COST EFFECTIVE ALTERNATIVES FOR DISPOSAL OF DISTILLERY SPENTWASH WITH A VIEW TO ACHIEVE ZERO DISCHARGE
Abstract: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 (<5000ppm) necessitating further treatment. Concentration of spent wash and its use as an animal feed additive is a common practice among countries producing alcohol from beet molasses in Europe and North America. The paper presents a critical techno-economic assessment on these aspects towards realizing the zero discharge concept. Wastewater treatment system for the distilleries needs to be decided based on the various factors viz quality of molasses and properties of the wastewater, climatic conditions and location of the distillery, availability land and raw materials, cost of fuel and electricity, market for byproducts and pollution control norms. Any one of the above factors can have deciding effect on selection of the wastewater treatment system. It is therefore essential to select the wastewater treatment method depending upon above and choose the suitable fermentation and distillation process accordingly. In other words cane molasses based distillery and it's wastewater treatment system should be made for each other. The technologies currently used by distilleries have certain limitations as high cost of treatment or inherent inability of technology to remove certain pollutants like total dissolved solids and colour to safe and acceptable limits for disposal into surface water or on land. The paper, therefore, concludes that there is a definite need for evaluating appropriate methods for Disposal of Distillery Spent Wash With A View To Achieve Zero Discharge through Cost Effective Treatment Systems.
Document Type: Research Article
Publication date: January 1, 2005
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