Optimization And Efficiency Of Priority Control Pollutants Removal Process In Wastewater Treatment Plant Tailwater For Landscape Reuse

The regeneration and reuse of effectively treated domestic/industrial wastewater is one of the most effective approaches to solve the current shortage of water resources.The safety of the reclaimed water quality is a prerequisite for ensuring effective reuse.The micro/trace optimal control pollutants in the reclaimed water are rich in variety and relatively toxic,threatening the growth of aquatic organisms and human health,and are the current research hotspots.In the topic,focusing on the quality and safety issues of reclaimed water,two eutrophication priority control pollutants（nitrogen,phosphorus）,organics,and eight high-frequency priority control pollutants with low concent and high toxicity（including atrazine（ATZ）,sulfamethoxazole（SMZ）,diclofenac（DCF）,ibuprofen（IBP）,naphthalene（Na P）,anthracene（Ant）,benzo[a]anthracene（Ba A）,benzo[a]pyrene（Ba P））as target pollutants,the removal efficiency of the priority control pollutants in different conditions using three advanced treatment processes,including coagulation,ozonation,ultrafiltration,and their combined processes were explored.The degradation pathways of priority control pollutants were analyzed.On the basis,the removal strategies of priority control pollutants were proposed.Three processes of coagulation,ozonation and ultrafiltration are used to remove pollutants in the secondary effluent,and the effluent quality is evaluated in terms of the removal efficiency of organic matter,nitrogen,phosphorus,and eight high-frequency priority control pollutants with low concent and high toxicity.Results showed ozonation was effective in removing organics.As the dosage of ozone increasing,UV₂₅₄ gradually decreased,indicating the structure of organics were deatroyed.When removing nitrogen and phosphorus,coagulation showed the best effect,especially TP.The concentration of ammonia nitrogen increased slightly with ozone dosage increase,while ultrafiltration membrane with a molecular weight cut-off of 10 KDa had no apparent effect.Coagulation have significant difference on priority control pollutants.Among them,the removal rates of DCF and ATZ were relativaly higher and respectively 82.28%,52.28%,and the remaining 6 priority control pollutants removal efficiency were not more than23.8%.When the dosage of ozone was 5-20 mg/L,the removal rate of SMZ,DCF,Na P,Ant could reach more than 90%,while ATZ,IBP,Ba A and Ba P had almost no degradation.When the ozone dosage was increased to 360 mg/L,the removal efficiency of ATZ,IBP,Ba A and Ba P could reach more than 95%.For antibiotics and polycyclic aromatic hydrocarbons（PAHs）,ultrafiltration showed different removal efficiency.The removal efficiency of antibiotics pollutants were all lower than 20.54%,while the four PAHs were basically completely removed.Compared with single process units,the combined process has significant significance for improving the removal of organic matters,nitrogen and phosphorus in the secondary effluent.Among them,coagulation-ozonation had the best removal effect on organic matter,and the removal rates of DOC and UV₂₅₄ were 46.67%and 63.18%,respectively.Expect for ozonation-ultrafiltration process,the removal of nitrogen and phosphorus by coagulation-ultrafiltration and ozonation-ultrafiltration could meet the requirements of"Urban Sewage Recycling,Landscape Environmental Water Quality"（GB/T 18921-2019）.The removal efficiency of Na P,Ant,SMZ,and DCF using three combined processes could reach more than 90%.ATZ and IBP had relatively higher removal efficiency in the coagulation-ozonation process and the removal efficiency was54.59%and 72.45%,respectively.Ba A and Ba P have higher removal efficiency in the two combined ultrafiltration processes.Through analysing the removal efficiency and mechanism of each pollutant and summarizing physical and chemical characteristics of priority control pollutants,the removal strategy of each pollutant in reclaimed water was proposed.The paper recommended to use the coagulation process for removing phosphorus,the coagulation-ozonation process for removing nitrogen,the ozonation process for removing antibiotics,and the coagulation-ultrafiltration process for removing PAHs.In addition,the evaluation indicators of the advanced treatment process were analyzed through analytic hierarchy process,and the evaluation indicators of each process through weight calculation and expert scoring were quantified,and a model for the advanced treatment processes optimization of pollutants in reclaimed water was established.Research results will provide theoretical basis and technical support for the removal of priority control pollutants in the secondary effluent.