Spontaneous Flocculation Research Articles

Extracellular polymeric substance profiling and biophysical analysis reveal influence factors of spontaneous flocculation in rich lipid alga Heveochlorella sp. Yu

Microalgae harvest and lipid accumulation were important factors influencing commercialized development of microalgae biodiesel. Spontaneous flocculation was an ideal method in microalgae harvest, but few rich lipid microalgae could be harvested by spontaneous flocculation. Rich lipid alga Heveochlorella sp. Yu has a characteristic of spontaneous flocculation to be harvested. Heveochlorella sp. Yu has high lipid productivity (105.24 mg L−1 d−1) and fine spontaneous flocculation efficiency (82.93 %, 2 h) on early stationary phase (day 9). The polysaccharides consisting of glucose, mannose, galactose, rhamnose and fructose (8.67:4.90:3.27:2.16:1) in loose-bound extracellular polymeric substance (LB-EPS) might make great contribution in microalgae flocculation. Meanwhile, the zeta potential close to zero was also beneficial to microalgae flocculation. Besides, the adhesion free energy related with cells adhesion was detected by thermomechanical analysis. Afterward, Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was utilized to quantitatively evaluate short-range interactions involved in the spontaneous aggregation among cells. Collectively, biophysical analyses indicated that content and composition of EPS, Zeta potential, thermodynamic parameter and total interaction based on XDLVO theory were closely connected with spontaneous flocculation in microalga Yu. Our study provided a harvest-simplified process of rich microalgae, which proposes a new idea for commercial development of microalgae biodiesel.

Effect of hydrodynamics on autoflocculation and gravity sedimentation of Chlorella vulgaris

Autoflocculation followed by gravity sedimentation is a promising method for harvesting of microalgae. However, the effect of hydrodynamics on spontaneous flocculation of Chlorella vulgaris is yet uncertain. In this study, where quantitative analysis was conducted to study the effect of hydrodynamics on autoflocculation of Chlorella vulgaris, it was found that hydrodynamic turbulence enhanced autoflocculation efficiency by 40–53.3%. Autoflocculation efficiency increased first and then decreased with the increase of turbulence strength. With shear strength of 0.0069 N/m2 and energy dissipation efficient ɛ of 0.45 × 10−3 m2/s3, the average floc size and settling velocity achieved their maximum at 373.5 ± 36.4 μm and 2.17 ± 0.29 m/h respectively. However, after shear strength exceeded 0.0115 Nm−2 and energy dissipation efficient exceeded 1.25 × 10−3 m2/s3, the Chlorella vulgaris flocs started to disaggregate under the shearing effect. Hydrodynamic turbulence not only increased the probability of contact between Chlorella vulgaris cells, but also the enhanced the accumulation of EPS, which serves as bridge for autoflocculation after binding with the bivalent cation presented in the aqueous medium. Under hydrodynamic conditions, Chlorella vulgaris flocs start to settle by gravity, with separation efficiency reaching up to 94.5 ± 4.5%. Therefore, hydrodynamic control presents a new approach for low cost harvesting of algae products.

Isolation and identification of a novel strain of Heveochlorella sp. and presentation of its capacity as biodiesel feedstock

The use of microalgal lipids in the commercial production of biodiesel is still not cost-effective and is hindered by various bottlenecks, including the harvesting of microalgal biomass. Spontaneous flocculation can be employed as a low-energy, convenient and environmentally friendly strategy to harvest microalgae. In the present study, a novel terrestrial microalga strain was isolated from the bark of a palm tree. The strain was identified based on genomic and morphological characterization and was named Heveochlorella sp. Yu. Compared with common microalgae in freshwater and marine environments, this terrestrial microalgal strain has advantages in spontaneous flocculation and lipid accumulation and can produce the value-added substance γ-aminobutyric acid (GABA). The spontaneous flocculation efficiency was 85.16% after a settling period of 2 h under gravity without physical or chemical treatments. The content and composition of loose-bound extracellular polymeric substance (LB-EPS) was closely associated with the spontaneous flocculation of microalga Heveochlorella sp. Yu; the polysaccharide component increased the adhesion and aggregation of the microalga, resulting in floc formation. The high lipid content (42.63%) and suitable fatty acid composition suggested that this alga is a potentially useful feedstock for biodiesel production. Furthermore, Heveochlorella sp. Yu had the ability to produce GABA at a concentration of 31.59 mg g−1.

