One of the most important environmental problems faced by the world is management of wastes. Industrial processes create a variety of wastewater pollutants; which are difficult and costly to treat. Wastewater characteristics and levels of pollutants vary significantly from industry to industry. Now-a-days emphasis is laid on waste minimization and revenue generation through byproduct recovery. Pollution prevention focuses on preventing the generation of wastes, while waste minimization refers to reducing the volume or toxicity of hazardous wastes by water recycling and reuse, and process modifications and the byproduct recovery as a fall out of manufacturing process creates ample scope for revenue generation thereby offsetting the costs substantially. Production of ethyl alcohol in distilleries based on cane sugar molasses constitutes a major industry in Asia and South America. The world’s total production of alcohol from cane molasses is more than13 million m3/annum. The aqueous distillery effluent stream known as spent wash is a dark brown highly organic effluent 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 extremely high COD and BOD values. 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 treatment alternatives for disposal of the distillery wastewater.
KEYWORDS
Distillery Spentwash, Revenue Generation, Byproduct Recovery.
INTRODUCTION
Production of ethyl alcohol in distilleries based on cane sugar molasses constitutes a major industry in Asia and South America. The world’s total production of alcohol from cane molasses is more than13 million m3/annum. The aqueous distillery effluent stream known as spent wash is a dark brown highly organic effluent 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 extremely high COD and BOD values. Because of the high concentration of organic load, distillery spent wash is a potential source of renewable energy.
The 295 distilleries in India produce 2.7 billion litres of alcohol and generating 40 billion litres of wastewater annually. The enormous distillery wastewater has potential to produce 1100 million cubic meters of biogas. The population equivalent of distillery wastewater based on BOD has been reported to be as high as 6.2 billion which means that contribution of distillery waste in India to organic pollution is approximately seven times more than the entire Indian population. The wastewater from distilleries, major portion of which is spentwash, is nearly 15 times the total alcohol production. This massive quantity, approximately 40 billion litres of effluent, if disposed untreated can cause considerable stress on the water courses leading to widespread damage to aquatic life.
ALCOHOL MANUFACTURING PROCESS AND NATURE OF DISTILLERY WASTEWATER
In India bulk of the alcohol is being produced from sugar cane molasses. Molasses is a thick viscous byproduct of the sugar industry which is acidic in nature, rich in salts, dark brown in colour and it also contains sugar which could not be crystallized. For manufacturing alcohol, the Molasses is diluted with water into a solution containing 15-16 % of sugars. This solution is then inoculated with yeast strain and is allowed to ferment at room temperature. The fermented wash is distilled in a series of distillation columns to obtain alcohol of adequate/ requisite strength and quality/specification. This alcohol is used for various purposes including potable and industrial. For manufacture of alcoholic beverages, the alcohol is, if required, matured and blended with malt alcohol (for manufacture of whisky) and diluted to requisite strength to obtain the desired type of liquor/ Indian Made Foreign Liquor (IMFL). This is bottled in bottles of various sizes for the convenience of consumers.
S.No. | Parameter | Range |
1. | pH | 4.3-5.3 |
2. | Total Suspended Solids | 12,000-14,000 |
3. | Total Dissolved Solids | 45,000-75,000 |
4. | B.O.D., 20 0C, 5 days | 40,000-50,000 |
5. | C.O.D. | 80,000-1,00,000 |
BIO-ENERGY POTENTIAL FROM DISTILLERY EFFLUENTS
In India there are 295 distilleries producing 3.20 billion litres of alcohol generating 45 billion litres of wastewater annually. The enormous distillery wastewater has potential to produce 1200 million cubic meters of biogas. The post methanation wastewater if used carefully for irrigation of agricultural crops can produce more than 85000 tonne of biomass annually. This biogas normally contains 60% methane gas, which is a well-recognized fuel gas with minimum air pollution potential. If this source of energy is tapped, it will fetch additional energy units worth 5 trillion-kilo calories annually. Besides, the Post Methanation Effluent (PME) can provide 245000 tones of potassium, 12500 tones of nitrogen and 2100 tones of phosphorus annually. Thus the manorial potential of effluent can be measured by the fact that one year’s effluent can meet the potassium requirement of 1.55 million hectare land, nitrogen requirement of 0.13 million hectare land and phosphorus requirement of 0.025 million hectare land if two crops are taken in a year.
