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Membranes have a lot of potential for harvesting microalgae, but mainly membrane fouling and high harvesting costs linked to low fluxes are hampering their breakthrough. Patterned membranes can reduce fouling by enchancing local turbulences close to the membrane surface on one hand, and by increasing the active area per m 2 of installed membrane on the other. Flocculation can further increase membrane permeance by increasing microalgal partical size and reducing the fraction of free organic matter in the feed. In current study, the effect of polyethylene glycol (PEG) in the casting solution of patterned polysulfone membranes was investigated to better tune the performance of the patterned membranes, together with the effects of cross-flow velocity and chitosan dosage on membrane fouling. The energy consumption and total harvesting cost, extrapolated to a full-scale microalgal harvesting, were then estimated. The patterned membrane prepared with a 28w% PEG concentration showed the highest clean water permeance (900±22 L/m 2 h bar) and membrane permeance in a microalgal suspension (590±17 L/m 2 h bar). Patterned membranes showed a lower filtration resistance (15% permeance decline at the end of filtration) than flat membranes (72%) at a cross-flow velocity of 0.0025 m/s. Increasing cross-flow velocity could increase membrane permeance in most cases. The highest stable membrane permeance (110±17 L/m 2 h bar) and the lowest filtration resistance were achieved when combining patterned membrane filtration with flocculation at optimized chitosan dosage. A very low energy consumption (0.28 kWh/kg) and harvesting cost (0.16 €/kg) were achieved under these conditions., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021. Published by Elsevier Ltd.)

Membranes have a lot of potential for harvesting microalgae, but membrane fouling is hampering their breakthrough. In this study, the effects of charge and corrugated surface on membrane filtration performance were investigated. The clean water permeance (CWP), the microalgae harvesting efficiency and the membrane flux for a microalgal broth were determined using patterned polysulfone (PSf) membranes with different shapes of the surface patterns and containing different charge densities by blending sulfonated polysulfone (sPSf). The flow behavior near the patterned membrane surface, as well as the interaction energy between membrane and microalgae were investigated using computational fluid dynamics (CFD) simulation and the improved extended "Derjaguin, Landau, Verwey, Overbeek" (XDLVO) theory, respectively. Membrane charge and pattern shape significantly improve the membrane performance. The critical pressures of all sPSf blend patterned membranes were higher than 2.5 bar. A 4.5w% sPSf blend patterned membranes with wave patterns showed the highest CWP (2300 L/m 2 h bar) and membrane flux in the microalgal broth (1000 L/m 2 h bar) with 100% harvesting efficiency. XDLVO analysis showed that sPSf blend patterned membranes prepared obtained the lowest interaction energy and highest energy barrier for microalgal attachment. CFD simulation showed a higher velocity and wall shear on the pattern apexes., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier Ltd.)

Membranes with a wave pattern on the membrane surface are now proposed for the first time to alleviate microalgal fouling and increase the membrane flux. The membrane morphology was observed via scanning electron microscope, and the clean water permeance, microalgae harvesting efficiency and membrane flux in a real broth were determined to investigate the effects of polysulfone (PSF) and polyethylene glycol (PEG) concentrations in the membrane casting solution. Furthermore, the influence of the height of the patterned waves and the inter-pattern distance on the fouling prevention were investigated. Higher PSF and PEG concentrations resulted in better pronounced patterns. Patterned membrane showed higher fluxes and critical pressures than the corresponding flat membranes. Larger patterns gave higher membrane fluxes and less fouling. Computational fluid dynamics simulation showed a higher velocity and shear on the pattern apexes., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The optimal operational parameters of a second generation magnetically induced membrane vibration (MMV) system were determined using the response surface methodology (RSM) combined with single-factor experiments. The membrane surfaces were characterized by scanning electron microscopy (SEM) and algae cell states by inverted microscopy. The effect of an intermittent vibration strategy on filtration performance and energy consumption was studied. The results showed that the responses could be fitted by RSM models. High membrane flux, low energy consumption, efficient fouling control and no damage to the microalgae could thus be realized. The filtration strategy tests suggested that an intermittent cycle time of 4 min with 50% vibration rate could be the best vibration strategy for harvesting the microalgae under investigation., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Five copper concentrations (0, 0.5, 1, 2, and 4 mg/l) were used to stress C. pyrenoidosa continuously for five days. The biomass, chlorophyll, and carotenoids of microalgae were measured, and Raman mapping spectral data and Raman single-point spectral data of microalgae were acquired. Principal component-linear discriminant analysis, back propagation-artificial neural network (BP-ANN), and sensitive wavelengths-linear discriminant analysis were used to build models to identify different copper concentrations using the spectral data after pretreatment. The results showed that the BP-ANN model was optimal to identify copper concentrations with prediction accuracy of 92% on day 4.

