COST EFFECTIVE ALTERNATIVES FOR DISPOSAL OF DISTILLERY SPENTWASH WITH A VIEW TO ACHIEVE ZERO DISCHARGE

Production of ethyl alcohol in distilleries based on cane sugar molasses constitutes large industry in tropical continents such as Asia and South America. The world's total production of alcohol from cane molasses is more than 13 million cum/annum. The aqueous effluent stream coming out of the distillation unit is a dark brown highly organic effluent known as stillage, vinase, or spent wash and is approximately 12-15 times by volume of the product alcohol. It is one of the most complex, troublesome, and strongest organic industrial effluents, having a COD value of 80-100 kg/m3 and 40-50 kg/m3 BOD. Because of the high concentration of organic load, distillery spent wash is a potential source of renewable energy. The paper reviews the status and appropriate cost effective solution for the waxed problem towards achievement of the proposed mandatory zero discharge regulation.Spent wash treatment is proposed by three different routes currently viz (a) Concentration followed by incineration, (b) Anaerobic digestion with biogas recovery followed by aerobic polishing and (c) Direct wet oxidation of spent wash by air at high temperature with generation of steam followed by aerobic polishing]. All of these processes are capital intensive. The incineration process involves an investment of the order of 400% of the distillery cost, whereas the other two processes along with the secondary treatment require an investment of 200-300% of the distillery cost. The unfavorable economics make it difficult to implement these treatment processes on the plant scale. Because anaerobic digestion and wet oxidation are less expensive, these alternatives are more attractive. However, there is a need for development of a suitable process with lower investments and higher energy recovery. The treatment of distillery wastewater has gained worldwide attention as in some regions it posing a serious threat to groundwater quality. Extensive research has been carried on treatment of distillery waste in many parts of the world. Since this effluent is an organic nutrients solution, it has wide spectrum of utility. There have been some attempts to use spent wash as a substrate for yeast growth or for biochemical production. However the BOD of effluent still remains quite high (