Phytoremediation of Drainage Water Containing Mono Ethylene Glycol Using a Duckweed (Lemna gibba) Pond System

This study investigated the treatment of drainage water containing mono ethylene glycol (MEG) using duckweed (Lemna gibba). Six identical continuous flow duckweed-based treatment systems (DBS) were used at different initial MEG concentrations and hydraulic retention times (HRTs). The MEG removal efficiency decreased from 85.9±1.3 to 79.3±2.1% by increasing the initial concentration from 200 to 400 mgMEG/L, respectively. However, the efficiency of DBS deteriorated significantly at higher MEG concentrations; i.e., the removal efficiencies decreased to 36.4±1.2% and 7.1±0.9% at concentrations of 800 and 1,200 mgMEG/L, respectively. The performance of DBS was completely inhibited at MEG concentrations exceeding 1,200 mg/L. The removal efficiency of MEG significantly increased from 37.2±1.3 to 79.3±2.1% when HRT was increased from 6 to 18 days. Nevertheless, the removal efficiencies of MEG remained unaffected when HRT was increased up to 21 days. The uptake process of MEG by duckweed typically followed first-order exponential decay relationships. These results support the recommendation that a duckweed pond system be operated at an HRT of 18 days, and with a MEG concentration below 400 mg/L.