Microalgae have been reported in many studies with high biomass, high carbohydrate content, fast growth rate and multiple bio-activities, while Dictyosphaerium sp. was rarely studied. Polysaccharide prove to be remarkable in many biological activities. To optimize the effects of the ultrasonic-assisted extraction parameters on the yield of polysaccharide from Dictyosphaerium sp., a single-factor experiment and response surface methodology (RSM) with a central composite rotatable design were employed. Four independent variables were investigated: X1 (ratio of raw microalgal powder to water), X2 (extraction temperature), X3 (extraction time), X4 (extraction power). The optimal conditions obtained via single-factor experiment were: X1 (1:25), X2 (50 °C), X3 (50 min), X4 (500 W), while according to the analysis of RSM, the optimum conditions were: X1 (1:26), X2 (58 °C), X3 (55 min), X4 (525 W). The refined polysaccharide were further prepared and characterized using SEM, FT-IR, XRD and TGA/DSC. Five kinds of antioxidant assays were carried out and the results indicated that the refined polysaccharide had strong scavenging ability to DPPH· and OH·. This study provides theoretical and experimental basis for the development and utilization of microalgal resources. [ABSTRACT FROM AUTHOR]

In order to utilize the microalgal biomass sufficiently, thermogravimetry experimentation analyses of five microalgal strains (Chlorella sorokiniana C74 (C. sorokiniana C74), Desmodesmus sp. WC08, Chlorella sorokiniana XS04 (C. sorokiniana XS04), Scenedesmus ecornis G2 (S. ecornis G2) and Dictyosphaerium sp. 1A10) were performed by using TG–DTG–DSC (thermogravimetric–differential thermogravimetric–differential scanning calorimetry) thermal analysis technology. The combustion indexes, parameters and synthetic combustion characteristics were investigated. Meanwhile, the combustion kinetics parameters were identified with heating rates from 5 to 40 °C min−1 and conversion fractions from 0.1 to 0.9. The results showed that the burning TG–DTG curves of all five microalgal strains were different and the exothermic regions of five microalgal strains in DSC curves were different as well. The variation trends of apparent activation energy of Dictyosphaerium sp. 1A10, C. sorokiniana C74, C. sorokiniana XS04 and S. ecornis G2 differed from Desmodesmus sp. WC08. The average apparent activation energy of Desmodesmus sp. WC08 was highest followed by C. sorokiniana C74, Dictyosphaerium sp. 1A10, C. sorokiniana XS04 and S. ecornis G2. [ABSTRACT FROM AUTHOR]

