Lipid metabolism in response to individual short chain fatty acids during mixotrophic mode of microalgal cultivation: Influence on biodiesel saturation and protein profile.

Critical influence of different short chain fatty acids as organic carbon source, during growth (GP) and nutrient stress lipogenic phase (NSLP) was investigated on biomass and lipid productivity, in mixotrophic fed-batch microalgae cultivation. Nutrient deprivation induced physiological stress stimulated highest lipid productivity with acetate (total/neutral lipids, 35/17) with saturation index of 80.53% by the end of NSLP followed by butyrate (12/7%; 78%). Biomass growth followed the order of acetate (2.23 g/l) >butyrate (0.99 g/l) >propionate (0.77 g/l). VFA removal (as COD) was maximum with acetate (87%) followed by butyrate (55.09%) and propionate (10.60%). Palmitic acid was the most dominant fatty acid found in the fatty acid composition of all variants and butyrate fed system yielded a maximum of 44% palmitic acid. Protein profiling illustrated prominence of acetyl CoA-synthetase activity in acetate system. Thus, fatty acids provide a promising alternative feedstock for biodiesel production with integrated microalgae-biorefinery.

Algal biocathode for in situ terminal electron acceptor (TEA) production: synergetic association of bacteria-microalgae metabolism for the functioning of biofuel cell.

Replacement of energy intensive mechanical aeration with sustainable oxygenic photosynthesis by microalgae at cathode was studied in dual-chambered microbial fuel cell (MFC). The synergistic association between bacterial fermentation at anode and the oxygenic photosynthesis of microalgae at cathode facilitated good power output as well as treatment efficiency. However, MFC operation during spring showed higher bioelectrogenic activity (57.0 mW/m(2)) over summer (1.1 mW/m(2)) due to the higher oxygenic photosynthetic activity of microalgae and respective dissolved oxygen (DO) levels. This can be attributed to RuBisCO inactivation under high temperatures and light intensity of summer, which prevented rich algal biomass growth as well as their photosynthetic activity. Unlike abiotic cathode, the algal cathode potential increased with operation time due to the algal biomass growth during spring but was negligible during summer. The catalytic currents on voltammetric signatures and the bioprocess parameters also corroborated well with the observed power output.