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The microorganisms in biofilms live in a self-produced matrix of hydrated extracellular polymeric substances (EPS) that forms their immediate environment. The objective of this paper was to investigate the relationships between culture conditions, EPS, microalgal biofilms growth and lipid accumulation. Fresh water alga Botryococcus braunii was attached culture in multi-layers photobioreactors with different culture media and substrates. The results indicated that the production of EPS was affected by culture period, nutrient, and substrate. Increasing the production of EPS may enhance the biofilm growth. However, the EPS components, namely proteins and polysaccharide had a more profound effect on biofilm formation compared to total EPS, with protein being more significant than polysaccharide. Nitrogen-free and EPS strategies were conducted to increase the lipid content of B. braunii biofilm from 11.6 to 42.3 % and 51.3 %, respectively. Compared to suspended culture, the lipid quality was enhanced. The dominant component of hexadecanoic acid (16:0) was enhanced from 21.78 to 48.17 % and 55.44 %, respectively.

The objective of this paper was to optimize the flocculation and biomass productivity of Botryococcus braunii by using an organic carbon source glycine. The effects of culture period and glycine dose with high, medium and low levels on both solid concentration achieved and biomass productivity were conducted. It was found that extracellular polymeric substances (EPS), which promotes flocculation, was produced not only by bacterial but also by microalgae. The productivity of EPS was affected by culture period, glycine dose and mixing time. The maximum EPS of 103.3 mg/L obtained with 11 day culture period and 0.1 g/L glycine, leading to the maximum solid concentration achieved of 51 g/L, the biomass recovery rate 72%.

Lipid extraction process claimed about 10-20% of the total cost of microalgal fuels. Cell disruption (bead beater, a high-pressure homogenizer, ultrasoniaction, etc) followed with solvent extraction (hexane, chloroform and methyl, etc) are commonly used in lab-scale experiments. However, it is time consuming and costly to apply these methods in large-scale production. Recently, some innovative methods, such as microwave-assisted process and enzyme treatment are also found effective in lipid extraction from wet microalgae biomass. This article reviewed the current techniques commonly used in lipid extraction from wet microalgae.

Keywords: Biodiesel, Base catalyst, Waste Fried Oil, Orthogonal design Abstract: In this article the biodiesel production procedure of base-catalyzed esterification was studied, and the optimal conditions of preparation were brought up. By applying orthogonal design, the optimal conditions of base-catalyzed esterification from waste frying oil with acid value of 4 mg/l KOH were: methanol/oil ratio, 8:1; catalyst dose, 1% oil weight; temperature, 85°C; reaction time, 1.5 h. The maximum oil conversion rate of 90% was achieved. The influence of each factor on the oil production in descending order was: methanol/oil ratio > catalyst dose > temperature > reaction time. The biodiesel refinement was carried out with three types of rinsing solutions: distilled water, satirized NaCl solvent and glacial acetic acid. Rinsing times, soap removing rate and final acid value of the biodiesel were considered as the critical factors in evaluating the effectiveness of the rinsing solution on the biodiesel refinement. The results turned out that the most suitable rinsing method for industrial application was rinsing with saturated NaCl solvent.

In this letter a Monte Carlo (MC) algorithm is used to simulate the propagation of polarized light in double-layer turbid media and the 2-dimentional backscattered Stokes vectors and Mueller matrices are obtained. Relationships between backscattered Mueller matrix and optical properties, such as scattering, absorption and layered structure, are discussed in detail. Integrating the 2-dimentional Mueller matrix elements along radial and azimuthal directions, we obtain a reverse trend with respect to the optical parameters for upper and lower layers, which suggests possibilities for discriminating subtle optical properties in a double-layer structure using backscattered polarization patterns such as Mueller matrix.

Extracellular polymeric substances (EPS) excreted by microalgae are effective for microalgal flocculation. An auto-flocculation strategy was conducted by adding adequate glycine into the medium, stimulating EPS secretion to achieve auto-flocculation, and recycling the supernatant medium for further cultivation. Bound EPS positively corresponded with the solid concentration achieved. Increasing the mixing time enhanced the secretion of bound EPS but the influence of glycine was affected by light intensity. Increasing the glycine dose decreased the production of bound EPS with light intensity of 250 μmol m(-2) s(-1), but increased the production of bound EPS with light intensity of 125 μmol m(-2) s(-1). Maximum solid concentration of 21.2 g l(-1) with biomass recovery rate of 71 % was achieved under light intensity of 250 μmol m(-2) s(-1), mixing time of 3 days and glycine at 0.1 g l(-1).

The influences of urea, nitrate and glycine with four concentration levels on attached culture of Nannochloropsis oculata were investigated. The organic nitrogen source glycine was effective on improving not only adhesion biomass productivity but also adhesion rate. The maximum adhesion biomass productivity of 15.76 ± 0.52 g m(-2) day(-1) with adhesion rate of 76.67 ± 0.42 % was achieved with 18 mM glycine. To increase the lipid production, three lipid enhancing strategies were conducted afterwards, including nitrogen starvation, high light, and the combination of nitrogen starvation and high light. In nitrogen starvation situation, although the lipid content was greatly increased, the adhesion biomass productivity dropped probably due to the low cell viability. Increasing light intensity was effective on enhancing both adhesion biomass productivity and lipid content. The results indicated that nitrogen starvation was effective on improving both lipid content and adhesion rate when high light was applied. The maximum lipid yield of 4.32 ± 0.14 g m(-2) day(-1) with adhesion biomass productivity of 21.32 ± 0.65 g m(-2) day(-1), adhesion rate of 86.81 ± 0.10 % and lipid content of 20.24 ± 0.06 % was achieved with the combination strategy.

The objective of this study was to understand and optimize the formation of microalgae biofilms in specific culture conditions. Firstly, the adhesion of six freshwater algae species was compared. Chlorococcum sp. was selected because of the high adhesion biomass productivity (ABP) and adhesion rate achieved. Secondly, the adhesion of Chlorococcum sp. was compared with nine commonly used supporting materials, and glass fiber-reinforced plastic proved to be the optimal substrata. Thirdly, based on response surface methodology experiments, a second-order polynomial model was developed to examine the effect of culture period, initial total nitrogen concentration (ITNC) in manure wastewater, pH and culture volume of the growth chamber on the adhesion of Chlorococcum sp. using glass fiber-reinforced plastic. The experimental and modeling results showed that ITNC, pH and culture volume as well as the interactions between culture period and ITNC, culture period and culture volume were significant on ABP. Optimum culture conditions were predicted at a culture period of 11 days, ITNC of 70 mg L(-1), pH of 8 and culture volume of 340 mL, under which the predicted maximum ABP was 4.26 g m(-2) day(-1). The prediction was close to validation experimental results, indicating that the model could be used to guide and optimize the attached culture of Chlorococcum sp. using glass fiber-reinforced plastic.