Although microalgal biomass and environmental benefits of microalgae surpass those of many other feedstocks, the costs associated with up- and downstream technologies still hinder their further development. Membrane technology is an emerging technology that has been applied in the microalgae industry for cultivation, harvesting, and biorefinery, and that has contributed to achieving the economic sustainability of microalgal cultivation and reducing energy input. In the most studied field (microalgae harvesting), the lowest energy consumption is currently 0.67 Wh/m3 when using vibrating, negatively charged, patterned PSf membranes with flocculation prior to filtration in an MMV system. However, the operational flux (95 L/m2 h) is not the highest, leaving room for optimization. Cost calculations indicated that the total electrical cost is only a very small fraction (3.05%) of the total production cost (using the energy costs of that period, i.e., 0.1 €/kWh), with CO 2 and labor suggested to be the key factors contributing to high production cost. Membrane-based microalgal biofilm systems recently gained a lot of attention as they offer a win-win strategy for low-cost simultaneous microalgae cultivation and harvesting. In addition, they can be used in other fields, such as wastewater treatment and the production of biochemicals. This review suggests that further studies should not only focus on developing new technologies but combine the existing technologies and find their synergistic effects to realize high performance and low costs. • Harvesting does not significantly influence the final production cost. • The reported lowest energy consumption for harvesting is currently 0.67 Wh/m3. • Patterned membranes can be used to improve microalgal biomass harvesting performance. • More focus on the synergistic effect of the existing membrane technologies is needed. • Membrane-microalgae technology can be used for wound healing. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cationic CNCs could achieve > 90% microalgae flocculation without pH-adjustment. • 0.34-PYR-CNC showed the best performance for both fresh and marine microalgae. • A record-low energy consumption of only 6.7 Wh/m3 was achieved. • Surface patterning can significantly enhance flux, while reducing energy input. • Increasing particle radius can mitigate fouling on the vibrating membrane surface. High energy consumption during harvesting is one of the main bottlenecks for sustainable microalgae production. Membranes can efficiently separate microalgae from liquids with low energy consumption, but membrane fouling remains an important issue. Flocculation prior to membrane filtration can increase membrane fluxes and decrease fouling, thus offering a low-cost and efficient solution to harvest microalgae. Biobased cationic cellulose nanocrystals were successfully used as flocculants for microalgae and were effective over a wide pH-range and for both freshwater and marine microalgae. Such flocculation was for the first time combined with vibration-assisted filtration using a charged, surface patterned membrane, enabling operation at very high flux (95 L/m2 h) using a vibration frequency of only 1 Hz, and even under sub-optimal flocculation conditions. Intermittent vibration decreased energy consumption further while keeping excellent filtration performance to finally achieve a record-low energy consumption for the membrane filtration of only 6.7 Wh/m3, which is >25-times lower than that of normal membrane filtration. Interaction forces revealed that increasing particle size through flocculation prior to membrane filtration can significantly prevent microalgae attachment on the vibrating membrane surface. This work opens a new direction for sustainable microalgae harvesting with an ultra-low energy consumption, combined with a very high microalgae recovery, reduced use of chemicals, and lower membrane investment cost. [ABSTRACT FROM AUTHOR]

• PEI-crosslinked PVDF membranes showed pH-responsive charge-switchable property. • Patterned membranes enhanced the biofilm formation. • pH = 7 was the optimal pH for biofilm formation on PEI-crosslinked PVDF membrane. • pH above 9 was best for microalgal harvesting on PEI-crosslinked membrane. • PEI-crosslinked PVDF membrane showed a positively charged surface below pH 8. Harvesting efficiency is one of the key issues restricting the further commercialization of microalgae. Traditional biofilm studies only tend to focus on enhancing biofilm formation, while neglecting the subsequent harvesting of the biofilm. In this study, a win–win strategy for high-density microalgal cultivation and low-cost harvesting through biofilm cultivation on a pH-responsive, charge-switchable, patterned membrane was investigated using a polyethylenimine (PEI)-crosslinked polyvinylidene fluoride (PVDF) membrane. The patterned membranes were prepared by spray-modified non-solvent induced phase inversion, and the effect of pattern height on biofilm formation and microalgal harvesting was investigated. The PEI-crosslinked PVDF membrane surface was positively charged below pH 8 and negatively charged above pH 9, resulting in a higher attractive energy below pH 8 and a repulsive energy above pH 9 according to the extended Derjaguin, Landau, Verwey, Overbeek model. Patterning of these membranes increased the active area for microalgal attachment, and created a low-shear area in the valleys that prevents early detachment of microalgal cells. Membranes with a higher pattern height resulted in faster biofilm development and increased final biomass accumulation. Low-energy membrane vibration was applied to enhance cell detachment. pH = 7 was found to be the optimal pH for enhanced microalgal biofilm formation on PEI-crosslinked patterned membranes, and a switch to pH = 10 was best for microalgal harvesting. [ABSTRACT FROM AUTHOR]

