Performance Evaluation of Horizontal Subsurface Flow-Constructed Wetlands for the Treatment of Domestic Wastewater in the Tropics

The lack of information on constructed-wetland performance in the tropics is among the factors that have hindered the adoption of low-cost wastewater-treatment technologies as alternatives to conventional wastewater treatment. A pilot scale study was undertaken in Juja (Kenya) to assess the performance of horizontal subsurface flow-constructed wetlands (HSSF-CWs) under tropical conditions. Primary domestic wastewater effluent was continuously fed into three replicate wetland cells, each with an area of 22.5 m(2) (7.5 x 3 m) and with gravel as substrate. The study revealed successful performance of the wetlands in terms of compliance with local discharge standards with respect to chemical-oxygen demand (COD), BOD5, total suspended solids (TSS), and SO42--S at an average mass removal efficiency between 58.9 and 74.9%. Moderate removal of NH4+-N and total phosphorus (TP) was recorded. The estimated first-order aerial-rate constant and the BOD5 background concentration showed the HSSF-CW to be area-requirement competitive. The good performance in organic matter and suspended solids removal reveals that HSSF-CW can help to alleviate the current environmental pollution problems experienced in developing countries caused by the discharge of partially treated or untreated domestic wastewater. DOI: 10.1061/(ASCE)EE.1943-7870.0000636. (C) 2013 American Society of Civil Engineers.