Treatment of an artificial sulphide containing wastewater in subsurface horizontal flow laboratory-scale constructed wetlands

In general, treatment wetlands seem to be a potential method of tackling the sulphide problem of post-treatment of anaerobic digester effluents. Because of insufficient practical experience and lack of knowledge of sulphide removal, sulphur transformation was investigated, particularly in horizontal subsurface flow constructed wetlands (depth of 35 cm) under laboratory-scale conditions with artificial wastewater. The plants affected a clear stimulation of the sulphide and ammonia removal rates. Sulphide concentration in the range of 1.5-2.0mgl(-1) was tolerated by the plants and completely removed in the planted model wetlands; sulphide concentration of >2.0 mgl(-1) caused instabilities in sulphide and nitrogen removal. Area-specific sulphide removal rates of up to 94 mg sulphide m(-2) d(-1) were achieved in the planted beds at hydraulic retention times of 2.5 d. Sulphate affected the sulphide removal. While in the unplanted control bed an almost stable removal in the range of 150-300 mgN m(-2) d(-1) was observed variations of hydraulic retention time, sulphide and sulphate concentrations influenced the ammonia removal rate within the planted beds in a broader range (600-1400 mgN m(-2) d(-1)). These results showed that nitrification, sulphide oxidation, denitrification and sulphate reduction can occur simultaneously in the rhizosphere of treatment wetlands caused by dynamic redox gradients (aerobic-anaerobic) conditions. (C) 2007 Published by Elsevier B.V.