Growth performance of tropical wetland species (Cyperus involucratus Rottb. and Thalia geniculata L.) in anaerobic digester effluent and their water treatment efficiency

Anaerobic digester effluent contains high concentrations of nutrients and other contaminants and has low dissolved oxygen. While there is increased interest nowadays in using constructed wetlands to treat wastewater, the ability of the wetland plants to grow in these stressful conditions is scantily investigated. Hence, this research investigated the growth performance of two tropical wetland species (Cyperus involucratus and Thalia geniculata) in anaerobic digester effluent and assessed their potential for treating the wastewater. Both C. involucratus and T. geniculata grew well in the wastewater probably because of aerenchyma development (28% air-space tissue) in the roots and radial oxygen loss from the roots. The pollutant level in the anaerobic digester effluent was significantly reduced with high removals of BOD (96-100%) and COD (69-73%). The remove of nutrients differed between species. T. geniculata had the better removal of PO4-P (48%), whereas C. involucratus had the better removal of NH4-N (99% in 28 days) and inorganic N (64% in 56 days). The removal of TSS (87-88%), EC (36-38%) and TDS (51-54%) in the systems were not significantly different between the two species. The study suggests that C. involucratus is a good candidate species for N removal in constructed wetlands whereas T. geniculata is better for removal of P.