Comparative study on cultivation of microalgae for nutrient removal and lipid production in different artificial wastewaters

Wastewater contains high concentration of nutrients,like nitrogen and phosphorus,which have been identified as the main reasons for water eutrophication and serious ecological issues.Therefore,cultivating a tolerant and adaptive microalgae strain in wastewater is considered as a promising approach for sustainable biomass/lipid production.The potential usages of Desmodesmus sp.for biomass and lipid production within different artificial wastewater(AW)were investigated and the removal efficiencies of nutrient were compared.The maximum removal rate of chemical oxygen demand,ammonia nitrogen,nitrate nitrogen and phosphate were 272 mg/(L·d),14.021 mg/(L·d),7.774 mg/(L·d)and 3.347 mg/(L·d),respectively in AW2,AW3,AW5 and AW2.Maximum biomass(1.159 g/L)and lipid(280 mg/L)productions were observed in AW5,while the highest lipid content achieved was 37.42%in AW1.Fatty acid analysis showed that lipids extracted from AW-cultivated Desmodesmus sp.contained 59.57%-77.79%polyunsaturated fatty acids(30.6%-44.47%was linoleic acid).

Selection and characterization of eight freshwater green algae strains for synchronous water purification and lipid production

The objective of this study is to select and characterize the candidate for synchronous water purification and lipid production from eight freshwater microalgae strains （Chlorella sp. HQ, C. emersonii, C. pyrenoidosa, C. vulgaris, Scenedesmus dimorphus, S. quadricauda, S. obiquus, Scenedesmus sp. LX1）. The strains Chlorella sp. HQ, C. pyrenoidesa, and S. obliquus showed superiority in biomass accumulation, while the top biomass producers did not correspond to the top lipid producers. S. quadricauda achieved higher lipid content （66.1%）, and Chlorella sp. HQ and S. dimorphus ranked down in sequence, with lipid content above 30%. Considering nutrient removal ability （total nitrogen （TN）： 52.97%; total phosphorus （TP）： 84.81%）, the newly isolated microalga Chlorella sp. HQ was the possible candidate for water purification coupled with lipid production. To further investigate the lipid producing and nutrient removal mechanism of candidate microalga, the ultra structural changes especially the lipid droplets under different water qualities （different TN and TP concentrations） were characterized. The results elucidate the nutrient-deficiency （TN： 3.0 mg·L^-1; TP： 0.3 mg·L^-1） condition was in favor of forming lipid bodies in Chlorella sp. HQ at the sub-cellular level, while the biomass production was inhibited due to the decrease in chloroplast number which could further suppress the nutrient removal effect. Finally, a two- phase cultivation process （a nutrient replete phase to produce biomass followed by a nutrient deplete phase to enhance lipid content） was conducted in a photo-bioreactor for Chlorella sp. HQ to serve for algae-based synchronous biodiesel production and wastewater purification.