Annual Bio energy Potential of Distillery Effluent in Various States of India | |||||||
State | Units | Capacity (M Ltr/Yr) | Effluent (M Ltr/Yr) | Biogas (M m3) | Total N (tones) | Total Ka (tones) | Biomass (tones) |
A P | 24 | 123 | 1852 | 50 | 566 | 11115 | 3704 |
Assam | 1 | 2 | 24 | 0.7 | 7 | 144 | 48 |
Bihar | 13 | 88 | 1323 | 35.7 | 397 | 7940 | 2646 |
Goa | 6 | 15 | 218 | 6 | 65 | 1304 | 436 |
Gujarat | 10 | 128 | 1919 | 51.8 | 576 | 11511 | 3838 |
Karnataka | 28 | 187 | 2799 | 75.6 | 840 | 16794 | 5598 |
M P | 21 | 469 | 7036 | 190 | 2111 | 42219 | 14072 |
Maharashtra | 65 | 625 | 9367 | 253 | 2810 | 56217 | 18734 |
Punjab | 8 | 88 | 1317 | 35.6 | 395 | 7902 | 2634 |
Tamilnadu | 19 | 212 | 3178 | 86 | 953 | 1971 | 6356 |
U P | 43 | 617 | 9252 | 250 | 2776 | 55512 | 18504 |
W B | 6 | 24 | 371 | 10.1 | 111 | 22223 | 742 |
Rajasthan | 7 | 14 | 202 | 3 | 61 | 1215 | 404 |
Kerala | 8 | 23 | 343 | 9.3 | 103 | 2064 | 686 |
Pondicherry | 3 | 11 | 165 | 4.5 | 50 | 990 | 330 |
Sikkim | 1 | 7 | 98 | 5.5 | 29 | 585 | 196 |
Nagaland | 1 | 2 | 24 | 0.7 | 7 | 144 | 48 |
J & K | 7 | 24 | 366 | 11 | 110 | 2196 | 732 |
H P | 2 | 3 | 39 | 1 | 12 | 234 | 78 |
Haryana | 5 | 41 | 615 | 16.6 | 185 | 3690 | 1230 |
Total | 285 | 2703 | 40,508 | 1096.1 | 12,154 | 263,070 | 81016 |
PRESENT STATUS OF TREATMENT AND DISPOSAL
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 stillage 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 unfavourable 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. Many distilleries in India are allowing their effluent for application on land as direct irrigation water, spent wash cake and spent wash-press mud compost. The advances manifesting the possibilities of energy conservation are also discernible in the case of distilleries. The methane gas generated in the digesters is used as a fuel to compensate the energy needs of the industry. A general estimate suggests that the cost of an anaerobic biological digester is recovered within 2-3 years of installation because of substantial saving of coal and other fuels.
COST RECOVERY METHODS FROM THE DISTILLERY EFFLUENTS
The wastewaters generated during the distillery and brewery operations contain high organic loads. It has a BOD from 30,000 to 60,000 mg/1. So due to this high organic contents, the wastewaters can be subjected to treatment for the production of biogas, composting, aquaculture and potash recovery.
(a) BIOGAS. For the production of biogas from distillery effluent, anaerobic biomethanation of the effluent is adopted, generally. High rate anaerobic technologies are utilized for biogas generation. Fluidised Bed Reactors and Up flow Anaerobic Sludge Blanket (UASB) Reactors are mostly utilized for the production of biogas from the effluents. Some of the biogas production processes being commercial1y established in India at present are:-
· BIOTHANE PROCESS: This process uses the UASB reactor for the production of biogas. This is a stable and automatic process with low operational costs.
· BIOBED PROCESS: It is similar to Bio thane process. It uses UFB reactors. It needs less installation area and its construction cost is lower compared to any other system.
· BIOPAQ PROCESS: In this process anaerobic bacteria are used to treat the distillery effluents for the production of biogas. UASB process is utilized here. The separated sludge in this process makes excellent manure. The generated biogas is used to produce steam for the distillation of alcohol and thus it replaces 50-60% of the total required energy in the process of distillation. For a plant having 40-45,000 kg COD/day 75-80% of COD can be reduced and nearly Rs. 25.50 lakhs can be saved annually for a distillery having 300 working days in a year. The generated biogas from UASB reactor of BioPaq process can be collected and be used as a fuel in gas/dual engine. Through suitable coupling the engine can be coupled with the A/C generator for generation of electricity from biogas. For a 45 klpd distillery 11 KV of power is generated which is then utilized in the distillery thus cutting down the power consumption.