The direct assembly of metalloporphyrin and Mg–Al layered double hydroxides nanosheets: a highly efficient catalyst for the green epoxidation of olefins

Co 5,10,15,20-tetrakis(4-sulfonatophenyl) porphyrin (CoTPPS) anions were successfully immobilized into the lamellar space of Mg–Al LDH through the spontaneous flocculation method by using exfoliated LDH nanosheets and guest molecules as building blocks. A variety of techniques including XRD, IR, UV–Vis, SEM, TEM and TG–DSC have been applied to characterize the morphology and microstructure of the obtained hybrids. It was found that the ratio between the metalloporphyrin molecules and LDH nanosheets has an important effect on the structure of restacking products. The interlayer spacing determined from XRD result suggests that a perpendicular orientation of the CoTPPS anions in the lamellar space. The surface charge changes associated with the flocculation process were traced through zeta potential measurements. The immobilized CoTPPS could act as an efficient and reusable heterogeneous catalyst for selective epoxidation of various alkenes including different cycloalkenes, styrene derivatives and long-chain alkenes. Cyclohexene undergoes up to 99% conversion within 2 h and 90% selectivity with molecular oxygen as environmentally friendly oxidant and isobutyraldehyde as co-reductant at room temperature. The CoTPPS/LDH2.0 can be easily recovered and reused for at least 5 times without obvious decrease of activity. This work provides a facile route to synthesize a highly efficient catalyst for the green epoxidation of olefins.

Inducing flocculation of non-floc-forming Escherichia coli cells.

The present article reviews several approaches for inducing flocculation of Escherichia coli cells. The common industrially used bacterium E. coli does not naturally have floc-forming ability. However, there are several approaches to induce flocculation of E. coli cells. One is induction by flocculants-polyvalent inorganic salts, synthetic polymeric flocculants, or bio-based polymeric materials, including polysaccharide derivatives. Another method is the induction of spontaneous flocculation by changing the phenotypes of E. coli cells; several studies have shown that physical treatment or gene modification can endow E. coli cells with floc-forming ability. Coculturing E. coli with other microbes is another approach to induce E. coli flocculation. These approaches have particular advantages and disadvantages, and remain open to clarification of the flocculation mechanisms and improvement of the induction processes. In this review, several approaches to the induction of E. coli flocculation are summarized and discussed. This review will be a useful guide for the future development of methods for the flocculation of non-floc-forming microorganisms.

The Algae Testbed Public-Private Partnership (ATP3) framework; establishment of a national network of testbed sites to support sustainable algae production

Well-controlled experiments that directly compare seasonal algal productivities across geographically distinct locations have not been reported before. To fill this gap, six cultivation testbed facilities were chosen across the United States to evaluate different climatic zones with respect to algal biomass productivity potential. The geographical locations and climates were as follows: Southwest, desert; Western, coastal; Southeast, inland; Southeast, coastal; Pacific, tropical; and Midwest, greenhouse. The testbed facilities were equipped with identical systems for inoculum production and open pond operation and methods were standardized across all testbeds to ensure accurate measurement of physical and biological variables. The ability of the testbed sites to culture and analyze the same algal species, Nannochloropsis oceanica KA32, using identical pond operational and data collection procedures was evaluated during the same seasonal timeframe. This manuscript describes the results of a first-of-its-kind coordinated testbed validation field study while providing critical details on how geographical variations in temperature, light, and weather variables influenced algal productivity, nitrate consumption, and biomass composition. We found distinct differences in growth characteristics due to the geographic location and the resulting climatic and seasonal conditions across the sites, with the highest productivities observed at the desert Southwest and tropical Pacific regions, followed by the Western coastal region. The lowest productivities were observed at the Southeast inland and Midwest greenhouse locations. These differences in productivities among the sites correlated with the differences in pond water temperature and available solar radiation. In addition two sites, the tropical Pacific and Southeast inland experienced unusual events, spontaneous flocculation, and unusually cold and wet (rainfall) conditions respectively, that negatively affected outdoor algal growth. In addition, minor variability in productivity was observed between the different experimental treatments at each site, much smaller compared to differences due to geographic location. Finally, the successful demonstration of the coordinated and standardized operation of the testbed sites established a rigorous basis for future validation of algal strains and operational conditions and protocols across a geographically diverse testbed network.

