Technologies for gainful utilisation of sugar industry waste

Code No: TMS132 Price: Rs1750/- Category: Foods & Agriculture: Sugar Technology

1. The Objectives and Scope of the Study

The objectives and scope of the study are as follows:

a. The relationship and the importance of the selected subset of technology to be broad one to which it belongs;

b. The current status of the technology in the world and in the country;

c. Assessment of the technology and options available to the India;

d. The economic aspects of technologies along with their feasibilities which leads to the preferred option(s);

e. Impact of the preferred option by itself, its linkages to the broad area of technology and spin offs, and

f. Recommendations:

- For implementations of preferred technology option(s) identify critical inputs such as raw material, capital goods and human resources required and their availability, investments required to commercialize, and benefits/returns expected. Maximum possible quantification is required.

- For R&D / Technology development identify the requirement of inputs and expected benefits.

g. Action Plan for implementation of recommendations alongwith identification of:

a) List of available technologies for Indian industry and
b) The agencies/groups/individuals for implementation.

h. Expected impact of recommendations, if implemented. The study to build upon the earlier studies of TIFAC and other organizations, with a fouce of details for action.

2. Methodology

The report is on the findings of mail survey and field visits and the information collected through desk research. Mail survey and field visits were conducted to elicit the views of different categories of respondents viz., Sugar mills, equipment / know-how suppliers, research organizations, experts and manufacturers’ associations.

3. The Indian Sugar Industry

In 1995-96, Indian sugar mills produced approximately 160 lakh tonnes of sugar. India is now the largest sugar producing and sugar consuming country in the world. The sugar industry plays an important role in India’s economy. It is the largest among the processing industries next to cotton textiles. Located in rural areas, sugar mills have been intrinsic symbiotic relationship with the rural masses and serve as a nerve centre for rural development.

During the process of manufacture of sugar, a sugar mill produces several wastes us as molasses, bagasse, filter press cake, waste water, bagasse ash. Of the above, molasses and bagasse have become valuable by-products of the sugar industry and cannot be therefore termed as wastes any longer. The te3chnologies of the gainful utilization of filter press cake, sugar mil waste water, spent was and bagasse ash have been discussed in this report.

4. Importance of the Topic

During 1995-96, India crushed 1,600 lakh tonnes of sugar cane for the production of 160 lakh tonnes of sugar. At this level of sugar production, India produced approximately 51.36 lakh tonnes of filter press cake and 736 lakh kl of sugar mill waste water. The distilleries produced 11 lakh kl of alcohol and produced approximately 160 kl of spent wash. The burning of bagasse produces fly ash and furnace ash. At present the quantum of fly ash collected in the country is not much because several sugar mills are still older boilers and/or they are yet to install proper fly ash collection devices. If all the sugar mills switch over to high efficiency boilers and also install modern air pollution control devices, fly ash collection is estimated at 8.32 lakh tonnes per annum at present levels of sugar production. During 1995-96, Indian sugar mills produced approximately 4.8 lakh tonnes of bagasse furnace ash.

Sugar industry waste waters (sugar mill waste water and spent wash), if not treated, can contaminate surface and subsurface waters. The high BOD of spent wash causes rapid depletion of the oxygen content of water, creates foul smell, and renders the stream unfit for propagating aquatic life and for drinking and other purposes. Fly ash is very light and contains a large percentage of fines. Fly ash, if not collected, escapes into the atmosphere through the chimney and pollutes the environment.

Filter press cake, sugar mill waste water, spent wash and bagasse ash are potential pollutants unless disposed off. Identification of technologies for the gainful utilization of these sugar industry wastes will convert these wastes into valuable by-products. This will improve the profitability and the health of the sugar industry and also ensure quick disposal of potential pollutants. According to some industry analysts, the profitability of a stand-alone sugar mill can be low or negative during years of excess cane supplies. With the selling price of sugar falling below the cost price of sugar of most mills during current year, mills that have diversified into by-product utilization are in a financially better position than stand –alone sugar mills.

5. Major Observations and Recommendations

5.1 Sugar mill waste water and spent was contain bio-degradable material of plant and spoil origin and do not contain toxic chemicals or pathogens. After primary treatment, easily oxidaisable material are eliminated and the pH is almost neutral. Spent wash is a rich source of potash because the potash found in sugar cane is passed on to molasses and then to spent wash. Sugar mills have large areas under sugar cane cultivation around their locations. Looking at the limited availability of water for irrigation in manu areas, irrigation of sugar cane fields using sugar industry waste waters can help in the conservation of water and repatriation of nutrients to the soil. It will also help in the disposal of large amount of waste waters generated by the sugar industry., however, adverse impact on the environment, specially on soil and ground water, due to utilization of sugar industry waste waters requires need to be studies. A detailed study should be conducted to suggest maximum acceptable levels of BOD and dissolved solids in sugar industry waste water, prior to its utilization for irrigation, depending upon crop, soil condition and impact on the environment.

