Addressing the challenges for sustainable production of algal biofuels: I. Algal strains and nutrient supply

Abstract

Microalgae hold promise for the production of sustainable replacement of fossil fuels due to their high growth rates, ability to grow on non-arable land and their high content, under the proper conditions, of high energy compounds that can be relatively easily chemically converted to fuels using existing technology. However, projected large-scale algal production raises a number of sustainability concerns concerning land use, net energy return, water use and nutrient supply. The state-of-the-art of algal production of biofuels is presented with emphasis on some possible avenues to provide answers to the sustainability questions that have been raised. Here, issues concerning algal strains and supply of nutrients for large-scale production are discussed. Since sustainability concerns necessitate the use of wastewaters for supply of bulk nutrients, emphasis is placed on the composition and suitability of different wastewater streams. At the same time, algal cultivation has proven useful in waste treatment processes, and thus this aspect is also treated in some detail.

Nitrogen availability influences phosphorus removal in microalgae-based wastewater treatment

“…To evaluate how the concentration of N influences the removal of P and vice versa, Chlorella and Scenedesmus were cultured in medium with varying concentrations of N and P. The range of N and P concentrations used here represents the range of concentrations observed in weak to medium strength domestic wastewaters (Abdelaziz et al, 2013). The medium had the same composition as the WC medium (see above) but with modified NaNO 3 and K 2 HPO 4 concentrations.…”

“…The concentrations of N and P in wastewater are quite variable. In domestic wastewater, N concentrations vary between 15 and 90 mg L À1 and P concentrations between 4 and 20 mg L À1 (Abdelaziz et al, 2013;Cai et al, 2013;Christenson and Sims, 2011). Because the sources of N and P in wastewater are different, N and P concentrations often vary independently from each other.…”

Utilization of biodiesel-derived glycerol or xylose for increased growth and lipid production by indigenous microalgae

“…Moreover, the direct and indirect toll on the environment and health systems is beginning to change the cost-benefit calculus of using this black gold. The transportation sector alone consumes more than 70% of the crude oil produced, making the development of biofuels an essential element in any strategy to decrease fossil fuel dependency (Abdelaziz et al 2013). …”

Microalgal cultivation with waste streams and metabolic constraints to triacylglycerides accumulation for biofuel production

“…However, a multidisciplinary approach that integrates advances in fundamental biology, microalgal cultivation systems, bio‐oil extraction and processing, and metabolic engineering of specific microalgal strains is required to uncover the full potential of microalgae as a sustainable biofuel feedstock. Environmental stresses, particularly macronutrient (N, P) depletion, are well‐known triggers for the accumulation of highly reduced, energy‐rich storage compounds such as starch and TAGs by ‐microalgae . However, TAG content and microalgal biomass productivity are often inversely correlated, i.e., nutrient limitation stimulates TAG accumulation at the expense of growth .…”