Biogas production was analyzed in the presence of four different Obeticholic Acid (NS, BES, CES and AHX) together with 10 mM sodium acetate as substrate (Fig. 3). The following concentrations were examined for NS, BES, CES, AHX: 0.55, 20, 20, 1.82 mM, respectively. AHX was prepared as stock solution (10 mg L−1 in 1 M NaOH). All experiments were performed in duplicate.
Voltages were used to calculate the current density (A /m2) according to P = IV/A, where I was the current, V was voltage, and A was cross-sectional area of anode (n = 2). Coulombic efficiency was calculated as CE = CP/CTi × 100%, where CP was the total Coulombs calculated by integrating the current over time and CTi was the theoretical amount of coulombs based on added substrates.
The observed biogas production and the cumulative gas volumes for each gas fraction was calculated as previously described (Logan et al., 2002). The expected biogas production was calculated as VE,t = CtV/2F, where, VE,t (mL) is electrostatic attraction the expected specific biogas production at sample time t based on integrated current over time in Coulombs (C), F Faraday’s number (96.485 C/mol), Ct the total Coulombs by integrating the current over time, and VM the molar gas volume (25.200 mL/mol at 30 °C). The cathodic hydrogen recovery was obtained from the ration of Vt over VE,t. The overall hydrogen recovery (RH2) was calculated using the following equation, RH2 = CERCAT. The hydrogen yield of the system (YH2) was the amount of hydrogen generated based on total substrate used ( Hu et al., 2008).