Biological conversion of low-grade coal discard to a humic substance-enriched soil-like material

Abstract

A mutualistic relationship between grasses, coal-degrading fungi, and arbuscular mycorrhizal fungi was proposed to account for the phyto-biodegradation of coal discard. In this study pot trial experiments were carried out to confirm transformation of the carbonaceous substrate, in the presence of a suite of coal degrading fungi and arbuscular mycorrhizal fungi, into a humic-enriched soil-like material in the Cynodon dactylon/coal rhizosphere. The results show that after 47 weeks of C. dactylon growth on coal discard the concentration of humics increased from (62.9 ± 1.5) to (112.1 ± 5.4) mg/kg. Substrate humic acid-like substance concentration positively correlated (r 2 = 0.95) with accumulation of above ground C. dactylon biomass. FTIR spectroscopy of the extracted humic-like substances confirmed both product identity and increased oxidation of the coal discard substrate. Substrate ash content and electrical conductivity declined coincident with an increase in humic acid-like substance concentration, which together reduced the intensity of acidity in the C. dactylon/coal discard rhizosphere. These observations support the proposal that biological oxidative degradation of coal discard leads to increased humic-like substance concentration and formation of a soil-like material. Results have profound implications for use of coal discard as an organic substrate to replace topsoil in phyto-bioremediation strategies for sustainable large-scale rehabilitation of coal discard dumps.

Bacterial degradation of coal discard and geologically weathered coal

“…(Laborda et al 1999), Phanerochaete chrysporium (Ralph and Catcheside 1994), Trametes versicola (Gotz and Fakoussa 1999), Pseudomonas putida (Machnikowska et al 2002), Coriolus versicolor (Basaran et al 2003), Trichoderma sp. (Kai-yi et al 2009), Pseudomonas stutzeri (Singh and Tripathi 2011) and Neosartorya fischeri (Igbinigie et al 2008;Sekhohola et al 2014;Sekhohola and Cowan 2017). While the detail of mechanisms involved in biodegradation of coal are still to be elucidated, oxidation of sub-bituminous coal by Pseudomonas fluorescens (Hazrin-Chong et al 2014), solubilisation of brown coal by Gordonia alkanivorans and Bacillus mycoides (Romanowska et al 2015), the production of humic substances from low-rank coal by strains of Bacillus mycoides, Microbacterium sp., Acinetobacter baumannii, and Enterobacter aerogenes (Valero et al 2014) together with release from liquefied coal of humic and fulvic acids by a novel recombinant Fusarium oxysporum laccase (Kwiatos et al 2018) and other coal biosolubilization mediators (David et al 2017), illustrate the potential to use microbes in developing sustainable rehabilitation strategies.…”

Geochemical Study of Weathered Coal, a Co-Substrate for Bioremediation of South African Coal Discard Dumps

“…In particular, information on the distribution and abundance of reacting mineral species within this material is needed. Additionally, its suitability as a carbon source to support mycorrhizal fungi that underpin fungal-plant mutualism [25,26] needs further elaboration. Such studies should focus on deriving data to predict the extent of acidification (where there is presence of pyrite) and neutralization (presence of carbonates and aluminosilicates) potential [35], determine the critical threshold levels of heavy metals [39,40], and address soil structure, microbe populations, and nutrient cycling in order to transform the land from its disturbed condition to a self-sustaining ecosystem.…”

“…In an effort to obtain confirmatory evidence for in situ formation of HA-like substances in coal discard treated with Fungcoal [26,29,30], substrate from commercial scale trials at Kleinkopje, Greenside and Kromdraai was collected 18 months after trial initiation and the samples analyzed geochemically. Similarly, substrate from small-scale trials treated with Fungcoal and initiated in 2006, were collected and analyzed geochemically ( Figure 12).…”

“…Indeed, other forms of weathered coal including coal from discard dumps and a highly oxidized coal obtained from an aged waste dump were unable to support fungal-plant bioremediation and revegetation [20]. Thus, the geochemical study of outcrop-weathered coal described here was undertaken to provide insight into the role of this material as a mineral/carbon source to ensure biologically induced humic acid (HA)-like substance enrichment of discard and spoil to facilitate breakdown of the carbonaceous material [21][22][23], plant-fungal mutualism [24,25], and revegetation without the need for topsoil [20,26]. Furthermore, a good understanding of the geochemistry of this outcrop weathered coal may improve our understanding of the geological processes involved in coal weathering in situ.…”

Influence of technological process parameters on qualitative characteristics of coal thermolysis products

“…The lowestgrade coal, its very fine frac tion and coal dust are processed and pressed into coal bri quettes, which are excellent for heating both industrial prem ises and private houses. In total, with the help of chemical processing of coal, more than 400 types of products are pro duced, which can cost tens of times more than the initial prod uct [4].…”