Abstract Various forms of carbon were screened for their ability to stimulate biogas production in batch fermenters and the commercial charcoal which was found to be most efficient was tried in a semi-continuous anaerobic digester. The addition of 5% commercial charcoal to cow dung on a dry weight basis resulted in augmentation of gas production by 17% and 34·7% in batch and semi-continuous fermenters, respectively. Analysis of the microbial profile of the fermenters showed that fermenters with charcoal had a higher number of both total anaerobic bacteria and cellulolytics. The decomposition of Volatile Solids increased from 30% to 34% and COD reduction from 55% to 69% on addition of charcoal to the semi-continuous digester. The Volatile Fatty Acid concentrations were similar and within the acceptable limits. Locally-produced wood charcoal was as good as the commercial charcoal in batch digestions, but other forms of carbon were not as efficient.