Management of Spent Wash in Distilleries

Published on 02/09/2014

First Update 16/03/2017

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 flavoring, 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. In terms of ethanol, India is the fourth largest producer of ethanol after Brazil, the United States and China and if the 5 percent blending of Petrol/Motor Fuel is made mandatory all over the country, the available molasses may be unable to meet the demand. Currently the 5 percent blending is only applicable in 10 States and three Union Territories and requires about 410 million liters of anhydrous alcohol. Increments in both percent blending and geographical spread are anticipated. 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 recent report suggests that there are 325 molasses based distilleries in the country producing 3063  million litres/year (M.Ltr/year) of alcohol and generating 45945 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.

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). 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 K Cals 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).

Environmental Impacts

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). Obnoxious odours and leaching into ground water are also major concerns.It was once regarded as the Environmentally most obnoxious industry.

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, irrigation 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.

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%.

Reverse Osmosis and Membrane Filtration have also been advocated and practiced in distillery effluent treatment. 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.

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.

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.

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.

 1.      Utilisation in Agriculture –The most sustainable option

Distillery spent wash does not contain any toxic heavy metals and being of plant origin and rich in  nutrient contents may serve as a good fertilizer for crops, more effective than inorganic or mixed fertilizers being used by farmers. Distillery effluents were once regarded as the most highly polluting effluents. The energy, fertilization and irrigation potential of distillery effluents has helped the industry to build immense social acceptability now. Distillery effluents are a rich source of Nitrogen, Phosphorous and Potassium. Potassium is the most richly represented. It also has appreciable quantities of micro nutrients. Being organic in nature, the nutrients are more rapidly taken up by plants from soil. They also contain large amounts of Ca, Mg, Na, S and Chlorides which can be used as a resource for crop production and reduce the use of inorganic fertilizers. Some authors have observed that spent wash irrigation may also lower the incidence of insect pests. Distillery effluents have been found to be more effective than a mixture of inorganic fertilizers and cow dung manure. The current technologies of concentration incineration and concentration need heavy expenditure and the potash and other salts present may create a fouling in the evaporators and boiler heat transfer sections. The rich organic and inorganic constituents allow spent wash to bring remarkable changes in the physical, chemical and biological properties of soil. Distillery effluents are used as a supplement to mineral fertilizer in Brazil. Nutrient recycling through the application of vinasse and filter cake to sugar cane crops in Brazil has reduced the consumption of fertilizers as compared to other crops and in other countries. In Australia spent wash is blended with additional crop nutrients and sold as manure. Spent wash could also be used for composting the trash in fields.

The CPCB had prescribed Guidelines for Water Quality Management in January 2008. These guidelines have recognized that the reuse and recycling of wastes for agricultural purpose would not only help to reduce the pollution and requirements of fresh water for such use but also would supplement the much needed nutrients and organic manure to plants. These guidelines also state that the resolution under CREP should also be adhered to.

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. The Central Pollution Control Board is however, through a resolution of May 2008, 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. Crop or soil application is not being encouraged. 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. The CPCB resolution of May 2008 which discourages biocomposting  does not find any demerit in its statement of January 2008 regarding the enormous irrigation and fertilization potential of spent wash.It only says that ferti-irrigation, composting and land application options did not work in rainy seasons. Interestingly the said minutes, which discourage use of spent wash in ferti-irrigation, composting and land application, on the very next page also recognize that “As per CPCB, the bio-compost contains 2.5% nitrogen, 1.8% phosphorus and 3% potassium. Based on the total production of bio-compost produced, the requirement of nitrogen on an all India basis is met up to 6.24%, phosphorus 9.06% and potassium 51.06%. Moreover, the above fertilizer is produced from organic matter substituting the imported chemical fertilizer, which is highly subsidized.”

