Removal of coliform and solids in a tropical constructed wetland

Abstract

Pilot scale studies were conducted to determine the performance of a subsurface horizontal flow constructed wetland in the tropics in the period April to July 2003. The wetland located at Jomo-Kenyatta University of Agriculture and Technology (JKUAT), Kenya, had sewage treatment works consisting of four cells set in parallel each 22.5 m2. Three of the cell had gravel and in two of the cells with gravel the tropical macrophyte Cyperus Papyrus was introduced. The wetland received a continuous feed of settled sewage from a primary facultative pond. Performance of the wetland was evaluated in terms of removal of bacterial pathogens and suspended solids. This was done under different hydraulic loading rates. Fecal coliform removal in the wetland of up to three log units was realized. The removal was found to be influenced by the influent coliform count and not the hydraulic retention time. When fecal count in the influent was less than or equal to 2 log units 99.9% removal was realized. A moderate removal rate of up to 50% for Total Suspended Solids (TSS) was obtained. The loading rates deduced from the study for TSS was 122 Kg/Ha. d.