Environmental Effects of Coal and Biomass Ash Generation

Abstract

There are apprehensions of presence of potentially toxic organic and inorganic substances in coal and biomass ash. Potentially toxic elements, PAHs, PCBs, and radioactive elements are some of the environmental concerns associated with the handling, utilization, and disposal of these ashes. During combustion in the power plant, volatile toxic elements are released from the coal and significant part of the element gets adsorbed on the ash particles at cooler zones of the furnace. These surface-associated metals are easily mobile and may get dispersed into the environment. Inorganic elements in the ash could be associated with the water-soluble phase, glass phase, bound to metal oxides or silicate matrix. The release of the elements is measured by leaching test. The concentration of elements in the leachate is compared with the values provided by regulatory authorities to evaluate the environmental acceptability of the ash. Weathering of ash or its interaction with water and CO2 and other reactive liquids in the disposal or utilization sites leads to decomposition of glassy phase and formation of new clay phases. These new clay phases fix the potentially toxic elements in immobile pools. Thus, the pond ash or weathered ash has fewer risks than the fresh ash. Depending on the presence of unburnt carbon, halides, and the prevailing combustion conditions in the furnace, some ashes have considerable amount of PAHs, PCBs, and different dioxins. But studies with these organic pollutants are relatively less. Construction materials prepared from ash could exhibit radiation hazard, however, most of the studies showed radiation levels within the permissible limits. All these potential hazards from ash depend on the nature of the ash, so judicious screening and adoption of appropriate abatement techniques has to be followed while utilizing the ashes for different gainful purposes.