Abstract
In-situ rehabilitation of fly ash at dumping sites has rarely been addressed for crop production due to growth-related constraints, largely of heavy metal (HM) contamination in soils and crops. Current communication deals with a novel approach to identify a suitable management option for rejuvenating the contaminated soils. In this background, a 60-days incubation experiment was conducted with different fly ash-soil mixtures (50 + 50%, A1; 75 + 25%, A2; 100 + 0%, A3) along with four ameliorants, namely, lime (T1), sodium sulphide (T2), di-ammonium phosphate (T3), and humic acid (T4) at 30 ± 2 °C to assess the ability of different fly ash-soil-ameliorant mixtures in reducing bio-availability of HMs. Diethylenetriaminepentaacetic acid (DTPA)-extractable bio-available HM contents for lead (Pb), cadmium (Cd), nickel (Ni), and chromium (Cr) and their respective ratios to total HM contents under the influence of different treatments were estimated at 0, 15, 30, 45, and 60 days of incubation. Further, the eco-toxicological impact of different treatments on soil microbial properties was studied after 60 days of experimentation. A1T1 significantly recorded the lowest bio-availability of HMs (~49–233% lower) followed by A2T1 (~35–133%) among the treatments. The principal component analysis also confirmed the superiority of A1T1 and A2T1 in this regard. Further, A1T1 achieved low contamination factor and ecological risk with substantial microbial biomass carbon load and dehydrogenase activity. Thus, liming to fly ash-soil mixture at 50:50 may be considered as the best management option for ameliorating metal toxicity. This technology may guide thermal power plants to provide the necessary package of practices for the stakeholders to revive their contaminated lands for better environmental sustainability.
Highlights
Licensee MDPI, Basel, Switzerland.Fly ash is the end residue from the combustion of crushed coal in the furnace of thermal power plants and comprises mineral constituents of coal which is not entirely burnt
Diethylenetriaminepentaacetic acid (DTPA)-extractable bioavailable fraction of heavy metals was varied across different stages of incubation for various fly ash-soil-ameliorants combinations used in this experiment (Figure 1)
The extractable amounts of Pb, Cd, Ni, and Cr significantly differed for different treatment combinations after 60 days of incubation (Figure 1a1–d1) and a noticeable reduction in metal concentration was detected in different combinations
Summary
Fly ash is the end residue from the combustion of crushed coal in the furnace of thermal power plants and comprises mineral constituents of coal which is not entirely burnt It contains fine powdery spherical, amorphous ferro-aluminosilicate particles and is globally considered to be a hazardous waste to the ecosystem since, it generally contains various toxic heavy metals such as Pb, Cd, Cr, Ni, Hg, V, B, As, Se [1]. The dumping sites do not support sound plant growth because of its nutritional deficiency (generally N and P), low microbial activity, high salt concentration along enhanced heavy metal loads [7,8]. Disposal of such a high amount of fly ash requires enormous water, energy, and land areas [9]. Appropriate fly ash management would remain a great apprehension of the century
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