Enhanced mass transport in an electrochemical reactor to promote degradation of organic compounds and improve biodegradability of a mature landfill leachate

This study aimed at further developing the electro-oxidation process for partial mineralization of organic pollutants and biodegradability enhancement before subsequent biological treatment. While electro-oxidation using BDD anode is usually limited for such applications by the promotion of organic compounds mineralization rather than fast degradation kinetics, electrode's morphology and mass transport/hydrodynamic conditions appeared to be key elements to consider. The use of plate or mesh electrodes in a 1.75 L reactor was first compared for degradation and mineralization of phenol. While similar mineralization kinetics were observed, local mass transport/hydrodynamic conditions at mesh electrodes further promoted phenol degradation and back-diffusion of degradation by-products into the bulk solution. Moreover, mesh electrodes allowed reducing the formation rates of undesired ClO₃⁻ and ClO₄⁻. This reactor configuration was then applied for treatment of a mature landfill leachate with high concentration of recalcitrant organic compounds (TOC = 1.43 gC L^-1). Partial mineralization (17 %), requiring 21.7 kWh m^-3, corresponded to a strong increase of biodegradability and average oxidation state of carbon, as well as more than 81 % of fluorophores removal, which appeared as relevant parameter for monitoring such combined process. Besides, competition phenomena associated with oxidation of chlorine and nitrogen compounds were also assessed.