Indian Distillery Industry, Manufacturing Process, Composition of Effluents, Environmental Impacts, Treatment Technologies

INDIAN DISTILLERY INDUSTRY, MANUFACTURING PROCESS, COMPOSITION OF EFFLUENTS, ENVIRONMENTAL IMPACTS, TREATMENT TECHNOLOGIES

By Dr. Yashpal Singh

Updated on 06/07/2023

For other topics related to the Distillery Sector and a review based on more than 350 publications  covering Utilization of Spent Wash In Agriculture, Impact On Soil, Crops And Yield, Pre-Sown Land Application, Ferti-Irrigation, Bio Composting, Soil Reclamation, International Practices in The Utilization of Spent Wash in Agriculture, Major Provisions of The Environment, Forest and Pollution Control Laws in India, Environmental Performance Rating, Major Policy Interventions and The Views Of The Honorable NGT On Sustainable Technology Adoption see Singh Yashpal 2020, Distillery Spent Wash and Its Utilization in Agriculture. Publisher – The Wealthy Waste School India. ISBN No. 978-93-5396-249-4. Pages 1 to 360 (Available at Amazon and Kindle Books)

Indian Distillery Industry

India is a major producer of Potable and Industrial Alcohol. The majority of distilleries use molasses as a feed stock. Some distilleries are grain based. Apart from its use in beverage, medicines, pharmaceuticals and flavouring, alcohol constitutes the feed stock for a large number of organic chemicals which may be used in the production of drugs, rubber, pesticides and solvents. Ethyl alcohol is an important feed stock for the manufacture of various chemicals like acetic acid and butanol, butadiene, acetic anhydride, polyvinyl chloride etc. Ethanol is a major by product and the production and sale of ethanol is a much more profitable enterprise than selling molasses. It has advantages in being a green source of renewable energy with reduced emissions as compared to gasoline. The estimated ethanol sales revenue in India as expected to be 15000 Crore INR. A blending capacity of 20% is required by 2025.   In terms of ethanol, India is the fourth largest producer of ethanol after Brazil, the United States and China. Molasses based distilleries are classified as a ‘Red’ category Industry by the Central Pollution Control Board. With the amount of highly polluting, spent wash being generated at 10 to 15 times the volume of spirit produced, it is an area of major environmental concern. A number of treatment and disposal technologies have been suggested. It is widely used as a manure in many countries. The Total installed capacity of molasses based distilleries in the country is about 4230 million litres per annum. The average capacities of Indian Molasses based distilleries ranges between 30 to 60 KLD. There are very few distilleries above 100 KLD and the largest distillery capacity is 420 KLD. (Office of Principal Scientific Advisor to the GOI, 2014)These Distilleries have a capcity to generate about 52000 M.Ltr/year of spent wash as waste annually.

The Manufacturing Process

Alcohol, in molasses based distilleries is manufactured by the fermentation of molasses in batch, continuous or bio still processes. The batch process involves diluting the molasses to reduce the sugar content from the existing 40-45% to 10-15%. Yeast inoculum is then mixed with this diluted molasses at about 10% concentration, volume/volume (v/v). This is then allowed to ferment for 30-40 hrs. After the fermentation is complete, the yeast sludge is removed from the bottom of the fermenter and the fermenter wash is sent to the analyser column for distillation with steam. A mixture of alcohol vapours and steam is collected at the top of the analyser column and spent wash drained out from the bottom. The alcohol and steam mixture are fed to the rectification column where water and alcohol vapours condense and rectified spirit is formed. The condensed steam is discharged as spent lees.

The continuous process recycles the yeast and the processes of fermentation and distillation are coupled to get a continuous flow of fermented beer for the distillation column. The yeast here is more active and the alcohol yields higher. Biostill is a trade name for one of the continuous processes where molasses is fed to the fermenter at a constant flow rate.

Fuel alcohol or absolute alcohol is produced by the dehydration of rectified spirit through azeotropic distillation or molecular sieve technology. The azeotropic distillation method involves the use of entrainer compounds like trichloroethylene, benzene, toluene, cyclohexane etc. which make the water in the azeotropic mixture of alcohol and water (96:4) more volatile allowing the water from the heterogeneous azeotropic mixture to be removed by decantation and dehydrate the alcohol. The regeneration column allows the water and the entrainment compound to be separated and the entrainer used back in the process. The molecular sieve technology works on the principle of Pressure Swing Adsorption (PSA) and removes water by adsorption on the surface of molecular sieves (zeolite balls) under vacuum.

