Study On Efficiency Of Compound Metal Modified Biological Sand Filter For Treating Effluent Of Wastewater Treatment Plant

With the improvement of wastewater discharge standards,it brings new challenges to the advanced wastewater treatment.Through the biological enhancement of the ordinary sand filter,the biological sand filter can enhance the biological purification function while ensuring the filtration capacity of the traditional filter.The difficulty of hanging film on the surface of ordinary quartz sand filter material limits the decontamination efficiency of filter.In this thesis,in order to solve these problems,the composite metal modification of ordinary quartz sand was used to improve the biological affinity of surface of the filter material and the stability of hanging membrane.The treatment system of modified biological sand filter was constructed by using modified quartz sand as filter material,and its application in advanced treatment of effluent of wastewater treatment plant was studied.After the pretreatment with acetone and hydrochloric acid,iron oxide modified sand（FS）,iron-manganese modified sand（FMS）and iron-zinc modified sand（FZS）were prepared from iron ion solution with 3 mol/L concentration and metal ion solution with Fe-Mn（Fe-Zn）ratio of 8:1,respectively.Ordinary biological quartz sand filter（QS）and three kinds of modified sands,FS,FMS and FZS were used to construct biological sand filter to carry out the membrane-hanging start-up test.The removal of COD by QS,FS,FMS and FZS reached final stability in 25 days,20 days,20 days and 19 days,respectively.It was shown that the composite metal modified sand filter shortened the membrane hanging time effectively.Compared with QS,the biofilm microbial biomass,microbial activity and attachment strength in FZS filters were increased by 51.15%,30.51%and 15%respectively.After successful membrane hanging and stable operation,it was found that the decontamination ability of the modified biological sand filter was higher than that of the QS.The removal rates of COD,NH₄⁺-N and TN of FZS reached 59.95%,88.81%and56.86%,respectively,which increased by 21.34%,14.11%and 19.64%compared with QS.EPS and community structure of biofilm on quartz sand filter were analyzed.As the depth of the filter bed increased,the amount of EPS decreased in turn,and the value of PN/PS of FZS was larger.The modified quartz sand surface enhanced the affinity between microorganisms.Microbial species were more abundant in FMS and FZS,and the shock load resistance and adaptability of biofilms were improved at the same time.The system process parameters were studied by filling the filter with iron-zinc modified quartz sand（FZS）.When the hydraulic load was 2.0 m³/（m²·h）and gas-water ratio was 3:1,along the depth direction of the filter bed which the height was 750mm,the removal of COD was mainly concentrated in the upper part of the filter bed:the removal of COD by the filter bed with the upper height of 400mm accounted for 68%of the total removal;the removal of NH₄⁺-N and TN was mainly in the middle and lower part:the removal of NH₄⁺-N and TN by the filter bed with a height of 300mm in the lower part accounted for 56%and 54%of the total removal,respectively.The effect of low temperature operation in winter showed that,the average removal rates of COD,NH₄⁺-N and TN in winter were 6.64%,12.35%and 5.38%lower than those in summer,respectively.It can be seen that the removal of COD and TN was less affected by season,while the removal of NH₄⁺-N was more affected by season.Under the best operating conditions,the value of COD,NH₄⁺-N and TN in the effluent reached 16.53 mg/L,0.23mg/L and 5.73 mg/L,respectively.Among them,except TN,other indexes all met levelⅣcriteria of the Environmental Quality Standards for Surface Water（GB 3838-2002）.