Dewatering of Scenedesmus obliquus Cultivation Substrate with Microfiltration:Potential and Challenges for Water Reuse and Effective Harvesting

In the microalgae harvesting process,which includes a step for dewatering the algal suspension,directly reusing extracted water in situ would decrease the freshwater footprint of cultivation systems.Among various algae harvesting techniques,membrane-based filtration has shown numerous advantages.This study evaluated the reuse of permeate streams derived from Scenedesmus obliquus(S.obliquus)biomass filtration under bench-scale and pilot-scale conditions.In particular,this study identified a series of challenges and mechanisms that influence the water reuse potential and the robustness of the membrane harvesting system.In a preliminary phase of this investigation,the health status of the initial biomass was found to have important implications for the harvesting performance and quality of the permeate stream to be reused;healthy biomass ensured better dewatering performance(i.e.,higher water fluxes)and higher quality of the permeate water streams.A series of bench-scale filtration experiments with different combinations of cross-flow velocity and pressure values were performed to identify the operative conditions that would maximize water productivity.The selected conditions,2.4 m·s^(-1)and 1.4 bar(1 bar=105 Pa),respectively,were then applied to drive pilot-scale microfiltration tests to reuse the collected permeate as a new cultivation medium for S.obliquus growth in a pilot-scale photobioreactor.The investigation revealed key differences between the behavior of the membrane systems at the two scales(bench and pilot).It indicated the potential for beneficial reuse of the permeate stream as the pilot-scale experiments ensured high harvesting performance and growth rates of biomass in permeate water that were highly similar to those recorded in the ideal cultivation medium.Finally,different nutrient reintegration protocols were investigated,revealing that both macro-and micro-nutrient levels are critical for the success of the reuse approach.

Effects of silica nanoparticles on growth and photosynthetic pigment contents of Scenedesmus obliquus

To assess the aquatic ecosystem safety for silica （SiO2） nanoparticles （NPs）, the growth inhibition and photosynthetic pigment contents of Scenedesmus obliquus in logarithm growth phase exposed to SiO2 NPs and SiO2 bulk particles （BPs） suspensions were measured. SiO2 NPs with 10-20 nm diameters were found to be toxic. The 20% effective concentration （EC20） values for 72 and 96 hr were 388.1 and 216.5 mg/L, respectively. The contents of chlorophyll decreased significantly under moderate and high concentration （50, 100, and 200 mg/L） of SiO2 NPs after 96-hr exposure, but the carotenoids did not. SiO2 BPs were found to be nontoxic up to 200 mg/L. The toxicity of SiO2 NPs probablely due to their sorption to algal cells surface. The results imply that there is potential harm to aquatic environment by using SiO2 NPs, and it should deserve special concern.

Removal of K^+,Na^+,Ca^(2+),and Mg^(2+) from saline-alkaline water using the microalga Scenedesmus obliquus

The capability ofScenedesmus obliquus to remove cations （K^＋, Na^＋, Ca^2＋, Mg^2＋） from saline- alkaline water was investigated at different salinities （0, 5, 10, 15, 20, 25） and carbonate alkalinities （0, 5, 10, 15, 20, 25, 30, 35 mmol/L）. K^＋, Na^＋, Ca^2＋, and Mg^2＋ in saline-alkaline water were efficiently removed by S. obliquus. The maximum removal of the cations （29.37 mg for K^＋, 185.85 mg for Na^＋, 23.07 mg for Ca^2＋, 66.14 mg for Mg^2＋） occurred at salinity 25. The maximum removal of K^＋ （2.28 mg）, Na＋ （6.62 mg）, Ca^2＋ （1.01 mg）, and Mg2＋ （0.62 mg） occurred at carbonate alkalinities of 25 mmol/L for K＊, 35 mmol/L for Na＋, 20 mmol/L for Ca2＋, and 25 mmol/L for Mf＋, respectively. Under a salinity stress, the concentration of Na＇ in S. obliquus increased significantly, while that of K~ decreased significantly. The concentrations of Ca^2＋ and Mg2＋ decreased as well. The ratios of K＋/Na~, Ca2＋/Na^＋, and Mg^2＋/Na^＋ were significantly lower in all salinity treatments than those of the control. Under alkaline stress, the concentrations of Nan and K＋ in S. obliquus decreased significantly and the ratios of K^＋/Na^＋, Ca2＋/Na^＋, and Mg^2＋/Na^＋ were significantly higher in all treatments than in the control. Moreover, the concentrations of Ca2＋ and Mg2＋ in S. obliquus at alkalinities of 5-10 mmol/L were significantly higher than those of the other treatments. The removal of Na＋ by S. obliquus mainly occurs through biosorption, and Mg^2＋ and Ca^2 ＋ were removed through both biosorption and bioaccumulation.

