Search

Coal bio-transformation technologies can convert the neglected low rank coal reserves to alternative fuels and non-fuel organic chemicals. Fungal mediated coal degradation can serve as biological beneficiation for alternative substances. For enhanced biodegradation, fungi can be isolated from coal environments and optimized for coal degradation processes. In this study, an indigenous fungal isolate AD-1, identified as Rhizopus oryzae by fungal ITS sequences, was isolated from a low rank coal sample collected from Darra Adam Khel, Frontier Region Kohat, Pakistan. The AD-1 mediated coal degradation was optimized and showed a substantial release of organics at 1.5% glucose and 0.5% coal loading ratio within 11 days. The GC–MS analysis of the black liquid from coal solubilization showed a variety of organic compounds including aromatic acids, fatty acids, alkanes, amines, and amides. The depolymerized liquid extract was analyzed by High-Performance Size-Exclusion Chromatography (HPSEC) for determining the molecular mass distribution of the released organics. The release of the organic fragments had molecular mass distribution ranging between 1.5 kDa and 26.7 kDa. In addition, the released fraction and residual coal sample after solubilization were analyzed with Fourier transform infrared spectroscopy (FT-IR) to explore the structural changes aroused by the AD-1 fungal treatment. The AD-1 fungal strain has the abilities of decarboxylation and deamination, as well as breaking the side chains of the aromatic rings. This demonstrates that indigenous fungi from coal environments can enhance the biodegradation and shows a potential for producing chemical feedstock or alternative fuels from low rank coal.

Coalbed methane (CBM) has great environmental and economic values in addition to its energy content. For years natural gas has been considered a transitional cleaner energy source as it emits less carbon dioxide and other pollutants than other fossil fuels. Due to thebiogenic origin of CBM in many reservoirs, microbial enhancement may also be used to stimulate gas production in coal seams; however, the CBM output is relatively low when compared to other sources of natural gas. Studies have shown that chemical pretreatment of coal prior to gas production can significantly increase the bioconversion rate of coal. This review summarizes and discusses the mechanisms of coal biotransformation and biodegradation in the context of CBM production using chemical pretreatment methods, as well as the latest development in the field, in order to promote the further development of CBM resources.

The development of bio-processing low rank coal into fuels and non-fuel products has received growing interest in recent years, e.g., production of alternative chemical stock (i.e., humic acids) by the fungal transformation. Previous studies have demonstrated that fungal strains isolated from coal environments can play an important role in the coal-transformation processes with in vivo optimization and chemical pretreatments. In this study, the influence of chemical pretreatments (nitric acid and hydrogen peroxide) with a fungal isolate from coal on the depolymerization of Pakistani subbituminous coal was conducted. The chemical pretreatment exhibited enhanced production of humic acid from 13.5% to 54.2% for nitric acid and 45.7% for hydrogen peroxide. Nitric acid was more effective pretreatment in individual and combination with fungal-mediated depolymerization than hydrogen peroxide. The production of fungal-transformed liquid-derived humic acids were 36.4% and 31.1% for nitric acid and hydrogen peroxide pretreated coal. The results showed that the fungal-transformed humic acid has a high molecular weight, elevated aromatic condensation with mono and poly-substituted functional groups than the chemically treated and raw coal-derived humic acids. The fungal treatment also increased the nitrogen content in the resultant extract, which can be beneficial to the functionality of humic acids. By combining chemical and fungal treatment, it is possible to improve the quantity and quality of humic acids extracted from low rank coal. This is a promising approach in the development of more sustainable-cleaner products from Pakistan’s coal resources for the production of bio-active humic acid.