A new approach for improving microalgal biohydrogen photoproduction based on safe & fast oxygen consumption

Abstract

Microalgal H2 photoproduction has the potential of being an affordable method for producing this alternative fuel; however extreme sensitivity of hydrogenase enzyme to photosynthetic O2 naturally prevents large-scale H2 production upon illumination. Although a two-phase sulfur deficiency method has been established to deal with this incompatibility, its time and cost demanding, so that this model is not commercially scalable. Despite much research has been conducted, no proper economic alternative for the sulfur deprivation model, with higher or even same productivity and sustainability, has been presented till now. Herein we propose a simple and viable alternative, through introducing a chemical O2 scavenger system, called oxysorb, to algal cultures.Oxysorb, in non-cytotoxic concentrations (including 50 or 100 mM sodium ascorbate and 5 ppm cupric sulfate) for CC124 as well as pgr5 cultures (containing 30 μg/ml chlorophyll) showed a fast, safe and persisted O2 removal capacity, initiating H2 production in the sulfur-containing cultures, either in photoheterotrophic or in autotrophic conditions. Total H2 production obtained with CC124 and pgr5 cultures, containing 100 mM oxysorb, was 2–5.5 times higher than sulfur-deprived ones (measured in a small closed system). This higher H2 productivity in the oxysorb approach was achieved due to anoxia establishment with no ROS production and without impacting PSII activity.