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

Abstract Coffee washing units in Sidama Regional State, Southern Ethiopia pose a serious threat to surface water sources and coffee growing soils. A comparison field performance test was conducted on the capacity of natural and constructed wetland on wastewater treatment. The study indicates that treating the effluent from the processing plants using constructed wetland supported by sedimentation pond, filtration, and gravity aeration can reduce pollutant levels significantly. The treated waste water can be safely disposed-of to the natural river. It was observed that BOD5 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 Ethiopian Environmental Protection Agency. Heavy metals from coffee beans produced from the surrounding farms using water from Gidabo River discharged with treated effluent from the processing units are within the permissible limits. It is evidenced that wetlands in general and constructed wetlands in particular are promising technologies to treat the effluent water and recommended to be adopted by all the processing units in the region.