Solubilization Of Low Rank Coal Research Articles

Production of humic substances through coal-solubilizing bacteria

In this paper, the production of humic substances (HS) through the bacterial solubilization of low rank coal (LRC) was evaluated. The evaluation was carried out by 19 bacterial strains isolated in microenvironments with high contents of coal wastes. The biotransformed LRC and the HS produced were quantified in vitro in a liquid growth medium. The humic acids (HA) obtained from the most active bacterial strain were characterized via elemental composition (C, H, N, O), IR analyses, and the E4/E6 ratio; they were then compared with the HA extracted chemically using NaOH. There was LRC biotransformation ranged from 25 to 37%, and HS production ranged from 127 to 3100 mg . L(-1). More activity was detected in the isolated strains of Bacillus mycoides, Microbacterium sp, Acinetobacter sp, and Enterobacter aerogenes. The HA produced by B. mycoides had an IR spectrum and an E4/E6 ratio similar to those of the HA extracted with NAOH, but their elemental composition and their degree of aromatic condensation was different. Results suggest that these bacteria can be used to exploit the LRC resulting from coal mining activities and thus produce HS in order to improve the content of humified organic matter in soils.

Solubilization of low-rank coal by Trichoderma atroviride; evidence for the involvement of hydrolytic and oxidative enzymes by using 14C-labelled lignite : Holker, U. et al. Journal of Industrial Microbiology & Biotechnology, 2002, 28, (4), 207–212

Solubilization of low-rank coal by Trichoderma atroviride; evidence for the involvement of hydrolytic and oxidative enzymes by using 14C-labelled lignite : Holker, U. et al. Journal of Industrial Microbiology & Biotechnology, 2002, 28, (4), 207–212

Solubilization of low-rank coal by Trichoderma atroviride : Evidence for the involvement of hydrolytic and oxidative enzymes by using 14 C-labelled lignite

Solubilization of low-rank coal by Trichoderma atroviride : Evidence for the involvement of hydrolytic and oxidative enzymes by using 14 C-labelled lignite

Solubilization of low-rank coal by Trichoderma atroviride: evidence for the involvement of hydrolytic and oxidative enzymes by using 14C-labelled lignite.

The deuteromycete Trichoderma atroviride is able to solubilize lignite in dependence on a given carbon source for growth. When cultivated on media containing glutamate, this mold excreted a set of different enzymes with hydrolytic activity. Addition of lignite to the growth media induced the synthesis of extracellular lignite-specific esterase activity but no evidence has been provided for its direct involvement in the process of lignite solubilization. Hence, the basic capability of T. atroviride enzymes to degrade a variety of ester and ether bonds at the surface or within the bulky lignite structure was tested using coal following its direct labelling with 14C-alkyl iodide. The participation of hydrolytic and oxidative enzymes in lignite degradation was assessed by measuring the release of 14C radioactivity from selectively alkylated carboxylic and phenolic OH groups. T. atroviride cleaved both carboxylic esters using esterases and the phenolic ether bonds by using oxidative enzymes, most likely laccases.

Biomimetic Solubilization of a Low Rank Coal: Implications for Its Use in Methane Production

There is substantial interest in processes that result in solubilization of low rank coal as a potential carbon source for anaerobic production of methane. It is known that certain fungi are able to solubilize selected low rank coals by secreting oxalate ions which chelate metal ions that are present. Apparently, metal ions form ionic bonds which link individual coal macromolecules. Once these metal ions are chelated and the ionic bonds are broken, the relatively polar coal macromolecules are soluble in water. Much research has focused on the coal-solubilizing ability of wood-rotting fungi. The wood-rotting fungi Trametes versicolor and Phanerochaete chrysosporium are known to be able to solubilize extensively an oxidized North Dakota lignite (leonardite). We have used a biomimetic approach to study oxalate-mediated solubilization of this low rank coal. A concentration of approximately 75 mM sodium oxalate was found to be near optimal for leonardite solubilization when the initial concentration of leonardite was 2 mg/mL. This is of importance because oxalate concentrations in liquid cultures of wood-rotting fungi are typically well below this concentration. Nevertheless, substantial leonardite solubilization was also observed at oxalate concentrations more typical of those found in these fungi. The effect of pH was also studied. It was found that oxalate-mediated leonardite solubilization increased with increasing pH and appeared to be a function of divalent oxalate ion concentration. Similar results were found for dihydrogen phosphate/hydrogen phosphate/phosphate and bicarbonate/carbonate ions. If the solubilized coal macromolecule from leonardite becomes a viable carbon source for use in anaerobic methane production, these studies suggest that chemical solubilization by common inexpensive Lewis bases would likely be more cost competitive than fungal solubilization processes.

Fungal attack on coal II. Solubilization of low-rank coal by filamentous fungi

The solubilization of low-rank coal by fungi is not accompanied by its depolymerization, which was proven by several screening programs. A total number of 728 fungal strains were yet tested for solubilizing a German low-rank coal (lignite). The coal were used oxidatively pretreated (3% H 2O 2) and natively. During the first screening, the nitrogen content of the media were reduced to select fungi, which solubilize coal under nitrogen-limited conditions. Among 480 micromycetous fungi tested, at least ten strains were able to solubilize native low-rank coal pieces on a nitrogen-reduced agar-medium. They all belong to the conidiospores forming deuteromycetes (molds). Under ‘solubilizing’ conditions, only two of these ten strains showed weak extracellular activities (oxidases, peroxidases) toward 2,2′-azinobis(3-ethylbenzthiazoline-6-sulphonate) [ABTS]. In a second screening, 256 wood and litter decaying basidiomycetes, above all white-rot fungi, were tested for their ability to solubilize low-rank coal under ligninolytic conditions: not any strain was able to form black coal droplets or conspicuous diffusion areas. By using a nitrogen-rich medium, a few basidiomycetes showed also coal solubilizing activities, however, their ligninolytic enzymes were inhibited. The ‘typical’ solubilization of low-rank coal (formation of black liquids from solid coal particles) by molds depends mainly on the nitrogen content of the medium (resulting in higher pH values) as well as on the oxidation grade of coal (e.g. H 2O 2-pretreatment). Extracellular oxidases and peroxidases, both ligninolytic and nonligninolytic ones, seem to play a minor, (or not any), role for this process.

Malthenes from solubilization of low rank coal by methanol/sodium hydroxide treatment

The possibility of O-methylation occurring during the treatment of low rank coals with methanol/sodium hydroxide is evaluated. Chemical and spectral data of malthene fractions confirm unequivocally the presence of methoxyl groups. Their content was found to correlate with the efficiency of treatment. Formation of methyl esters after saponification of ester bridges in lignites is also probable. Reactions of O-alkylation contribute to stabilization through methylation of reactive intermediate species formed after cleavage of ether or ester linkages in coal organic matter, thus improving solubilization.