· SULZER' S PROCESS: The technology of this type of biogas plant is provided by Sulzer Brothers Limited, Switzerland. It is specifically made for Indian conditions. A biogas plant at the distillery of Padmashri Dr. Vitthalrao Vikhe Patil S.S.K. Ltd., Pravaranagar, Ahmednagar District, Maharashtra is based on Sulzer's technology. The capacity of this distillery is 6,000 lpd which generates 900 m3 of spent wash per day. The biogas production is in the range of 16,550 to 21,870 m3 per day. The savings in the cost of fuel is in the range of Rs. 312 lakhs to Rs. 652 lakhs per year.
o ECONOMICS OF THE BIOGAS PLANT OF SULZER’S DESIGN
These calculations are made for a distillery producing 30,000 litres of alcohol per day. The effluent characteristics are for conventional batch type fermentation process.
o EFFLUENT CHARACTERISTICS
Before Treatment After Treatment
Flow m3/day 450 450
pH 4.0 to 4.5 7.0 to 7.8
BOD mg/l 45,000 to 50,000 6,000 to 8,000
COD mg/l 80,000 to 1000,000 25,000 to 35,000
o PERFORMANCE
Reduction of BOD % 80 to 85 %
Reduction of COD % 65 to 70 %
Biogas Production Nm3/day 12,300
Specific Biogas Production Nm3/kg of COD degraded 0.4 to 0.5
% of methane in biogas 60 to 65 %
o ECONOMICS
Calorific value of biogas 6000 Kcal/ Nm3
Calorific Value of Coal 4000 Kcal/Kg
Coal equivalent of Biogas per day 18.45 tonnes
Cost of Coal at Rs 1800 per tonne Rs 33,210 pd
Annual fuel savings Rs 99.63 lacs
Capital cost of plant Rs 230 lacs
Interest at 15 % on 75 % of the capital cost** Rs 26,73,750
Maintenance costs Rs 2,00,000
Staff Salary Rs 1,50,000
Power 40 KW at Rs 2/- per unit Rs 5,76,000
Total Annual Cost Rs 36,00,000
Net Savings per year Rs 99.36 – 36
= Rs 63.63 lacs
Total Pay back period = 230 / 63.63
= 3 to 4 years.
(b) COMPOSTING In this process, press mud generated from sugar mill is utilised to produce compost by mixing distillery effluent. Both anaerobic and aerobic composting systems are practiced. In some plants composting with treated effluent treated through bio-methanation plant is also practiced. This system can achieve zero effluent if the press mud quantity matches with the effluent generated.
· ECONOMICS OF BIOEARTH COMPOSTING
Capacity of the Distillery 50 KLPD
Number of working days in a year
In the Distillery 300
In the Composting Plant 275
Generated spentwash 350 KLPD (Biostil Plant)
Solid content in spentwash 17 %
Spentwash to Press mud Ratio 2.5 KL : 1 MT
Man Power Required 50
Culture Requirement 31.5 MT/annum
Press mud requirement 43,000 MT/ annum
Cost of Culture Rs 1.75 lakhs per MT
Cost of Press mud Rs 12 per MT
Man Power cost Rs 50 per day
Capital Cost Rs 175 lakhs (excluding land)
Land Requirement 25 acres
Bio Earth Production 38,000 MT per year
Annual Maintenance Costs 1.5 % of equipment costs
% Costs of Funds 20 % per annum
· OPERATION COSTS
Cost of Culture 55.13 lakhs
Average Cost of Funds 17.5 lakhs
Cost of Diesel 11.32 lakhs
Cost of Press mud 5.16 lakhs
Cost of Transportation of Press mud 0.00
Annual Man Power Cost 6.88 lakhs
Depreciation (@ 10 %) 15.00 lakhs
Maintenance 2.25 lakhs
Annual Operational Cost of Compost Plant 113.24 lakhsCost of One Metric Tonne of Bioearth =Annual Operational cost of plant
 |
Compost Produced in MT
= 11324000 38000
= Rs 298.00 per MT
· NET COST/BENEFIT FOR DIFFERENT SELLING PRICES OF COMPOST
SP of Bioearth Net Cost / Benefit
in Rs in Rs
0 -11324000.00
100.00 -7524000.00
200.00 -3724000.00
298.00 0.00
350.00 1976000.00
400.00 3876000.00
500.00 7676000.00
Net annual cost/benefit of Compost = Sales value of 38000 MT of compost less annual operating costs
· COMPUTATION OF PAY BACK PERIOD
1. SP of Bioearth - Rs 250.00
Initial cash outflow - Rs 17500000.00
Net annual cash inflow - Rs 1738000.00
Pay Back Period - 10.06 Years (17500000/1738000.00)
2. SP of Bioearth - Rs 350.00
Initial cash outflow - Rs 17500000.00
Net annual cash inflow - Rs 5226000.00
Pay Back Period - 3.34 Years (17500000.00/5226000.00)
3. SP of Bioearth - Rs 500.00
Initial cash outflow - Rs 17500000.00
Net annual cash inflow - Rs 10926000.00
Pay Back Period - 1.6 Years (17500000.00/10926000.00)
