Pollution control technologies for sugar industry

Code No:TMS102 Price:Rs1300/-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 focus of details for action.

2. Methodology

The report is based 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 such as sugar mills, equipment / know-how suppliers, R & D organizations, experts and manufacturers’ associations.

3. The Importance of the Indian Sugar Industry

India is the largest sugar producing country in the world. The sugar industry plays an important role in India’s economy. It is the second largest industry in the country, next to textiles and provides direct employment to more than 3.6 lakh persons. The cultivation and transportation of sugarcane to the sugar mills provides a source of income to large number of farmers, labourers, technicians, transport operators. It also supports a number of engineering industries located both in rural and urban areas.

Molasses, press mud and bagasse are the three important by-products of the sugar industry. For every 100 lakh tonne of sugar produced, the sugar industry produces 45 lakh tonne of molasses, 32.1 lakh tonne of press mud and 333 lakh tonne of bagasse. These by-products are potential pollutants unless disposed off.

4. Waste Waters of Sugar Manufacturing Process

Indian Sugar mills generate 0.16-0.76 m3 of waste water for every tonne of cane crushed by them. During 1993-94, India produced 98 lakh tonne of sugar. At this production level, on an average, the Indian sugar mills generated about 4,50,800 lakh litre of waste water. The combined sugar mill waste water has a BOD of 1,000 to 1, 500 mg/l. the pollution standards stipulate that BOD of waste water should be less than 30 mg/l for disposal into inland surface waters and less than 100 mg/l for disposal on land. BOD can be 500 mg/l, in case land application of treated waste water is envisaged as a secondary treatment system for further removal of BOD.

The sugar mill waste water, as it leaves the premises, has a relatively clear appearance, however, after stagnating for sometime, the waste water turns black and starts emitting foul odour. If discharged in water courses, its high BOD depletes dissolved oxygen in water and makes the environment unfit for fish and other aquatic life. Oil and grease in waste water hasten such mortalities. If untreated waste water is discharged on land, decaying organic solid and oil and grease present in the waste water clog the soil pores. The waste waters from some of the sections contain considerable amount of suspended solids which deposit and cause blockage in drains and ditches.

5. Air Pollutants

Most of the sugar mills use bagasse as a fuel in boilers. The burning of bagasse in boilers produces particulate matter, oxides of nitrogen, carbon, sulphur and water vapour. Except for particulate matter, other emissions of bagasse fired boilers are within the limits prescribed by the pollution control authorities. The particulate matter, usually referred to as fly ahs, consists of ash, unburnt bagasse and carbon particles. Fly ash is very light and it contains a large percentage of fines. If air pollution control equipment are not installed, fly ash will fully escape into the atmosphere through the chimney. The particulate matter coming out of the chimney will travel distances depending on particle size and atmospheric conditions. There is a reduced visibility in the areas surrounding the sugar mill. The heavier particles settle on vegetation and damage them. There are reports of dizziness and physiological effects like irritation in the eye, nose, throat and lungs, in the surrounding areas.

As per the general emission standards, particulate matter is required to be within 150 mg/Nm3. in case of horse shoe/pulsating grate and spreader stroker bagasse fired boilers, the particulate matter emission is required to be within 500 mg/Nm3 and 800 mg/Nm3 respectively.

6. World Trends

in 1992-93, the world production of sugar was 1,124.39 lakh tonne. India is the largest producer of sugar followed by Brazil. However, at 13.4 kg, the Indian per capita consumption of sugar is low when compared to that of developed countries. Indi’as share is world wide exports of sugar is negligible.

The choice of a pollution control method in a region or a country depends on a number of factors such as characteristics of the pollutant, pollution norms of the country, equipment and operating costs etc. land application without treatment and land application after biological treatment are the common methods of treating sugar mill waste water in different parts of the world. Bagasse is used as fuel in furnaces. The furnaces are either of stepped grate or spreader stoker design Mechanical Separators and multi-cyclones are used as air pollution control equipment.

7. Observations and Recommendations

7.1 During the process of sugar manufacture, condensates are available from juice heaters, multiple effect evaporates, vacuum pans etc. condensates, if contaminated with juice, have to be disposed off as waste water. It is therefore, desirable to take preventive steps to avoid contamination of condensates. The uncontaminated condensates can be recycled. A large quantity of eater is required for cooling of bearings, glands of machinery, air compressors, sulphur burner, C massecuites etc. it is estimated that a 2,500 tcd sugar mill requires 129.50 m3 of cooling water per hour or 1.24 m3 of cooling water per tonne of can crushed. It is suggested that cooling water be recycled instead of being released as waste water.

Recycling of condensates and cooling water helps in minimizing the amount of water joining the waste water stream. This also helps in conservation of water, which has become a scare resource for several sugar mills. Besides, sugar mills have to take steps to minimize the amount of pollutants joining the waste water stream.

7.2 The sugar mill waste water contains large quantities of bio-degradable organic matter and therefore biological treatment processes are most commonly used for its treatment. In general, anaerobic biological processes (oxidation ponds and biomethanation) have several advantages over aerobic processes (aerated lagoons, activated sludge process). Anaerobic processes decompose the organic compounds in an atmosphere free of oxygen and consequently require significantly less energy as compared to aerobic processes. As compared to aerobic processes, anaerobic processes are easier to control and operate, produce a lower quantity of sludge and their annualized costs are lower. In view of the above, it is preferable to treat sugar mill waste waters by anaerobic processes rather than aerobic processes. Treated waste water with a BOD level of about 100 mg/l can be used for irrigation of sugar cane fields.

