The influence of various parameters, namely nutrient medium
(Norris and Barr [22] and 9 K), initial pH (1, 1.5 and 2) and the addition
of ferrous sulphate (0, 0.02 and 0.05 M), on the total sulphur
removal and ash content of coal samples was investigated using
an L-18 Taguchi design. One additional experiment was carried
out at the condition of run 18 to evaluate the repeatability of
experiments. Moreover, in order to address the role of microorganisms
in ash and sulphur reduction, another experiment was performed
in the absence of microorganisms while other conditions
were similar to those in run 18. This un-inoculated run was sterilized
with 2% (w/w) of thymol in ethanol (2% v/v). The biodesulphurisation
period lasted 30 days and during this period, redox
potential (vs. Ag/AgCl electrode) and pH were daily measured
and when the pH value was higher than the adjusted value, it
was brought back to the set point by sulphuric acid (3 M).