Environmental concern, leachability and leaching modelling of fly ash and microbes: State-of-the-art review

Quantification and appraisal of the effects of potentially hazardous materials in the environment are of great importance. Revamping of environmental hazard assessment technique has been suggested which primarily focuses on the release of contaminants from waste bodies instead of conventional estimation of waste concentration limits during the release. Production of waste like fly ash and slag in massive amounts from industrial units, thermal, iron and steel plants leads to leaching of contaminants that can have deleterious effect on different components of ecosystem. Different leaching methods are available for predicting the natural leaching of harmful contaminants from fly ash in the laboratory, but it is challenging to select a distinct procedure that can precisely predict the actual scenario for a precise evaluation of different contaminants. The physical–chemical properties of waste, waste disposal life, source configuration and the climatic circumstances of the disposal area must be regarded specifically to select the most appropriate leaching system according to a particular circumstance. As these considerations cannot be established, researchers have suggested several leaching methods and models with the appropriate equipment, which are based on their requirements data on different situations, in the deficiency of a specified procedure and non-standardization of equipment. The present review paper presents state of the art on fly ash, leachability tests, bio-stabilisation methods and various numerical models for determining the contaminant transport.