Key issues for membrane technology in harvesting microalgae are to reach high fluxes and to alleviate fouling by microalgal cells and extracellular organic matter. To achieve this goal, negatively charged patterned membranes were prepared from polysulfone/sulfonated polysulfone (PSf/sPSf) blends using a spray-modified phase inversion method, and the effect of sPSf on the membrane morphology and filtration performance was investigated. The patterned membrane with highest sPSf concentration exhibited the highest clean water permeance (2420 ± 260 L/m2 h bar), lowest membrane intrinsic resistance (6.1 m-1) and highest critical flux (55 L/m2 h) for harvesting microalgae. Membrane vibration could mitigate membrane fouling both for the patterned and flat membranes. The vibration system can easily achieve turbulent flow at frequencies higher than 7 Hz. The synergy between membrane vibration, surface pattern and charge thus resulted in a clearly enhanced membrane performance. Image 1 • Negative charges on PSf-membranes increase performance in algae broth filtrations. • Negative charges were successfully introduced by blending sPSf in PSf. • Patterned membranes reduce filtration resistance and fouling. • Vibration-assisted filtration reduces filtration resistance and fouling. • Synergy between three approaches intensively increased membrane fluxes. [ABSTRACT FROM AUTHOR]

To exploit indigenous microalgae with potential for antioxidant activity, 10 microalgal strains (expressed as genus and species) were isolated from fresh and sea waters in Hainan Province, China, according to their high biomass, strong antioxidant capacity and antioxidant enzyme activity. The strains were identified based on their morphology, 18s rDNA and internal transcribed spacer (ITS) sequence analysis. Five strains were identified as Dictyosphaerium sp. 1A10, Desmodesmus armatus (D. armatus) B38, Masaia oloidia 2Fg, Chlorella vulgaris B43 and Chlamydomonas chlamydogama WC11. Microalgal antioxidant capacity was determined. Dictyosphaerium sp. 1A10 showed the highest superoxide dismutase activity (940 ± 10 U/g tissue), 2,2′-diphenyl-1-picryhydrazyl radical scavenging capacity (100 ± 10%) and oxygen radical absorbance capacity (620 ± 10 μmol Trolox/g); D. armatus B38 showed the highest glutathione peroxidase activity (110 ± 10 U/g tissue), ferrous ion chelating capacity (93 ± 7%) and hydroxyl radical-scavenging capacity (97 ± 2%); Scenedesmus ecornis (S. ecornis) G2 showed the highest 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulphonate) scavenging capacity (92 ± 5%). PCA also suggested that D. armatus B38, Dictyosphaerium sp. 1A10 and S. ecornis G2 with highest comprehensive scores (1.83, 1.23, and 0.59, respectively) could be the most appropriate candidates for antioxidants. Image 1 [ABSTRACT FROM AUTHOR]

• A vibrating membrane was combined with flocculation to harvest microalgae. • Filtration-flocculation gave a higher harvesting efficiency and membrane flux. • The synergy also existed under sub-optimal flocculation conditions. • Efficiency and filterability of three flocculants for two microalgae was assessed. • Chitosan was the most efficient flocculant to harvest microalgae. Flocculation of two different fresh-water green microalgae, Chlorella vulgaris and Dictyosphaerium sp., was explored using chitosan, FeCl 3 and NaOH as flocculants. The most optimal dosage of each flocculant under certain pH was determined. Both chitosan and FeCl 3 gave a higher flocculation efficiency then flocculation induced by pH increase. Flocculation induced by chitosan could be achieved with lower dosage. The optimal dosages of chitosan for Chlorella vulgaris and Dictyosphaerium sp. were 10 mg/L and 5 mg/L, respectively. Furthermore, the synergy between membrane filtration and flocculation was investigated and showed a higher membrane filtration performance and harvesting efficiency compared with the filtration without flocculation in both dead-end filtration and filtration with vibration. The filtration under sub-optimal flocculation conditions also showed significant potential. Introducing such flocculation into the membrane filtration process prominently reduced both energy input and required membrane area. [ABSTRACT FROM AUTHOR]