Marwa M. El-Dalatony

Cultivation of a new microalga, Micractinium reisseri, in municipal wastewater for nutrient removal, biomass, lipid, and fatty acid production

Coupling of advanced wastewater treatment with microalgae cultivation for low-cost lipid production was demonstrated in this study. The microalgal species Micractinium reisseri and Scenedesmus obliquus were isolated from municipal wastewater mixed with agricultural drainage. M. reisseri was selected based on the growth rate and cultivated in municipal wastewater (influent, secondary and tertiary effluents) which varied in nutrient concentration. M. reisseri showed an optimal specific growth rate (μopt) of 1.15, 1.04, and 1.01 1/day for the influent and the secondary and tertiary effluents, respectively. Secondary effluent supported the highest phosphorus removal (94%) and saturated fatty acid content (40%). The highest lipid content (40%), unsaturated fatty acid content, including monounsaturated and polyunsaturated fatty acids (66%), and nitrogen removal (80%) were observed for tertiary effluent. Fatty acids accumulating in the microalgal biomass (M. reisseri) were mainly composed of palmitic acid, oleic acid, linoleic acid, and a-linolenic acid. Cultivation of M. reisseri using municipal wastewater served a dual function of nutrient removal and biofuel feedstock generation.

Long-term production of bioethanol in repeated-batch fermentation of microalgal biomass using immobilized Saccharomyces cerevisiae.

Separate hydrolysis fermentation (SHF) and simultaneous saccharification fermentation (SSF) processes were studied for bioethanol production from microalgal biomass. SSF was selected as an efficient process to enhance the bioethanol yield through repeated-batches using immobilized yeast cells. Combined sonication and enzymatic hydrolysis of Chlamydomonas mexicana generated 10.5 and 8.48g/L of ethanol in SSF and SHF, respectively. Yeast utilized maximum portion of total reducing sugar (TRS) reaching a consumption efficiency of 91-98%. A bioethanol yield of 0.5g/g (88.2% of theoretical yield) and volumetric productivity of 0.22g/L/h was obtained after 48h of SSF. Immobilized yeast cells enabled repetitive production of ethanol for 7 cycles displaying a fermentation efficiency up to 79% for five consecutive cycles. The maximum ethanol production was 9.7g/L in 2nd-4th cycles. A total energy recovery of 85.81% was achieved from microalgal biomass in the form of bioethanol. Repeated-batch SSF demonstrated the possibility of cost-effective bioethanol production.

Enhancement of microalgal growth and biocomponent-based transformations for improved biofuel recovery: A review

Microalgal biomass has received much attention as feedstock for biofuel production due to its capacity to accumulate a substantial amount of biocomponents (including lipid, carbohydrate, and protein), high growth rate, and environmental benefit. However, commercial realization of microalgal biofuel is a challenge due to its low biomass production and insufficient technology for complete utilization of biomass. Recently, advanced strategies have been explored to overcome the challenges of conventional approaches and to achieve maximum possible outcomes in terms of growth. These strategies include a combination of stress factors; co-culturing with other microorganisms; and addition of salts, flue gases, and phytohormones. This review summarizes the recent progress in the application of single and combined abiotic stress conditions to stimulate microalgal growth and its biocomponents. An innovative schematic model is presented of the biomass-energy conversion pathway that proposes the transformation of all potential biocomponents of microalgae into biofuels.