5.2 The manorial value of sugar industry wastes can be improved by composting by two different methods viz. Window composting (bioearth process) and pit composting. Composting can be carried out using filter press cake, or filter press cake and bagasse ash, in combination with spent wash or sugar mill waste water. Bioearth composting is carried out on leveled, compacted and well drained land that permits heavy equipment operation. A specially formulated microbial culture is added to enhance decomposition of organic matter. The composting cycle takes 11 weeks. Bioearth composting is achieved using a specially designed aeration equipment called the aero tiller. In pit composting, each compost pit is filled with filter press cake and spent wash (2.5 kl of present wash per tonnes of filter press cake) and cow dung is used as a culture. The thickness of the compost layer is kept below one meter so as to maintain aerobic conditions in the biomass. Spent wash and filter press cake are mixed with the help of mechanical loaders. After three weeks, the material is removed and stacked for maturation for about five weeks. The composting process takes about eight weeks for completion. About 20/25 labourers are employed in a typical composting unit. The composting process requires about 5-8 hectares of land depending upon the composting method and capacity. During rainy season, window composting (bioearth) process has to be discontinued. Seepage proof holding tanks have to be built for storing spent was produced during the rainy season. Pit composting can be carried out in all the seasons.

The quantum of filter press cake available form a 2,500 tcd sugar mill is not adequate for composting of spent wash produced by a batch distillery. Cost-benefit analysis also indicated that composting of filter press cake with spent wash of continuous distillery can be carried out by bioearth process at a cost of Rs. 359 per tonne and the pay back period is only 3.75 years. The pay back period of the process increases with decrease in COD of the effluent. The pay back period increases to 5.85 years if spent wash of batch type distillery is use. Composting of sugar mill waste water and filter press cake results in cash losses. In view of the above factors, bioearth composting is bet suited to composting of spent wash produced by a continuous fermentation distillery.

The bioearth composting process has become popular in may parts of the world. In India, the bioearth process was first implemented at Warna CO-operative Sugar Mill, Kolhapur, Maharashtra, a 4,000 tcd sugar mill, in 1987. The bioearth compost produced by the mill is purchased by more than 5,000 farmers at concessional rates. Use of bioearth, coupled with improved irrigation, contributed to the increase in sugar can yield from 86 tonnes to 136 tonnes per hectare. Trials conducted by M.S. Swaminathan Research Foundation, Pondicherry showed that application of bioearth @ 5 tonnes per hectare increased rice grain yield by 20-25%. The study indicated that bioearth is better than farm yard manure in increasing grain yield. Five tonnes of bioearth, in combination with 75% of the recommended dose of chemical fertilizers, increased grain yield by about 19%.

During 1995, India had to import about 30 lakh tonnes of chemical fertilizers, in nutrient terms, at a considerable cost. With demand for chemical fertilizers projected to increase to 168.57 lakh tonnes by the year 2000, the import bill is likely to go up further. Besides, the cost of production of chemical fertilizers has been increasing steeply due to the spiraling cost of petroleum products and the heavy capital investment required for the setting up of new fertilizer plants. It is therefore necessary to lay greater emphasis on supplementing the use of chemical fertilizers through renewable and cheaper sources of plant nutrients such as composts. One tonne of bioearth compost contains soil nutrients valued at Rs. 1,173.60. the country could have produced approximately 42.63 lakh tonnes of compost, 3.20 lakh tonnes in nutrient terms, valued at Rs. 500 crores from 5`.36 lakh tonnes of filter press cake produced in India during 1995-96.

5.3 A large amount of biogas is generated during anaerobic digestion of organic waste waters. Biogas contains methane. It can be recovered by carrying out anaerobic digestion process in a closed reactor and used as a fuel in the boilers. The modern anaerobic reactor or the digester is a closed reactor with provision for continuous flow of waste water, continuous mixing, temperature control, removal of biogas and digested water. As a pollution control technology, biomethanation, an anaerobic process, has several advantages over aerobic processes. Anaerobic process decompose organic compounds in an atmosphere free of oxygen and consequently require significantly less energy than aerobic processes which are relatively poor intensive for a comparable degree of waste stabilization. The area requirement of the biomethanation process is much less than that of an oxidation pond or an aerated lagoon. As the biomethanation process is fully enclosed, there is not problem of waste water percolation and contamination of subsurface water streams as in the case of lagoons or oxidation ponds. There is no offensive odour ion the surrounding areas as in the case of lagoons. The sludge can be kept active without feeing during the non-crushing period. This facilities quick start-up of the biomethanation process during the crushing season.

Biomethanation of spent wash of a 30,000 lkpd distillery can yield biogas valued at Rs. 112.54 lakhs per annum and the payback period of the project is only 1.75 years. The payback period improves with increase in distillery capacity due to economies of scale. The payback period of a biomethanation plant based on sugar mill waste water, a low COD waster water, is as high ass 175 years and therefore not satisfactory.

