Performance of subsurface flow constructed wetland mesocosms in enhancing nutrient removal from municipal wastewater in warm tropical environments.

Nutrient-rich effluents from municipal wastewater treatment plants (WWTPs) have significantly contributed to eutrophication of surface waters in East Africa. We used vertical (VF, 0.2 m(2)) and horizontal (HF, 0.45 m(2)) subsurface flow (SSF) constructed wetland (CW) configurations to design single-stage mesocosms planted with Cyperus papyrus, and operating under batch hydraulic loading regime (at a mean organic loading rate of 20 g COD m(-2) d(-1) for HF and 77 g COD m(-2) d(-1) for VF beds). The aim of the investigation was to assess the performance of SSF CWs as hotspots of nutrient transformation and removal processes between the WWTP and the receiving natural urban wetland environment in Kampala, Uganda. C. papyrus coupled with batch loading enhanced aerobic conditions and high efficiency regarding the elimination of suspended solids, organic matter, and nutrients with significant performance (P < .05) in VF mesocosms. The mean N and P elimination rates (g m(-2) d(-1)) were 9.16 N and 5.41 P in planted VF, and 1.97 N and 1.02 P in planted HF mesocosms, respectively. The lowest mean nutrient elimination rate (g m(-2) d(-1)) was 1.10 N and 0.62 P found in unplanted HF controls. Nutrient accumulation in plants and sediment retention were found to be essential processes. It can be concluded that whereas the SSF CWs may not function as independent treatment systems, they could be easily adopted as flexible and technologically less intensive options at a local scale, to increase the resilience of receiving environments by buffering peak loads from WWTPs.

Pioneering water quality data on the Lake Victoria watershed: effects on human health.

Four forest reserves within 50 km of Kampala in Uganda act as a critical buffer to the Lake Victoria watershed and habitat for local populations. Over a 9-month period we capture a pioneering water quality data set that illustrates ecosystem health through the implementation of a water quality index (WQI). The WQI was calculated using field and laboratory data that reflect measured physical and chemical parameters (pH, dissolved oxygen, biological oxygen on demand, nitrates, phosphates, fecal coliform, and temperature turbidity). Overall, the WQI for the four forest reserves reflect poor to medium water quality. Results compared with US Environmental Protection Agency and World Health Organization drinking water standards indicate varying levels of contamination at most sites and all designated drinking water sources, with signatures of elevated nitrates, phosphates, and/or fecal coliforms. As critical health problems are known to arise with elevated exposure to contaminants in drinking water, this data set can be used to communicate necessary improvements within the watershed.