Biogas generation from microalgal biomass and the effect of pretreatment

Abstract

Microalgal cultures have growing attention due to their diverse applications in the field of waste management such as removal of nutrients, organic contaminants, heavy metals and pathogens from domestic wastewater, treatment of olive oil, pulp and paper, and iron and steel industry wastewaters. Moreover, the harvested microalgal biomass, itself, constitutes a raw material for the production of different high-value chemicals and bio-fuels such as biodiesel / bio-ethanol and of biogas via anaerobic digestion. In this study, biogas production from two microalgal biomasses, namely, axenic Chlorella vulgaris culture and mixed microalgal culture (Karabük biomass) was investigated. The effects of ultrasonication (at 22 and 44 kHz) and thermal treatment (at 105^oC for 2 hours and at 121^oC, 15 psi for 5 min) on hydrolysis of microalgal biomass and biogas production were examined via biochemical methane potential (BMP) tests. Results revealed the significant effect of thermal treatment on biogas production from both algal biomass types. Thermal treatment was found to be superior to ultrasonication. Despite being less effective compared to thermal treatment, ultrasonication also resulted in increased biogas production from axenic biomass. However, it had no effect on the biodegradability of Karabük algal biomass.