Performance of a vertical subsurface flow constructed wetland in treating biomethanation effluent

A system consisting of a biomethanation plant whose effluent is fed to a constructed wetland, can serve as a multipurpose waste-to-wealth system. It can safely treat domestic sewage, and organic solid waste while providing cooking fuel (biogas), reclaimed water and plant biomass. This study evaluates the performance of an outdoor 30 LPD constructed wetland setup in treating the effluent from an existing biomethanation reactor fed with blackwater and organic solid waste. The constructed wetland units contained Vetiver zizanioides and Canna indica and earthworms (Lumbricus terrestris) and the changes in BOD, NH4, NO2, P, total solids (TS) and pH of the effluent were measured. The constructed wetlands were effective in reduction of BOD, N and P. The effect of bed depth and series arrangement of wetland units was studied. The system was modeled using a 1^st order differential model assuming plug flow and steady state. The model predictions partly matched the measured values and the trends and the sources of deviations have been discussed. Overall, the performance of vertical subsurface flow constructed wetlands for treating biomethanation effluent was found to be highly encouraging and it warrants further studies to realize the full waste-to-wealth potential of multipurpose biomethanation-constructed wetland systems.