Treatment Of Waste Compression Transfer Station Leachate With Coagulation/Air Floatation-A/O Combined Process

The leachate of waste compression transfer station contains a large number of suspended solids and many kinds of high concentration organic pollutants which cannot be directly discharged into the town sewer.The existing treatment processes with too many structure units are not suitable for distributed and crowded waste compression transfer station.In this paper,we proposed a simple and economical combined process with coagulation/air floatation-A/O for the leachate treatment.After the combined process treatment,the turbidity,and the concentration of COD,NH₃-N,TN and total phosphorus of the leachate were far below the A-class standard of the Wastewater Quality Standards for Discharge to Municipal Sewers（GB/T31962-2015）.After the A/O unit was stabilized,environmental microbial diversity analysis were performed on the sludge samples taken from the A/O unit to reveal the composition and abundance of bacterial communities.The effects of the dosage of CaCl₂,PAC,PAM and the hydraulic retention time of coagulation/air floatation on the removal efficiencies of turbidity and COD of the leachate were studied by single factor test.Under the optimum process parameters,the coagulation/air floatation unit runs continuously.The results showed that the optimal dosage of CaCl₂,PAC and PAM were 800mg/L,2mg/L and 1 200mg/L,respectively,and the optimal hydraulic retention time was 40 min.The removal efficiencies of turbidity and total phosphorus of the leachate treated by coagulation/air floatation unit were more than 90.0%,the turbidity and total phosphorus of the effluent were 55.1±26.4 NTU and 2.62±1.38mg/L,which were lower than the discharge standard.The average concentration of COD,NH₃-N and TN of the leachate treated by A/O unit were 94±37.3mg/L,2.44±1.21mg/L and 12.2±4.69mg/L,respectively,which were far below the discharge standard,the removal efficiencies were 98.4%,98.0%and 96.0%.When the hydraulic retention time was shortened from 72 h to 36 h,the average concentration of COD,NH₃-N and TN of the leachate treated by A/O unit were 458±81.2mg/L,25.4±7.51mg/L and 67.1±7.10mg/L,the removal efficiencies of COD,NH₃-N and TN decreased to92.0%,81.9%and 76.6%,respectively.The COD and TN of the effluent might exceed the discharge standard when the influent concentration was too high.The turbidity of the leachate was further reduced to 2.79±1.36 NTU.As a whole,the combined process of coagulation/air floatation-A/O can effectively remove the pollutants in the leachate.After the A/O unit was stabilized,high-throughput sequencing was performed on the sludge samples taken from the A/O unit.The results showed that Firmicutes,Bacteroidetes and Actinobacteria were the dominant bacteria groups at phylum level.Trichococcus,Norank＿F＿＿Propionibacteriaceae and Lentimicrobium were the main genera in the sludge samples taken from the anoxic reactor.Proteobacteria,Bacteroidetes,Chloroflexi and Firmicutes were the dominant bacteria groups at phylum level.Thauera was the dominant genera in the sludge samples taken from the aeration reactor.