Energy-efficient Landfill Leachate Treatment Via Integrated Advanced Oxidation Processes & Bioelectrochemical Systems

A number of biological and physico-chemical technologies have been designed to decontaminate landfill leachate for the last couple of decades.Conventional biological treatments are hindered by the presence of certain bio-recalcitrant compounds,especially in the case of mature leachate.Similarly,physico-chemical techniques such as membrane separation,air stripping,coagulation-flocculation etc.are often costly in terms of initial plant outlet,energy demands and frequent use of certain chemicals.In this context,Advanced Oxidation Processes?AOPs?,which are oxidation methods relying on the action of highly reactive species such as hydroxyl radicals,could be a viable alternative for the removal of recalcitrant organic pollutants difficult to treat using conventional methods owing to their high chemical stability and/or low biodegradability.Likewise,Bioelectrochemical systems?BESs?are considered as energy-efficient treatment techniques.This thesis considers two major and broad-spectrum technologies to deal with landfill leachate efficiently along with energy production:?)coupling AOPs;where aged refuse bioreactor/biofilter-based pre-treatment and photochemical(UV irradiated titanium dioxide photocalaysis[UV/TiO₂]&persulfate oxidation[UV/S₂O₈^2-])post-treatment were applied to effectively decontaminate the mature landfill leachate;and?)bioelectrochemical systems?BESs?;employing microbial fuel cell?MFC?-driven electro-Fenton oxidation?BEF?and microbial electrolysis cell?MEC?to treat and generate electricity with the former and hydrogen from the later technology from landfill leachate.The effectiveness of anoxic aged refuse-based bioreactor?ARB?for biological leachate pretreatment followed by AOPs by TiO₂/UV and S₂O₈^2-oxidation was tested?chapter 3?.The results obtained after ARB based pre-treatment demonstrated a mean 72%,81%and 92%degradation of COD,NH₄-N and TN,respectively.However,this treated leachate cannot be discharged without another treatment;hence,it was further treated by UV-mediated TiO₂ photocatalysis and S₂O₈^2-oxidation.An average 82%of COD was abated at optimum condition(1 g L^-1;TiO₂;pH 5)whereas;using an optimum 1.5 g L^-1 S₂O₈^2-at pH 5,81%COD reduction occurred.Acidic and alkaline pH favored COD and NH₄-N removal respectively.The results of this study demonstrated that coupling ARB with AOPs is potentially applicable process to deal with bio-recalcitrant compounds present in mature landfill leachate.The feasibility of employing Microbial Electrochemical Technology?MET?-driven electro-Fenton oxidation?or simply bioelectro-Fenton,BEF?was evaluated as a post-treatment of an anammox system treating sanitary landfill leachate.In the first experiment?chapter 4?,the system performance was evaluated at various iron species?iron???sulfate and iron???chloride?and iron???dosages(150,300 and 500mg L^-1)as Fenton catalyst.A simultaneous anolyte and catholyte COD removal efficiency of 71-76%and 77-81%occurred respectively,having glucose substrate?anolyte?and synthetic leachate?catholyte?.Upon switching the system to 80%and then 100%real leachate as anolyte affected the COD removal efficiency and CE,but no significant effect was noticed in terms of current density.A maximum current density of 1.7 A m^-2 was obtained throughout the experiment.At an optimized iron concentration(300 mg L^-1),20-42%cathodic COD removal occurred from real landfill leachate;whereas,iron???catalyst showed slightly better efficiency than iron???.Two MET systems were operated using effluent from partial nitrification-anammox reactor treating leachate?chapter 5?.In spite of the lower organic matter biodegradability of the anammox's effluent?<0.1?,the technology was capable to attain COD removal rates of 1077-1244 mg L^-1 d^-1 with concomitant renewable electricity production(43.5±2·1 Am^-3NCC).The operation in continuous mode versus batch mode reinforced the removal capacity of the technology.The recirculation of highly acidic catholyte into anode chamber hindered the anodic efficiency due to pH stress on anodic electricigens.The results demonstrated the potential of an MFC based BEF oxidation as sustainable and efficient route for simultaneous anodic and cathodic pollutant removal coupled with power production.Finally the use of simulated landfill leachate to produce virtually pure hydrogen gas??99%?was evaluated in a set of rectangular shaped dual-chamber microbial electrolysis cells?MEC-1 and 2?,with 1.0 and 0.5 L total working volume,under controlled?30??and ambient?12-22??temperatures,respectively?chapter 6?.Applied voltage and temperature exhibited clear influence on overall system performance.At applied voltage of 1.0 V,relatively low energy consumption of 4.5×10^-3±5.3×10^-3-0.264 kWh kg^-1-COD with>100%energy recovery was obtained.In the anode chamber,current generation led to COD oxidation(1.53-2.68 g L^-1 d^-1)and ammonium abatement in the range of 62-72%obeying different removal pathways.The highest hydrogen production of 0.04-0.148 L H₂Lanode^-1 d^-1 was found at a low cost(0.667±0.216€kg^-1 H₂)than the estimated market value of hydrogen(5.66 €kg^-1 H₂)and lower than the US Department of Energy threshold cost of hydrogen for 2020(1.89-3.77 € kg^-1 H₂).Based on these results,this study gives an energy-efficient approach for landfill leachate treatment coupled with electricity and energy production in terms of hydrogen using BESs.However,further research is needed to overcome certain limitations,technical challenges,cost effectiveness and scaling-up these technologies operating in realistic conditions.