major contents were as follows:(1) After switching the influent point to the second gallery of the anoxic zone, the denitrification capacity of the the anoxic zone had been greatly improved. When water temperature was 12.63℃, the organic load of influent reached 0.8 kgCOD/m³d, the N load of influent reached 0.1 kgN/m³d, HRT of the aerobic zone reached 5.0h and the aeration volume was 345L/h, the effluent concentrations of COD, NH₃-N and TN were 55.58mg/L, 3.8mg/L and 14.68mg/L, the concentrations of NH₃-N and TN met the grade A standard of the Urban Sewage Treatment Plant Standards for Discharge of Water Pollutants. The removal rate of COD, NH₃-N and NO₃-N reached 84.12%, 91.42% and 73.21%.(2) The removal effect of COD mainly depended on the organic load of the influent. When the system was running below 0.80kgCOD/m³d of the organic load of the influent, the effluent concentration of COD could reach the grade B standard of the Urban Sewage Treatment Plant Standards for Discharge of Water Pollutants. When the organic load of the influent was over 0.80kgCOD/m³d, the removal capacity of organics would degrade. When the organic load of the influent was over 1.0kgCOD/m³d, the removal effect of COD turned bad, and sludge bulking would probably be triggered.(3) The appropriate aeration volume mainly depended on the N load of the influent. Under the condition of 5h HRT of the aerobic zone, when the N load of the influent was 0.04 kg N/m³d, 220L/h of the aeration volume was enough for the system to get nice processing results. The effluent concentrations of NH₃-N and TN were 3.05mg/L and 11.91mg/L. When the N load of the influent was between 0.06⁰.11 kgN/m³d, 320L/h³50L/h of the aeration volume was siutable for the system, and the system would get 3.8mg/L and 14.68 mg/L of the effluent concentrations of NH₃-N and TN. When the N load of the influent reached 0.14 kg N/m³d and the aeration volume was at 400L/h, the effluent concentration of NH₃-N was 8.76mg/L, the removal rate was 86.77%. When the N load of the influent was over 0.20 kg N/m³d, the N-removal capacity of the system turned bad. Matching the aeration volume in such discipline could control the DO of the aerobic zone at 1.0¹.5 mg/L.(4) Red worms would consume the activated sludge, weaken its sedimentary capacity and do harm to the nitrification effects of the system. When the water temperature was feasible and the DO of the aerobic zone was over 2.0 mg/L would lead the red worms to bloom. When DO of the aerobic zone was below 0.5 mg/L, the red worms would be restrained. To match the aeration volume according to (3) could not only assure the nice processing effects but also be able to restrains the growths of the red worms in the system.(5) The system realized 8-month successive and stable running without sludge removing, which proved the 6:5 volume ratio of anoxic zone and oxic zone was able to realize the design demands of storing sludge and sludge digestion of the anoxic zone. But the volume use of the anoxic zone was not at its best condition. The sludge space distribution was uneven, the up-flow galleries stored more sludge while the down-flow galleries stored less sludge, which would have negative impacts on retention time of sludge digestion. Raising the dam-board in the anoxic zone would effectively make more sludge staying in the bottom of the anoxic zone which added the sludge volume of the anoxic zone.