Distillery operations use water both for process and non process uses. The process applications involve yeast propagation, preparation of molasses for fermentation and steam requirements for distillation and the non-process applications include cooling water, wash water, boiler water and water used in making potable alcohol. Waste waters are discharged as spent wash from the analyser column, fermenter sludge, spent lees, cooling water, waste wash water, water treatment plant, boiler as blow down, bottling plant and other wastes.

The resource utilisation efficiency has a high impact on environmental performance and profitability.  There is a need for the bad performers to emilate the better performers.

Composition of effluents   

Average spent wash generation is lowest in the bio still process (6 to 8 liter per liter alcohol), higher in the cascade continuous process (8.5 to 11.0 liter per liter alcohol) and highest in the batch process (11.1 to 15.0 liters per litre alcohol). It is possible to reduce the spent wash generation to 3.0 to 5.5 litres per litre of Ethanol produced through the cascade and Biostil continuous fermentation coupled with an integrated heat recovery system. The concentration of contaminants from the Biostil process is however the highest. The concentration of pollutants is highest in the bio still process. It has been reported that the 45 billion liters of spent wash produced in the country annually have a potential to produce 1,200 million cubic meters of bio gas (containing 60% methane) and the post methanated water if used carefully can produce more than 85,000 tons of bio mass annually. It has also been estimated that utilization of spent wash may provide 5 trillion KCals energy annually and the post methanated effluents can provide 2,45,000 tons of Potassium, 12,500 tons of Nitrogen and 2,100 tons of Phosphorous annually and one year’s effluents can meet the Potassium requirement of 1.55 million hectare land, Nitrogen requirement of 0.13 million hectares and Phosphorous requirement of 0.025 million hectare lands if two crops are taken in a year.

Spent wash exhibits a very high level of Biological Oxygen Demand (40,000 to 65,000 mg/L) and Chemical Oxygen Demand (50,000 to 1,40,000 mg/L) with a high BOD: COD ratio. It is highly acidic with a pH of 3.0 to 4.5. The recalcitrant nature is due to the presence of melanoidins, caramel, polyphenols and a variety of sugar decomposition products such as anthocyanin, tannins and different xenobiotic compounds. The obnoxious odour may be due to the presence of skatole, indole and other sulphur compounds. Evaporated spent wash may contain a dry matter of about 30.5%. Spent wash also contains the major plant nutrients like Total Phosphorous as P₂O₅ (400-600 mg/L), Total Potassium as K₂0 (10,000-13,000 mg/L), Total Calcium (2,100-3,000 mg/L), Total Magnesium (2,000-3,300 mg/L), Total Sulphur (4,000-5,000 mg/L). Spent wash may also contain metal ions like Zinc, Iron, and Manganese. Organic compounds extracted by alkaline reagents are reported to be of humic nature and similar to these in soil except folic acid which predominated over humic acid. Spent wash has also been reported to contain vitamins (largely group B), proteins rich in exogenous amino acids and mineral components. Although it does not contain any toxic substances, yet the discharge of this highly polluting effluents to streams causes immense damage to the flora and fauna. The high COD, Total Nitrogen and Phosphate contents of spent wash can result in eutrophication of natural water bodies. The methane emission factor for distilleries is 0.2 kg/kg COD.  Molasses based Brazilian distilleries also produce spent wash (vinasse) having a high organic matter content, high Potassium (3.5 to 7.6 kg per m³ of vinasse), relatively poor Nitrogen (0.75 to 0.79 kg per m³ of vinasse), Phosphorous (0.10 to 0.35 kg per m³ of vinasse) and Magnesium (0.84 to 1.40 kg per m³ of vinasse).

The BOD of distillery effluents in Australia may be as high as 35,000 mg/L, a total Kjeldahl nitrogen content ranging from 500 to 1,700 mg/L, total Phosphorous 100 to 400 m/L and 1,300 to 2,100 mg/L of Potassium.

