Biodesulphurization of coal was carried out under four modes of operation namely: conventional batch, constant volume pulse feeding (CVPF), increasing volume pulse feeding (IVPF) and leachate recycle. The effects of different pulse feeding strategies and leachate (product) recycle on biological performance were studied and compared with a conventional batch process. The sulphur removal rates for each of the four processes were 0.04 g/day (batch), 0.09 g/day (CVPF), 0.19 g/day (IVPF) and 0.05 g/day (leachate recycle). The values
of iron solubilization rate (batch-83 mg/ml/day; CVPF-136 mg/ml/day; IVPF-198 mg/ml/day; leachate recycle-133 mg/ml/day) also followed the same trend. The percentage sulphur removal on the 30th day using batch, CVPF, IVPF and leachate recycle processes was 72%, 93%,
97% and 90%, respectively. IVPF was found to be the best operational strategy for biodesulphurization process at enhanced rates for longer duration.