Study On Enhanced Performance Of Ultrafiltration Combined Process For Removal Of Secondary Effluent Contaminants

The regeneration and reuse of wastewater can improve the water pollution and alleviate the shortage of water resources.There are various types of pollutants in the sewage and the nature of the pollutants is complex,but the conventional deepening treatment process has insufficient ability to remove residual pollutants in the water.This experiment centered on the reuse of the effluent from the municipal wastewater treatment plant for landscape,and used three different pretreatment methods of ultrafiltration membranes to achieve simultaneous implementation of multiple materialization processes.The ability to reduce pollutants in the secondary effluent were explored,the biotoxicity level of the effluent of each process and the operating status of the membrane process were evaluated.In the high-density sedimentation tank-ultrafiltration process which coagulant was simply added,the coagulant was polyaluminum chloride(PACL).Through a static beaker experiment,the optimal dosage of PACL was determined to be 40 mg/L,and the best reflux volume was 50%.Under this condition,a high-density sedimentation tank-ultrafiltration process was run.The removal rate of turbidity and total phosphorus was 99.9% and 51.10%,respectively,and the effect was significant.The average removal rates of CODCr,TN,and ammonia nitrogen were lower.They were 27%,14.69% and 14.87%;the average removal efficiency of trace contaminants(OMPs)was 32.05%.After examining the transmembrane pressure difference,it was found that the coagulation and sedimentation pro cess can reduce the particulates and colloids in the water.The transmembrane pressure difference of the single ultrafiltration within 15 days is 15.6 kPa higher than that of the combined process.Powder activated carbon(PAC)was used as the adsorbent mat erial.Through the PAC static test,the optimal concentration of PAC was determined to be 100 mg/L.At this dosage,a PAC/high-density sedimentation tank-ultrafiltration device was run,and explore the effectiveness of the PAC pretreatment process for secondary effluent treatment.The combined process had good effect on the removal of suspended particles in water.The effluent turbidity was kept stable below 0.01 NTU,and the removal rate of turbidity is above 99.9%.The average removal rates of CODCr,UV254,TN,ammonia nitrogen,and TP were 55.5%,49.5%,10.9%,23.33%,and 66.3% for the combined process,and the average removal rate for the 14 OMPs was 86.10%.The growth rate of the transmembrane pressure difference of the single ultrafiltration membrane process was 3.07 kPa/d,and the growth rate of the transmembrane pressure difference of the PAC combination process was 0.8 kPa/d,which indicates that the PAC combination process could significantly prolong the use time.The preoxidation test uses potassium ferrate as an oxidant.From the economic and water quality perspectives,the Fe(VI)/high density sedimentation tank-ultrafiltration process was determined to had 20 mg/L potassium ferrate and 25 mg/L PACL.Compared with the high-density sedimentation tank-ultrafiltration process where the coagulant was added alone,the Fe(VI)/high-density sedimentation tank-ultrafiltration process greatly increased the removal rates of CODCr,total nitrogen,ammonia nitrogen,and total phosphorus.The average removal efficiency of CODCr,total nitrogen,ammonia nitrogen and total phosphorus was 26.28%,26.28%,40.40% and 68.9%,respectively.The average removal rate of OMPs was 45.97%.During the operation of the process,there is a certain amount of irreversible pollution formed.By genotoxicity analysis,the genotoxicity of the secondary effluent was 24.3-26.3?g/L,and the genetic toxicity of the high-density sedimentation cell-ultrafiltration process was 19.3-21.4?g/L,which had no significant effect on genotoxicity;Fe(VI)/ high-density sedimentation tank-ultrafiltration process had a genetic toxicity removal rate of 55%.Compared with the high-density sedimentation tank-ultrafiltration process,the removal rate of genetic toxicity was greatly increased.The genotoxicity of the effluent from the PAC/high density sedimentation tank-ultrafiltration combined process dropped sharply to 0.6-1.2 ?g/L and the removal rate reached 94%,indicating that the PAC has a significant genotoxic effect on wastewater reduction and greatly reduces the risk to the water environment.In summary,after the PAC/high-density sedimentation tank-ultrafiltration combination process was used to treat the secondary effluent of a municipal sewage treatment plant,the overall removal rate of all pollutants was significantly improved,and the use of recycled water for landscape water by this way was a promising choice.