Biodesulfurization of organic sulfur in Tondongkura coal from Indonesia by multi-stage bioprocess treatments

Multi-stage bioprocess treatments (designated MBT) by employing a mixotrophic bacterium Pseudoclavibacter sp. strain SKC/XLW-1 capable of producing biosurfactants and oxidizing iron and sulfur were carried out to investigate the biodesulfurization of organic sulfur in Tondongkura coal from Indonesia. MBT consisted of biooxidation, followed by biomodification and ended with column flotation (called bioflotation). The bacterial strain was successfully employed to remove organic sulfur and other sulfur forms (i.e., pyritic sulfur, sulfate and total sulfur) from Tondongkura coal by MBT. This observation was also supported by FTIR analyses, which detected the existence of CS bond and SH bond (attributed to aliphatic thiols). In addition, transmission and scanning electron microscopic observations showed that over the course of the experiment the bacterial cells produced extracellular polymeric substances (EPS) which interact with coal particles. These results indicate that the bacterium Pseudoclavibacter sp. strain SKC/XLW-1 and its metabolic products such as EPS are suggested to play a strategic role in removing sulfur contents from Tondongkura coals by MBT; the ability to oxidize sulfur and a continuous supply of EPS (for environmentally friendly flotation bioreagents). These results also reveal that the utilization of the bacterium Pseudoclavibacter sp. strain SKC/XLW-1 and its metabolic products is highly potential to be a more eco-friendly alternative flotation reagent in biodesulfurization processes of coals. Thereby, the findings of this study may provide an encouraging insight into the improvement of biodesulfurization processes in recalcitrant organic sulfur-containing coals by employing bacteria and their metabolites using multi-stage bioprocess treatments in order to create an economical and more eco-friendly desulfurization process.