Investigation of an appropriate treatment system for a wet coffee processing in the Maraba District of Rwanda

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Coffee processing plants have been a major source of environmental pollution. This study focuses on the treatment of the coffee wastewater from wet coffee processing in order to avoid coffee wastewater from polluting the environment. From the characterisation of the coffee wastewater, Biological Oxygen Demand (BOD5), Chemical Oxygen Demand, (COD), Suspended Solids (SS), Phosphates (P04-3), and Nitrates (N032-) had values of 2000 mg/l, 4700 mg/l, 256 mg/l, 25.2 mg/l, and 4.0 mg/l respectively. These values were far above the GH-EPA (Environmental Protection Agency) acceptable limit for wastewater disposal into the environment. Based on these findings, two treatment options were investigated and these were yeast and Ordinary Portland cement. Ordinary Portland cement (2.5g/l) as a flocculent was chosen to be the best option for the primary treatment of coffee wastewater. This option gave a remarkable reduction in BOD5, COD, PO4-3, SS, and N032- with 69%, 79%, 98%, 98%, and 35% respectively. However the values of BOD5, COD and Nitrates were still high above the acceptable level of GH-EPA standards for wastewater disposal into the environment. To further augment reduction in BOD5, COD and Nitrates, secondary treatment system comprising of Anaerobic and Aerobic units was designed. The final quality effluent from the treatment plant had a percentage reduction of BOD, COD, PO4-3, NO32-, SS, by 98%, 96%, 98%, 97%, 98% respectively and pH of 8.25 which met the acceptable level of GH- EPA standards for wastewater disposal into the environment.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the award of the degree of Master of Science in Water Supply and Environmental Sanitation, 2003