The potential of aquatic biomass for CO2-enhanced fixation and energy production

In this review, the use of micro- and macroalgae to fix CO2 and produce energy is discussed. The fixation of CO2 into aquatic biomass is an option which has recently come under intensive investigation as it can be utilized to stimulate the growth of seaweed or microalgae. Aquatic biomass has long been cultivated and used at industrial level as a source of chemicals (agar, alginate, carragenans, and fucerellans) or as food for humans or animal feed. Recent interest in its use as a source of biofuels is due to the need to shift from first-generation biofuels (biodiesel and bioethanol produced from edible biomass) to non-food sources that may grow without the use of arable land. Aquatic biomass can be grown in salty water or fresh wastewater (municipalities or process water) or else in bioreactors to produce different fuels such as bio-oil, biodiesel, bioalcohol, biohydrogen. Biogas can be produced from residual biomass after liquid fuel extraction. Microalgae are attracting much attention as they are photosynthetic renewable resources, with high lipid content and faster growth rate than terrestrial plants; they can grow in saline waters which are not suited for agriculture. While the lipid content of microalgae on a dry cellular weight basis usually varies between 20 and 40%, a lipid content as high as 85% has been reported for selected microalgal strains. They can be easily manipulated through physical stress or genetic engineering. They can also produce bioethanol. The barrier to their exploitation is the high cost (up to 5000 US$/t) of growth and processing. Seaweeds produce less biofuel per t-dry weight, but their growing and processing costs are much lower. In perspective, aquatic biomass can become an interesting and ubiquitous source of energy. (c) 2011 Society of Chemical Industry and John Wiley & Sons, Ltd.