Indian and Canadian researchers are combining fly ash from electricity generating plants, municipal sewage sludge, and — in some cases — the water hyacinth plant to produce a potent soil replacement for Indian communities. Each of these, on its own, is an environmental menace. Together, they could hold huge benefits for worn-out soil. Called Land Restoration Through Waste Management the project is funded by the International Development Research Centre (IDRC), the Canadian International Development Agency (CIDA), the India-Canada Environment Facility (ICEF) and the Indian Institutes of Technology.

Raw Materials

    Four-fifths of India’s electricity is generated by coal-fired turbines . The 200 million tonnes of low-grade coal that they burn each year discharge up to 100 million tonnes of fly ash into enormous settling ponds, causing siltation, flooding and contamination of water sources for millions of people. Cities in India produce huge amounts of mostly untreated sewage sludge, another water contamination risk. Finally, water hyacinth, a free floating weed introduced from South America before 1900, now infests an estimated 200,000 hectares of the country’s waterways, choking off plant, fish, and animal growth.Yet mixing the three materials creates a tonic, rather than a toxic, for soils where nothing has grown for a century or more.

Soil Replacement

    With some primary treatment, sewage sludge can be mixed with fly ash and sometimes hyacinth to yield more than just a fertilizer. Combining the sludge’s nitrogen and organic matter with the minerals found in fly ash yields a potent soil replacement substance.

    Fly ash does a lot for the soil. It reduces bulk density, increases water holding capacity, buffers soil acidity and adds both macro and micro nutrients. The major elements are potassium, phosphorus, calcium, magnesium and carbon from unbound coal. Potential trace elements include boron, molybdenum, selenium, nickel, copper, zinc, and many exotic elements whose functions are not fully understood in plant physiology. The trick is getting just enough to be beneficial but not enough to be toxic.


    So far, the data show that vegetation grown on lands treated with this mix absorbs low levels of heavy metals. For now, the Indian private sector is using it to grow commercial tree species for plywood and some sugar cane. Public sector users have hopes to produce non-timber forest products for local villages such as fuel wood, animal feed, medicinal plants, and grasses on marginal or wasteland and salt effected soils. Researchers have also planted small plots of edible crops to compare different ratios of ash and sludge and to analyse the plants for metal uptake from the reconditioned soil.

    All the data to date prove that the amount of metal uptake is within international guidelines. There are a couple of exceptions in the case of lead and chromium but even these are not far from the upper allowable limits. This technology can be used on edible crops although it is still in experimental phases.

Fly Ash

    In certain badly depleted soils where climatic conditions and long use have eroded soil and leached out nutrients, the fly ash mix seems more effective than standard chemical fertilizers. But it is tricky to compare it directly with chemical fertilizer in growing plots because Indian planting programmes hold many variables.

    In poorly operated programmes where, say, eucalyptus trees get one application of chemical fertilizer at planting and no subsequent watering, only half of the trees may survive, growing to a spindly and useless few centimetres in diameter after seven years. With more careful planting and tending in good social forestry programmes, harvest-ready trees can be produced in the same length of time. The question is whether or not this new technology produces higher yields in the same amount of time.

Biomass Yields

    Preliminary data show that we will get around two to three times the biomass using the technology. These are best-case results from a private sector plot that combined sophisticated fertilizer and drip irrigation techniques. But if the feasibility study is any indication, we should get from a 50 to 100 per cent improved growth rate. This is only a prediction — we’ll know much more by next year.

    Social forestry schemes in India usually invest about Rs12,000 to 20,000 to reforest each hectare with chemical fertilizers. By contrast, the fly ash mix costs about Rs 30,000 to 60,000 per hectare. However, the initial reforestation is a labour-intensive process. So it provides short-term local employment at the outset. Moreover, the trees grow bigger and perhaps twice as many live. By the time they mature a community can recoup its investment three or four times over. There is a real financial or economic benefit to using our material.


    The current supporters of this technology include the Cuttack Municipal Corporation in Orissa which is funding use of the fly ash mix.States like Uttar Pradesh and Madhya Pradesh and dozens of villages rehabilitating their lands.Once this research is further advanced in India, it could be applied around the world in countries that already use fly ash and sewage as soil supplements. Still the mix is no panacea. High transportation costs limit its suitability to communities near large cities like Kolkata which have coal-fired power plants and plenty of sewage. Much research and longer-term monitoring remains — to determine how the mix performs with different species of trees, plants, and agricultural crops and to fully assess its potential.

Inputs : Courtesy Keane Shore, Ottawa-based writer and editor