Flyash

With the boom in population and industrial growth, the need for power has increased manifold. Nearly 73% of India’s total installed power generation capacity is thermal, of which 90% is coal-based generation, with diesel, wind, gas, and steam making up the rest. Thermal power generation through coal combustion produces minute particles of ash that causes serious environmental problems.

Commonly known as fly ash, these ash particles consist of silica, alumina, oxides of iron, calcium, and magnesium and toxic heavy metals like lead, arsenic, cobalt, and copper.

The 80-odd utility thermal power stations in India use bituminous coal and produce large quantities of fly ash. According to one estimate, up to 150 million tonnes of fly ash will be produced in India in the year 2000, primarily by thermal power plants and, to a lesser extent, by cement and steel plants and railways. This poses problems in the form of land use, health hazards, and environmental dangers. Both in disposal and in utilization utmost care has to be taken to safeguard the interest of human life, wild life, and such other considerations.

The prevalent practice is to dump fly ash on wastelands, and this has lain to waste thousands of hectares all over the country. To prevent the fly ash from getting airborne, the dumping sites have to be constantly kept wet by sprinkling water over the area. The coal industry in USA spends millions of dollars on lining fly ash dumping grounds. But in India, these sites are not lined and it leads to seepage, contaminating groundwater and soil. It lowers soil fertility and contaminates surface and ground water as it can leach into the subsoil. When fly ash gets into the natural draining system, it results in siltation and clogs the system. It also reduces the pH balance and portability of water. Fly ash interferes with the process of photosynthesis of aquatic plants and thus disturbs the food chain. Besides, fly ash corrodes exposed metallic structures in its vicinity.

In Delhi, the problem of fly ash is particularly severe as three power stations are located here. Being very minute, fly ash tends to remain airborne for a very long period leading to serious health problems as the airborne ash can enter the body. It causes irritation to eyes, skin, and nose, throat, and respiratory tract. Repeated inhalation of fly ash dust containing crystalline silica can cause bronchitis and lung cancer.

            
Tackling the problem of fly ash

Fly ash management has taken considerable strides over the past few years. Researches have been attempting to convert this waste into wealth by exploring viable avenues for fly ash management. Fly ash is oxide-rich and can be used as the raw material for different industries.

Today, fly ash bricks can be used as a building material. The American Embassy in India has used fly ash bricks in some of its recent construction. Use of fly ash as a part replacement of cement in mortar and concrete has started with the Indian Institute of Technology, Delhi taking the lead. Use of fly ash in the construction of roads and embankments has been successfully demonstrated in the country and it is gaining acceptance. The NTPC (National Thermal Power Corporation) is setting up two fly ash brick manufacturing plants at Badarpur and Dadri near Delhi.

At TERI, researchers have proven that fly ash dumps can be reclaimed by suitable addition of organic matter and symbiotic fungi, making it commercially viable for activities like floriculture and silviculture. TERI researchers have successfully reclaimed a part of an ash pond at the Badarpur Thermal Power Station by introducing a mycorrhizal fungi-based organic bio-fertilizer. As the fungus germinates, it sustains on the partner plant and quickly spreads to the roots and beyond. It improves the plant's water and nutrient uptake, helps in the development of roots and soil-binding, stores carbohydrates and oils for use when needed, protects the plants from soil-borne diseases, and detoxifies contaminated soils. This helps in keeping both air and water pollution under control. It also helps revive wastelands and saves millions of litres of precious water from going down the fly ash slurries. Marigold, tuberose, gladiolus, carnation, sunflower, poplar, sheesham, and eucalyptus now grow at the demonstration site of the power station.

Use of fly ash in agricultural applications has been well demonstrated and has been accepted by a large number of farmers.

The National Capital Power Station of the NTPC has come up with an innovative technology for commercial utilization of this by-product. Known as the dry ash technology, it is considered environment-friendly. Under the dry ash technology, the fly ash is collected in huge mounds with a filter bed provided at the bottom of the mound. Grass is planted on the slopes of the fly ash mounds and polymer layering is also done to prevent the ash from being blown by the wind. Fly ash treated by this method develops certain physical properties that make it more suitable for commercial purposes.