It has been claimed that the 290 odd distilleries in India produce 40 billion liters of effluents (spent wash) per annum with an annual value of Rs. 500 crores in terms of N, P, K, and S; 150 crores for micro nutrients and organics; a Rs. 100 crores saving in the annual environmental cost; Rs. 100 crores in terms of loss to fisheries; 500 crores savings in water treatment costs, 100 crores in public health and another 100 crores in landscape costs. Energy savings in respect of the secondary and tertiary systems of treatment could be as high as Rs. 1400 crores per annum.

The Ministry of Environment & Forest (MoEF)  launched the Charter on “Corporate Responsibility for Environmental Protection (CREP)” in March 2003 with the purpose to go beyond the compliance of regulatory norms for prevention & control of pollution through various measures including waste minimization, in-plant process control & adoption of clean technologies. The Charter has set targets concerning conservation of water, energy, recovery of chemicals, reduction in pollution, elimination of toxic pollutants, process & management of residues that are required to be disposed off in an environmentally sound manner. The Charter enlists the action points for pollution control for various categories of highly polluting industries. The Task Force was constituted for monitoring the progress of implementation of CREP recommendations/ action points. This was a voluntary and consultative initiative of the Ministry which has recommended the following technologies / processes for spent wash treatment

                    i.            Reboiler

                  ii.            Bio-methanation

                iii.            Reverse Osmosis (R.O) System

                iv.            Multi Effect Evaporator (MEE)

                  v.            Bio-composting and one time controlled land application

                vi.            Ferti-irrigation

              vii.            Turbo Mist Evaporation

            viii.            Concentration and Incineration

The Industry was advised to treat its effluent to achieve zero discharge and no liquid discharge was allowed either on land or in any water body. After thorough study of the processes and technologies, it was left to the industry to adopt any one or combination of 2-3 technologies out of the above mentioned various technologies.

The bio composting system helps distilleries to utilize the sludge materials segregated from the distillery processes, incineration, spent wash and R.O. plant rejects to convert it to valuable bio compost using sugar unit press mud. The falling population of livestock has brought down the availability of Farm Yard manure. Bio-compost is now filling up this gap as an organo-mineral supplement. Bio-compost prepared from distillery spent wash was reported to contain higher Organic Carbon (15.5%), N (2.0%), P (2.5%) and K (3.0%). The pH of the compost was found ideal (7 to 7.5) with a C: N ratio of 15: 1. Application of bio-compost and 50% NPK application was found to have enhanced the available N, P and K status of soil and recorded maximum yields of cane over the yield when 100% NPK was used.   Spent wash-press mud compost has been observed to improve the stability of aggregates and porosity. Composting also assists in the degradation of colored organics in the distillery effluents which also enrich the compost with nutrients specially potassium. In order to provide a balanced nutritional value and enrich it more, the compost could be enriched with the use of rock phosphate, gypsum, yeast sludge, bagasse, sugarcane trash, boiler ash, coir pith and water hyacinth. Both Aerobic and Anaerobic composting techniques have been suggested requiring about 30 days for active reactions and another 30 days for maturing. Spent wash utilization in aerobic composting is more than spent wash consumptions in anaerobic composting. The application of composted sugar industry wastes in the form of bio-compost not only enhances the soil nutrient status and cane yield but also serves as a means for eco-friendly management of industrial by-products. The above fertilizer is produced from organic matter substituting the imported chemical fertilizers which are highly subsidized.

The present CPCB protocol specifies the utilisation of SW as 2.5 ton per ton of press mud, and 3.5 ton per ton of press mud, for 45 and 60 days cycles, respectively. These values depend on the average ambient temperature during the compost cycle and the organic solids content of the SW. Since distilleries are going for concentration of SW used for compost preparation, there is a need to re-evaluate the utilisation rate of the SW and quality of the compost. CPCB may consider sponsoring studies in different regions of the country for this purpose.

The protocol requires that the distillery should not operate for more than 270 days in a year. Presumably because of 90 days of rainy season. The period of closure should correspond to the length of rainy season. In semi-arid areas when the rain is less than 40 cm/year composting may be permitted throughout the year. During incidental rains the leachate shall be collected and pumped back for reuse. Where the rainfall is between 40-100 cm/year, the duration of rainy season may be shorter than 90 days. For areas where the rainfall is greater than 100 cm/year, it may be taken as 90 days.

