The effect of different inorganic acids viz., HNO 3 , HCl, H 2 SO 4 and H 3 PO 4 on inoculum pretreatment to selectively enrich hydrogen (H 2 ) producing acidogenic bacteria was evaluated in anaerobic sequencing batch bioreactors. Relative positive efficiency of HNO 3 pretreated consortia in enhancing H 2 production (11.85molH 2 /kgCOD R ) was noticed compared to other acids (HCl, 5.64molH 2 /kgCOD R ; H 2 SO 4 , 7.65molH 2 /kgCOD R ; H 3 PO 4 , 6.90molH 2 /kgCOD R ) and untreated-parent consortia (control, 6.80molH 2 /kgCOD R ). On the contrary, substrate degradation (COD removal) was higher with the control operation (ξ COD , 66.3%; substrate degradation rate (SDR), 1.42kgCOD R /m 3 -day) compared to pre-treated culture. HNO 3 pre-treatment resulted in a shift in the fermentation pathway towards more acetic acid production, while other acid pretreatment and untreated culture showed mixed type fermentation (acetic, butyric, propionic acids). The bio-electrochemical analysis and dehydrogenase activity supported the biocatalyst performance after HNO 3 pretreatment with specific enrichment of Firmicutes and Bacillus.