Microalgae recycling improves biomass recovery from wastewater treatment high rate algal ponds

Microalgal biomass harvesting by inducing spontaneous flocculation (bioflocculation) sets an attractive approach, since neither chemicals nor energy are needed. Indeed, bioflocculation may be promoted by recycling part of the harvested microalgal biomass to the photobioreactor in order to increase the predominance of rapidly settling microalgae species. The aim of the present study was to improve the recovery of microalgal biomass produced in wastewater treatment high rate algal ponds (HRAPs) by recycling part of the harvested microalgal biomass. The recirculation of 2% and 10% (dry weight) of the HRAPs microalgal biomass was tested over one year in an experimental HRAP treating real urban wastewater. Results indicated that biomass recycling had a positive effect on the harvesting efficiency, obtaining higher biomass recovery in the HRAP with recycling (R-HRAP) (92–94%) than in the control HRAP without recycling (C-HRAP) (75–89%). Microalgal biomass production was similar in both systems, ranging between 3.3 and 25.8 g TSS/m2d, depending on the weather conditions. Concerning the microalgae species, Chlorella sp. was dominant overall the experimental period in both HRAPs (abundance >60%). However, when the recycling rate was increased to 10%, Chlorella sp. dominance decreased from 97.6 to 88.1%; while increasing the abundance of rapidly settling species such as Stigeoclonium sp. (16.8%, only present in the HRAP with biomass recycling) and diatoms (from 0.7 to 7.3%). Concerning the secondary treatment of the HRAPs, high removals of COD (80%) and N-NH4+ (97%) were found in both HRAPs. Moreover, by increasing the biomass recovery in the R-HRAP the effluent total suspended solids (TSS) concentration was decreased to less than 35 mg/L, meeting effluent quality requirements for discharge. This study shows that microalgal biomass recycling (10% dry weight) increases biomass recovery up to 94% by selecting the most rapidly settling microalgae species without compromising the biomass production and improving the wastewater treatment in terms of TSS removal.

Classical Keggin Intercalated into Layered Double Hydroxides: Facile Preparation and Catalytic Efficiency in Knoevenagel Condensation Reactions.

The family of polyoxometalate (POM) intercalated layered double hydroxide (LDH) composite materials has shown great promise for the design of functional materials with numerous applications. It is known that intercalation of the classical Keggin polyoxometalate (POM) of [PW12 O40 ](3-) (PW12 ) into layered double hydroxides (LDHs) is very unlikely to take place by conventional ion exchange methods due to spatial and geometrical restrictions. In this paper, such an intercalated compound of Mg0.73 Al0.22 (OH)2 [PW12 O40 ]0.04 ⋅0.98 H2 O (Mg3 Al-PW12 ) has been successfully obtained by applying a spontaneous flocculation method. The Mg3 Al-PW12 has been fully characterized by using a wide range of methods (XRD, SEM, TEM, XPS, EDX, XPS, FT-IR, NMR, BET). XRD patterns of Mg3 Al-PW12 exhibit no impurity phase usually observed next to the (003) diffraction peak. Subsequent application of the Mg3 Al-PW12 as catalyst in Knoevenagel condensation reactions of various aldehydes and ketones with Z-CH2 -Z' type substrates (ethyl cyanoacetate and malononitrile) at 60 °C in mixed solvents (V2-propanol :Vwater =2:1) demonstrated highly efficient catalytic activity. The synergistic effect between the acidic and basic sites of the Mg3 Al-PW12 composite proved to be crucial for the efficiency of the condensation reactions. Additionally, the Mg3 Al-PW12 -catalyzed Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate demonstrated the highest turnover number (TON) of 47 980 reported so far for this reaction.

Flocculation of Escherichia coli Cells in Association with Enhanced Production of Outer Membrane Vesicles.

Microbial flocculation is a phenomenon of aggregation of dispersed bacterial cells in the form of flocs or flakes. In this study, the mechanism of spontaneous flocculation of Escherichia coli cells by overexpression of the bcsB gene was investigated. The flocculation induced by overexpression of bcsB was consistent among the various E. coli strains examined, including the K-12, B, and O strains, with flocs that resembled paper scraps in structure being about 1 to 2 mm. The distribution of green fluorescent protein-labeled E. coli cells within the floc structure was investigated by three-dimensional confocal laser scanning microscopy. Flocs were sensitive to proteinase K, indicating that the main component of the flocs was proteinous. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and nano-liquid chromatography tandem mass spectrometry analyses of the flocs strongly suggested the involvement of outer membrane vesicles (OMVs) in E. coli flocculation. The involvement of OMVs in flocculation was supported by transmission electron microscopy observation of flocs. Furthermore, bcsB-induced E. coli flocculation was greatly suppressed in strains with hypovesiculation phenotypes (ΔdsbA and ΔdsbB strains). Thus, our results demonstrate the strong correlation between spontaneous flocculation and enhanced OMV production of E. coli cells.

