Electrochemical Removal of Ammonium Ion and Organic Substances from Landfill Leachate

Abstract

The efficiency of two different types of onsite leachates and simulated leachates, the latter containing endocrine disruptor bisphenol A and refractory humic acid as organic constituents with NaCl and NH4Cl electrolytes, was examined by an electrochemical treatment method. The mechanisms for the removal of organic substances and ammonium ions are discussed based on the analyses of total organic carbon (TOC), nitrogen compounds, and evolved gas. The results suggested that, for the removal of ammonium ions, indirect oxidation by active chlorines is an important process during electrochemical treatment. The degradation of organic substances with chloride-containing leachate is a two-step mechanism consisting of (1) indirect oxidation of active chlorines and (2) cathodic reduction as a result of methane formation, which was proved to be an important process. This two-step mechanism in the electrochemical treatment method was found to be more effective than chlorination or ozonation treatment. For leachate containing a low concentration of chloride ions, direct oxidation by an anodic surface was also important for the degradation of the organic substances during electrochemical treatment. In particular, assimilable organic substances are preferentially degraded by direct oxidation over ammonium ions. In addition, some reactive compounds, such as bisphenol A and p-nitrosodimethylaniline (RNO), might be converted by the oxidizability of chloramines.