Effects of organic loading rate on biogas production from macroalgae: Performance and microbial community structure.

Macroalgae biomass has been considered as a promising feedstock for biogas production. In order to improve the efficiency of anaerobic digestion (AD) of macroalgae, semi-continuous fermentation was conducted to examine the effects of organic loading rate (OLR) on biogas production from Macrocystis pyrifer. Results showed that, under OLRs of 1.37, 2.74, 4.12 and 6.85kgVSsubstrate/(m3·d), the average unit biogas yields were 438.9, 477.3, 480.1 and 188.7mL/(gVSsubstrated), respectively. It indicated that biogas production was promoted by the increased OLR in an appropriate range while inhibited by the OLR beyond the appropriate range. The investigation on physical-chemical parameters revealed that unfavorable VFAs concentration, pH and salinity might be the main causes for system failure due to the overrange OLR, while the total phenols failed to reach the inhibitory concentration. Microbial community analysis demonstrated that several bacterial and archaeal phyla altered with increase in OLR apparently.

[Simultaneous production of hydrogen and volatile fatty acid from Macrocystis pyrifera].

Batch experiments were conducted to analyze the effects of pretreatment conditions, inoculum-substrate ratio (ISR) and initial pH on the hydrogen and volatile fatty acid (VFA) production from anaerobic digestion of Macrocystis pyrifera biomass. The results indicated that M. pyrifera could produce hydrogen and VFA simultaneously. In addition, thermo-alkaline pretreatment was proved as the best method for hydrogen and VFA production. The optimal pretreatment conditions, ISR, initial pH value were determined as thermal-alkaline pretreatment at 100 degrees C with 4 g x L(-1) NaOH, 0.3 and 6, respectively. Under these conditions, the maximum hydrogen production was 36.21 mL x g(-1) per unit volatile solids, which resulted in 77.82% improvement compared with the yield from untreated M. pyrifera. Furthermore, the TVFA yield under the optimal conditions was found to be 0.15 g x g(-1) per unit volatile solids and the VFAs mainly consisted of acetate and butvrate