(c) POTASH RECOVERY It is done by incinerating the distillery spent wash. In this process, the raw distillery spent wash is first neutralized with lime and filtered. This is further concentrated to about 60% solids in multiple-effect forcer circulation evaporators. Now this thick liquor from the evaporator is burnt in an incinerator and is converted into ash. The dry solids of the spent wash in the form of coke in the incinerator has an average calorific value of 2 Kcal/kg, which is sufficient for supporting self-combustion of the thick liquor in the incinerator. The resulting ash is found to contain about 37% of potash as potassium oxide on an average. This ash is further leached with water to dissolve the potassium salts. Then it is neutralized with sulphuric acid and is evaporated. The potassium salts are crystallized in a crystal1izer. The crystallized mixed potassium salt contains 73.5% of potassium sulphate (K2SO4) 16.5% potassium chloride (KCl) and 5% of sodium salts. It is estimated that a distillery discharging about 300 m3 of spent wash per day could recover 3 tonnes of Potassium as Potassium oxide or about 5.34 tonnes of Potassium sulphate and 1.2 tonnes of Potassium chloride per day. This potassium is used as a fertilizer.
(d) DISTILLERY WASTEWATER UTILISATION IN AGRICULTURE Being very rich in organic matters, the utilisation of distillery effluents in agricultural fields creates organic fertilization in the soil which raises the pH of the soil, increases availability of certain nutrients and capability to retain water and also improves the physical structure of soil. Mostly the distillery wastewaters are used for pre-sowing irrigation. The post-harvest fields are filled with distillery effluents. After 15-20 days, when the surface is almost dried, the fields are tilled and the crops are sown and subsequent irrigation is given with fresh water. However, the effluent is diluted 2-3 times before application on crops. Apparently, the irrigation with distillery wastewater seems to be an attractive agricultural practice which not only augments crop yield but also provides a plausible solution for the land disposal of the effluents. One cubic metre of methanated effluent contains nearly 5 kg of potassium, 300 grams of nitrogen and 20 grams of phosphorus. If one centimetre of post methanation effluent is applied on one hectare of agricultural land annually, it will yield nearly 600 kg of potassium, 360 kg of calcium, 100 kg of sulphates, 28 kg of nitrogen and 2 kg of phosphates. The distillery effluent contains 0.6 to 21.5 percent potash as KO, 0.1 to 1.0 percent phosphorus as PO and 0.01 to 1.5 percent Nitrogen as N2. The irrigational and manorial potential of distillery wastewaters is given below:
i) Total Volume available in Million m3 /annum : 6.87
ii) Nutrients Contribution Potential (tonnes/annum) :N - 69380
PO - 11335
KO - 27480
· ECONOMICAL ASPECTS
When the distillery effluents are used for irrigation in fallow lands, the microbes present in it transform the lands into fertile ones, giving high yields of paddy and sugarcane. Farmers could save nitrogenous fertilisers worth Rs 1335 crores per annum if at least 200 distilleries of out country recycled their wastes to the agricultural fields. However, it is predicted that the utilisation of distillery effluent for irrigation of land would make available nitrogen, phosphorous and potash valued at about Rs 500 crores each year. The added advantage of this application would be that these fertilisers would be available to soil in organic form. As the secondary and tertiary systems for the treatment of distillery effluent are highly energy intensive and according to the estimates of the Union Ministry of Energy a total connected load of 200 M.W. would be required to energising these systems if 246 distilleries endeavour to reduce the BOD level of effluent to the extent possible. The generation of the desired energy would need an installed load of 350 M.W. which would require capital investment of the order of about Rs 1400 crores. So it will be an attractive practice to utilise the distillery effluents for ferti-irrigation of land after primary treatment, as land is available in abundance around the distilleries which are located in the sugarcane belts.
RECOMMENDATIONS
7. Reviewing the magnitude of pollution potential of distillery wastewaters and the experiences gained over years on recovery of residues and treatment of wastewater the following recommendations are made :-
· In-plant control measures for conservation and reuse of water and good house-keeping for prevention of spillage and leakages should be the prerequisite.
· For recovery from the treatment of distillery spentwash, depending on the availability and cost of land in a particular area, simple treatment in anaerobic lagoon to generate biogas followed by treatment in aerated lagoon or oxidation ditch may be considered. Where the availability and cost of land are the main constraints, activated sludge type of aeration treatment in a deep oxidation ditch would be more economical than the conventional or extended aeration sludge process.
