Owing to its inhibitory effect on microbial growth, soap present in crude glycerol (CG) is a concern in biological valorization of the biodiesel manufacturing waste. By salting out strategy, up to 42% of the soap has been removed and the approach has beneficial effect on H-2 production; however, removal of more than 7% of the soap was found to be inhibitory. Actually, soap is utilized as a co-substrate and due to removal; the carbon nitrogen ratio of the medium might have decreased to reduce the production. Alternatively, without changing the carbon nitrogen ratio of CG, MgSO4 treatment can convert the soap to its inactive form (scum). The approach was found to increase the H-2 production rate (33.82%), cumulative H-2 production (34.70%) as well as glycerol utilization (nearly 2.5-folds). Additionally, the treatment can increase the Mg (a nutrient) content of the medium from 0.57 ppm to 201.92 ppm. (C) 2013 Elsevier Ltd. All rights reserved.