Lignite biosolubilization and bioconversion by Bacillus sp.: the collation of analytical data

Abstract

The vast metabolic potential of microbes in brown coal (lignite) processing and utilization can greatly contribute to innovative approaches to sustainable production of high-value products from coal. In this study, the multi-faceted and complex coal biosolubilization process by Bacillus sp. RKB 7 isolate from the Kazakhstan coal-mining soil is reported, and the derived products are characterized. Lignite solubilization tests performed for surface and suspension cultures testify to the formation of numerous soluble lignite-derived substances. Almost 24% of crude lignite (5% w/v) was solubilized within 14 days under slightly alkaline conditions (pH 8.2). FTIR analysis revealed various functional groups in the obtained biosolubilization products. Analyses of the lignite-derived humic products by UV-Vis and fluorescence spectrometry as well as elemental analysis yielded compatible results indicating the emerging products had a lower molecular weight and degree of aromaticity. Furthermore, XRD and SEM analyses were used to evaluate the biosolubilization processes from mineralogical and microscopic points of view. The findings not only contribute to a deeper understanding of microbe–mineral interactions in coal environments, but also contribute to knowledge of coal biosolubilization and bioconversion with regard to sustainable production of humic substances. The detailed and comprehensive analyses demonstrate the huge biotechnological potential of Bacillus sp. for agricultural productivity and environmental health.

Keywords:

• Biosolubilization
• lignite
• Bacillus sp
• humic acid

Acknowledgements

The authors wish to thank Prof. A.A. Zhubanova (al-Farabi Kazakh National University, Kazakhstan), Prof. Zhao Ji and Dr. Xiaohui Qiao (Inner Mongolian University, China), Dr. Eva-Maria Geenen and Mr. Fouad Alexander Azar (Aachen University of Applied Sciences, Germany) for many inspiring discussions and suggestions for this work.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The study was funded by the Ministry of Education and Science of the Republic of Kazakhstan.