Assessment of the effect of effluent discharge from coffee processing plants on river water quality in south western Ethiopia

Abstract

South Western Ethiopia is a major coffee growing region with coffee refineries located along rivers water. With intensification of wet coffee processing and rampant waste discharge, an increased pressure on fauna and flora of river water bodies becomes evident. This study was conducted to find out the effects and extent of effluents generated from coffee refineries on river water quality based on the physico-chemical and nutrient parameters and macro-invertebrate assemblages as biological indicators. The experiment was done using CRD with 3 replications and composite. Sampling sites were selected to represent different ecological and environmental variations within each river, in order to understand the influences of effluent discharge by coffee refineries induced stress on physical, chemical, nutrient and biological attributes of the river water quality. A total of 72 water samples were collected at 6 sampling sites (INF, EFF, UPS, ENP, DS1 and DS2) in 4 rivers. The physic-chemical and nutrient parameters and biological indicators sampling was done immediately during the peak time of coffee refineries. The results were subjected to different statistical analyses to analysis of variance (ANOVA) using SAS. Results of physico-chemical and nutrient parameters and biological indicators analysis revealed that highly significant difference interaction effect among 4 rivers and sites at (p<0.01). This study indicated that mean value of river water parameters analysis exceed the maximum permissible limit set by WHO at DS2. It was observed during the study that coffee refineries discharge their rampant waste into ambient and in rivers water bodies. These effects were observed to have serious impact on the Limu Kosa District of river water and ecosystem. The mean average abundance of UPS of all river water were dominated by pollution sensitive taxa (Ephemeroptera, Hemispheres, Trichoptera, Plecoptera and Coleoptera) while DS were dominated by pollution tolerant families (Simulidae, Chironomidae, leeches). The UPS and DS river water quality was distinctly different when described by physico-chemical and nutrient parameters and biological assemblages (species richness, diversity and abundance) indicators. From these results, it can be revealed that river water quality of DS of Limu Kosa District were adversely affected and impaired by effluents discharged from the coffee refineries as compared to UPS. The alteration in river water quality parameters were more pronounced immediately during the peak time of coffee refineries. The high AF and RRC of BOD, COD and NH3-N at DS might be a pointer to the efficiency of the river’s no aeration mechanism which was no free flow of river water. All physico-chemical and nutrient parameters were negatively and significantly correlated among all biological indicators, while DO and pH were positively significantly correlated at (p<0.05). This study shows that only tolerant taxa inhabit the impacted sites, especially over the peak time of coffee refineries. It was also observed at some private sites influences of effluent discharge by coffee refineries wastes dumped in river water making conditions worse than government site. Therefore, thus concluded that the investigated area of Ketalenca river water, almost all the measured physico-chemical and nutrient parameters analysis showed an increasing trend from UPS to DS it has not yet been so polluted and might not causes any health effects on aquatic ecosystem as compared to that of the Kebena and Awetu river water. The result of the present study is used as a basis for further research needs to be conducted on the effects and extent of effluents generated from coffee refineries. Further in depth study and technology assessment is highly recommended.