Enhanced biohydrogen and biomethane production from Chlorella sp. with hydrothermal treatment

This study was the first attempt to investigate the effect of hydrothermal treatment on energy recovery of Chlorella sp. via two-stage anaerobic fermentation (TSAF). A maximum biohydrogen yield of 8.29 +/- 0.33 mLH(2)/gVS was achieved at the control group (CG), and a highest biomethane yield of 434.38 +/- 5.72 mLCH(4)/gVS was obtained for the group at the weakest hydrothermal treatment severity (HTS) (2.49). Compared with CG, the energy recovery was increased by 12.78% for the group at HTS 2.49, reduced by 6.05% and 32.09% for groups at HTS 4.06 and 5.21, respectively. Compared to single anaerobic digestion, TSAF significantly increased the energy recovery by 22.23-146.78%. 5-HMF and furfural were degraded by 17.65-71.08% and 46.58-82.20%, respectively, after first-stage biohydrogen fermentation. The analysis of microbial structure revealed that Peptococcaceae and Desulfovibrio related to inhibitors degradation were enriched with increasing HTS during first-stage fermentation. During the second-stage biomethane fermentation, the family Enterobacteriaceae was reduced as a symbiosis with hydrogenotrophic methanogens, accompanied with a decrease of Methanobacteriaceae. In comparison, the family Methanosaetaceae and Methanosarcinaceae belonging to acetoclastic methanogens, were remarkably increased due to the VFAs-rich effluents.