The application of spontaneous flocculation for the preparation of lanthanide-containing polyoxometalates intercalated layered double hydroxides: highly efficient heterogeneous catalysts for cyanosilylation

The lanthanide-containing polyoxometalates (POMs) have been intercalated into layered double hydroxides (LDHs) successfully through the spontaneous flocculation method, resulting in the formation of new heterogeneous LDHs–POMs catalysts Mg3Al–LnW10 (Ln=Eu, Tb and Dy). The synthetic method can prevent Mg2+/Al3+ cations leaching out of the LDHs during intercalation and successfully control the final Mg2+/Al3+ ratio in the corresponding Mg3Al–LnW10. Most importantly, the as-prepared Mg3Al–LnW10 can be obtained without the formation of the impurity phase. The heterogeneous Mg3Al–EuW10 exhibits highly efficient catalytic reactivity for cyanosilylation of various aldehydes and ketones under solvent-free conditions. The Mg3Al–EuW10 can be easily recovered and reused for at least 10 times without obvious decrease of catalytic activity and the composition and the structure of the Mg3Al–EuW10 catalyst remain stable. Moreover, the Mg3Al–EuW10-catalyzed cyanosilylation of benzaldehyde and hexanal gives the highest TON of 119,950 and 119,906, respectively.

Characterization of a spontaneous flocculation mutant derived from Candida glabrata: A useful strain for bioethanol production

A spontaneous flocculation mutant (Cgflo1) was obtained from Candida glabrata. Flocculation of Cgflo1 was dependent on divalent cations such as Ca(2+) and Mg(2+) and was inhibited by galactose. Cgflo1 is believed to be a useful strain for bioethanol production based on its flocculation ability at higher temperatures.

Layer-by-Layer Assembly and Spontaneous Flocculation of Oppositely Charged Oxide and Hydroxide Nanosheets into Inorganic Sandwich Layered Materials

Exfoliated oxide nanosheets such as Ti0.91O2 and Ca2Nb3O10 and layered double hydroxide (LDH) nanosheets of Mg2/3Al1/3(OH)2 were restacked into inorganic sandwich layered materials. Sequential adsorption of these oppositely charged nanosheets from their colloidal suspensions yielded multilayer ultrathin films while their simple mixing produced lamellar flocculates. Eliminating carbonate ions from the reaction system was found to be essential for successfully achieving the sandwich structures. The flocculated materials as well as the films were characterized by atomic force microscopy (AFM), UV-visible absorption spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and chemical analysis, which all supported the formation of the ordered sandwich structures. AFM observations revealed alternate dense tiling of LDH nanosheets and oxide nanosheets onto a substrate surface. UV-visible absorption spectra exhibited progressive enhancement of optical density due to oxide nanosheets as a function of deposition cycles, providing strong evidence for regular growth of multilayer films. The combinations of Mg2/3Al1/3(OH)2/Ti0.91O2 and Mg2/3Al1/3(OH)2/Ca2Nb3O10 produced XRD Bragg peaks having multilayer spacings of 1.2 and 2.0 nm, respectively. These basal spacing values are compatible with the sum of thickness of LDH nanosheets and corresponding oxide nanosheets. TEM images of flocculated samples displayed lamellar features with two different constituent layers appearing alternately.

Changes During Storage of Electrically Conductive Blends Polyaniline–Poly(Ethylene‐co‐vinyl Acetate)

