Experimental Study Of Landfill Leachate Treatment By Multistage Active Biological Process

With the development of society and accelerated urbanization,the production of urban refuse in China has increased sharply,and sanitary landfill is one of the main ways of garbage disposal at present.Landfill produces large numbers of landfill leachate.Its organic matter concentration is high,the quality and quantity change of water is big,the nutrient element proportion is out of balance and there are many kinds of heavy metal ions.If the treatment is not appropriate,landfill leachate will have a serious impact on the environment,ecology and human health.It is urgent to realize the standard treatment of landfill leachate.This research treats landfill leachate by multistage active biological process.Study on the starting and operating rules of the reactor(12 stages,3 sections).Optimize technical operation parameters,and study the operation characteristics of reactor under the conditions of the step-feed influent.Meanwhile,based on the research of operation,the community information was analyzed,and the succession law of bacteria community structure was studied.The concentration ratio(10:0,9:1,7:3,5:5,3:7)of COD(Chemical Oxygen Demand)of the landfill leachate and glucose was gradually changed in the fixed influent COD(2000mg/L)to start the the reactor.Starting process is for a total of 60 days,and COD removal rate reached more than 80%,NH3-N more than 30%in each stage.We think that the starting is successful.The influent NO2--N concentration is 0?1.2mg/L,the effluent concentration 0.07?37.08mg/L,the influent NO3--N concentration is 0?1.25mg/L,the effluent concentration 0?8.16mg/L.After a successful starting process,the dilution of landfill leachate was used as influent,the COD concentration(2000;3000;4000;5000mg/L)was gradually increased,and the operating characteristics of the system under different COD loads were investigated.The results showed that the removal rate of COD decreased slowly from abput 90%to 85%in the 30 days,and the removal rate of pollutants was high in the reactor.NH3-N removal rate dropped sharply from about 75%down to about 28%.In the 4 stages of the operating process,the removal amounts of NH3-N were maintained at about 200mg/L,which showed that under the condition of sufficient COD,the reactor's ability for treating NH3-N is general.The influent concentration of NO2--N is 0?1.01mg/L,the effluent concentration 0.16?19.49mg/L;The influent concentration of NO3--N is 0.24-4.15mg/L,and the effluent concentration 1.17?72.82mg/L.During the starting and operating process of 90 days,the removal of COD and NH3-N is mainly concentrated in the first section of the reactor,but the contribution rate is moving to the backward sections gradually.NO2--N and NO3--N are mainly accumulated in the second and third section and there are almost no accumulations in the first section of the reactor.NO2--N and NO3-N are easier to accumulate in last 3 stages of the starting process and the first 2 stages of operating process.Select the influent COD concentration,aeration,T(Temperature),HRT(hydraulic retention time,HRT)as the optimization parameters.Select effluent COD and removal rate,effluent NH3-N and removal rate,effluent TN and removal rate,the effluent comprehensive concentration and removal rate as evaluation indexes.L9(34)orthogonal experiment is carried out to explore the corresponding optimal parameter values and the influence order.The results show that the optimal operating parameters of the system are COD=4000mg/L,the aeration rate =9L/min,T=35,HRT=24h,and the influence order of each factor is:T>aeration rate>HRT>COD concentration.The pollutants are consumed in the first section of the reactor,and efficiencies of the second and the third section are low.In order to improve this phenomenon,through the way of different influent flow ratios(10:0,9:1,7:3)in the first compartment and the fifth compartment,the effect of the step-feed water on the operating characteristics of the reactor is studied.The results showed that the influent flow ratio had little influence on the removal of COD,the average removal rate of influrnt flow ratio of 7:3 is more than 10:0 for 2%,The influent flow ratio had more influence on the removal of NH3-N and TN,and the average removal rate of influent flow ratio of 7:3 is more than 7:3 for more than 9%.The succession of bacteria community structure(2nd,6th,10th compartment)in different influent stages(starting fourth stage,operating first stage,operating fourth stage)is studied by high throughput sequencing.The results show that in the reactor the main dominant bacteria is are Saprospiraceae_uncultured(Bacteroidetes,aerobiotic heterotrophic bacteria).When the influent COD changes from low to high,the main trend of variation of the second,sixth,tenth compartment is:the ratio of Trichococcus(Firmicutes,anaerobic heterotrophic bacteria)gradually becomes higher.The ratio of Saprospiraceae_uncultured(Bacteroidetes,aerobiotic heterotrophic bacteria)decreases gradually.The ratio of Comamonadaceae_unclassified(Proteobacteria,anaerobic denitrification bacteria)decreases gradually.This shows that with the increase of COD of landfill leachate,the increase of toxic substances will inhibit the activity of aerobic heterotrophic bacteria and denitrification bacteria,and anaerobic denitrification bacteria can not become the dominant bacteria under aerobic conditions.Anaerobic heterotrophic bacteria lives in the interior of biofilm,the inhibiting effect is small.Therefore,with the increase of landfill leachate COD,anaerobic heterotrophic bacteria gradually increased.