Effect of light conditions on mixotrophic cultivation of green microalgae.

Current research aimed to increase mixotrophic biomass from various organic carbon sources by exploring best light conditions. Three substrates glucose, acetic acid and glycerol were studied for their effects on mixotrophic microalgae cultivation under four light conditions. Light irradiance exhibited variability in growth response and photosynthetic efficiency based on type of substrates used in mixotrophic growth. Each substrate showed variability in light requirements for their effective assimilations. From growth responses, glucose and acetic acid respectively exhibited heterotrophic and mixotrophic (better growth in light) natures. Continuous light-deficient condition was adequate for effective mixotrophic growth as well as energy saving for glucose. However, light-sufficient condition required for effective acetic acid supported mixotrophic growth. Mixotrophic benefits from glycerol and its uptake by Chlorella protothecoides was negligible in all light conditions. Investigation of heterotrophic biomass contribution by various substrates in overall mixotrophic yield, glucose offered maximum approx. 43% contribution.

Development of large-scale and economic pH control system for outdoor cultivation of microalgae Haematococcus pluvialis using industrial flue gas.

The aim of this study was to develop the economic and effective buffer system for microalgae mass cultivation using industrial flue gas. Due to the continuous flue gas supplement, culture media acidified, therefore cell growth inhibited. Although buffering agent was added, this result increase in cost for overall culture process. Therefore combined buffer system of bicarbonate and phosphate (BP) for large-scale use was investigated. The bicarbonate buffer system generated from CO2 dissolution, additionally phosphate buffer system improves the buffer performance under the continuous CO2 supplementation from flue gas. The microalgae Haematococcus pluvialis was cultivated under autotrophic outdoor conditions using these buffer solutions. As a result, the autotrophic BP buffer system enhanced the biomass and astaxanthin productivity of H. pluvialis to 105% and 103%, respectively. The results confirm that the BP buffer system reduces the cost of microalgal CO2 conversion process, particularly for the outdoor mass cultivation.