Electrochemical treatment of municipal landfill leachates and implications for poly- and perfluoroalkyl substances (PFAS) removal

This work reports the electrochemical treatment of municipal solid waste landfill leachates in a parallel plate cell provided with boron doped diamond (BDD) anodes. Two types of samples were electrooxidized at three current densities between 200 and 800 A/m2: (i) raw leachates; and (ii) the leachate after treatment in a membrane bioreactor (MBR), characterized by its near-zero ammonia content. In absence of ammonia, the electrogenerated chlorine oxidants accelerated the removal of chemical oxygen demand but barely influenced the mineralization of persistent organic pollutants still retained in the MBR-treated leachate. Furthermore, we investigated the removal of 17 poly- and perfluoroalkyl substances (PFAS) contained in the real MBR-treated leachate (∑17PFAS = 3456 ng/L). The operation at 200 A/m2 increased perfluorocarboxylic acids (PFCAs) concentration, indicating the presence of unknown precursors in the MBR-treated leachate. Working at 800 A/m2 successfully reduced the Σ17PFAS content by 95% in 6 h. Σ17PFAS showed decreasing trends, and only perfluoropentanoic and perfluorobutanoic acids showed temporal increases that later on went down as the long chain PFCAs were degraded into shorter chain homologs. 1-log (90%) Σ17PFAS reduction was achieved in 4.5 h, when the formation of undesirable perchlorate was still near undetectable. We estimate that the PFAS electrooxidation rate in the leachate matrix was one-sixth of the removal rate observed in a previous study treating a cocktail of PFAS in synthetic contaminated groundwater. Overall, this work provides useful data to guide the design of advanced onsite treatment of landfill leachates, one of the main secondary PFAS entry to the environment.