Environmental Impacts

Raw spent wash discharge has a highly deleterious effect on fish life. Spent wash also contains significant amounts of recalcitrant compounds which severely pollute the receiving bodies of water and present a serious health hazard to the rural and semi-urban population that depend on such water bodies for drinking water and other requirements. Waste waters are also a source of green house gas emissions (CO₂, methane and nitrous oxide).

Spent wash Treatment

Various technology options are available for the treatment of distillery spent wash. They may include biomethanation, biomethanation and secondary treatment followed by irrigation or disposal in surface water, composting after or without biomethanation, activated sludge treatment, concentration and incineration, anaerobic digestion followed by evaporation and composting, co-incineration, reverse osmosis, multi effect evaporators, recovery of potash or disposal into sea or estuary after or without biomethanation.

Distillery spent wash treatment of the yesteryears revolved round the open lagooning system with its inherent problems of land, odour and seepage into use and degradation and the ground water. Subsequent technologies, from bio-methanation to co-incineration which utilise the energy generating and fertility potential of spent wash, have improved the management of distillery spent wash to change it into an environmentally friendly, socially acceptable, Zero effluent discharge industry.

The cost of anaerobic bio-digesters can be recovered in 2 to 3 years of installation because of substantial savings in fuels. The generally used reactors are the up or down flow fixed film reactors, up flow partially fluidized bed reactors commonly called the up flow anaerobic blanket reactors and slurry reactors. These reactor systems are capable of bringing down a reduction in influent BOD by about 90 to 95% and produce biomethanated effluents with a BOD of about 500 mg/L and gas @ 0.4 to 0.5 m³/kg COD removed which can be used on fuel. Continuous stirred reactors and UASB based digesters have proved to be more suitable than media based and thermophilic digesters. Coupled with Biogas based cogeneration, regeneration of power steam and chilled water and the production of bio compressed natural gas, higher value additions can be obtained. The UASB reactors have been observed to produce methane with high efficiency, a better quality effluent and stable sludge and  have been suggested as one of the best options for treatment of distillery waste water, with or without dilution.

In order to gainfully utilize the biomethanated spent wash and/or make it suitable to conform to the requirements of Zero effluent discharge, distilleries generally adopt the practice of anaerobic digestion of spent wash followed by composting. If sufficient filler material (Press mud) is not available the effluent quantities are reduced through reboilers/evaporation/RO to match the quantity of press mud. The concentrated effluent can also be dried in spray driers as powder which can be sold as a fertilizer.

Secondary biological treatment processes (two stages) may also be used after biomethanation to reduce the BOD. The activated sludge process is generally used. Final BOD concentrations of 300 to 500 mg/L can be achieved. Further dilution may be required if it is used for irrigation. Ferti-irrigation requirements may be different from these. Bio filtration systems have also produced impressive results. Here the microorganisms are not suspended in the medium but separated from it and immobilized to the bedding material while the treated effluent flows through it.

Hybrid Anaerobic Baffled Reactors (HABR) along with advanced oxidation to reduce COD from distillery wastes has also been tried. A two stage system could produce a COD of 6,000 mg/L from an initial value of 82,000 mg/L. It is coupled with production of gas and makes the effluents colorless and fit for irrigation.

Membrane bio reactors are also being recognized as an effective method of treatment of distillery wastes. The COD removal efficiency has been reported at 94.7%.

Ultrafiltration and Reverse Osmosis processes have been successfully used for the removal of colour and other contaminants from the distillery effluents. Permeate from the U.F. was also used as a feed for Reverse Osmosis. Nano filtration followed by R.O. hybrid process could be successfully used for the removal of TDS, colour and COD of spent wash.

 The disc and tube membranes have been successfully used. There are about 100 distilleries in India that are operating R.O. plants to treat their anaerobically digested or raw vinasse. The permeate can be recycled after proper treatment (aeration to remove dissolved gases and activated carbon adsorption) as make up water for cooling towers for molasses dilution. The operational cost is slightly less than that for the MEE with 50% reduction.

The technique generates about 50% colorless reusable water and the balance 50% concentrate which can be easily composted by available press mud. The concentrated stream contains almost double the levels of COD, BOD and TDS.

Clarification of vinasse by a combined treatment of coagulation/flocculation followed by activated carbon adsorption has been tried in Brazil. Although significant reduction in colour, turbidily and COD have been observed after coagulation/flocculation yet it failed to remove phenolic compounds. The colour and turbidity also increased after adsorption because of proliferation of yeast cells during adsorption. This adsorption process was not found to be efficient.