THE TOXICITY OF TWO NEWLY-SYNTHESIZED COMPOUNDS ON SCENEDESMUS OBLIQUUS KǖTZ

LY-04 and WSQIF are newly-synthesized compounds which were presented by the Institute of Pesticides Chemistry, Central China Normal University. LY-04 belongs to α-oxophosphonic acid derivatives, while WSQIF is an aromatic acetyl oxophosphonic acid derivative. In this study, the toxicity of LY-04 and WSQIF on Scenedesmus obliquus Kütz was examined. The EC 50 of LY-04 and WSQIF were determined in S. obliquus cells at 24h, 48h, 72h, 96h represented by cell density. Our data showed that the 24h, 48h, 72h, 96h EC 50 of LY-04 were 1983mg/L, 2943mg/L, 240mg/L and 65.0mg/L acetone, respectively, and the 24h, 48h, 72h, 96h EC 50 of WSQIF were 15.9mg/L, 53.0mg/L, 98.0mg/L and 28.8mg/L respectively. LY-04 displayed a higher insecticidal activity, while WSQIF showed a higher phytocidal activity. As LY-04 and WSQIF were designed to act as insecticide and herbicide, respectively, the results were in contrast to the anticipated ones. According to the toxicant classification standard, EC 50 of both substances was far higher than 3mg/L, while the toxicity of LY-04 and WSQIF to aquatic algae were fairly low, indicating that these two pesticides are rather safe to the aquatic ecosystem.

Assessment of Biomass Productivities of Chlorella vulgaris and Scenedesmus obliquus in Defined Media and Municipal Wastewater at Varying Concentration of Nitrogen

Microalgae are emerging as one of the most promising long-term sustainable sources of renewable energy. Studies were conducted on two freshwater Chlorophytes, Chlorella vulgaris and Scenedesmus obliquus to evaluate heterotrophic growth rate and biomass productivity in filter-sterilized defined medium (BG 11) and municipal wastewater, both with varying concentrations of nitrogen (N). For each isolate, cultures were separately incubated in triplicate at room temperature with constant agitation on a shaker at 150 rpm for 9 days. In 0.25 mg N/L BG11 medium, the growth rate and biomass productivity of C. vulgaris were 0.28 day-1 and 3.5 g·L-1, respectively. In wastewater, the same amount of N addition resulted in a higher growth rate 0.44 day-1 and associated biomass productivity of 4.96 g·L-1. Increasing N levels to 0.5 mg N/L in BG11 caused an increase in growth rate (0.37 day-1) and biomass productivity (4.28 g·L-1), while the increase in N in wastewater caused growth to decline to 0.32 day-1 with decreased biomass productivity of 2.19 g·L-1. A further increase in N to 1.0 mg N/L in BG11 caused an increase in the growth rate (0.43 day-1) and a decrease in biomass productivity (3.64 g·L-1), while in wastewater, growth rate and productivity of C. vulgaris were 0.32 day-1 and 2.31 g·L-1, respectively. Overall, C. vulgaris grew faster and produced greater biomass than S. obliquus under comparable conditions. Based on high growth rate and biomass productivity of C. vulgaris, it could be a potential candidate for further consideration for simultaneous wastewater treatment and biofuel production.

Toxic effects of enrofloxacin on Scenedesmus obliquus

In this article, the toxic effects of Enrofloxacin （ENFX） on Scenedesmus obliquus were studied, through investigating the growth, photosynthetic pigments, and protein contents. The possible toxic mechanisms of ENFX were analyzed by determining the superoxide dismutase （SOD） activity, malondialdehyde （MDA） content, proline content, and superoxide anion （O2） generation rate. Results showed that the growth of algae was inhibited by ENFX and the 50% effective concentration （EC50） values for 24, 48, 72, and 96 h of ENFX were 88.39, 63.86, 45.10, and 59.16 mg .L^-1, respectively. After treated with ENFX for 96h, the contents of photosynthetic pigments decreased with the increase of ENFX concentration, the content of soluble protein and the activity of SOD increased and then decreased, and the generation rate of superoxide anion （O2^-） increased continually. The contents of MDA and proline changed little in lower ENFX concentration groups, but increased rapidly when treated with higher concentration groups. These results suggested that ENFX affected the growth ofS. obliquus, and the main toxicity mechanism was that algal cells generated the reactive oxygen species under ENFX stress, and then the reactive oxygen species （ROS） induced the oxidation damages of biologic macromolecules and changed the biomembrane permeability further.

