Strategies for enhancing phosphorous removal in Vertical Flow Constructed Wetlands

Constructed wetlands (CWs) are among the fastest emerging treatment methods for wastewater treatment. Unlike their organics and nitrogen removal capacities, the potential of CWs as a sink for phosphorous is still debatable. In this study, the secondary data from several CWs treating domestic sewage were compiled and assessed. Curves were plotted between orthophosphate-phosphorous (PO₄^3--P) loading and the corresponding removal rates. Other factors affecting PO₄^3--P removal like depth of the CW, surface area, organic loading rate etc. Were also analyzed. Removal rates of PO₄^3--P were conforming to a linear positive relation with the loading rates. Pea gravel as a CW medium performed consistently well (60-80% removal) for a wide range of influent PO₄^3--P loading (0.5-1.5 g/m³-d). The increased depth of the wetland appears to favor phosphate removal. PO₄^3--P removal was found to be correlated with outlet dissolved oxygen, total Kjeldahl nitrogen removal and effluent nitrate. The study suggests that proper design, optimal organic loading and suitable pre-treatment may increase the applicability of CWs for phosphate removal from domestic wastewater. Larger area requirements can also be avoided by increasing their depth while keeping the volume of the filter media the same.