An In-situ Anaerobic Bio-oxidation Process For Landfill Leachate Contaminated Groundwater Remediation

Leachate is a high concentration organic wastewater which produced in the burying process of the landfill.It has the characteristics of complicated composition,high concentration of organic matter and ammonia nitrogen,and quality of which varies greatly.In case of leachate was leaked,it will be a serious threat to groundwater environmental safety and human health.Refractory organics and ammonia nitrogen are the primary typical pollutants in the leachate.It could act as scientific basis by illuminating the migration of the leachate in unsaturated zone and groundwater aquifer for the investigation and control of actual groundwater contamination site.Microbial Fe?III?reduction process is an important component of natural attenuatio n in subsurface environment.It not only affects the cycle of nutrient element?e.g.C,N,P?in terrestrial ecosystem deeply,but also play an important role in the natural degradation of groundwater pollutants.So taking artificial measures to strengthen this process and applying to groundwater remediation have the desirable interest.This study has simulated the migration and transformation of organic matter and ammonia nitrogen of aged leachate in the vadose zone and aquifer.Through cultivating and acclimating the microorganism-dissimilatory Fe?III?reducing bacteria in paddy soil,we study removal capability and reaction mechanism of anaerobic biological oxidation process,in which natural hematite acts as electron acceptor,for organic matter and a mmonia nitrogen.Furthermore,column tests and Seepage tank experiment are studied to simulate in-situ anaerobic bio-oxidation remediation process for groundwater,contaminated by landfill leachate.The main conclusions are as follows:Humic acid is easier adsorbed and entrapped than fulvic acid by soil.Organic matter and ammonia nitrogen present the phenomenon of vertical unevenness subsidence in aquifer,which could be affected by the facts that refractory organics in the aged leachate,such as humic-like substances,usually contain DNAPL whose density is bigger than water and negative charge,which could precipitate together with ammonia nitrogen by electrostatic adsorption.The batch experiment shows that COD concentration was 600 mg/L,and ammonia concentration was 25 mg N/L in groundwater contaminated by aged leachate.Biological reaction after 50 th days COD removal rate can reach 91.06%,in which hydrocarbonate is the most important degradation product,and the ammonia removal rate is only 13.85%,in which nitrite nitrogen is the primary removal product.When the initial COD concentration varies between 50 to 600mg/L,the time for reaction will be longer by the increase of the COD concentration.It is because of the limits of degradation for organic po llutions in the metabolism of microorganism by utilizing organic carbon source.In column experiment,the initial COD concentration of groundwater is 400mg/L,ammonia concentration is 16 mg N/L,and the highest removal of COD and ammonia is 77.50% and 45.12%,respectively.In Seepage tank experiment,the initial COD concentration of groundwater is 884.82mg/L,ammonia concentration is 203.16 mg N/L,and the highest removal of COD and ammonia is 81.51% and 12.26%,respectively.The filled media in aquifer is uniform quartz sand?grain size varies between 1 to 2mm?.When HRT is set as 48 h,permeability of hematite?grain size varies between 1 to 2mm?is good and permeability coefficient?the value of K?varies between?1.87 to 5.52?×10³ cm·d^-1.The results of simulated restoration process reveals anaerobic biological oxidation process contribute to good removal efficiency for groundwater contaminated by aged leachate as a whole,but remain the low removal rate for ammonia nitrogen.This research could provide the effective theoretical basis for the investigation in actual groundwater contamination and pollution control.Moreover,it could act as a new solution for high cost in treating refractory organics by conventional leachate treatment and obstacle of decrease of membrane filtration concentrate.Finally,the new in-situ anaerobic biooxidation remediation technology for groundwater contaminated by leachate could provide the effective theoretical basis for actual contaminated project,which is related to aged leachate contaminating groundwater,in aspect of dosage of hematite,the way of culturing and enriching microorganism,calculation of HRT,permeability coefficient of reaction medium.