Constructed wetland-based wastewater treatment of a coffee-washing plant and its impacts: a case study of Kege processing plant, Ethiopia

Coffee-washing units in the Sidama region pose a serious threat to surface water sources and coffee-growing soils. This study indicates that treating the effluent from the processing plants using a constructed wetland supported by a sedimentation pond, filtration and gravity aeration can reduce pollutant levels significantly. The treated wastewater can be safely disposed off to the natural river body. Biochemical oxygen demand (BOD) was reduced by 90 and 96% in natural and constructed wetlands, respectively. TDS was reduced substantially, whereas nitrate was reduced by 63%. Soil quality parameters from the wetland are within the permissible limits of the Ethiopian Environmental Protection Agency. Metallic elements of coffee beans produced from the surrounding farms using the river water discharged with treated effluent from the processing units are within the permissible limits. Constructed wetland is a promising technique to treat the effluent water and is recommended to be adopted by all the processing units in the region.