7.3 Multi-cyclones, wet collectors, bag filters and electrostatic precipitators can reduce particulate matter in boiler emissions by 90% or more. These equipments can reduce he concentration of particulate matter to 450 mg/Nm3 or less, in case particulate matter concentration in boiler emissions is in the range of 4,500 mg/Nm3. Electrostatic precipitators exhibit a very high collection efficiency. However, given their high capital cost, the present emission standards do not warrant installation of electrostatic precipitations for the control of particulate matter from bagasse boilers. A sugar mill may choose one of the three remaining air pollution control equipment, viz. multi-cyclones, wet collectors and bag filters, depending upon the actual emission standards stipulated by the State Pollution Control Board.

Comparison of Air Pollution Control Equipment for Bagasse Boiler Emissions

Evaluation criteria MC WC BF ESP
Collection efficiency 90% 90-95% 99% 99%
Capital cost (Rs. Lakh)
(2,500 tcd mill)
35 50 100 300
Land required (m2)
(2,500 tcd mill)
250 300 250 500
Operating cost (Ranking)@ 3 2 1 2
Indigenous availability Yes Yes Yes Yes
@ 1 is the highest ranking followed by 2, 3, and 4.
MC Multi-cyclones
WC Wet Collectors
BF Bag Filters
ESP Electrostatic Precipitators

7.4 A number of sugar mills have already installed waste water treatment plants and air pollution control equipment. A committee of experts should be constituted for identifying at least one waste water treatment plant and one installation of air pollution control equipment, in each geographic zone in the country as demonstration plants. The sugar mill owning the demonstration plant should be required to extend full co-operation to the government designated agencies to evaluate the pollution control technology, carry out mutually agreed experiments and improvements, share information regarding plant design, maintain and provide information regarding different operating parameters and operating economics and permit visitors to see the plant in action . in returns, the government should compensate the sugar mill by fully reimbursing the operating cost of the demonstration pant.

7.5 Bagasse, molasses, press mud, waste water and fly ash are produced during the manufacture of sugar. As bagasse, molasses and press mud are gainfully utilized, they do not cause much environmental pollution though they are potential pollutants. It is suggested tat a detailed study be conducted to identify technologies for gainful utilization of sugar mill waste water and fly ah. This will encourage the sugar industry to install pollution control equipment at the earliest.

7.6 There is no adverse technological gap between India and the rest of the world in the area of pollution control technologies for sugar mills. This observation has been corroborated by almost all the respondents to the survey viz. sugar mills, pollution control equipment manufacturers and experts. It is also noted that several Indian organizations are already having technical collaboration agreements or representation/license arrangements with leading foreign companies specializing in the field of pollution control technologies.

7.7 Sugar mill waste water has low BOD. The distillery waste water is low I pH, highly coloured and very high in BOD. The paper mill waste water is alkaline in nature and its intensity of colour is less tan that of distillery waste water. Mixing of waste waters of sugar mill, distillery, paper mill and sugar mill in proper proportions is likely to reduce the installation and operating cost of waste water plants. The above arrangement is possible in an integrated sugar complex consisting of sugar mill, molasses based distillery, and a bagasse based paper mill. It is suggested that detailed studies be conducted to arrive at the cost and the benefits of installing a combined waste water plant for treating the different waste waters of a sugar complex.

7.8 Most of the sugar mills do not have the financial strength to invest on in-plant pollution abatement measures or pollution control equipment. In view of the above, the government should do away with all types of taxes and excise duties on pollution control equipments so as to reduce their capital cost. besides, the present scheme of allowing 100% depreciation on pollution control equipment cannot act as a source of funding for loss making mills and as such a different set of incentives should be provided. This could include lowering of promoter’s margins, longer repayment period, lower interest rate etc.

7.9 A number of organizations claim to have developed pollution control technologies which meet the norms prescribed by the pollution control boards. The sugar mills are hesitant to invest large sums of money on these equipments without knowing the true efficiency or the cost aspects of these equipments. Short-listing and approval of pollution control equipments and technologies by pollution control boards will enable the sugar industry to select the equipment/technology without any hesitation and within a short span to time. Newer but unproven technologies should be identified by a committee of experts. In order to encourage sugar mills and venture capitalists to participate in the scheme, the government should subsidize a part of the project cost. Funding of the project through venture capital will ensure that sugar mills are not put to financial loss in case the project fails to meet its objectives. Besides, in case of a project failure, the pollution control board should give sufficient time to the concerned sugar mill for meeting the pollution standards.

7.10 It is suggested that the pollution control activities of a sugar mill be entrusted to qualified environmental engineer. Besides supervising the activities of the pollution control plants, he can also assist the sugar mill in developing pollution abatement measures. There is a need for training operators of pollution control equipment in basics of environmental science so that they can understand the importance of various process parameters and take basic decisions, if required. It is therefore suggested that specialized training institutes be set up in every state for conducting short duration courses for operators for pollution control equipment. Besides, these institutes can train chemists to scientifically analyze the characteristics of pollutants before and after the treatment.