Multi effect evaporation is being utilised for water removal and a concentration of 30% can be obtained through present technologies. MEE plant concentrates with a solid content of 33% to 34% may have have very high BOD, COD and TDS. The MEE plants are however susceptible to scaling which may be difficult to remove and the process condensate requires polishing. Concentrated spent wash at 55 to 60% solids or vinasse powder can be successfully used to generate steam in specially designed boilers and the steam can be used to generate electricity and in plant operation. This technology does not appear to have been established yet in India. Condensates generated from volume reduction of distillery spent wash in multi effect evaporators may contain large amounts of volatile organic compounds causing the COD levels to be as high as 8000 to 10000 mg/L and a volume of about 800 to 1000 cubic meters in a 300 KLD distillery. Spent lees with a volume of about 300 KL in a 300 KLD distillery, is also expected to have a high COD of about 8000 to 16000 mg/L. With a BOD of more than 50% of the COD, these wastes can be treated biologically. Anaerobic digestion followed by a two stage activated sludge process coupled with tertiary treatment through multi media filtration has been tried in some experiments. An overall COD reduction of 96% of the COD has been indicated. It has been claimed that waste waters so treated could be reutilised and replace the water demand by almost 80%. The amount of investment requirement for the project was about 1 to 2% of the capital cost of the distillery.

 It has been estimated that concentrating and treating spent wash may involve an expenditure of 400% of the distillery cost .Concentration and incineration is estimated to make the production of Alcohol dearer by Rs. 8-10 per litre of Alcohol produced as compared to the more sustainable technologies.

Spray evaporation, used by some distilleries presents a possibility of suspended particles getting carried away and impacting ambient air quality. State Boards are not allowing this method of vinasse disposal.

It is also possible to gasify concentrated vinasse as such or in combination with other biomass and generate syngas and biochar.

During concentration and incineration the large quantum of spent wash is reduced by increasing the viscosity then finally it is dried as ash in furnace chambers to let out as solid material. Concentrated spent wash at 55 to 60% solids or spent wash powder can be used to run a specially designed boiler with or without subsidiary fuel. Steam generated can be used to run a steam turbine to generate electricity and exhaust steam can be used for distillery and evaporation plant operation. Distiller’s wet gram still age from the MEE can also be used as cattle feed. Concentration and incineration systems are economically better for distilleries beyond 60 KLPD capacity.

Concentration and incineration technologies however present problems of disposal of sludges from storage tanks, condensates from evaporators and rejects from the RO plant. The co-incineration initiative of the CPCB involves incineration of concentrated spent wash as fuel in cement/steel industries along with other fuel/raw materials. This facilitates destruction of wastes at higher temperatures of 1,200 to 1,400 ^oC and incorporation of the inorganic contents of the pollutants in the clinker. Any acidic gases released are neutralized in the kiln.

Decolorization by capillary seepage system through mobilized whole cells incorporated in artificial soil bed and bio methanation coupled with decolourisation and crop cultivation in artificial soil bed  has been suggested to be a novel design system which could deliver zero discharge with good ROI through crop cultivation. Many fungi and bacteria have been successfully screened to give upto 44% reduction in COD, either singly or in combination. Some workers report a high COD reduction of up to 99% during simultaneous decolorization and crop cultivation. The soil from the bed could be sold in for kitchen  and terrace gardens.  Pseudomonas fluorescence, Enterobacter, Aeromonas, Acinetobacter and Klebsiella have been reported to give a maximum of 44% COD reduction either singly or in combination. Several types of fungi have also been found useful.

High rate transpiration technology has also been employed to treat distillery effluents. HRTS is a land application system wherein the waste water is applied in specially designed field layouts with wide ridges and furrows. Trees with a high transpiration rate are planted in the ridges while the waste water is allowed to flow through furrows. The high transpiration rate provides a bio-pump. NEERI has recommended this system as being a cost effective and environmentally acceptable solution to manage coloured waste waters. The HRTS has various environmental benefits ranging from waste treatment, reuse of effluents, biomass production and  prevention of air and water pollution. Wet land plants like Phragmites karka have also been  successfully tried for treatment of distillery waste waters both during the post monsoon (hydraulic load of 300 m3/ha/day, COD 10000 mg/L) and premonsoon periods. (Hydraulic load of 500 m3/ha/day with a COD of 10000 mg/L).

