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To improve microalgae biomass utilization efficiency during biofuel production process, medium-low temperature hydrothermal hydrolysis pretreatment was adopted in this study. The pretreatment kinetic characteristics of concentrated wet microalgae Chlorella vulgaris biomass (50 g/L) under medium-low temperature hydrolysis (100°C-200°C) were experimentally investigated. The hydrothermal hydrolysis kinetics describing the coupled effects of temperature, initial pressure and retention time then were proposed using response surface methodology (RSM). The maximum carbohydrate yield reached 327.3 mg/g dried biomass under initial pressure of 4 MPa at reaction temperature of 150°C for 120 min. The maximum protein yield (321.5 mg/g dried biomass) was obtained under initial pressure of 4 MPa at reaction temperature of 200°C for 60 min. Based on the hydrothermal hydrolysis kinetic models, it was confirmed that temperature was the most important factor affecting both carbohydrate and protein release during hydrothermal hydrolysis process. Hydrothermal initial pressure and retention time were significant to carbohydrate release, but not to protein release. While, lipid was mainly distributed in microalgae residual and almost did not exist in supernatant (about 8.03 mg/g). And with assistance of mixed hexane and methanol (the ratio of hexane to methanol was 7:3), 67.69% of microalgae lipid was extracted out from hydrothermal hydrolysed microalgae residual (123.3 mg/g dried biomass). [ABSTRACT FROM AUTHOR]

Using microalgae to treat wastewater has received growing attention in the world because it is regarded as a novel means for wastewater treatment. It is commonly recognized that large-scale cultivation and commercial application of microalgae are limited by the development of photobioreactor (PBR). Although there are a lot of PBRs for microalgae pure cultivation which used culture medium, specialized PBRs designed for wastewater treatment are rare. The composition of wastewater is quite complicated; this might cause a very different photosynthetic effect of microalgae compared to those grown in a pure cultivation medium. Therefore, PBRs for wastewater treatment need to be redesigned and improved based on the existing PBRs that are used for microalgae pure cultivation. In this review, different PBRs for microalgae cultivation and wastewater treatment are summarized. PBR configurations, PBR design parameters and types of wastewater are presented. In addition, the wastewater treatment efficiency and biomass productivity were also compared among each type of PBRs. Moreover, some other promising PBRs are introduced in this review, and a two-stage cultivation mode which combines both closed and open system is discussed as well. Ultimately, this article focuses on current problems and gives an outlook for this field, aiming at providing a primary reference for microalgae cultivation by using wastewater. [ABSTRACT FROM AUTHOR]

In this study, hydrothermal catalytic liquefaction method was adopted to produce bio-oil from microalgae. The influence of supported Ni-Catalysts doped neodymium (Nd) on the bio-oil yield from microalgae liquefaction was investigated, aiming to find the optimal preparation procedure of bio-oil. It proved that under the condition of a temperature of 270°C and a reaction period of 30 min, the bio-oil yield of hydrothermal catalytic liquefaction of spirulina powder could reach 55.1% by means of the catalyst prepared with 1 mol/L neodymium nitrate as the dipping solution after a calcination for 4 h at 800°C. In addition, the characterization on catalyst was discussed in this research. [ABSTRACT FROM AUTHOR]

Botryococcus braunii is a colonial green microalga which can produce extracellular hydrocarbons at a high rate, it is considered as one of the most promising feedstocks for sustainable biofuel production. However, B. braunii is generally recognized difficulties for cultivating and has limited amount of substantive scale-up and productivity assessments with conventional aqua-suspended cultivation systems (open pond and varieties of closed photobioreactors). This paper introduces a novel cultivation system based on biofilm technology, which is called "attached cultivation". To investigate the potential of attached cultivation method, attached cultivation of B. braunii SAG 807-1 was compared with aqueous-suspension cultivation (flat plate reactors). The growth, hydrocarbon accumulation and metabolites were studied under identical conditions (e.g. temperature, light intensity, CO2 concentration). The main research results obtained are as follows: compared with conventional aqueous-suspension cultivation, the biomass productivity of B. braunii under biofilm attached cultivation was 4.78 g/(m²·d), which was higher than of 4.43 g/(m²·d) by aqueous-suspension, and hydrocarbon productivity of the two cultivation methods were 2.52 g/(m²·d) and 2.37 g/(m²·d), respectively. The contents of carbohydrate and protein were also similar. This attached cultivation method showed a new model of commercialization for the microalgae-derived biofuels. [ABSTRACT FROM AUTHOR]

Flotation is considered as an effective and energy efficient method for harvesting microalgae. However, the interaction mechanism between bubble-algae cell and cell-cell interfacial boundaries in microalgae flotation is not completely clear. To better understand the effects of surface characteristics on microalgae flotation performance, the hydrophobicity and the zeta potential of two different microalgae species were quantified based on experimental measurements and the extended DLVO (Derjagin-Landau-Verwey-Overbeek) theory. Flotation experiments were then carried out and the effects of surface characteristics on microalgae flotation performance were analyzed. Algae Chlorella vulgaris and Anabaena vasriabilis show naturally hydrophilic and hydrophobic properties, respectively. The addition of a cationic surfactant (C16TAB) can modify hydrophilic microalgae cells into hydrophobic and further Chlorella hydrophobicity is enhanced with increased C16TAB concentrations. The zeta potentials of both algae strains are negative in the tested pH range. Compared with Chlorella vulgaris, the magnitude of zeta potential of Anabaena vasriabilis is found larger at the same pH, resulting in a more dispersed distribution in the suspension. In addition, flotation experiments demonstrated that microalgae hydrophobicity and zeta potential have significant impacts on the harvesting efficiency and concentration factor. The hydrophobic attraction is found to play a more important role in determining the harvesting performance than electrostatic repulsion between the interacting surfaces, especially for hydrophobicity algae in the present study. Finally, the highest flotation efficiency and the highest concentration factor could not be concurrently obtained for both algae strains, suggesting that optimized flotation conditions should be selected as a compromise. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]