Metabolism and kinetic study of bioH2 production by anaerobic sludge under different acid pretreatments

•The electron equivalent balance closure was within −12 to +10% for all experiments.•The Gibb's free energies (ΔG°) were fluctuated from −2.2 to −5.9 (kJ/mol).•The Gompertz model depicts that Hmax 1551 mL was occurred at H2SO4 treatments.•The longest lag phase is related to HCl pretreatment.

This study presents results pertaining to bioH2 production carried out in batch experiments under different inorganic acid pretreatments of sludge. The sludge was collected from an anaerobic digester and was subjected to different acid (H2SO4, H3PO4, HNO3, and HCl) pretreatments at pH 3 for 24 h. The results showed that electron equivalent balance closure was within −12 to +10% for all experiments; the portion of electrons as bioH2 fluctuated from 16% to 25%. H2SO4 pretreatments significantly increased H2 yields to 3.3 mol H2/mol glucose followed by HNO3, HCl, and H3PO4 pretreatments which averaged 2.5 ± 0.5. Enthalpy (ΔH°) and Gibb's free energies (ΔG°) fluctuated from 120.5 to 192.7 (kJ/mol) and from −2.2 to −5.9 (kJ/mol). The modified Gompertz was assessed and determined that the maximum bioH2 production potential, 1551 mL and maximum rate of bioH2 production, 303 mL/h occurred using the H2SO4 pretreatment.

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