Wenyan Liang

Harvesting Chlorella vulgaris by magnetic flocculation using Fe₃O₄ coating with polyaluminium chloride and polyacrylamide.

The harvesting of Chlorella vulgaris was investigated by magnetic flocculation, where the natural magnetite was used as magnetic seeds and the polyaluminium chloride (PACl) and polyacrylamide (PAM) were used as the coating polymer on the Fe3O4 surface. The composite modes of PACl, PAM, and Fe3O4 and their effects on harvesting were studied. The results showed that adding the composite PACl/Fe3O4 first (at (0.625 mmol Al/L)/(10 g/L)) followed by the addition PAM (at 3mg/L) was the optimum dosing strategy. Following this strategy, 99% of cells could be harvested in less than 0.5 min, and it could overcome negative impacts from pH and algal organic matter. Compared to PACl, ζ-potentials of PACl/Fe3O4 were found to be increased substantially from -4.9-8.5 mV to 1.5-19.5 mV at pH range 2.1-12.3. The charge neutralization of PACl/Fe3O4 and sweeping of PAM play an important role in magnetic harvesting of microalgal cells.

In-situ self-assembly of plant polyphenol-coated Fe 3 O 4 particles for oleaginous microalgae harvesting

Plant polyphenol (PP), a natural polymer from the Larix gmelinii, was selected as the surfactant to synthesize Fe3O4. The Fe3O4-PP composite was prepared by in-situ self-assembly in solvothermal synthesis, and characterized using FE-SEM, TEM, XRD, FTIR, XPS, TGA, and VSM. The harvesting efficiency of Chlorella vulgaris was investigated under different parameters, including algal organic matter, dosage, and pH. The results showed that the core-shell sphere of Fe3O4-PP (∼150 nm) was coated by ∼50 nm PP with a saturated magnetization of 40.0 emu/g. The Fe3O4-PP could be directly applied to the culture broth (1.5 g dry cell weight/L, pH = 9.03), achieving 93.0% of harvesting efficiency at 20 g/L. Cells were detached from the harvested aggregates by adjusting pH value to 9.80 and with ultrasonication, which achieved 95.6% of recovery efficiency. The recycled Fe3O4-PP showed high stabilities in surface properties, maintaining more than 87.5% of harvesting efficiency after five recycles.

Ecotoxicity assessment of soil irrigated with domestic wastewater using different extractions

The toxicity of soil irrigated with treated domestic wastewater (site A) and untreated gray wastewater (site B) were investigated. Soil extracts were prepared using distilled water, acid solvent (0.1 mol·L−1 HCl), and organic solvent (acetone:petroleum ether: cyclohexane = 1:1:1) to understand the type of pollutants responsible for the ecotoxicity associated with wastewater irrigation. The soil toxicity was assessed using a luminescence inhibition assay with Vibrio fischeri for acute toxicity, a micronucleus assay with Vicia faba root tips and a single cell gel electrophoresis assay of mice lymphocytes for genotoxicity. The physicochemical properties and the heavy metal (HM) contents of the irrigated soil were also analyzed. The results indicated that the wastewater irrigation at site A had no effects on the soil properties. With the exception of Pb, Zn, Fe, and Mn, the accumulation of HMs (Cu, Ni, and Cr) occurred. However, the irrigation at site A did not result in obvious acute toxicity or genotoxicity in the soil. The soil properties changed greatly, and HMs (Cu, Ni, and Cr) accumulated in site B. There were significant increases in the acute toxic and genotoxic effects in the soils from site B. The ecotoxicity in site B came primarily from organic-extractable pollutants.

Lipid accumulation of Chlorella pyrenoidosa under mixotrophic cultivation using acetate and ammonium

Acetate and ammonium were used as organic carbon and nitrogen sources, respectively, during mixotrophic cultivation of Chlorella pyrenoidosa. Cell growth, content of neutral lipid (NL), productivity of biomass and total lipid, and fatty acid profiles were investigated. Results showed that C. pyrenoidosa could endure high concentrations of NH4+-N (100-200 mg/L) and immediately entered logarithmic growth, when the culture media contained 2.0-10.0 g/L NaAc. The 2.0-10.0 g/L NaAc in the media also resulted in the NL content of 1.87-3.05 mg/109cells, much higher than 0.5 mg/109cells of the controls. The maximum productivities of biomass and total lipid were achieved under 50 and 10 mg/L NH4+-N respectively when the 2.0 g/L NaAc was dosed. The fatty acids were mainly composed of C16:0, C16:1, C18:0, and C18:1 under the mixotrophic cultivation, with the higher saturation compared to the controls.