Although
Scenedesmus is capable of producing many kinds of
biofuels such as biohydrogen, biodiesel, bioethanol and drop-in fuels, most extensive research has been done on the use of
Scenedesmus for biodiesel production. Like all algae systems, the implementation of integrated biofuel production of
Scenedesmus from the laboratory findings has challenges in large-scale production. Major challenges include nutrient supply and recycling, gas transfer and exchange, PAR (Photosynthetically Active Radiation) delivery, cultural integrity, environmental control, land and water availability, harvesting, and genetic and metabolic engineering Algae produce H2 gas under anaerobic conditions by providing hydrogenases with hydrogen ions derived from splitting of water molecules via photosynthesis. However, enzyme activity is transient due to inhibition from O2 production via photosynthesis, a problem that continues to plague H2 production.
S. obliquus is traditionally known to utilize a nickel-iron hydrogenase, but usage of other iron hydrogenases in H2 production is also reported. Hydrogenase enzyme activity in
Scenedesmus species is reported to be lower than that of
Chlamydomonas reinhardtii. H2 production independent of Photosystem II in
Scenedesmus has also been performed using redox equivalents of fermentative metabolism under dark anaerobic incubation. Research findings suggest that a sulfur-deprived environment triggers an imbalance in the photosynthesis and respiration relationship, resulting in net consumption of O2, causing anaerobiosis, and switching to hydrogen production. Biohydrogen production research using
Scenedesmus is actively spurred by its applications to
wastewater treatment. (See subsequent section on waste management by
Scenedesmus).
Biodiesel production Scenedesmus is known to have high biomass productivity among green algae, and has been actively researched for its use for biodiesel production. Its heterotrophic production of biomass and lipid in optimized conditions is reported to have higher efficiency than its autotrophic production. Optimization of biomass productivity as well as lipid content through varying concentration of supplemental nutrients has been done in numerous studies; currently,
Scenedesmus lipid yield after optimization has reached ~60% dry cell weight, lower than some other algae. However,
Scenedesmus is more efficient at capturing CO2 than other algae. A significant improvement (up to six-fold) of feedstock yields was achieved by adding varying concentrations of ethanol under a 12-hour photoperiod and in the dark. The most significant improvement in lipid production was obtained when stationary phase cultures were transferred to media deficient in nitrate for 7 days and phosphate for 3 days, respectively.
Scenedesmus abundans was isolated from Dal Lake, Kashmir and proved to be a suitable raw material for biodiesel production. The alga increased significantly in biomass and lipid content with the nitrogen concentration of 0.32
g/
L of
nitrogen. A two-step transesterification was found to be best suited for
transesterification, while Folch extraction was best for lipid extraction. In one study,
Scenedesmus was used to yield high biomass productivity; its carbohydrate-rich biomass was then hydrolyzed with 2%
sulfuric acid and underwent an SHF (Separate Hydrolysis and Fermentation) process to produce 8.55 g L−1 of ethanol and a maximum yield of 0.213 g ethanol / g biomass within 4 hours of ethanol fermentation.
Drop-in fuels Isoprenoids are considered important metabolites that can be utilized as drop-in fuels, often as alkane chains.
Scenedesmus conducts a pyruvate/glyeraldehyde 3-phosphate non-mevalonate pathway to synthesize isoprenoids. However, isoprenoid yields were too low (1.5~15 mg per 10 liter of
Scenedesmus culture when cells reached 0.5-0.6 g L−1) to be considered viable for future drop-in fuel production. ==Wastewater management==