Research on One-Step Advanced Treatment of Old Landfill Leachate by Sequential Electrochemical Peroxidation-Electro-Fenton Process

Abstract

Electrochemical technology is an alternative method for the removal of high concentration ammonium-N (NH 4 + -N) and refractory organics from old landfill leachate (OLL). However, the limited performance of a single electrochemical process and the subsequent long tertiary treatment time to meet the water quality standards are the key technical problems that hinder its practical application. This study demonstrates that the sequential ECP-EF process can realize one-step advanced treatment of OLL. Under the optimal conditions (ECP: j =30 mA cm -2 , initial pH=9.0; EF: j =30 mA cm -2 , initial pH=3.5), the removal efficiencies of COD, TOC, NH 4 + -N, and TN can be achieved 95.9±0.4%, 85.1±0.8%, 99.4±0.1%, and 99.2±0.1%, respectively, to meet the first-class standard of integrated wastewater discharge standard of China. The organics in OLL are mainly removed by ECP process and further mineralized or converted to small molecular hydrophobic components in EF process. The sequential ECP-EF process can reduce the aromaticity and complexity of organics, as well as can decrease the acute cytotoxicity (ACT) and hydrophilicity. A proper electrolysis time can effectively avoid the rise of ACT, energy consumption, and cost. The treatment cost ($0.0134 L -1 ) is approximately 32% less than the previously reported electrochemical processes of electrocoagulation/electro-Fenton. These findings obtained with real OLL provide a basis for scaling up this new sequential electrochemical treatment approach.

Keywords: Sequential electrochemical process, Old landfill leachate, Ammonium-N, Refractory organics, Advanced treatment