Performance Evaluation Using a Three Compartment Mass Balance for the Removal of Volatile Organic Compounds in Pilot Scale Constructed Wetlands

To perform a general assessment of treatment efficiency, a mass balance study was undertaken for two types of constructed wetlands (CWs), planted gravel filters and plant root mat systems, for treating VOC (benzene; MTBE) polluted groundwater under field conditions. Contaminant fate was investigated in the respective water, plant, and atmosphere compartments by determining water and atmospheric contaminant loads and calculating contaminant plant uptake, thereby allowing for an extended efficiency assessment of CWs. Highest total VOC removal was achieved during summer, being pronounced for benzene compared to MTBE. According to the experimental results and the calculations generated by the balancing model, degradation in the rhizosphere and plant uptake accounted for the main benzene removal processes, of 76% and 13% for the gravel bed CW and 83% and 11% for the root mat system. Volatilization flux of benzene and MTBE was low (