Assessment of the effluent quality of wet coffee processing wastewater and its influence on downstream water quality

The objective of this study was to evaluate the impact of effluents from traditional wet coffee processing plants on the downstream water quality in Ethiopia. Composite water samples were collected from 11 rivers/streams associated with wet coffee processing plants at the peak hours of coffee processing, and water quality parameters were measured for the wastewater discharged as well as for the river water upstream and downstream of the discharge point. Acidic pH values were recorded for all plant effluents. The organic content of the effluents varied from one plant to another but was considerably high overall, with maximum values of 7200 mg/L and 871 mg/L for COD and BOD5, respectively. This high level of organic content in the effluents depleted the oxygen content to the level of 0.25 mg/L. The organic load and the presence of nutrients invoke a large risk of eutrophication. We found that variations in coffee bean soaking time, pulp fermentation, and the absence of appropriate treatment facilities were the major factors affecting the water pollutant parameters. In general, the measured values of effluent parameters significantly deviated from both the Ethiopian-EPA and US-EPA guidelines. Thus, water bodies and ecosystems located downstream of the traditional wet coffee processing plants are at an alarming risk of ecological disruption, and there may also be severe health consequences for the nearby residents. These findings raise the need for further research into the design and implementation of coffee waste valorization and treatment in view of sustainable coffee production.