Photosynthetic hydrogen production as acclimation mechanism in nutrient-deprived Chlamydomonas

Influence of Sulfur and Light Intensity in Nutrient Removal, and Hydrogen and Ethanol Production by Optimized Biomass of Chlamydomonas Reinhardtii in Batch Anaerobic Photobioreactors

“…Thus, a higher amount of biomass was obtained in the rst step at a lower pH (6.2) and light intensity of 200 µmol m − 2 s − 1 . It is believed that this biomass optimization provided the inoculation of a greater amount of biomass in the photobioreactors and favored the hydrogen production variable test as studies have reported that an increased amount of biomass can improve the hydrogen production yield [6][7][8]21].…”

“…Sulfur deprivation decreases photosynthetic activity and consequently decreases oxygen production, which is consumed by respiration. There is a compensatory point between photosynthesis and respiration that results in an anaerobic environment [6,8,10,41]. Reports show that low sulfur concentrations (around 12.5 to 100 µmol L − 1 ) can improve the compensatory point between photosynthesis and respiration and obtain better results in hydrogen production [13,14].…”

“…Indirect biophotolysis occurs from oxidation of organic carbon and directs the ow of electrons to PSI (photofermentation) or to the fermentative pathway in dark, anaerobic conditions (dark fermentation). Thus, the indirect pathway in the PSI occurs regardless of PSII [7][8][9][10]. In the presence of oxygen and light energy, the electrons in PSI pass through a transport chain to the nal electron acceptor, ferredoxin, which reduces NADP to NADPH which is then oxidized in the CO 2 xation reactions in the Calvin cycle [10].…”

“…Some green algae, such as Chlamydomonas, have this ability and can grow using acetate as the only carbon source, in addition to having a versatile fermentative metabolism [9,16] and the potential for production of biofuels under autotrophic, mixotrophic or heterotrophic conditions [7,17]. Therefore, related to the presence of speci c cellular metabolism and the compensatory point between respiration and photosynthesis, there are several factors that can interfere and are important in hydrogen production, such as pH [18], nutritional stress by phosphorus or nitrogen [19], as well as light intensity and the effect of low sulfur concentrations, which are being investigated in order to the improve the process [8,14,15,20]. Furthermore, some researchers reported that greater biomass of microalgae allows higher hydrogen production e ciency [6-8, 21, 22].…”

“…As mentioned above, microalgae also have the ability to utilize various organic molecules to generate other products, such as organic acids and ethanol, through dark fermentation pathways [6,8,23].…”