Microbial desulfurization of low-grade Balochistan coal using Bacillus licheniformis and Bacillus pumilus

Coal is an abundant source of energy; however, the use of Pakistani coal is limited due to its high sulfur content, which causes environmental and health issues. Hence, pre-combustion desulfurization of coal is imperative for quality enhancement. The present study investigates the microbial desulfurization of coal from the Balochistan mine by using local bacterial strains, Bacillus pumilus and Bacillus licheniformis, isolated from the same coal mine, for their sustainability, adaptability, and local availability. Batch incubation experiments with a coal particle size of 75 and 150 µm and incubation periods of 7 and 14 days were conducted to evaluate the effect of particle size and incubation period on the sulfur removal efficiency. Proximate analysis was conducted in accordance with ASTM D3173, ASTM D3174, and ASTM D3175 to determine the moisture content (MC), ash content (AC), and volatile matter (VM), while ultimate analysis was performed using a CHNS analyzer. Additionally, XRD was used to determine changes in composition and structure before and after treatment. The results showed that microbial treatment increased calorific value, specifically at smaller particle sizes and longer incubation periods. The maximum sulfur removal achieved by B. licheniformis was 32.73% and 41.06%, whereas B. pumilus exhibited a removal of 20.75% and 33.48% at a particle size of 75 µm after 7 and 14 days, respectively. These findings demonstrate that bio-desulfurization using indigenous microorganisms is an effective and environmentally sustainable approach for upgrading low-grade Pakistani coal for cleaner energy production.