The electrical conductivity behavior of polyaniline–poly(ethylene‐co‐vinyl acetate) (PANI–EVA) blends was variable and dynamic during their storage. It was shown that the apparent concentration of the intrinsically conductive polymer at which a conductivity jump of the blends occurs (Φ c ) is not a constant value over time. The electrical conductivity of the films of low PANI content (below 2.5 wt.%) increased by several (ca. 5) orders of magnitude. It was found that the PANI phase undergoes a flocculation process subsequently resulting in the formation of conductive pathways and a continuous network. Besides, the shape of percolation curves was found to change during storage of the films. Decreased conductivity deviations were registered for blends of low PANI content (<2.5 wt.%), indicating that an improvement (or decreasing number of defects) of the conductive pathways took place within the bulk of the insulating EVA matrix. These results and observed phenomena are discussed by means of the interfacial model for electrically conductive polymer blends. They supported the dispersion/flocculation phase transition within similar composite materials. The phase separation and conductivity jump are attributed to the interfacial interactions between the polymeric constituents. It was shown that the microstructure of the blends consists of highly ordered PANI paths embedded in the insulating EVA matrix. Long fibrils of PANI and interconnected fractal‐like networks were observed. It was found that the sizes of the PANI domains also varied during storage of the films. Due to the spontaneous flocculation of the primary PANI particles, conductive pathways are formed at extremely low percolation threshold (Φ c , loading level ca. 5 × 10−3 wt. fraction). Thus, an important property of the conductive constituent, namely its solid‐state rearrangement, was proved. This PANI self‐organization is also interpreted according to the interfacial model of polymer composites. On the other hand, the competition between self‐organization of the complex of PANI with dodecylbenzenesulfonic acid and crystallization of EVA matrix has resulted in structural changes and formation of continuous conductive networks within the blends, responsible for their significantly increased conductivity.

Influence of Phytoplankton Composition on Biomass Removal from High‐Rate Oxidation Lagoons by Means of Sedimentation and Spontaneous Flocculation

The objective of this study is to analyze the influence of phytoplankton species composition on biomass removal from high‐rate oxidation ponds or lagoons (HROPs) by means of sedimentation with spontaneous flocculation. Two experimental systems each consisting of an HROP (with a surface area of 1.54 m2 and depth of 0.3 m) with a clarifier (surface area = 0.025 m2) for phytoplankton biomass removal were operated with different hydraulic retention time criteria over a period of a year. Phytoplankton biomass removal rates reached a yearly average of 70 to 80% in both HROPs. During periods with large amounts of the algal species Scenedesmus acutus, which was present as discrete, unflocculated particles, both systems operated unsatisfactorily, with effluent total suspended solids (TSS) concentrations greater than 30 mg/L. Phytoplankton biomass removal from HROPs by means of sedimentation and spontaneous flocculation is unreliable for year‐round use (at least for 6 months of the year) if TSS effluent concentration is required to be less than 30 mg/L. Additional treatment, such as pH or chemical augmentation, is needed to reduce TSS and improve the effluent quality of HROPs with clarifiers.

New Evidence Supporting the Interfacial Model of Electrically Conductive Polymer Composites. 3. Morphological Study of Polyaniline-Poly(ethylene-co-vinyl acetate) Composites

A detailed study of the morphological features of polyaniline-poly(ethylene-co-vinyl acetate) (PANI-EVA) composites is presented. It is shown that their microstructure consists of highly ordered electrically conductive PANI paths embedded in the insulating EVA matrix. Long fibrils of PANI and interconnected fractal-like networks were also observed. It was found that the size of the primary PANI particles was ca. 5–10 nm. A spontaneous flocculation of these particles contributed to the formation of conductive pathways at extremely low percolation thresholds (Φc) (loading level ca. 0.005 wt. fraction). The sizes of the PANI domains varied during storage of the films and a key property of the conductive constituent (the PANI phase) was observed, namely a tendency for its solid state rearrangement. This PANI self-organization has been interpreted according to the new interfacial model of polymer composites.

New Evidence Supporting the Interfacial Model of Electrically Conductive Polymer Composites. 3. Morphological Study of Polyaniline-Poly(ethylene-co-vinyl acetate) Composites

A detailed study of the morphological features of polyaniline-poly(ethylene-co-vinyl acetate) (PANI-EVA) composites is presented. It is shown that their microstructure consists of highly ordered electrically conductive PANI paths embedded in the insulating EVA matrix. Long fibrils of PANI and interconnected fractal-like networks were also observed. It was found that the size of the primary PANI particles was ca. 5–10 nm. A spontaneous flocculation of these particles contributed to the formation of conductive pathways at extremely low percolation thresholds (Φc) (loading level ca. 0.005 wt. fraction). The sizes of the PANI domains varied during storage of the films and a key property of the conductive constituent (the PANI phase) was observed, namely a tendency for its solid state rearrangement. This PANI self-organization has been interpreted according to the new interfacial model of polymer composites.

Étude de la floculation spontanée des formes R de certaines enterobactériacées

Étude de la floculation spontanée des formes R de certaines enterobactériacées