As per the protocol,storage of raw, biomethanated and /or concentrated SW meant for composting only may be allowed in lagoons of 15 day capacity, to take care of compost yard machinery repairs and variation in seasonal utilisation of SW for composting.

2. Concentration and incineration not found suitable

It was recognized in 2001 by the CPCB that concentrating or drying the spent wash and burning it with ancillary fuel, with energy recovery in the form of steam, is the most attractive alternative as it leaves a small amount of residue, which could be used as a fertilizer. The CPCB however accepts that experience with continuously operating full scale plants is not yet available. The Charter on Corporate Environmental Responsibility for Environmental Protection recognizes this as one of the suggested measures prescribed to be used in combination. Importantly the CPCB does not rely on any one measure totally and prescribes that molasses based distilleries will ensure compliance with any combination of methods.

Only a small number of distilleries, about 27 have adopted concentration and incineration process. In Uttar Pradesh there are just 03 Distilleries which have adopted incineration. This process of concentration and incineration is at present still in a trial phase and is very expensive to adopt with high capex( INR 60 Crores) and also high running cost( Rs. 6-8 per BL of Alcohol) that raises the cost of production of alcohol exorbitantly. In addition this process creates problems of scaling, choking of boilers, frequent failing of furnace refractory material which affects bed fluidization, heavy sludge accumulation  and frequent stoppages of the plant for de-scaling, which hampers not only the production process but also the effluent treatment process as well. Apart from this Installation of special type of boiler which needs to be replaced every 3-5 years due to high wear and tear and quick erosion, disposal of ash after effluent incineration, loss of Bio-Gas are major concerns associated with this technology and the sustainability of this technology may still need to be established

The co-incineration initiative of the CPCB suggested burning concentrated spent wash as fuel in cement/steel industries along with other fuels/raw materials. Co-processing of spent wash concentrate has been recommended to the extent of 3.0 to 3.5% of heat/coal substitution – a concentration up to which co-processing of spent wash has not been considered to influence clinker quality or change kiln behavior. A maximum loading of 1000 Litres per hour has been experimented. This would only mean about 24 KLD of concentrated or about 50 KLD of raw spent wash per day in a 3000 TPD cement kiln.This is a very small quantity as compared to the total spent wash available. Also the availability of willing cement mills, furnaces and TPPs may be limited in the area of the distillery. U.P. has been reported to have 56 molasses based distilleries, with only 1 cement plant and 11 TPPs. This would again support the view of a mix of technologies with bio-composting, ferti-irrigation and one time land application also being considered on account of their ecological and agronomical advantage. Co-processing could however be a preferred option for standalone distilleries and in Karnataka, Madhya Pradesh and Rajasthan where the ratio of cement plants/TPPs to distilleries is higher.

Even though the initial trials on coprocessing appear to be encouraging, the effect of inorganic constituents in spent wash on the finished product is to be assessed and the applicability of the technology for distilleries, which are located far away is to be assessed in terms of cost effectiveness.The guidelines given by the CPCB for co-processing of concentrated spent wash in cement kilns require certain modifications in the cement kilns. The transportation of spent wash from the distillery to the cement factory also require careful handling in tankers specially designed for this purpose. Air pollution concerns have also to be addressed. The co-processing plants have to  be designed, equipped built and operated in such a way as to prevent emission into the air giving rise to significant ground level air pollution; in particular exhaust gases have to be discharged in a controlled fashion by means of a stack, the height of which is calculated in such a way as to safeguard human health and environment.

3. Need to use mix of options

There is a need to use a mix of treatment options with adequate protocols and guidelines so that spentwash can be gainfully utilized for biogas generation, bio-compost, ferti-irrigation, one time land application, irrigation, sodic land reclamation and co-processing. Unit specific combinations could be prescribed based on availability of land, sodic land, clinker manufacturing units and other furnaces etc.