Fly-Ash (FA) – a coal combustion residue of thermal power plants has been regarded as a problematic solid waste all over the world. Disposal of high amount of fly-ash from thermal power plants absorbs huge amount of water, energy and land area by ash ponds. The coal ash byproduct has been classified as a Green List waste under the Organization for Economic Cooperation and Development (OECD). However, in many countries this industrial byproduct has not been properly utilized rather it has been neglected like a waste substance (in a table 1).
Тable 1 – Generation and utilization of fly-ash in different countries
|Country||Fly-ash production (milliontonsperyear)||Fly-ash utilization (%)|
Many experiments and studies on the effect and potentiality of fly-ash as an amendment in agricultural applications have been conducted by various agencies, research institutes at dispersed locations all over the world. In this paper, utilization of fly-ash as a value-added product of agriculture is reviewed with the aim of helping opening up the usage of fly-ash and reducing the environmental and economic impacts of disposal.
Mixing alkaline fly-ash with highly carbonaceous acidic material to make compost for soil treatment had been suggested. The low nitrogen content of fly-ash is an important constraint for its agricultural application.
Use of fly-ash along with chemical fertilizers and organic materials in an integrated way can save chemical fertilizer as well as increase the fertilizer use efficiency.
Agriculture plays a major role in the global fluxes of the greenhouse gases like carbon dioxide, nitrous oxide, and methane. According to IPCC, agricultural lime application contributes to global warming through emission of CO2 to the atmosphere. Use of fly-ash instead of lime as soil ameliorant can reduce net CO2 emission and thereby lessen global warming. Fly-ash is also useful for stabilizing erosion-prone soils. Phytoremediation can prevent cycling of toxicants from fly-ash and growing of multipurpose tree species on problem soils.
FA can be used as a potential nutrient supplement for degraded soils thereby solving the solid waste disposal problem to some extent. However, the bioaccumulation of toxic heavy metals and their critical levels for human health in plant parts and soil should be investigated.
An ultimate goal would be to utilize FA in degraded/marginal soils to such an extent as to achieve enhanced fertility without affecting the soil quality and minimizing the accumulation of toxic metals in plants below critical levels for human health.