Study On The Process Of Suspended Biofilter Combined With Biological Filter For Town Sewage Treatment

Biological aerated filter because of its small area,producing less sludge,simple operation and low cost has become the preferred process for the upgrading of urban sewage treatment plant.At present,the most application is pre-denitrification process,which combined with the combination of A/O process and biological aerated filter,using water through nitrification liquid reflux in organic compounds nitrogen.However,in practice,more defects have been exposed,such as large head loss,high requirement for pretreatment,poor biological phosphorus removal and low efficiency of nitrification and denitrification.In view of the above shortcomings,this paper proposes a new type of municipal wastewater treatment process based on suspended media expanded bed,namely anoxic aerobic anoxic suspended media combined biological filter process,which combined with pre denitrification and denitrification characteristics,and its main advantage is small head loss,assimilative ability,easy backwashing and low energy consumption.This paper studies the water inlet mode of the first stage denitrification filter,pretreatment process and factors affecting denitrification efficiency,improve nitrification efficiency second stage nitrification filter,and the third stage anoxic enhanced nitrogen and phosphorus removal function,which has practical significance for the design,development and application of municipal wastewater treatment plants.The main results are as follows:(1)The first stage suspension filter has better anoxic pretreatment and denitrification,the blood flow inlet mode has stronger retention capacity in water conditions without pre sedimentation tank,enhanced anoxic tank removal capacity of COD and TN,shortened the recoil cycle,but the backwash cycle can still reach 72h,far higher than the BAF in present day flushing,that combination of suspended media filter process without pre sedimentation pretreatment,shorten the conventional process,which has better adaptability.(2)The first level of suspended media anoxic filter height has great influence on denitrification,the height of filter layer better denitrification effect,in order to ensure the efficiency of denitrification in the anoxic tank.The filter layer thickness is 3.5m,the application of the reflux ratio is 100%~200%,the filter layer thickness is 4m,the reflux ratio is applicable100%~250%,in the filter layer thickness is 4.5m,the applicable return ratio is 100%~300%.With the increase of the thickness of filter media,the increase of the head loss of the filter is smaller,and the treatment efficiency of the filter and the maximum reflux ratio can be enhanced by increasing the thickness of the filter material.(3)The increase of hydraulic loading,reduce the efficiency of denitrification filter,hydraulic load more than 6 m~3/(m~2·h),anoxic removal of TN and COD decreased significantly,the anoxic tank water inlet end of the dissolved oxygen concentration will also affect denitrification in the anoxic tank,the dissolved oxygen concentration was 1.9mg/L,TN the highest removal rate of backwashing on denitrification efficiency greatly,but a short time to restore the treatment effect,reduce the temperature in the long run,denitrification efficiency will be affected.(4)The volume of anoxic and aerobic stage is 1:1.5,the aerobic nitrification pond has good nitrification efficiency,continue to increase the proportion of aerobic segments,nitrification efficiency was not significantly increased;hydraulic load and volume load,gas water ratio,backwash and temperature will nitrification the effectiveness of the aerobic pool of the impact,and the actual results show that the influence factors on the effect of ammonia nitrogen in aerobic tank effluent is larger,less influence changes in effluent organic matter.(5)Suspension filter combined process of biological phosphorus removal effect is relatively poor,through the third level filter after adding a small amount of flocculant effluent TP is less than 0.5mg/L,far less than the total phosphorus concentration of effluent from wastewater treatment plant,at the same time by adding carbon source in the third level filter can further reduce the total nitrogen concentration in the effluent,showed that the third level filter has a stable and efficient removal the function of nitrogen and phosphorus,and the influent hydraulic loading in the 4~6 m~3/(m~2·h)to ensure the efficiency of nitrogen and phosphorus removal is better,the third level filter layer thickness of at least 3~3.5m.(6)When the water load is 4m~3/(m~2·h),reflux ratio is 150%,the aerobic effluent dissolved oxygen of 3mg/L,the removal of suspension filter combined process at COD,ammonia nitrogen,total nitrogen,SS and TP were respectively 86.2%,92.7%,63.1%,96.6%,90.2%,water quality fully meet the"urban sewage water treatment plant pollutant discharge standard"(GB18918-2002)level of A standard.