• PAGE ONE
• INDEX
• HOME

Tackling water pollution from small units

Mahendra Pandey

Meenu Mishra

SMALL-SCALE industries, falling under a wide spectrum of small, tiny and cottage sectors, occupy an important position in India's economy. The SSI sector accounts for 45 per cent of industrial production and 36 per cent of total exports, and employs abou t 19 million people in 3.2 million SSI units in the country.

This sector, which manufactures more than 8,500 products, supplies the lower income groups with inexpensive consumer goods and services and also meets the requirements of sophisticated technology-based industries in India and abroad. However, the unplann ed, uncontrolled and haphazard growth of these industrial units has resulted in a serious pollution problem.

One of the main objectives of promoting SSIs is to induce regionally balanced development. Most of the SSIs are located near major industrial areas, except for agro-based industries, which come up close to the source of raw materials.

The SSI units are thus located in organised industrial estates or in unauthorised clusters or scattered across non-conforming areas. As per the recent issue of a newsletter brought out by the Central Pollution Control Board, there are 867 industrial esta tes in the country.

Even going by the conservative estimate that 10 per cent of the small-scale units are polluting in nature, about 3.2 lakh units are causing harm to the environment. This would amount to nearly the same impact as all the large and medium industries put to gether. This situation, therefore, is grave, especially because several small-scale units are located in non-industrial areas, be it residential or commercial.

Though individual SSI units discharge only a small volume of polluting effluents, they cause immense damage when located in clusters. Such clustering is advantageous if the effluents and solid wastes are handled through common treatment facilities. But n either old industrial estates nor many of the new ones have common effluent treatment plants and common hazardous waste disposal facilities.

The share of small-scale industries in wastewater generation among different classes of industries is about 40 per cent. The total volume of wastewater generated by the most polluting sector of small-scale industries is 3,881 million litres per day (mld) .

The characteristics of wastewater from the industrial units have a bearing on the type of treatment, while its volume dictates the size of the treatment units and their economics. The wastewater from a unit may be alkaline, acidic, organic, toxic, inorga nic and so on. Segregation of these various categories is desirable for accomplishing effective treatment and economy.

The primary consideration for segregating various streams is the enhancement of treatment ability. The combined treatment of wastewater, in a common effluent treatment plant (CETP), remains the ideal choice where all the units in the industrial estate ar e engaged in similar operations.

But the best solution to the water pollution problem in SSI units is the adoption of new technologies that minimise the generation of polluted waste even at the source. For instance, in electroplating units, as much as 60-70 per cent of water consumption is reduced by adopting counter current rinsing; another 50-60 per cent reduction is achieved by eliminating acid treatment at the pre-treatment stage. And adding a neutraliser for derusting reduces chemical use, resulting in savings of Rs 1,80,000 per a nnum.

The rollers in cotton roller ginning industries are made of chrome composite leather fixed to an iron shaft. The roller contains about 18,000-36,000 ppm of total chromium. When seed cotton is processed, the ginned lint contains an appreciable amount of c hromium. To offset this problem, a new roller for ginning machines has been designed and developed by the Indian Cotton Development Council, Mumbai. This roller is made up of rubberised cotton canvas which has a surface finish conducive to high ginning e fficiency. With this roller covering, ginning units and textile mills could prevent chrome-related pollution problems, and chromium-free fabrics can be manufactured.

Studies indicate that the adoption of better water management, optimised raw material and energy use, recycling of waste streams, close process control and good house-keeping could result in savings of Rs 67.2 lakhs per annum in silk textile mills. Simil arly, spent wash from textile hosiery processing is proposed to be reused for detergent manufacture to reduce the pollution load and effect benefits worth Rs 5,00,000 per annum.

Process synchronisation, scope machines and simultaneous scouring and bleaching of fabric can bring down water consumption by 20 per cent, and process time by 50 per cent. The treated wastewater from the ETP can be used for blanket washing in printing ma chines, resulting in a 20 per cent saving in water consumption.

In the existing textile dyeing practices, wastage of dye, water and fuel occurs due to low loading factor and wastage of used water in non-critical areas. The reuse of the dye bath is proposed to reduce chemical and fuel consumption, resulting in an esti mated savings of Rs 1,50,000 per annum. The use of jet-dyeing machines increases the loading factor, leading to 60 per cent enhanced production capacity and reduction in chemical, fuel and water consumption. Thermic fluid heating in place of direct gas h eating reduces fuel consumption by 50 per cent and power consumption by 90 per cent. The pollution load is cut by 50 per cent.

In the leather tanning industry, using the back-wash water after filtration and addition of chemicals may result in reduced quantities of chemicals used by about 75 per cent, and reduce the overall pollution load by 11 per cent. Alkaline bath, after scre ening, can be recycled and used for next batch. This could reduce chemical consumption and pollution load. Hazardous waste generation and the disposal problem can be eliminated by going in for common chrome recovery from the chrome liquor, resulting in r esource conservation and financial savings.

Total wastewater recycling and replacement of chemical use by an environment-friendly dyeing system based on electrolyte technology is proposed for cotton dyeing in the small scale industry. Caustic soda used instead of soda ash in the dyeing process cou ld cut chemical consumption worth Rs 3,00,000 per annum. The new electrolytic technology cuts fuel consumption by 10 per cent. And the use of hydrochloric acid instead of formic acid further trims processing time by 30 per cent.

``Small is beautiful'' can no longer remain so for SSIs if they increasingly pollute the environment. No doubt, the number of SSIs is burgeoning, and they will continue to play a key role in economic development, but the reduction of environmental pollut ion is equally important. A set of innovative measures needs urgently to be put in place to ensure the environmentally sustainable growth of SSI units.