Effects of CO_2 Enrichment on Microstructure and Ultrastructure of Two Species of Freshwater Green Algae

order to investigate the morphological response of freshwater green algae to elevated CO2 concentration, Chlamydomonas reinhardtii Dang and Scenedesmus obliquus Kutz were cultured with enriched CO2, and their microstructure and ultrastructure were examined by microscopy and electron microscopy. The effect of CO2 enrichment to 186 mumol/L, was insignificant on the shape and size of C. reinhardtii, but significant in reducing the volume of S. obliquus. High-CO2 increased the amount of chloroplast. The pyrenoids occurred in low-CO2-grown cells but not in high-CO2-grown ones and more starch granules were observed in the former.

Microalgal Cultivation in Secondary Effluents:Enhancement of Algal Biomass,Nutrient Removal,and Lipid Productivity

The growth performance,nutrient removal,lipid accumulation and morphological changes of Cyanobacterium aponinum OUC1 and Scenedesmus obliquus which were cultured in secondary effluents from two wastewater treatment plants:Tuandao Wastewater Treatment Plant(ETD)and Licun River Wastewater Treatment Plant(ELR)were investigated.The results showed that both C.aponinum OUC1 and S.obliquus have superior growth performances in both undiluted effluents,while the better of them was that in ETD effluent,with cell densities of C.aponinum OUC1 and S.obliquus increased by 159%and 66%over that of BG11(control),respectively.Regarding nutrient removal,S.obliquus could completely remove inorganic phosphorus,and decrease ammonia nitrogen in ETD effluent by 81%.In addition,both C.aponinum OUC1 and S.obliquus cultivated in ETD exhibited extraordinary potential for biofuel production,increasing lipid productivities by 133%and 89%of that cultivated in ELR,respectively.As to ultrastructural changes,the differences in the lipoidal globules and glycogen granules of S.obliquus and C.aponinum OUC1 among the ETD and ELR treatments were mostly related to phosphorus limitations.The findings from this research reveal the probability using the secondary effluents as cultivation media to enhance algal biomass,nutrient removal and lipid productivity.

营养盐磷浓度对斜生栅藻生长的影响

设置0.01、0.05、0.10、0.15、0.20 mg/L 5个不同营养盐磷浓度梯度培养试验,研究不同磷水平对斜生栅藻(Scenedesmus obliquus)生长速率的影响。结果表明,斜生栅藻的生长与水体中磷浓度相关,在培养周期内,与对照组相比,不同磷浓度对斜生栅藻生长有促进作用,在磷浓度0.15 mg/L条件下,藻密度达到最高值,为129.25×10^(4)个细胞/mL,当磷浓度提高到0.20 mg/L时,藻密度降低到108.18×10^(4)个细胞/mL,说明在5个磷浓度梯度中,磷浓度0.15 mg/L为斜生栅藻生长最适浓度,而高于该浓度时会限制斜生栅藻的生长。单因素方差分析表明,在营养盐氮充足条件下,磷浓度提高促进了藻类暴发式生长,说明水体中磷浓度升高是水华产生的重要因素。

Efficient harvesting of green microalgae cells by magnetic flocculated Fe_(3)O_(4)nanoparticles combined with chitosan

Microalgae harvesting remains a challenging step in microalgae industrialization,thereby provoking the necessity to explore sustainable and economically feasible approaches.This research investigated the use of magnetic flocculated nanoparticles in the harvesting of the common microalgae Chlorella pyrenoidosa and Scenedesmus obliquus.The results showed that magnetic flocculated nanoparticles efficiently adsorbed negatively charged microalgae cells,and a magnetic field could adsorb the magnetic flocculated nanoparticles,thereby harvesting the microalgae cells.Harvesting efficiency was remarkably increased at the optimum magnetic field strength of 0.5 T with the magnetic flocculated nanoparticles at 0.738 g/L,and microalgae broth at pH 9.0,whereas the recovery rates of both C.pyrenoidosa and S.obliquus were around 97%and the sedimentation speed of both was above 2.63 cm/min.This study exemplified the magnetic flocculated nanoparticles-based approach to effectively harvest the microalgae cells.

酚类对栅列藻细胞的影响

作者测定了120余种化学药物,其中30余种为酚类化合物对斜生栅列藻的毒性影响。所用方法为在培养基内混入溶解后的各种药物,接种藻类后进行培养,观察效果。实验证明邻羟基苯甲醛和5,5’-二氯-2,2’-二羟基二苯甲烷及5种胺类化合物对藻类具有毒性。50ppm剂量的邻羟基苯甲醛和DDM足以杀死藻类,使藻类由绿色变成白色,叶绿体破坏,叶绿素消失。扫描电镜和透射电镜照片表明,两种药物的作用主要在破坏叶绿体和贮藏物淀粉粒。