5.4 Sugar cane contains fatty and waxy lipids. During cane milling 50% to 60% of the lipids become detached and find their way into sugar cane juice and, during clarification of cane juice, a portion of the lipids and up in filter press cake. Crude wax can be recovered from filter press cake by solvent extraction process. Crude wax is a mixture of hard and soft waxes with other minerals, colouring and resinous matter. The refining of crude was consists of three distinct steps de-ashing, defatting and bleaching. In India, the average crude was content of air dry sulphitation filter press cake (about 10% moisture content) is approximately 10%. Therefore, approximately 561.75 kg of refined wax can be produced from 1,000 tonnes of sugar cane crushed for sugar manufacture.

India is almost entirely dependent upon foreign sources for supply of carnauba, candelilla and other vegetable waxes. During 1993-94, India imported 494 tonnes to vegetable wax valued at Rs. 2.42 crores at an average price of Rs. 49 per kg. The anticipated rise in industrial activity in the country is bound to further increase the requirement of wax. Besides, with the increasing shortage of vegetable waxes in the world, there is a possibility of exporting cane was if high quality refined cane wax can be economically produced in the country. This will enable the country to earn precious foreign exchange and also stop outflow of foreign exchange towards imports. India has the potential to manufacture about 0.90 lakh tonnes of refined cane wax from 1,600 lakh tonnes of sugar can crushed in 1995-96, Assuming that refined cane wax is aggressively priced at Rs. 34 per kg, at 70% of price of carnauba was, he country has the potential to manufacture refined cane wax valued at Rs. 306 crores.

At present, reliable techno-economic data regarding cane wax production is not available because there are no working cane wax extraction and refining plants in India and abroad. In view of the above, it is suggested that an expert committee be set up to examine the techno-economic feasibility of indigenous cane wax production and also find solutions to the problems which caused the closure of earlier units.

5.5 “Vermi” stands for earthworms. Earthworms can easily biodegrade complex organic matter such as sugar industry wastes. Earthworms eat organic matter, break it down into small particles measuring less than two microns and subject the ground organic waste to complex biochemical changes in their intestine using enzymes. Approximately 5 -10% of the digested organic matter is assimilated and the rest is excreated in the form of granular castings of earthy smell. Bhawalkar earthworm research Institute, Pune (BERI) has developed a vermiculture process to treat non-toxic waste waters with BOD as high as 2,00,000 mg/l and simultaneously produce vermin castings and earthworms. Vermin composting does not involve major recurring expenses. There are no major repairs and maintenance expenses as pumps are the only machinery used by the process. Total power requirement is not more than 10-15 kw for treating 400 m3 of spent wash per day using process developed by BERI. Labour requirement is nominal.

Vermi compost can be utilized as biofertilizer. It contains enzymes which help in the biodegradation of macromolecules of agricultural residues. Vermin compost also contains earthworm cocoons. It thus promotes earthworm population and continuous production of vermin castings in the soil itself. Earthworms till the soil upto 3 m depth without harming the roots and make the soil porous. This improves water infiltration capacity of the soil. Considerably. The excellent moisture holding properties of vermin castings help in supplying of moisture to crops during long dry spells. However, sufficient and reliable date is not available regarding the yield of different crops when vermin compost is used as a fertilizer. Reputed agricultural research institutions such as Indian Agricultural Research Institute, New Delhi and University of Agricultural Sciences, Bangalore should be requested to conduct field studies to arrive at reliable information on the effect of vermin compost on crop yield.

5.6 Fly ash from bagasse boilers is primarily unburnt bagasse particles. Its heating value is about 2,688 kcal/kg and abut 60% of that of coal. Bagasse fly ah can be utilized for the production of smokeless briquettes. Bagasse fly ash is mixed in a batch type mixer with some water and an appropriate binder and the mix is extruded. The briquettes can be used for domestic and industrial purposes. The ignition of these briquettes is easier than that of coal dust briquettes available in the market. The combustion is completely smokeless. The short flame combustion of fly ash briquettes facilities local heating and higher heat utilization. Fly ash briquettes cost only Rs. 34 per tonnes compared to Rs. 1,818 per tonne of rice husk briquettes. The calorific value of fly ash briquettes is marginally lower than that of rice husk briquettes.

5.7 Fields visits and discussions indicate that there is no adverse technological gap between India and the rest of the world in technologies for utilizing sugar industry wastes. This observation has been corroborated by almost all the respondents to the survey viz. Sugar mills, equipment manufacturers and experts. Several India organizations are already having technical collaboration agreements or representation/ license arrangements with leading foreign companies specializing in the field of biomethanation and composting.

5.8 The poor mechanical condition of the plant, uneconomic plant size and competition from gur and khandsari units are some of the factors which have adversely affected the profitability of several Indian sugar ills. Most of the sugar mills are not in a financial potion to invest on modernization or new projects for the utilization of wastes. In view of the above, the government should constitute a committee of experts to shortlist waste utilization technologies which are technically and commercially viable but not implemented for want of long term funds. The viable short listed technologies should be encouraged for implementation by offering long term loans with low promoter margins and low rates of interest. The government should do away with all types of taxes and excise duties, on plant and machinery required for the implementation of short listed technologies s as to reduce the capital cost of the projects. Considering that most of the waste utilization technologies are yet to be established on commercials scale, 100% depreciation should be allowed on these projects so as to encourage sugar mills to proceed with such projects.