Constructed wetland as tertiary treatment for municipal wastewater

An assessment is made of the performance of a horizontal flow sub-surface constructed wetland (SSCW) for polishing effluent from an activated sludge process (ASP) treatment plant. The results of experiments conducted at Mother Dairy Pilot Plant, New Delhi, India are reported in this study. The treated wastewater from the ASP was retreated by subsurface CW planted with Phragmites australius. CW has been extensively researched in Europe and USA. Very limited studies on the suitability of the CW have, however, been reported under tropical and subtropical climatic conditions. The parameters studied were pH, total suspended solids (TSS), total dissolved solids (TDS), chemical oxygen demand (COD), biochemical oxygen demand (BOD), PO4-P, total Kjeldahl nitrogen (TKN), total coliforms (TC) and faecal coliforms (FC). The study was carried out for various temperatures, hydraulic and organic loading conditions. The average efficiency for TSS, BOD, TC and FC was found as 81.02, 88.93, 97.16 and 99.31% respectively under hydraulic loading varying from 24 to 74.8 l/m(2)/day. The highly encouraging results of these experiments have proved the viability of CW as tertiary (polishing) unit in tropical and subtropical climatic conditions.