UV-C pretreatment of wastewater-grown algal biomass for recover of biofuel precursors

Abstract

In the present study, ultraviolet radiation C (UV-C) was used as a pretreatment tool for the optimal recovery of biofuel precursors from algae Chlorella vulgaris. The pretreatment efficiency of UV-C with fixed light intensity (1.173 mWcm−2) on 1.5 gL-1 algal biomass was observed at 0, 0.5, 1, 2, 5, 10, and 20 h of irradiation by measuring the released sugar content and soluble chemical oxygen demand (sCOD). The UV-C pretreated algal cells were also analyzed through impedance spectroscopy, fluorescence microscope, and digital images to assess the degree of cell wall disintegration. The released sugar content reached a maximum of 73.61 mg L-1 at 10 h of exposure, whereas the maximum sCOD of 190 mg L-1 was achieved at 20 h exposure. Image analysis indicated that the chlorophyll content declined exponentially from 7.21 to 0.14 µgmL-1 with UV-C exposure. An increase in UV-C exposure time resulted in decreased impedance and increased conductance. The SYTOX green fluorescence also increased with 10 h of exposure, followed by a decline. Therefore, the cell wall stability gets compromised and the permeability increases with increment in UV-C exposure. This triggers extensive release in cell wall sugar content with exposure. Further exposure destabilizes the cell wall leading to discreet breakage. This breakage disperses internal content to bulk liquid, causing elevated sCOD with reduced sugar content. The present study showed that UV-C to be a potential pretreatment strategy to release precursors to derive biofuels such as biohydrogen, bioethanol and others.