Research On Efficiency Of Anaerobic-oxic Biological Filter Combination Process For Middle And Small Towns' Domestic Sewage Treatment

With the development of the conservation and recovery of water ecological environment,valley harnessing has been the one of the significant task of the national conservation work of water environmental protection.The wastewater treatment of the small town,as an essential part of valley harnessing,being received national invests and supports,is growing rapidly in small towns throughout the country for both the new-built and extending-built projects.But the combined sewer system is the mainly drainage system in majority of small towns in china,the urban sewage has the characteristics of water quality and quantity changes,so the small towns' sewage treatment has some problems,including the bad performance for removing N and P,the ineffectiveness on the condition of low carbon source and low temperature.To improve the sewage processing efficiency of small town,the research used the anaerobic-oxic biological filter comnination process to treat sewage,as its advantages of high efficiency,low spacing and financial cost and high resistance for the hydraulic load.The study carried on the characteristics of small town sewage,and effectively improve the efficiency of nitrogen and phosphorus removal and operation stability of the process,improve the treatment effect and operation stability both in low temperature and low carbon source condition,research analysis the anaerobic-oxic biological filter on mechanism of pollutant removal,the effect factors of pollutant removal efficiency and the efficiency effects of low temperature sewage and low C:N ratio on the process,analysis the stability,the cause and mechanism of biofilm detachment.Finally,the experimental research findings can be successfully used in the industrial application.The test used inoculation sludge process to quick start the anaerobic-oxic biological filters,we carried out the research after the biological filters stable operation.Firstly,analysis the effects of the key factors on the system performance which contained hydraulic load?DO?p H?reflux ratio?anaerobic/areobic volume ratio?water temperature and backwashing after monitored data being steady.Then the migration and transformation rules and the main pollutants removal mechanism in the system were both analyzed.The system has different partitions of pollutant removal function,the partitions of pollutant removal function were mainly affected by the hydraulic load,DO and reflux ratio.Then the factors influenced the effectiveness of removing N and P were studied in the tests to improve removal rate of N and P of the system through the optimization of operating conditions and the application of Chemical enhanced phosphorus removal for the biological filter in respectively.The efficiency of eliminating pollutant was compared in different conditions of receiving water with various ratios between COD and NH₄⁺-N.Moreover,the experimental research objects turned to be communtiy and structure of microbe in biological filter.The relationship between variance of microbe strain and ability of macroscopic treatment was defined by analyzing the changing laws of form,structure,quantity of biofilm and activity of microbe under different microbe surviving environment and system operating conditions and the various structures of operating microbe communtiy during different period and at different altitude.The tests also studied the stability of the biofilm and the reason of biofilm detachment to find out the rules between backwashing and biofilm detachment.The suitable backwashing promotes the normal detachment of the biofilm and ensures the stability of the biofilm structure.The optimization operating conditions of system were:anaerobic/aerobic column volume ratio 1:2,total influent hydraulic load 1.75 m³/m_?²h,reflux ratio100%,gas-water ratio of aerobic filter column 3:1,two points dosing?before anaerobic and aerobic column,respectively?,dosing ratio 3:1,the dosage of PAC50 mg/L,the system of has good pollutants removal effect,the average removal rate of COD,NH₄⁺-N,TP,TN and SS were up to 89.95%,99.24%,96.57%,70.11%and 98.56%,respectively.At the same time,anaerobic-oxic biological filter combination process has good effect on the treatment of low temperature sewage,The test results showed that reduced hydraulic load and raised the reflux ratio appropriately can improve the pollutants removal efficiency of the system.Furthermore,to simulate the experiment conditions more close to the actual working situations,we had established the pilot-scale device,and applied the research results of the will test into the pilot-scale,and further optimized the operation conditions in pilot-scale.The average COD removal rate was 85.98%,the average NH₄⁺-N removal rate was 97.33%,the average TN removal rate was62.09%,the average TP removal rate was 96.54%,the average SS removal rate was 98.02%when pilot-scale device was treating the sewage of small sewage,and the water quality can meet the class A standard.Finally,an experimental and monitoring measurement was carried out at a WWTP in a small town in cold regions in the north of china.The operating situation and the relevant data were monitored in the optimized conditions in winter and in summer,respectively.The average removal rate of COD,NH₄⁺-N,TP and TN reached 83.13%,91.67%,95.29%and 56.89%in winter while the counterparts in summer were 86.34%,96.45%,95.32%and 59.4%.According to the records statistics and calculations for the energy and financial costs during the experimental monitoring measurement,the average unit cost of treatment of the factory was controlled to only 0.427 RMB/m³ with the daily wastewater treatment in the level of 7500m³.Data show that the research achievements has received good results in engineering practice,the process has a good treatment efficiency,and also effectively improve the stability of low temperature sewage treatment.Therefore,the process has a good engineering application value in the small towns sewage treatment,its application prospect is wide.