Study On The Co-treatment Of Landfill Leachate And Municipal Sewage Based On MUCT Process

Resourceful disposal of landfill leachate has always been an intractable worldwide problem.The ever-increasing output of landfill leachate has brought great follow-up treatment pressure to sanitary landfills.Therefore,it is widely practiced at home and abroad to transfer a certain amount of landfill leachate to municipal sewage plants for co-treatment.However,the high concentration of organic and toxic substances in the leachate will cause a huge load impact on the original system,resulting in unstable denitrification effect of mixed treatment,high sludge yield and even breakdown of biochemical systems.In this study,the experiment was based on the actual co-treatment project of a wastewater plant in Shenzhen.Aiming at the problems that the influence mechanism of co-treatment was unclear,the optimal addition strategy has not yet been mastered,and the corresponding measures need to be supplemented,the optimal mixing proportion and operation parameters were studied by simulating the operation of the Modified University of Cape Town(MUCT)process in the wastewater treatment plant,and the corresponding optimization scheme of the mixed treatment effect was discussed.At the same time,the structural characteristics of microbial community and the changes of denitrification gene activity were explored.The results of the simulation experiments showed that under the following working conditions: HRT=8.3 h,ASR1=77%,ASR2=105%,MLR=250%,SRT=10 d,DO in theanaerobic tank was less than 0.2 mg/L,DO in the first and second anoxic tank were 0.2 mg/L and 0.5 mg/L,DO in the first and second aerobic tank were 2.0 mg/L and 4.0 mg/L.The MUCT system realized the efficient removal of ammonia nitrogen,nitrate nitrogen,total nitrogen and COD,and the effluent concentrations were 0.14 mg/L,9.7 mg/L,10 mg/L,and<10 mg/L.When the landfill leachate mixed ratio was processed within 1.25‰,the effluent concentrations of ammonia nitrogen,nitrate nitrogen,total nitrogen and COD were 0.75 mg/L,12.2 mg/L,12.8 mg/L and 14.1 mg/L,while the average removal rates of ammonia nitrogen,total nitrogen and COD were 97.5%,57.2% and 88.1%,respectively,which can meet the level A dischaging limits of GB18918-2002.According to the experimental results,it can be seen that increasing DO in the second aerobic area was the most significant to improve the ammonia nitrogen effluent of the co-treatment,and DO in the second aerobic area should not be less than 4.0 mg/L.With the increase of MLR from 150% to 350%,the positive effect on nitrate nitrogen removal rate was the most obvious,and the optimal MLR=350%.Increasing ASR1 can promote the co-treatment effect of ammonia nitrogen,nitrate nitrogen,total nitrogen,COD,and the optimal ASR1=100%.Increasing the HRT from 7.1 h to 8.3 h has a significant promotion effect on improving ammonia nitrogen removal effect,while increasing it from 8.3h to 10 h has a significant promotion effect on improving nitrate nitrogen removal effect.The results of denitrification performance evaluation illustrated that the denitrification rates of methanol,molasses and sodium acetate were 7.7 mg/(g·h),7.9 mg/(g·h)and 26.4 mg/(g·h),respectively.Adding sodium acetate as a mixed carbon source during the co-treating process can enhance the denitrification effect of the system.The optimal mixing strategy was determined as follows: C/N=3.2～5.0 and the mixing ratio was 1.25 ‰ ～2.0 ‰.Under this condition,the maximum denitrification rate and COD removal rate were 62.28 mg/(g·h)and 96.7%,respectively,wherea the consumption of sodium acetate can be reduced by 6.9% ～ 26.7%.Based on the results of 16 S r DNA amplicon sequencing we could know that the average abundance of Betaproteobacteriales、Chitinophagales、Sphingomonadales increased by 9.5%,9.62% and 3.11% respectively after putting landfill leachate into MUCT system and treating them together,while the average abundance of Competibacterales and Rhizobiales decreased by 6.04% and 4.25% respectively,which did not cause significant changes in the originalbacteria community structure of the system.Methyloversatilis,Zoogloea,and Thauera were the most effective bacteria in the methanol,molasses,and sodium acetate systems,and the corresponding abundances increased by 35.82%,18.76%,and 50.44%,respectively.And the results of q PCR analysis reflected that the effect of different mixing ratios on different denitrification genes was different nar G,nir S,nor B and nos Z in sodium acetate systems were significantly higher than that in methanol and molasses systems,but nir K was lower than that in methanol and molasses systems.Nar G,nir S,nor B and nos Z in the sodium acetate system decreased with the addition of landfill leachate,while the relative abundance of nir K increased.