OPTIMAL DISPOSAL SYSTEMS FOR DISTILLERY EFFLUENTS

Abstract

The problem of waste management is especially significant for cities in the developing world, where population and economies are rapidly expanding, but the infrastructure necessary to manage these problems is inadequate. Industrial processes create a variety of wastewater pollutants, characteristic to that particular industry and the same are difficult and costly to mitigate or treat. Wastewater characteristics and levels of pollutants vary significantly from industry to industry. Moreover, fluctuations may occur in flow, strength and composition of the effluents on hourly or daily basis. Today, stress is laid on pollution prevention and waste minimization. While pollution prevention focuses on preventing the generation of wastes; waste minimization aims at reducing the volume or toxicity of wastes by employing the techniques of recycling and reuse, and process modifications. Production of ethyl alcohol in distilleries based on cane sugar molasses constitutes one of the largest industries in tropical continents of Asia and South America. The world's total production of alcohol from cane molasses is more than 13 million cubic meters per annum. The aqueous effluent stream coming out of the distillation unit is a dark brown highly organic effluent known as stillage, vinasse, or spent wash. The generation of spent wash is approximately 12 to 15 times by volume of the product alcohol depending upon the manufacturing process and housekeeping practices of the industrial unit. It is one of the most complex, troublesome, and strongest industrial effluents, having a very high organic content. In India, the molasses based distillery industry, producing rectified spirit for use as industrial alcohol and for human consumption, is considered as one of the most polluting industries. In spite of the distillery industry in the country being two centuries old, proper and trouble free management of the distillery wastewater has not been possible. This is mainly due to the fact that the treatment of the wastewater to an extent that would make it innocuous Ji6stract when disposed in the environment is difficult and costly. In 2003, Central Pollution Control Board (CPCB); the premier regulatory body for pollution prevention and abatement in India has stipulated a road map to achieve zero discharge of spent wash. Though this charter stipulated that the road map shall be accomplished by December 2005; presently not even 50% of the distilleries have been able to comply with the stipulations. Hence, the present work has been undertaken to arrive at appropriate treatment technologies for distillery wastewater that are economically viable, technically sound and practically feasible while at same time co-opt the existing on ground effluent treatment system into their fold. The study also aims at fulfilling the criterion of zero discharge as specified in the CPCB Charter by proposing certain 'Optimal Disposal Systems for Distillery Effluents'. The gamut of the study encompasses a techno-economic analysis carried out for assessing the feasibility of certain cost effective recovery methods for generating essential revenue for the distillery industry so as to offset the capital and treatment costs; while simultaneously meeting the effluent discharge standards. The aspect of ferti-irrigation i.e. irrigation with the anaerobically digested spent wash has also been examined and the corresponding economic aspects worked out. The study has been conducted by choosing a wide range of alcohol generating capacities of cane molasses based distilleries to cover their entire gamut almost - starting with a five kilo litre per day alcohol producing unit to a fifteen hundred kilo litre a day unit. The aspects of inherent and coherent revenue generation and cost offsetting have been given due weight age while at the same time striking a balance between the techno-economic feasibility and practical viability of the suggested improvements. Each of the forty selected volumes of wastewater were analyzed for four viable treatment alternatives with two disposal options namely ferti-irrigation and incineration. The costing was done by actual designing. The cost comparative statements were developed and same analyzed. Graphic plots were in abstract developed for the costs in terms of Present worth, Project, Construction, Operational, Maintenance, Energy and Loan Amortization for the entire range of capacities. From the plots, equations for the cost curves were arrived at by carrying out the nonlinear regression analysis with two unknowns. The costs of treatment per unit of spent wash (per m ) for various alternatives were evolved. Further, case studies were also taken up for designing a suitable ferti-irrigation system with the treated effluent, as also for assessing costs and benefits and the corresponding payback period for bio-composting alternative. The aspects of reuse of methanated spent wash were also studied. From the research studies carried out, it is inferred that the CPCB Road Map Criterion of 100% utilization of waste stream or zero discharge for the Indian cane molasses based distillery industry can be fulfilled by: - ♦ Existing Distillery Units; through gainful utilization of the waste stream with a minimum burden on the exchequer by co-opting or amalgamating the prevailing treatment schemes with improvements as suggested by the study. ♦ Also for New Distillery Units; by adopting techno-economically feasible, practically viable and ecologically friendly treatment and disposal methods as suggested by the study. ♦ The option of reuse of partially treated spent wash for reducing the fresh water consumption thereby causing waste minimization and ultimately bringing down the overall treatment costs can also be pursued. ♦ Also the study suggests that the sugar mill and the cane molasses based distillery should be co-located or established as one comprehensive unit for gainful utilization of the wastes. IV