**6. Scalability of the process**

The sulphate reduction was monitored under anaerobic condition in a 9-litre bioreactor for 25 days, and the percentage of mean reduction was 56.3 ± 11.03. In case of 78-litre bioreactor, the sulphate reduction was monitored for 361 days, and the percentage of average reduction was 62.36 ± 24.81 with the saturation obtained at around 331 days. The probability distribution of the data was found to be normally distributed. It was evident from the above observations that the efficiency of sulphate reduction was increased by 1.10-fold with scaling up of the bioreactor volume. Our results were quite similar to the study of Sarti et al. [28], where they had also successfully demonstrated sulphate reduction in an anaerobic bioreactor with maximum efficiency of 99%. A similar study of fed batch bioreactor used for sulphate reduction was demonstrated by Silva et al. in the year 2002 with an efficiency of 97% [29]. Although both the studies are similar to ours in terms of reduction efficiency, but unlike those, our system retains the reduction efficiency consistently once it gets stabilized.
