AMD (acid mine drainage) with low pH and high content of heavy metals is a serious environmental problem in mining activities. Proper AMD management is crucial to ensure compliance with the standards of environmental quality before allowing the flow to the public water system. The objective of this study was to assess the efficacy of increasing pH and decreasing Fe alongside the concentrations of Mn in AMD with the addition of coal fly ash (CFA) and empty fruit bunch of oil palm (EFBOP). A total of four treatments, namely: (1) control (soil without treatment), (2) soil+EFBOP, (3) soil+CFA, and (4) soil+EFBOP+CFA were tested for the ability to improve AMD quality in a batch reactor experiment for 90 days. Weekly observations were carried out for pH, Fe, and Mn concentrations during the experiment, where part of AMD in the reactor was drained and replaced with fresh ones. The results showed that single treatment of EFBOP or CFA caused a pH increase at 2.8 to 5.1–5.4 and 6.3–6.8, respectively. Furthermore, a greater increase occurred from 2.8 to 7.0–7.8 when EFBOP was combined with CFA application. This combination also showed a greater reduction in the concentrations of Fe and Mn compared to the single treatment of EFBOP or CFA. The increase in pH and decrease in Fe alongside the Mn concentrations began in the 3rd week, and this effect was stable during the 90 days of the experiment. The results underscore the potential of EFBOP and CFA as agricultural and industrial wastes in long-term AMD management.
The utilization of nitrogen (N) fertilizer in peatlands, with the aim of increasing crop growth and production, is also reported to increase carbon dioxide (CO2) emissions. The application of coal fly ash (CFA) to soil may change soil physico-chemical characteristics, thereby influence carbon mineralization, but its effect on CO2 production is not yet clear. Consequently, the purpose of this study was to quantify the CO2 production of tropical peatlands that received N fertilizer and CFA. In the laboratory experiment, CFA equivalent to the application of 150 Mg•ha−1 in the field was added to peatlands with and without N fertilizer. These mixtures were then incubated at 70% waterfilled pore space (WFPS) for 30 days at room temperature. Carbon mineralization was measured on a 5-day basis, while several chemical characteristics of treated peatlands, including pH, hot water-soluble C, exchangeable-Ca, -Mg, -Fe, and -Al were measured at the conclusion of the incubation period. This study identified that N fertilizer application increased the CO2 production of tropical peatlands from 29.25 g•kg−1 to 37.12 g•kg−1. Furthermore, the application of CFA on tropical peatlands reduced CO2 production of tropical peatlands with and without N fertilizer. Decreasing the amount of hot water-soluble carbon from peatlands may account for the reduced CO2 production of peatlands with CFA. The study also showed that exchangeable-Ca, -Mg, -Fe, and -Al increased in peatlands with CFA application, and these multivalent cations were also attributed to a reduction of CO2 production. In conclusion, the negative effects of N fertilizer application on peatlands in increasing CO2 emission may be reduced by the application of CFA.
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