Environmental Protection

afterflyashbioremediation

A Re-think on Fly Ash Ponds in India

“Today's problems cannot be solved if we still think the way we thought when we created them.” - Albert Einstein

Fly ash, generated during the combustion of coal for energy production, is an industrial byproduct that is recognized in India as an environmental pollutant (pdf).

Disposal of fly ash in storage ponds and in landfills prevents valuable agricultural land from being used to feed people and thus stimulate the economy . This practice also:

  • lowers soil fertility,
  • contaminates soil and groundwater,
  • interferes with pH balance and the portability of water, and
  • corrodes exposed metal.

In the air, fly ash can cause people to suffer from such health hazards as bronchitis, silicosis, asthma, and lung cancer. Under such circumstances, management of fly ash is of utmost importance.

India produces about 112 million metric tons of fly ash annually. Britain produced only about 4 million metric tons and is expected to produce only half that much in 2010.

A look at the statistics show that, out of India's total installed power capacity of 159,398.49 megawatts, 64.6 percent comes from thermal energy and 80 percent is derived from coal.

An estimated 65,000 acres of land is occupied by ash ponds, indicating that more than 80 million metric tons is being stored in ponds or disposed of in landfills today. The consensus is that at least by 2025, coal-burning power stations will provide more than 50 percent of India’s energy needs. The nation uses only about 38 percent of its total fly ash production for cement manufacturing (approximately10.42 million metric tons), land filling, brick manufacturing, mine filling, agriculture and other uses. Under these circumstances and with the continued reliance on coal, India will have huge supplies of fly ash in the years to come: an estimated 225 million metric tons of fly ash that will be stored in more than 1.8 million acres of ponds in 2032.

Table 1. Present Status of Fly Ash Utilization in India

Can a country like India afford this? The answer is categorically, no. It is imperative that the country undertake major initiatives in research and development for the use of fly ash.

Concrete Management
Considerable awareness about the use of fly ash in concrete and the benefits of the high-volume fly ash concrete technology are evident in India. Unfortunately, the central and state agencies are still living in the past and, under the cloak of public safety, refuse to acknowledge the new facts and advances in supplementary cementing materials, and in general, prohibit their use in concrete.

Developing a fly ash collection system is one management method. The final product is normally taken to a simple air classifying plant (costing less than US $ 4.5 million or Rs 198 million) that removes very coarse particles. Thermal plants typically store the resulting beneficial product in a silo until it is sold to the cement and concrete industry. A plant producing 1 million metric tons of fly ash generates about US $10 million annually.

India imports about 15,000 metric tons of silica fume (average particle size of 0.1 micron) at a price on the order of US $800/ton (approximately Rs 35,000/t). This material is used in preparation of high-strength/high-performance concrete. Fly ash with particle sizes approaching 1 to 3 microns can replace silica fume, with some modifications to mixture proportions, to produce the above types of concrete. There is considerable market potential for this kind of material, but process standardization and quality guarantees are lacking at this time.

Another option for reusing fly ash involves the construction of small plants. Electrical utilities located within 100 km of large cities and towns can set up fly ash lightweight aggregate plants at a cost of less than US $10 million (approximately Rs 440 million). The coarse lightweight aggregate can be sold to the construction industry at a subsidized cost. However, the techno-economic feasibility of setting up such plants is questionable. Moreover, transportation of fly ash over long distances is costly and would defeat the principle of sustainable technology.

Considering the challenges of the spatial distribution of thermal power plants and possible costs, onsite reclamation of fly ash ponds holds much greater scope and potential.

Onsite Ash Reclamation
Bioremediation of ash ponds has the potential to return the contaminated environment to its original condition. The following technologies should be considered.

Phytoremediation ─ Biomass production and landscaping. Plants can act as effective barriers by intercepting airborne fly ash and heavy metals. Checking air pollution by plantation of tree species with high dust-capturing efficiencies (teak, Banyan tree, fig, jackfruit) can be done. Apart from growing trees, herbs such as sweet basil, Mentha and Vetiver; ornamental plants like Aster, Helianthus, Tegetes erecta, and a nitrogen fixer like Sesbania aculata can be used to reclaim the soil in ash ponds.

Vermi-composting. Fly ash in compost has been found to complement various biosolids, including treated sewage sludge, and thus opens up a new avenue for its use, helping to lower the general application of chemical fertilizers.

Bio-pesticidal use, Lignite and coal-based fly ash can be used as eco-friendly insecticides and/or carriers for other biopesticides in a dust formulation (pdf). They can be used to keep both chewing and sucking pests of rice and vegetables away. More than 50 species of insect pests of various major crops are susceptible to fly ash treatment.

Biofuel production. Plants like Jatropha curcas plantation on ash ponds have been found successful, and these ash ponds can be used to grow these oil-bearing plants, which can be blended to create biodiesel fuel.

Myco-remediation. With mycorrhizal technology, as the fungus germinates, it sustains on the partner plant and quickly spreads to the roots, improving the plant’s water and nutrient uptake. It helps the development of plant roots, detoxifies contaminated soils and improves soil-binding capacity and carbohydrate storage. This technology can reduce the level of heavy materials present in contaminated sites to a considerable level.

Table 2. The percent reduction of heavy metal profile after two years applying Mycorrhizal technology at an experimental site.

Heavy metal Percent
Aluminum 62
Chromium 90
Cobalt 50
Nickel 64
Arsenic 43

Source: The Energy and Resources Institute

 Table 3. Fly ash properties before and after applying Mycorrhizal technology.

Properties Before After 2 years
pH (1:2.5 soil:water) 8.7 8.1
Phosphorus (ppm) 7.1 21.1
Nitrogen (%) 0.1 0.6
Organic carbon (%) 0.2 0.9

Source: The Energy and Resources Institute

Thus, agricultural and biotechnological interventions hold tremendous potential for reclamation of ash ponds. Besides this, integrated organic/biotechnological approaches should be applied to reduce the toxicity level of fly ash sites near thermal power plants.

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