Published on 31/03/2014
First Update 16/03/2017
Distillery Spent Wash
Distillery spent wash is a highly polluting effluent generated from fermentation of molasses to produce alcohol. Molasses based distilleries may have a very high BOD and COD. The recalcitrant nature of spent wash 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 unpleasant odour is due the presence of skatole, indole and other organic compounds. The melanoidins, because of their anti-oxidant properties can make the effluent toxic to many microorganisms. The spent wash may also have high suspended solids, inorganic solids, low pH and a dark brown colour. It also has a high level of inorganic impurities as chlorides, sulphides, phosphates, calcium and potassium.
India has about 620 sugar mills and about 400 molasses based distilleries with an installed capacity of 400 billion litres of alcohol and a potential to generate on an average of 40 billion litres of spent wash. The spent wash generation depends on the type of fermentation process, type of distillation process, distillation with or without reboiler, evaporation systems, molasses quality, yeast culture and recycle. Generation of effluents in the continuous process (6 to 9 LPLA) is less than that in the batch process but the BOD and COD of effluents in the batch process (45000 to 50000 BOD and 80,000 to 1,00,000 COD) is lower than the BOD and COD of effluents in the continuous (55,000 mg/L to 65,000 mg/L BOD and 1,10,000 mg/L to 1,30,000 mg/L COD) and biostill process (60,000 to 70,000 BOD).
The highly polluting nature of spent wash arises from the fact that the high BOD and receiving COD exert an immediate demand on dissolved oxygen of bodies making them anaerobic. With the death of aerobic organisms, the anaerobic biota sets in, creating a fermentative, obnoxious, putrefying environment, where the end products of respiration are gases like H2S, NH3 and hydro-carbons – spreading a stench all round and creating a breeding ground for pathogens and vectors. If disposed untreated on land and in an uncontrolled manner, it may also be hazardous to vegetation and affects ground water quality due to dissolved leachates and colour.
The Fertilisation potential of Spent Wash
In spite of the recalcitrant nature of spent wash and the enormous damage, which may be caused as a result of uncontrolled discharge of untreated spent wash into water bodies and lands, many authors have classified it as a dilute organic fertilizer with 7 to 9% solids and 90 to 93% water. More than 75% of the solids are organic in nature and about 25% are inorganic. The occurrence of nitrogen in a mostly colloidal form allows it to behave as a slow release fertilizer and better than any inorganic source of nitrogen. The presence of phosphorus in the organic form has also enabled a better availability. In a study comparing spent wash to farm yard manure, it has been observed that spent wash solids contained more ether soluble, alcohol soluble and hot water soluble fractions than farm yard manure and a total potassium content almost 12 times higher than farm yard manure. It has been estimated that the 40 billion liters of spent wash being discharged every day could provide 480,000 tonnes of potassium, 52000 tonnes of Nitrogen and 8000 tonnes of phosphorous annually. This manurial potential has further been estimated to meet the potassium requirement of 3 million hectares, nitrogen requirement of 0.25 million hectare and phosphorous requirement of 0.2 million hectare land, if two crops are taken in a year. Because of its high organic matter, the spent wash is also a potential source of bioenergy. If this energy is trapped, distilleries producing 3.2 billion litres of alcohol can generate 5 trillion kilo calories of energy annually. The NPK contents of post methanated effluents are reduced, yet they have a capacity to supply 240,000 tonnes of Potassium, 12,000 tonnes of nitrogen and 800 tonnes of phosphorous annually and meet the potassium requirements of 1.5 million hectare land, N requirement of 70, 000 hectare land and P requirement of 20,000 hectare land. Spent wash also contains large amounts of secondary elements such as Copper (Cu), Manganese (Mn) and Zinc (Zn). It also contains 29.1% reducing sugar, 9.0% protein, 1.5% volatile solids, 21.0% gums, 4.5% combined lactic acid, 1.5% combined organic acids and 5.5% glycerol. The spent wash, being loaded with organic and inorganic compounds could bring remarkable changes in the physical, chemical and biological properties of soils and thus, significantly influence the fertility of soil. Organic compounds extracted by alkaline reagents have been found to be humic in nature and similar to those in soil. They also do not contain any toxic elements or compounds and the highly acidic nature and rich calcium and magnesium contents make them a good agent for reclamation of non saline sodic soils.
