Microalgae-bacteria flocs (MaB-Flocs) as a substrate for fermentative biogas production

Biogas production from the microalgae-bacteria flocs (MaB-Flocs) in batch reactors was conducted in this study. A batch test was performed to determine optimum inoculums that were taken from a running biogas plant (BP), a municipal wastewater treatment plant (MWTP) and a river sediment (RS). The maximum biogas yield (304.83 ± 4.23 mL per gram volatile solids introduced (mL g-VS−1)) was obtained with the inoculum from MWTP. Subsequently, the effect of substrate-inoculum (S/I) ratios, temperature and pre-treatment methods on fermentative biogas and methane production was investigated. The optimum S/I ratios and incubation temperature were determined as 0.2 g VSsubstrate/g VSinoculum and 37 ± 1 °C, respectively. The results of the CH4 fermentation show that the methane yields could be increased from 216.72 ± 3.52 mL CH4 g-VS−1 to 271.34 ± 6.65 mL g-VS−1 by using enzymatic pre-treatment at the S/I ratio of 0.2 g VSsubstrate/g VSinoculum and mesophilic conditions.