Study On Performance And Optimization Of Pre-Denitrification Biological Aerated Filter

In recent years,with the shortage of water resources and the water pollution,a large number of domestic sewage and industrial wastewater were discharged into rivers,which caused ammonia nitrogen and total nitrogen in water excessive.Groundwater quality in most cities was exceeded severely,and ammonia nitrogen in water became a main objects.Otherwise,treatment technology in sewage becomes strict increasingly.Most sewage plants are faced with updated technical problems.Pre-denitrification biofilter is a new technology of high efficiency,energy-saving,small size,easy operation,and high water quality.The experiment by researching system parameters pre-denitrification biofilter for start-up and subsequent packing height,air-water ratio and reflux ratio in stable operation to observe influence of pre-denitrification biofilter on COD and ammonia nitrogen and determine backwash cycle,backwash duration and recovery time.The following conclusions were obtained:Pre-denitrification biofilter was started by sludge discharging,which mainly contained three stages.The start-up duration was determined through analyzing treatment effect of pre-denitrification biofilter in each stage.When it increased gradually to designed hydraulic load values(aerobic column was 2.04 m3/(m2·h)designed,anaerobic column was 4.08 m3/(m2·h)),reflux ratio was 100%,gas-water ratio in aeration column was 5.6:1,the mean value effluent COD,NH3-N and TN were less than 50 mg/L,5 mg/L,15 mg/L,achieved a national emission standards.The startup duration was determined to be 49 days.It was shown that processing efficiency will gradually improve along with packing height,but part of packing for treatment efficiency effect was very small.It is concluded that optimal processing performance of anaerobic column was 20-100 cm,and optimal processing performance of aerobic column was 0-80 cm.Determined best gas-water ratio by pre-denitrification biological aerated filter was 6:1,and the removal for COD,NH3-N,TN removal rate were 90.94%,93.52%,76.44%,and the effluent concentration were 27.82 mg/L,2.65 mg/L,13.56 mg/L.Optimum reflux ratio was 200%.Removal for COD,NH3-N,TN were 90.78%,93.40%and 78.44%respectively.Effluent COD,NH3-N,TN average concentration under this reflux ratio were 28.45 mg/L,2.27 mg/L,12.45 mg/L.Through the experiment of backwash,backwash cycle could be determined to be 7 days,this backwash mode was water pulse coupled with mixed air-water and water backwash.This backwash mode had shorter duration than normal backwash.Water backwash time was 2 min.mixed air-water wash was 5 min,and water washing time was 3 min.Total duration of backwash was 10 min.Recovery time after backwash was 10 h.