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For biofuel applications, increasing net lipid productivity from continuous flow microalgal cultures is critically important. Parameters that affect net lipid productivity include: cell lipid content, culture flow rate or hydraulic retention time, and biomass concentration. However, these parameters are interlinked and cannot be independently altered. This research is aimed at probing the interdependence between variables and maximizing net lipids from outdoor algal cultures. Three representative algal species for biodiesel production namely, Nannochloris sp., Selenastrum capricornutum , and Scenedesmus dimorphus , were grown in an outdoor continuous-flow system at four different Hydraulic Retention Times (HRT) of 6, 12, 18 and 24 h. The highest biomass cell concentration (250 mg/L) occurred at the longest HRT (24 h) and decreased progressively with shorter HRTs. However, net aerial biomass productivity numbers did not follow a specific pattern. The highest net aerial productivity of 43.4 g/m 2 /day was achieved with Nannochloris sp. species at 6 h HRT, compared to 32.1 g/m 2 /day at 24 h HRT by S. capricornutum species. Net lipid productivity was found to be significantly higher at 24 h HRT, achieving 7.9, 9.6 and 10.4 g/m 2 /day for Nannochloris sp., S. capricornutum , and S. dimorphus respectively. When the media flow was curtailed, the lipid concentrations increased at the expense of protein and carbohydrate contents of the cell. |
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