Removal of Bacteria Pathogens from Domestic Wastewater in a Tropical Subsurface Horizontal Flow 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) sewage treatment works consisted of four cells set in parallel each 22.5m2. Three of the cells 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. The observations made in the study have highlighted the potential of the subsurface flow in the constructed wetland with respect to bacterial pathogen removal from wastewater. Thus it is possible for developing tropical countries to exploit and harness the potential of wetland wastewater treatment technology in the prevention and management of waterborne diseases by provision of cheap, effective, reliable and sustainable way of treating wastewater.