Performance Evaluation of Pilot Scale Verticalflow Subsurface Constructed Wetland Treating Municipal Wastewater

Abstract

Constructed Wetland is being used as a low cost treatment system by most ofthe developing countries to treat wastewater. A pilot scale vertical sub surfaceflow Constructed Wetland was constructed in the premises of BASP,Kathmandu for the treatment of wastewater. The pilot scale constructedwetland consists of two units/beds of equal size i.e., 6m x 2m x .7m. One of thebeds was planted with locally available reeds, Phragmites karkaand anotherwas left unplanted and treated as blank. Gravel and sand was used as the mediain the bed. To evaluate the pollutants removal efficiency of the treatment bedsin four different flow rates, composite wastewater samples were collected andanalyzed from April 2006 to Oct2006. The two treatment beds show excellentremoval percentage of pollutants, however planted bed was found to be moreeffective than unplanted bed. Removal efficiency were reduced from 95.75 %to 76.7% for BOD, 94.07% to 77.7% for COD, 95.58% to 72.76% for TSS,61.16% to 39.97% for TKN, 72.87% to 24.78% to 48.11% for NH -N, 52.46%to 24.78% for TP, when the flow rate was increased from 0.464 m /d to3.05m 3 /d. Dissolved Oxygen (DO) found to be increased in the effluents.Fecalcoliformremoval efficiency was above 90%. Biomass percentage of reeds wasfound 57.07 %, which indicates high productivity and can be used in makingfertilizer, mulch and handicrafts.