Treatment of Chlorinated Benzenes in Different Pilot Scale Constructed Wetlands

Abstract

Chlorinated benzenes (CBs) are common pollutants in groundwater due to their broad usage in industry and agriculture. Remediation of CBs from contaminated groundwater is of great importance. Biodegradation has proved to be a suitable approach in eliminating CBs from polluted water, and constructed wetland (CW) is an alternative as cost efficient technology to remove CBs from wastewater. In the present study, a comparison covering five growing seasons (from May 2006 to November 2010) was carried out among four pilot-scale CWs: (1) unplanted horizontal subsurface flow (HSSF) CW; (2) planted HSSF CW; (3) planted HSSF CW with tidal flow; (4) hydroponic root mat (HRM). The unplanted HSSF CW was not efficient for CBs removal, with removal efficiency less than 23 % for the four CBs, and no capability to remove 1,2-DCB. Planted HSSF CW exhibited significantly better treatment performance than the unplanted HSSF CW, and the CBs removal efficiency can be enhanced to some extend (especially after 3 m from the flow path) when running under tidal flow operation. Highest CBs removal efficiency was reached in the HRM system, with mean removal rates for monochlorobenzene, 2-chlorotoluene, 1,4-dichlorobenzene (DCB) and 1,2-DCB were 219, 0.92, 7.48 and 0.86 mg/m2/d, respectively. In conclusion, the HRM is the best variant CW to treat chlorinated benzenes, and it can be an option for the treatment of pollutants which prefer aerobic degradation.