Removal of organic pollutants by effluent recirculation constructed wetlands system treating landfill leachate

Abstract

The leachate of municipal solid waste landfills contains various types of organic substances, increasing the difficulty of efficient treatment. This study built an effluent recirculation (1:4 ratios) vertical subsurface flow constructed wetlands (CWs) system treating actual landfill leachate (LL). In order to better monitor and evaluate the removal of organic pollutants in LL by CWs, Three-Dimensional Fluorescence (3D-EEM) and Solid Phase Extraction–Gas Chromatography–Mass Spectrometry (SPE–GC–MS) analysis of CWs influent and effluent water was performed to investigate the removal of Dissolved organic matter (DOM), Organochlorine pesticides (OCPs), Organophosphorus pesticide (OPPs), Polycyclic aromatic hydrocarbons (PAHs), and Volatile organic compounds (VOCs). Results showed that during the treatment of LL by CWs, the average removal rate of conventional pollutants (COD, NH4+-N and TP) was over 85%, with a majority of microbial metabolites and humic acids in DOM effectively degraded. The concentrations of OCPs, OPPs, PAHs, and VOCs in the CWs influent LL ranged between 378.6 and 4746.32 ng L−1, accounting for only a small proportion (3.7×10−7–4.6×10−6) of COD. The achieved organic micro-pollutants total removal rates were: OCPs(56.9%), OPPs(41.4%), PAHs(58.3%), and VOCs(78.3%), with relatively higher removal rates observed for DDT (83.6%), dimethoate (89.2%), benzo(a)anthracene (82.0%). Therefore, the effluent recirculation CWs system can effectively remove organic pollutants in LL, indicating that this is a promising technology with good application for the effective treatment of wastewater.