Botany · Ch 4 — Principles and Processes of Biotechnology
Biofuel: Algal Biofuel
Biofuel: Algal Biofuel
Algal biofuel (algal fuel, or algal oil) is presented here as an alternative both to conventional petroleum-based liquid fossil fuels and to first-generation biofuels made from food crops like corn and sugarcane - the key advantage being that algae can be farmed specifically as a source of energy-rich oils on land that is unsuitable for growing ordinary food crops, sidestepping the food-versus-fuel land-use conflict that dogs corn- or sugarcane-based biofuel production. The alga Botryococcus braunii is the organism normally used for this purpose, prized for naturally accumulating a particularly high proportion of oil within its own cells. Beyond conventional oil-based biodiesel, algae also offer a genuinely different biofuel route: biological hydrogen production. Under normal conditions, the alga Chlamydomonas reinhardtii carries out ordinary photosynthesis and releases oxygen as its by-product, exactly like most other photosynthetic organisms. But when this same alga is deliberately deprived of sulfur, its metabolism switches tracks entirely: instead of using its photosynthetic electrons to fix carbon dioxide as usual, it redirects them, via the electron carrier ferredoxin, t …
What this figure shows. A circular process diagram showing algae grown using sun energy and CO2 (a renewable resource); the harvested algal biomass undergoes oil extraction, yielding oil that is converted by existing biodiesel-production technology into biodiesel (a renewable fuel) plus co-products protein residue and glycerin, closing the loop back …
What this figure shows. A schematic of the photosynthetic electron-transport chain in the alga Chlamydomonas reinhardtii under sulfur deprivation, showing water (2H2O) being split at Photosystem II (PSII, releasing O2, H+ and electrons), electrons passing through the PQ pool, Cytochrome b6f and Plastocyanin (PC) to Photosystem I (PSI), then to ferredoxin (Fd); under normal (-O2 +CO2) conditions the electrons go via FNR toward CO2 fixation, but under sulfur-deprived (-O2 -CO2) conditions they are instead redirected to the [Fe]-hydrogenase enzyme (H2 ase), which comb …