Enzymatic and Hydrothermal Pretreatment of Newly Isolated Spirulina subsalsa BGLR6 Biomass for Enhanced Biogas Production

The complex structure and biochemical composition of the cell wall of microalgae impede their anaerobic digestion. To enhance the microalgae anaerobic biodegradability, various pretreatment approaches have been utilized. In this study, the enzyme and hydrothermal pretreatment methods were evaluated for microalgal biomass pretreatment and biogas yield. The optical and scanning electron microscopy along with Fourier transform infrared spectroscopy analysis confirmed the efficient action of both the pretreatment methods. The hydrothermal pretreatment resulted in more structural changes, though the increase in enzymatic concentration was also found to have a pronounced effect on both structural and chemical changes. The FTIR spectra determined that mostly the protein and carbohydrate structures of the microalgal cells were affected. Further upon quantitative analysis, it was observed that 10% dose (w/w) for 24 h of exposure time released significantly more soluble chemical oxygen demand compared to others. The multi-enzyme 10% dose for 24 h resulted in significantly higher biogas production potential (P) of 768.92 mL g(-1) VS at a maximum biogas production rate (R-m) of 32.16 mL g(-1) d(-1) with a very short lag phase (lambda) of 0.09 days at the end of 30 days, in comparison to untreated and other pretretment conditions in this study. Both the pretreatment approaches in the present study enhanced the microalgal biomass disintegration, digestibility and biogas production. However, more research is required to optimize the process parameters of these pretreatment approaches to make them more reasonable and applicable.