Study On Advanced Treatment Of Domestic Wastewater By Two-stage Aerobic Tandem Walnut Shell Biofilter

With the rapid development of economy and society,the generation of domestic sewage is increasing day by day,and the reuse of domestic sewage has become an important method to solve the shortage of water resources.Biological Aerated Filter?BAF?has the advantages of high biological concentration,reasonable bacterial structure,strong impact resistance,little influence by temperature,simple operation and so on.In this paper,a two-stage aerobic tandem walnut shell biofilter is used to deeply treat domestic sewage.The performance indicators and adsorption characteristics of different walnut shells are compared.The best walnut shell filler is selected to form a two-stage aerobic tandem walnut shell biofiller.Filter,used to treat secondary effluent,so that the quality of the effluent reaches the Grade A standard in the"National Urban Wastewater Treatment Plant Pollutant Discharge Standard"?GB 18918-2002?and"Urban Wastewater Recycling and Urban Miscellaneous Water Quality"GB/T18920-2002),and in depth exploration of the optimal design operation parameters and optimized control strategies of walnut shell filler aerated biological filter,the following conclusions were obtained:?1?Preparation of walnut shells with particle sizes ranging from 3.35 to 4.00mm,2.50 to 3.35 mm and 2.00 to 2.50 mm,and after modification,the apparent density,strength,moisture and other performance indicators of six walnut shell fillers and Adsorption characteristic parameters,using the analysis method of principal component analysis,comprehensively considering the preparation cost of the modified walnut shell,and finally using unmodified walnut shell filler of 2.50-3.35mm.?2?The time required for the two-stage aerobic series walnut shell biological filter to hang up the membrane was 23 days.During the start-up,the removal rates of ammonia nitrogen and COD_Crin the final effluent remained above 80%and 60%,respectively.Through a single factor comparison test,comprehensively considering the removal efficiency of the two-stage aerobic series walnut shell biological filter,the operating parameters were determined as:hydraulic load 0.65 m³/?m²·h?,and the gas-water ratio of the first-stage reactor was 6:1 The height of the packing layer is 50cm,the gas-water ratio of the secondary reactor is 1:1,and the height of the packing layer is 50 cm.?3?The two-stage aerobic tandem walnut shell biological filter operates stably after determining the operating parameters.The average removal rate of the effluent water quality indicators of the first-stage reactor can reach:ammonia nitrogen 78.34%,COD_Cr61.75%,TN 16.90%,TP 26.40%,the average removal rate of the effluent quality indicators of the secondary reactor is respectively stable:ammonia nitrogen97.29%,COD_Cr83.14%,TN 29.82%,TP 33.94%.?4?In order to further optimize the two-stage aerobic tandem walnut shell biological filter for domestic sewage treatment,gas-water combined backflushing is used as the backwashing method.The flushing process is as follows:the first-stage reactor uses air-strike intensity of 10 L/?m²·s?,Flushing time is 5 minutes,air flushing alone,then water flushing strength is 8 L/?m²·s?and air flushing strength is15 L/?m²·s?,combined flushing is 4 minutes,and finally 8 L/?m²·s?.The flushing strength of the water was 8 minutes;the secondary reactor was first flushed for 3minutes under the gas impact intensity of 15 L/?m²·s?,then at the water flush intensity of 8 L/?m²·s?and the gas impact intensity Joint flushing for 15 min at 15 L/?m²·s?,and finally 8 min at a flushing strength of 8 L/?m²·s?.?5?From the treatment efficiency,backwashing cost and production cost,comparing the two-stage aerobic tandem walnut shell biological filter and the two-stage aerobic tandem activated carbon biological filter,the final removal rate of the effluent is close,and the two-stage aerobic tandem walnut shell biological filter the ammonia nitrogen content in the pond effluent is only 0.09mg/L higher than the two-stage aerobic tandem activated carbon biological filter,and the COD_Crcontent is only 2.11 mg/L higher;and the backwash cycle time of the walnut shell filler aerated biological filter is long,and the filler preparation is simple.low cost.