Polishing the Treated Domestic Wastewater Effluent in Tropical Climate by Subsurface Flow Constructed Wetland (SSFCW)

Many lakes and streams in Malaysia are receiving polluted water containing pollutants which include suspended solids, organics, heavy metals and nutrients. This study focuses on the effectiveness of subsurface flow constructed wetland (SSFCW) in polishing the treated domestic wastewater effluent. A model of SSFCW system was constructed downstream of a sewage treatment plant (STP) to provide further treatment of the STP effluent. The SSFCW consists of four concrete cell of 0.1 m thick, built parallel to each other. The dimensions are 2.5 m long x 0.45 m wide x 0.50 m deep with a bed slope of 1% for each cell. Three cells were planted with different plants (Limnocharis flava. (L), Hymenacallis littoralis and Eleocharis ovata obtusa) and the forth cell was kept as an unvegetated control cell. The STP effluent was pumped into the SSFCW at a flow rate of 1.9 m3/day. At this flow rate, the organic loading was 0.061 kg/m2.day. After 3 months of monitoring, the planted wetlands were found to be able to reduce most of the pollutants including TSS, BOD5, COD, ammonia, nitrate and total phosphorus where the removal were up to 81.4%, 71.6%, 57.8%, 95.1%, 86.3% and 74.7%, respectively. The findings of this study show that SSFCW is an effective method for the treatment of effluent from sewage treatment plants to meet the discharge limit of 20 mg/L BOD5 required by law for discharge in catchments of drinking water source.