Arbuscular Mycorrhizal symbiosis plays an important role in phyto remediation. The system enhances the interface between plants and the soil environment through the fungal mycelia radiating from the colonized root cortex far into the surrounding soil which enhance the uptake of macro nutrients and micro nutrients. Mycorrhiza also help to improve the structure of the soil and act as filters reducing toxicity impacts on plants. They also influence the physiology of their host plants and make them less susceptible to pathogens, soil pollution, salinity, drought and a number of other environmental stress factors.

Coagulation and fungal application to biomethanated spent wash to remove color (85%) and COD (75%) has been successfully tried. The electrocoagulation process has been applied to biomethanated spent wash using aluminum anode and stainless steel cathode. A removal of 99.4% color and 77.58% COD has been reported in 6 hours.

The electro dialysis reversal process uses mild electricity to transmit ions and other charged species through membranes. This gives separate purified and concentrated streams.

The rich nutrient contents of spent wash make its use in agriculture very viable. Pre-sown land application, bio-composting and ferti-irrigation have been variously applied. These technologies had been accepted for implementation through the Charter for Corporate Environmental Responsibility decided between the CPCB and Distillers. Sugar mill effluents may be used as a suitable diluent for spent wash to reduce the pollution load and subsequently used in fertigation with a 1:1 dilution ratio, the BOD has been expected to come down to 3600 mg/L from 51023 mg/L, COD to  62075 mg/L from 90179 mg/L and TDS to 32700 mg/L from 72090 mg/L.  The Central Pollution Control Board is however not encouraging stand alone distilleries to practice these technologies. However, distilleries attached to sugar units may follow biomethanation and bio-composting and concentration and incineration technologies. It has also been suggested that attached distilleries which are not achieving the standards should changeover from composting, one time land application and ferti irrigation in a time bound manner.

Some authors believe that distillery effluents being full of renewable energy, organic nitrogen and micro nutrients could be used as an alternative feed substitute in feeding of dairy animals. It has been suggested that 10% of grains could be replaced with bio methanated distillery spent wash in the diet of growing calves without any adverse  effect on intake, utilisation of nutrients and blood metabolites.

Soil reclamation is another technology for utilization of distillery spent wash. Application of 500 m³/ha of spent wash to sodic soils followed by 2 to 3 leaching with water achieved effective reclamation after 60 days with a reduction in soil pH and increase in organic carbon content, available nutrient and microbial activity.

Spent wash has also been used in the preparation of flyash bricks. Some workers have evaluated the compressive strength of flyash bricks where spent wash was used instead of water. It was found that the spent wash treated bricks gave a higher stregth  as compared to standard flyash bricks.

Waste materials, such as effluent from pulp and paper mill and distillery industries, converted into sugars by pretreatment methods such as acid or enzymes are frequently used across the world for the production of Alcohol. The use of sucrose containing distillery effluents also allows the production of Ethanol at low costs through enzymatic hydrolysis and fermentation.  One of the most successful methods for ethanol production from distillery effluents is combination of the enzymatic hydrolysis of pretreated distillery effluent and fermentation in one step, termed simultaneous saccharification and fermentation using Bacillus species prior to S. cerevisae.

The National Green Tribunal has in its judgement passed on 13-07-17, restrained  the regulatory authorities from prescribing zero Liquid Discharge and online monitoring systems across the Board. Instead the regulatory authorities have been asked to ensure that the standards are met and ZLD, if necessary, applied on a case to case basis after giving due consideration to technology, financial viability, limitation of the unit and the processes adopted by the Industry but in all circumstances, ensuring that the discharge of effluents from the unit has to be in strict conformity to the prescribed standards.

Also See:

• Distillery Effluents Utilisation in Agriculture
• Using Distillery Spent Wash For One Time Controlled Land/Presown Land Application
• Using Distillery Spent Wash For Ferti Irrigation
• Using Distillery Spent Wash For Bio-composting
• Some International Practices on the Use of Distillery Spent Wash in Agriculture
• Using Distillery Spent in Sodic Land Reclamation