American Journal of Environmental Engineering 2012, 2(1): 12-18 DOI: 10.5923/j.ajee.20120201.03 Decolorization of Anaerobically Digested Molasses Spentwash by Coagulation Mrityunjay Singh Chauhan 1 , Anil Kumar Dikshit 2,3,4,* 1 Department of Civil Engineering, Maulana Azad National Institute of Technology, Bhopal, 462051, India 2 Centre for Environmental Science and Engineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India 3 School of Civil Engineering, Survey and Construction, University of KwaZulu-Natal, Durban, 4041, South Africa 4 School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore Abstract Treatment of molasses spentwash has always posed a challenge to the environmental engineers. Problem becomes more difficult in the countries like India where more harsh environmental parameters of spentwash on one hand and limitation of treatment cost on the other is crude reality. Inability to grow micro-organisms in undiluted spentwash further limits the options. In this work, various options of coagulation were tried as primary treatment to make spentwash fit for further biological treatment without dilution. Poly aluminium chloride(PAC) was found to be the best coagulant. Keywords Coagulation, Decolorization, Distillery, Spentwash 1. Introduction There are about 300 distilleries in India, producing about 2.75 billion litres of alcohol annually[1]. India is the fourth largest producer of ethanol in the world and the second largest in Asia. Though, the alcohol production from starchy material is also practiced on a very limited scale, most of the Indian distilleries use sugarcane molasses as raw material. About 4-10 kg of molasses is required for production of one litre of alcohol[2]. Apart from its use for beverage, medicinal, pharmaceutical and flavouring, alcohol constitutes the feedstock for large number of organic chemicals, which are used in manufacturing a wide variety of intermediates, drugs, rubber, pesticides, solvents etc.[3]. Distillery ranks as the top most industry among the list of 17 heavily polluting industries identified by Ministry of Environment & Forests, Govt. of India, and are covered under Central Action Plan. Distillery spentwash is not only high on organic and inorganic loading, but also has dark brown colour even after industry standard treatment by anaerobic digestion/ bio-methanation. The anaerobically treated spentwash does not meet Central Pollution Control Board(CPCB) standards of discharge into streams or land application. Groundwater colorization is growing concern for areas having land application of distillery spentwash. Spentwash is toxic to aquatic organisms as LC 50 value for distillery spentwash was found to be 0.5% for fresh water fish Cyprinus carpio var. Communis[4]. It behaves much * Corresponding author: dikshit@iitb.ac.in (Anil Kumar Dikshit) Published online at http://journal.sapub.org/ajee Copyright © 2012 Scientific & Academic Publishing. All Rights Reserved more hazardously when disposed into water bodies, since it may result in the complete depletion of dissolved oxygen and aquatic life will be destroyed[5]. Rao et al. conducted laboratory scale studies on methods of removing color from distillery wastewater. Aluminium sulfate and ferric chloride were found very effective in color removal from anaerobically treated diluted molasses and distillery wastes[6]. Color removal of molasses based distillery effluent was studied by Migo et al[7] using a commercial inorganic flocculent, a polymer of ferric hydroxyl sulfate with a chemical formula of [Fe 2 (OH) n (SO 4 ) 3-n/2 ] m . For decolorization of anaerobically digested spentwash combined chemical and biological methods were also tried[8]. The first treatment included calcium oxide and hydrogen peroxide. This was followed by second treatment, which involved hydrogen peroxide and microbes at 144 hrs incubation. Goto et al.[9] reported super critical water oxidation(SCWO) of distillery wastewater for removal of its color. In this process, oxidation reaction took place in water above its critical point(647 o K, 22.1 MPa). Experiments were carried out with different amounts of biopolymer chitosan. This gave decolorization of the order of 94% along with 93% reduction in COD. Ten times diluted distillery wastewater(COD as 2800 mg/L) was used for experimentation[10]. Ozonation of distillery(yeast fermented beer) waste was also tried to evaluate the process in terms of organic matter removal and decolorization efficiencies. Ozone generation system used was based on the production of ozone from the reaction of oxygen with UV light[11]. Pikaev et al[12] carried out study on combined electron beam and coagulation method for treatment of molasses based distillery effluent. Nandy et al.