Experimental Research On Domestic Wastewater Treatment By The Modified Step-feed Cyclic A/O Process

With the improvement of people’s living standard,people are more and more strict to the water environment,and the sewage discharge standards are continue to improve.For the treatment of high ammonia-nitrogen,low carbon and nitrogen ratio, higher phosphorus wastewater,the traditional biological treatment technology has been unable to meet the first level A emission standards.Now the old craft systems need upgrading or developing efficiency and low consumption’s new synchronized nitrogen and phosphorus removal processes.The Modified Step-feed Cyclic A/O Process is used in the experiment. The experiments study the performance of treatment on high ammonia-nitrogen,low carbon and nitrogen ratio, higher phosphorus wastewater under the flow distribution ratio and dissolved oxygen.The experiments study the water quality changes and microbial community structure of each segment of the process system.The mean concludes as follows:(1) The operating conditions of the experiment are as follows :the total water flow rate is 3.6 L/h, the water temperature is kept at 22 ±1 ℃, the HRT is 12 h,the SRT is 15 d, the internal reflux ratio is 100%, and the external reflux ratio is 50%.The effects of 1:1:1, 2:1:1, 3:2:1 and 4:2:1 on the performance of the process system is studied under the concentration of dissolved oxygen in 1.5mg/L.The results show that the process system has the best treatment under the flow rate distribution ratio of 2:1:1.The best processing effects’ s water qualities are:the average COD concentration of the effluent is 25.7 mg/L, the average ammonia concentration of the effluent is 0.96mg/L, the average total nitrogen concentration of the effluent is 12.41 mg/L,the average total phosphorus concentration of the effluent is 0.44mg/L. The corresponding average removal rates respectively are 92.87%,98.40%,80.95% and 93.23%.The water qualities indicators of the effluent have reached the A standard.In the flow distribution ratio of 2: 1: 1, the experiment study the influence of dissolved oxygen on the process system performance,the average dissolved oxygen concentrations are 1.0mg/L, 1.5mg/L, 2.0mg/L and 2.5mg/L.The results show that in the average dissolved oxygen concentration of 1.0mg/L, the processing system can make the effluent achieving highly efficient and low energy consumption reach the grade A standards.The water qualities are:the average COD concentration of the effluent is 22.7 mg/L, the average ammonia concentration of the effluent is 1.08mg/L, the average total nitrogen concentration of the effluent is 9.80 mg/L,the average total phosphorus concentration of the effluent is 0.39mg/L. The corresponding average removal rates respectively are 93.74%, 98.21%, 85.17% and 94.06%.(2) In the preferred conditions,researching the paragraphs water qualities of process system finds that under the dilution effect, the sludge adsorption, microbial metabolism, denitrification and anaerobic phosphorus release of the process system,after the influent entering the system,six water quality indicators(COD, ammonia, nitrogen, nitrite, nitrate, total phosphorus) are significantly reduced.The COD, ammonia nitrogen, total nitrogen, nitrite nitrogen and total phosphorus of the A pool are slightly higher than the O pool.Due to the better nitrification of the O pool, the nitrate nitrogen of the O pool is slightly higher than the A pool.The six water quality indicators of the O pool of the three stage reactor shows a trend of decreasing trend along the direction of the water flow.The COD, ammonia nitrogen, total nitrogen,nitrate nitrogen of The third stage reactor O pool is slightly higher than the effluent,the nitrite nitrogen and total phosphorus is slightly lower than the effluent.(3) Under the 16 Sr DNA metagenomic sequencing technology,the experiments study the microbial community structures of the inoculated sludge,the sludge of improved process system and original system under best conditions,comparing their community structures changing.The results show that the Modified Step-feed Cyclic A/O Process’ s dominant microorganism are Proteabacteria, Bacteroidetes and Actinobacteria, Firmicutes,the superiority of microorganisms genus of the Modified Step-feed Cyclic A/O Process are Zoogloea and Candidatus Accumulibacter.