The following options appear to be available for the utilization of spent wash in agriculture:
- Biomethanation followed by irrigation
- Biomethanation and secondary treatment followed by irrigation
- Composting after or without biomethanation
- Controlled land application, after or without biomethanation
- Raw spent wash as an amendment to non calcareous sodic soil
The Economics of using spent wash in Agriculture
The practice of applying post methanated effluents in agricultural fields either as presown or post sown appear to be beneficial. Proper balancing for nutrient supply needs to be done to solve the problem of excessive salt loading. The conventional approach to treating effluents even up to secondary or tertiary levels does not provide an environmentally compatible solution. Agricultural utilization of waste water offers a low cost alternative where the manure and irrigation value of spent wash are utilized and savings generated in fertilizers and water use. Farmers could save Rs. 1335 crore per annum that they spend on nitrogenous fertilizers if only 200 of the existing distilleries recycled there wastes to the agricultural fields. The secondary and tertiary treatment systems for distillery effluents are highly energy intensive and may need 350 MW installed load to cater to just the secondary and tertiary systems. This may require a capital investment of the order of about Rs. 1400 crores. The environmental costs of these effluents is put at Rs 800 crores, which includes Rs 100 crores to fisheries, 500 crores to water treatment, 100 crores on public health and 100 crores on landscape.
Impact on Crop Yields and soil
Raw, postmethanated and diluted spent wash have been successfully utilized (where applied) as manure in cultivating various crops like rice, maize, wheat, pulses, cash crops, paddy, sugarcane, oil seed crops, medicinal plants, flowering plants and vegetables like potato, lady finger, pumpkin, bottle gourd, brinjal, beans, cauliflower, cucumber, etc. The application of spent wash as manure has resulted in increased yield of crops, increased root and shoot length, leaf area index, chlorophyll content and pod formation. Substantial increase was also recorded in case of germination, oil and protein content of crops, nutrient availability of soil, nutrient uptake by crops and mineralization of soil. It has also enhanced the nutrient availability and uptake without any post harvest detrimental impacts on the soil texture, chemistry and biology.
The Brazilian Practice
Brazilian experience suggests that efficient application technologies and spray applications reduce the damage to soil and prevent ground water pollution. Up to 70% crops are being irrigated by spent wash.
The Australian Initiative
CSR Ethanol is the second largest Australian producer of fuel ethanol. CSR Sugar produces 40% of Australia’s sugar. Ethanol products and Fertilizer products are the two main product streams at the Sarina Distillery in Mackay near North Queensland. The distillery is marketing Bio-dunder, a process co product which is value added into a complete liquid fertilizer. Dunder (or concentrated spent wash) from the Sarina Distillery was also blended with Nitrogen, H2SO4 and Phosphorous and converted into Liquid One Shot for application as fertilizer in cane and other crops. Bio-dundertm is certified as organic and has been granted, “Beneficial Use” status by the E.P.A. They key advantages of using Bio-dunder are the recycling of nutrients back into the soil, reduced nitrogen volatilization in case of Liquid One shot products, rapid uptake by plants and in being cost competitive. In Australia Bio-dunder fertilizer is now precision applied using variable rate application technology. The fertilizer returns are positively supported by projections in agriculture outputs. The Australian Government has recognized that CSR’S Sarina Distillery has changed from an environmentally unacceptable industry in the local community to a welcome industry. Apart from process innovations, they have turned a pollutant into a saleable, import replacing product and improved its business position through an increased community acceptance. The communities complaints have also ended.
This was a world first for Sarina and achieved
- Conversion of dunder to a by-product called Biodunder which was sufficiently concentrated to be used as a cane field potassium fertilizer.
- Elimination of odour and contamination of water bodies.
- Increased plant productivity.
- Improved quality of ethanol production.
- Reduction in steam usage within the plant by 30%.
- Reduction in water consumption by 70%.
Bio-dunder has been accepted by cane and other farmers as a valuable potassium-rich fertilizer and 100% of the Bio-dunder product at the Sarina distillery is now recycled into this market. In 1992, the Australian Chemical Industry Council awarded its annual Environment Award to CSR employees who had been instrumental in developing the Biodunder concept.