Phosphorus retention and mass balance in an integrated constructed wetland treating domestic wastewater

This study quantified the contributions of different P removal pathways in an integrated constructed wetland (ICW) treating domestic wastewater. Findings over the study period (February 2008 to March 2012) showed average P retention rates of 31±2mg/m²/day for molybdate reactive phosphate (MRP) and 40±3mg/m²/day for total P. Near complete P removal was achieved during the first 2 years of operation. Thereafter, effluent concentrations increased slightly. According to the mass balance estimation, assimilation by plants accounted for approximately 16% of the total P retained, while sediment storage contributed nearly 60%. Sediment storage was the major P removal pathway in the ICW. Thus, high effluent concentrations recorded during high effluent flow volumes was due to remobilisation of P from the sediment. Management of ICW systems may therefore require implementing sediment removal schemes. The combination of plants with high biomass production can be beneficial for improving ICW performance.