Tianzhong Liu

Biodiesel production from algae oil high in free fatty acids by two-step catalytic conversion

The effect of storage temperature and time on lipid composition of Scenedesmus sp. was studied. When stored at 4°C or higher, the free fatty acid content in the wet biomass increased from a trace to 62.0% by day 4. Using two-step catalytic conversion, algae oil with a high free fatty acid content was converted to biodiesel by pre-esterification and transesterification. The conversion rate of triacylglycerols reached 100% under the methanol to oil molar ratio of 12:1 during catalysis with 2% potassium hydroxide at 65°C for 30 min. This process was scaled up to produce biodiesel from Scenedesmus sp. and Nannochloropsis sp. oil. The crude biodiesel was purified using bleaching earth. Except for moisture content, the biodiesel conformed to Chinese National Standards.

Attached cultivation technology of microalgae for efficient biomass feedstock production

The potential of microalgae biofuel has not been realized because of low productivity and high costs associated with the current cultivation systems. In this paper, an attached cultivation method was introduced, in which microalgae cells grew on the surface of vertical artificial supporting material to form algal film. Multiple of the algal films were assembled in an array fashion to dilute solar irradiation to facilitate high photosynthetic efficiency. Results showed that a broad range of microalgae species can grow with this attached method. A biomass productivity of 50-80 g m(-2) d(-1) was obtained outdoors for Scenedesmus obliquus, corresponding to the photosynthetic efficiency of 5.2-8.3% (total solar radiation). This attached method also offers lots of possible advantages over traditional open ponds, such as on water saving, harvesting, contamination controlling and scale-up. The attached cultivation represents a promising technology for economically viable production of microalgae biofuels.

The contamination and control of biological pollutants in mass cultivation of microalgae

The potential of microalgae as a biomass feedstock for biofuels, bioproducts and as a technological solution for CO(2) fixation is subject to intense academic and industrial researches. However, current microalgal mass culture technologies have failed to produce bulk volume of microalgal biomass at low cost, because the contaminations of biological pollutants become a big constraint in mass cultivation and impede the industrial process. Here the transmission routes, contamination mechanisms of biological pollutants both in open ponds and photobioreactors are described and recent attempts to overcome the barrier are reviewed. What worth noting, unlike conventional microbial fermentation which uses a pure monoculture, the cultivation of microalgae is a complicated symbiotic system of microalgae-bacterial-zooplankton where the target microalgae dominate, cross infection or contamination by biological pollutants is inevitable and it will require much further research. Further investigation and development of control methods are necessary, particularly microalgal strain selection.

Utilization of simulated flue gas for cultivation of Scenedesmus dimorphus

Effects of flue gas components on growth of Scenedesmus dimorphus were investigated and two methods were carried out to eliminate the inhibitory effects of flue gas on microalgae. S. dimorphus could tolerate CO(2) concentrations of 10-20% and NO concentrations of 100-500 ppm, while the maximum SO(2) concentration tolerated by S. dimorphus was 100 ppm. Addition of CaCO(3) during sparging with simulated flue gas (15% CO(2), 400 ppm SO(2), 300 ppm NO, balance N(2)) maintained the pH at about 7.0 and the algal cells grew well (3.20 g L(-1)). By intermittent sparging with flue gas controlled by pH feedback, the maximum biomass concentration and highest CO(2) utilization efficiency were 3.63 g L(-1) and 75.61%, respectively. These results indicated that S. dimorphus could tolerate high concentrations of CO(2) and NO, and the methods of CaCO(3) addition and intermittent sparging have great potential to overcome the inhibition of flue gas on microalgae.

Subcritical co-solvents extraction of lipid from wet microalgae pastes of Nannochloropsis sp

In this paper subcritical co-solvents extraction (SCE) of algal lipid from wet pastes of Nannochloropsis sp. is examined. The influences of five operating parameters including the ratio between ethanol to hexane, the ratio of mixed solvents to algal biomass (dry weight), extraction temperature, pressure, and time were investigated. The determined optimum extraction conditions were 3:1 (hexane to ethanol ratio), 10:1 ratio (co-solvents to microalgae (dry weight) ratio), 90°C, 1.4 MPa, and 50 min, which could produce 88% recovery rate of the total lipids. In addition, electron micrographs of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were conducted to show that the algal cell presented shrunken, collapsed with some wrinkles and microholes after SCE extraction. The main composition of total lipids extracted under the optimum conditions was TAG which represented more than 80%. And the fatty acid profile of triglycerides revealed that C16:0 (35.67 ± 0.2%), C18:1 (26.84 ± 0.044%) and C16:1 (25.96 ± 0.011%) were dominant. Practical applications: The reported method could save energy consumption significantly through avoiding deep dewatering (for example drying). The composition of the extracted lipid is suitable for the production of high quality biodiesel.

Integration process of biodiesel production from filamentous oleaginous microalgae Tribonema minus.

