Display omitted •H2 production from rice mill wastewater was enhanced by NiO and CoO NPs addition.•H2 yield was improved by 109% (NiO) and 90% (CoO) for 1.5 mL/g dosage of the NPs.•Inclusion of the NPs favored acetate and butyrate pathways of biohydrogen synthesis.•COD reduction efficiency was substantially enriched due to the NPs incorporation.•Gompertz model fitted well with experimental results of NPs assisted fermentation. This study highlights biohydrogen production enrichment through NiO and CoO nanoparticles (NPs) inclusion to dark fermentation of rice mill wastewater using Clostridium beijerinckii DSM 791. NiO (~26 nm) and CoO (~50 nm) NPs were intrinsically prepared via facile hydrothermal method with polyhedral morphology and high purity. Dosage dependency studies revealed the maximum biohydrogen production characteristics for 1.5 mg/L concentration of both NPs. Biohydrogen yield was improved by 2.09 and 1.9 folds higher for optimum dosage of NiO and CoO respectively, compared to control run without NPs. Co-metabolites analysis confirmed the biohydrogen production through acetate and butyrate pathways. Maximum COD reduction efficiencies of 77.6% and 69.5% were observed for NiO and CoO inclusions respectively, which were higher than control run (57.5%). Gompertz kinetic model fitted well with experimental data of NPs assisted fermentation. Thus, NiO and CoO inclusions to wastewater fermentation seems to be a promising technique for augmented biohydrogen production.