· For the treatment of distillery spent wash, removal and/or recovery of yeast should be prerequisite to reduce the load and eliminate certain undue problems in the waste treatment/recovery plants. This recovered yeast can be utilised as a good cattle feed. Recovery of spent grains and yeast and their utilisation as animal feed and feed supplement might be encouraged not only for reducing the pollution load form the wastewaters but also in providing for a reasonable return on their capital investment of the industry.
· Where the availability of land is a severe constraint, evaporation and incineration of distillery spent wash to recover potash would appear to be the only choice. In spite of high capital investment required for such type of plants, heat recovery would defray significantly the organisation and maintenance costs and contribute towards conservation of energy.
· In the countries like ours, where indigenous sources of potash are scarce or not available, recovery of potash from crude ash by evaporation and incineration of spent wash would appear to be an economically attractive alternative. If heat recovery is simultaneously used, the pay back period of the plant can be substantially reduced.
· Anaerobic digestion of spent wash in a closed digester followed by its treatment under an activated sludge process, especially in an oxidation ditch to reduce costs, might be adopted as the most cost-effective system for the distilleries which are located away from sugar factories. Moreover, the treated effluent can be conveniently used for irrigation of cane fields or other crop lands, subsequently.
· Biogas generated from the distillery effluents, can be effectively utilized in production plant boilers thus saving about 50 to 60 percent fuel/steam. The treated effluent having almost all the potash retained in it may be utilised for irrigation purposes.
· The utilisation of the distillery effluent in agricultural fields will not only enrich these further with essential plant nutrients like nitrogen, phosphorous and potash but also compensate the expenditure on fertilizers for crop growth. This practice will result in revenue generation and further lead to offsetting the costs substantially.
· Similarly spentwash utilization in bioearth composting, where adequate land is available, being a simple process and not involving any heavy machinery is also one of the cost effective methods of disposal. Moreover it is feasible alternative for utilization of treated effluent; as the same generates revenue thus offsetting the costs and further leading to reduction in pay back period.
CONCLUSION
8. One of the most important environmental problems faced by the world is management of wastes.
Now-a-days emphasis is laid on waste minimization and revenue generation through byproduct recovery. Pollution prevention focuses on preventing the generation of wastes, while waste minimization refers to reducing the volume or toxicity of hazardous wastes by water recycling and reuse, and process modifications and the byproduct recovery as a fall out of manufacturing process creates ample scope for revenue generation thereby offsetting the costs substantially.
Now-a-days emphasis is laid on waste minimization and revenue generation through byproduct recovery. Pollution prevention focuses on preventing the generation of wastes, while waste minimization refers to reducing the volume or toxicity of hazardous wastes by water recycling and reuse, and process modifications and the byproduct recovery as a fall out of manufacturing process creates ample scope for revenue generation thereby offsetting the costs substantially.
9. The cost of effluent treatment in distilleries is likely to be compensated substantially by availability of methane gas. Effluent application will reduce the nutrient requirement through fertilisers. However, high salt load, mainly potassium and sulphur, into the soil system may hamper the sustained crop yields due to continued long-term application of effluents. Therefore the effect on crop productivity has to be visualised on long-term and sustainable basis. Application of post methanation effluent suitably diluted according to crop requirements and soil conditions seems to be viable alternative. If all the distilleries present in India resort to biomethanation, then approximately 2.0 million cubic metres of biogas shall be generated per day, with a calorific value of approximately 5000 Kcal/m. This is equivalent to saving of 2240 tonnes of coal per day, in turn avoiding CO of about 3100 tonnes per day.
10. The present study coupled with the corresponding techno market survey has been aimed at reviewing the existing technological status of treatment and disposal of distillery spentwash in our country and comparing with that of the contemporary international technologies, thus identifying the gaps in the technologies and suggesting an action plan for overcoming these. Some relative issues in the areas of quality criteria with respect to gaps in technologies and financial implication in implementing the technological options, has been highlighted in this study. It has to be stressed that recovery from the distillery effluents is a better way to reduce the cost of wastewater treatment for decreasing its pollution level which is actually a very costly affair. So this is a matter great importance for the Indian distilleries and breweries. Various recommendations are given for the establishment of recovery plants in India. It has also been elucidated during the study that several technological options that are available in our country need to be exploited to the maximum so that, this will help to control the pollution created by the distillery wastewaters and also enable to derive by-products which are commercially beneficial.
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