Flyash Characteristics and Its Incorporation Effects on Soil Health
H. C. Joshi
M. C. Jain
S. K. Sharma
AbstractThe disposal of huge amounts of ash produced in modem society is a major concern. Although this material finds uses in civil construction, cost considerations have limited such applications. the use of ash as landfill or for reclaiming acid/sodic soils are major disposal options, but these are not able to utilize the appreciable amount of ash produced. Thermal power stations thus require large spaces for storage, which may bring drastic changes in land-use patterns in the areas nearby. Authorities may have to maintain stricter associated air and water pollution limits. This article reports ash characteristics, ambient air quality, and ash incorporation effects on soil health at the National Capital Power Project (NCPP), Dadri, Ghaziabad, Uttar Pradesh, which is the only single dry ash disposal unit using electrostatic precipitation collection devices in India. the low particle density of ash establishes its potential for dust formation. the high water-holding capacity of ash is due to characteristic silt and clay size fractions. Ninety-three percent of the ash is composed of oxides of silicon, aluminium and iron. pH is neutral to slightly alkaline, whereas electrical conductivity was 0.65 mmhos/cm. Heavy metals, present in the oxide forms, in flyash exhibited concentrations considerably higher than in coal and in normal soils. Dust fall rate, averaged annually, in adjoining villages lay in a range of 4.91-15.92 g/m3/30d, indicating ash fall, on annual basis, of less than 1 percent of surface soil mass. the fall rates were high during dry summer season, decreased in rainy season, and thereafter increased as winter progressed. Ambient air quality in villages adjoining NCPP was maintained well within safe limits, due to management controls adopted by the authorities. Addition of flyash (up to 40% ash in the soil-ash admixture) decreased bulk density and hydraulic conductivity, whereas enhanced moisture retained at field capacity, wilting point and surface mechanical impedance, primarily due to modifications in pore size distribution from ash addition. Differences in physico-chemical characteristics over the Control (no ash) due to ash incorporation were narrowed with time, indicating a high buffering capacity of the soil. Microbial activity was enhanced by ash incorporation up to 5 percent ash level in the soil-ash admixture. Thereafter inhibitory symptoms in the microbial activities were noticed. This trend was not observed in agricultural fields around Thermal Power Station, which were exposed to ash-added environments for longer periods of time.
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