Treatment of Woodwaste Leachate in Surface Flow Mesocosm Wetlands

Abstract

Abstract Woodwaste leachate is usually acidic, of high oxygen demand, and toxic. To prevent potential adverse impacts of the raw leachate on heterotrophic bacteria and aquatic plants, woodwaste leachate was diluted before discharge to constructed wetlands. This study compared treatment performance among four vegetated surface flow mesocosm wetlands fed with different dilutions of woodwaste leachate over a period of 12 weeks. During another period of 13 weeks, the effluent of a vegetated wetland fed with the raw leachate was further treated in a vegetated wetland and an open wetland. The highest reduction rates for chemical oxygen demand as well as tannin and lignin were achieved in the wetland fed with the raw leachate. The most diluted (6x) woodwaste leachate yielded the lowest reduction rates and highest reduction efficiencies. Up to 47 mg L-1 volatile fatty acids in influent were depleted through wetlands with a hydraulic retention time of 13 d. Vegetation made insignificant performance differences for treatment of woodwaste leachate. Chemical oxygen demand as well as tannin and lignin were further removed through the wetlands in series, though at lower reduction rates. Wetland performance for treatment of woodwaste leachate was likely regulated by dissolved oxygen concentration and availability of bacterial substrates.