School of Engineering, Department of Chemical & Process Engineering
Moi University, P. O. Box 3900 - 30100, Eldoret , Kenya
Alcohol distilleries produce effluents which are strongly acidic, have high Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD), contain strong odour and are dark brown in colour. They cause detrimental environmental effects if they are freely disposed off to the environment. Adopted anaerobic treatment techniques with associated biogas generation have not proved to be very efficient on high strength distillery effluents as substrates. The improvement on mean product yield, effluent stabilization and sterile air tolerance was explored through microbial immobilization on activated natural zeolite and calcium alginate supports. Three experimental set-ups were performed with the first acting as a control and having no support material whereas the second and third having microbial system immobilized unto activated natural zeolite and calcium alginate supports respectively. At the marginal organic loading of 75 kg/m3 (corresponding to undiluted waste water), the unsupported system showed a low yield of 2.1 X 10-3 m3/kg CODt in biogas, whereas the calcium alginate system registered the highest yield of 84.5 X 10-3 m3/kg CODt . Activated natural zeolite system on the other hand showed a yield of 43.6 X 10-3 m3/kg CODt. Based on the effluent stabilization over the same initial marginal organic loading, activated natural zeolite system demonstrated the highest degree in effluent stabilization of 44.0 % as opposed to the unsupported and the calcium alginate system that registered 24.0 % and 41.3 % respectively. Finally, activated natural zeolite supported system showed the longest tolerance to sterile air exposures of 90 minutes. The unsupported system registered a tolerance of 30 minutes whereas the calcium alginate system demonstrated 60 minutes of oxygen tolerance.