Biodiesel production from microalgae has been receiving considerable attention. Past studies mainly relied on tiny sized single-cell oleaginous microalgal species, the biodiesel based on filamentous oleaginous microalgae was rarely reported. Thus, integrated process of biodiesel production from filamentous oleaginous microalgal strain Tribonema minus was studied in this work. The filamentous microalgae was cultivated for 21 days in 40 L glass panel, microalgae cells was harvested by DAF without any flocculants after the lipid content was 50.23%. After that, total lipid was extracted by subcritical ethanol from wet algal paste and 44.55% of crude lipid was triacylglycerols. Two-step catalytic conversion of pre-esterification and transesterification was adopted to convert the crude algal oil to biodiesel. The conversion rate of triacylglycerols reached 96.52% under the methanol to oil molar ratio of 12:1 during catalysis with 2% potassium hydroxide at 65°C for 30 min. The biodiesel product from T. minus conformed to Chinese National Standards.

Attached cultivation for improving the biomass productivity of Spirulina platensis

To improve cultivation efficiency for microalgae Spirulina platensis is related to increase its potential use as food source and as an effective alternative for CO2 fixation. The present work attempted to establish a technique, namely attached cultivation, for S. platensis. Laboratory experiments were made firstly to investigate optimal conditions on attached cultivation. The optimal conditions were found: 25 g m(-2) for initial inoculum density using electrostatic flocking cloth as substrata, light intensity lower than 200 μmol m(-2) s(-1), CO2 enriched air flow (0.5%) at a superficial aeration rate of 0.0056 m s(-1) in a NaHCO3-free Zarrouk medium. An outdoor attached cultivation bench-scale bioreactor was built and a 10d culture of S. platensis was carried out with daily harvesting. A high footprint areal biomass productivity of 60 g m(-2) d(-1) was obtained. The nutrition of S. platensis with attached cultivation is identical to that with conventional liquid cultivation.

Special biochemical responses to nitrogen deprivation of filamentous oleaginous microalgae Tribonema sp.

Both filamentous microalgae Tribonema and unicellular microalgae Nanochloropsis are promising feedstock for biodiesel production. Nitrogen starvation increased lipid content in Nannochloropsis but decreased that in Tribonema. In this study, biochemical responses of Tribonema under different levels of nitrogen (0N, 0.05N, 0.1N and 1N-BG11) were investigated. 1N-BG11 was sufficient during 15-day-cultivation, while the other levels were nitrogen limited. Cell growth was interrupted with 0N-BG11, but no differences in biomass among 0.05N, 0.1N and 1N-BG11. Both protein and lipid contents (% of dry weight) declined gradually inversely to the increment in carbohydrate contents under the decreasement of nitrogen levels. Both assays and TEM results showed that the cytoplasm in Tribonema contained no starch. Compared to nitrogen-replete condition, the TAG content (% of dry weight) decreased obviously under nitrogen starvation. Different levels of nitrogen did not cause fundamental shifts in fatty acid profiles in Tribonema.

Harvesting of microalgae Scenedesmus sp. using polyvinylidene fluoride microfiltration membrane

Abstract In this paper, polyvinylidene fluoride (PVDF) microfiltration membrane was used for harvesting microalgae Scenedesmus sp. The changes of permeation flux and OD750 of the algae medium during membrane filtration process were investigated. In order to reduce membrane fouling, both ventilation into algae medium and backwashing were adopted. The results showed that backwashing was better than ventilation to control membrane fouling. The optimized procedure was backwashing for 1 min every 20 min of continuing filtration. When the volume reduction factor (VRF) was up to 10, the recovery rate of the algae cells could reach above 90%. In addition, this paper showed that VRF and the initial concentrations of algae broth significantly affected the recovery rate. Higher VRF and higher initial concentrations of algae could make the recovery rate lower. Therefore, in order to obtain the needed recovery rate, these above factors needed to be considered. Generally, these results provided the feasible way to harv...

Effects of nitrogen source and nitrogen supply model on the growth and hydrocarbon accumulation of immobilized biofilm cultivation of B. braunii

The immobilized biofilm cultivation was a promising method to greatly improve the biomass productivity of microalga Botryococcus braunii, which was considered as an feedstock of renewable biofuel. In this research, the effects of different nitrogen sources and supply methods on growth and hydrocarbon production of B. braunii under immobilized biofilm cultivation (attached cultivation) were studied. Of the total 5 different nitrogen sources, NaNO₃ was selected as the best one with which the high biomass productivity and hydrocarbon productivity of 6.45 gm(-2)d(-1) and 2.79 gm(-2)d(-1) were obtained respectively. The optimized nitrogen concentration was 0.99 mM for non-circulating medium supply model, while for the circulating model, the optimized nitrogen concentration as well as medium volume was 1.49 mM and 1.2L, respectively. Furthermore, nitrogen inputs based on growth of 1 kg dry algae biomass was only 28.92 g with circulating model. Attached cultivation was high efficient in light, nutrient and water utilization.