Investigating flocculation mechanisms and ecological safety of cationic guar gum for rapid harvesting of microalgal cells.

Addressing the drawbacks of traditional flocculants on microalgae biomass harvesting is crucial for large-scale industrial applications of microalgae production. In this study, cationic bioflocculant was successfully prepared by introducing cationic groups into the side chain of guar gum, achieving in-situ algae flocculation efficiency of 83.5 % with the dosage of 18.0 mg/L under pH = 10.0. Through a harmonious integration of predictive modelling and practical experimentation, a superior cell flocculation capacity of 23.5 g/g was achieved. In addition, the environmental safety and biocompatibility of cationic guar gum was assessed, using the typical suspension quantitative bacteriostatic method and the fluorescent double-staining technique. The results showed that the inhibition efficiency of Staphylococcus aureus in the system containing 60.0 mg/L cationic guar gum was only 12.0 % and there was no inhibition against Escherichia coli colonies. These findings provide a safe and green flocculant for efficient microalgae harvesting and spent medium treatment.

Influence of chitosan properties and operating parameters on the flocculation efficiency and harvesting of microalgae (Scenedesmus sp.).

Physicochemical and structural characteristics of chitosan prepared from Deep-sea shrimp (DCs), including degree of deacetylation (DD), molecular weight (Mw), viscosity, crystallinity index (CrI) and surface morphology were compared with a commercial chitosan (CCs). The DCs had a higher DD of 81.33 ± 0.40 %, whereas the CCs had a lower DD of 74.62 ± 0.64 %. Additionally, the DCs exhibited a lower Mw of 192.47 ± 2.5 kDa and viscosity of 646.00 ± 4.00 cP compared to the CCs, which had a Mw of 202.44 ± 0.28 kDa and viscosity of 689.67 ± 5.91 cP. This study investigated the influence of chitosan properties, particularly DD and Mw on the harvesting of Scenedesmus sp. along with the chitosan dosage, pH of the culture medium, mixing speed and time. Under optimal operating conditions, the microalgae removal efficiency of the DCs reached a significantly higher level (94.71 ± 0.20 %) compared to that of CCs (88.25 ± 0.41 %). Chitosan with a higher DD and low Mw demonstrated superior flocculation efficiency. The results highlight the significance of DD and Mw of chitosan and its influence on the flocculation of microalgae, providing valuable insights for optimizing the harvesting process with the non-toxic and natural flocculent, chitosan.

Suitability of inorganic coagulants for algae-laden water treatment: Trade-off between algae removal and cell viability, aggregate properties and coagulant residue.

Inorganic coagulants could effectively precipitate algae cells but might increase the potential risks of cell damage and coagulant residue. This study was conducted to critically investigate the suitability of polyaluminum (PAC), FeCl3 and TiCl4 for algae-laden water treatment in terms of the trade-off between algal substance removal, cell viability, and coagulant residue. The results showed that an appropriate increase in coagulant dosage contributed to better coagulation performance but severe cell damage and a higher risk of intracellular organic matter (IOM) release. TiCl4 was the most destructive, resulting in 60.85% of the algal cells presenting membrane damage after coagulation. Intense hydrolysis reaction of Ti salts was favorable for the formation of larger and more elongated, dendritic structured flocs than Al and Fe coagulants. TiCl4 exhibited the lowest residue level and remained in the effluents mainly in colloidal form. The study also identified charge neutralization, chemisorption, enmeshment, and complexation as the dominant mechanisms for algae water coagulation by metal coagulants. Overall, this study provides the trade-off analyses between maximizing algae substance removal and minimizing potential damage to cell integrity and is practically valuable to develop the most suitable and feasible technique for algae-laden water treatment.

Starch engineered with Moringa oleifera seeds protein crosslinked Fe3O4: A synthesis and flocculation studies.

This study aimed to utilize cationic protein extracted from the Moringa oleifera seed in the fabrication of cationic starch crosslinked with magnetic nanoparticles (MagCS). Important synthesis parameters include starch to cationic protein volume ratio, magnetic nanoparticles mass fraction, reaction and crosslinking time, reaction and crosslinking temperature and crosslinker concentration. At optimum synthesis conditions, MagCS yield a 38.55% amide content, 2.46 degree of substitution, 1.1 mmol/g charge density and 78.6% crosslinking, which are much higher compared to other starch derivatives. A series of characterization analyses such as Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, elemental analysis and vibrating sample magnetometer concluded that MagCS was embedded with amide group, has high crystallinity structure, is thermally stable and shows a promising magnetic characteristic. Based on the synthesis parameters and characterization studies, the synthesis mechanism of MagCS was also postulated. The flocculation performance of MagCS was successfully assessed for the treatment of palm oil mill effluent. At optimum dosage, initial pH and settling time of 1.0 g/L, 9.0 and 15 min, the MagCS flocculant was able to remove 90.48, 83.95 and 58.19% of turbidity, color and chemical oxygen demand, respectively. This study provides an alternative eco-friendly materials in the wastewater treatment application.

Inactivation of SARS-CoV-2 by ß-propiolactone causes aggregation of viral particles and loss of antigenic potential.

Inactivated viral preparations are important resources in vaccine and antisera industry. Of the many vaccines that are being developed against COVID-19, inactivated whole-virus vaccines are also considered effective. ß-propiolactone (BPL) is a widely used chemical inactivator of several viruses. Here, we analyze various concentrations of BPL to effectively inactivate SARS-CoV-2 and their effects on the biochemical properties of the virion particles. BPL at 1:2000 (v/v) concentrations effectively inactivated SARS-CoV-2. However, higher BPL concentrations resulted in the loss of both protein content as well as the antigenic integrity of the structural proteins. Higher concentrations also caused substantial aggregation of the virion particles possibly resulting in insufficient inactivation, and a loss in antigenic potential. We also identify that the viral RNA content in the culture supernatants can be a direct indicator of their antigenic content. Our findings may have important implications in the vaccine and antisera industry during COVID-19 pandemic.

One-step removal of harmful algal blooms by dual-functional flocculant based on self-branched chitosan integrated with flotation function.

Harmful algal blooms induce severe environmental problems. It is challenging to remove algae by the current available treatments involving complicate process and costly instruments. Here, we developed a CaO2@PEG-loaded water-soluble self-branched chitosan (CP-SBC) system, which can remove algae from water in one-step without additional instrumentation. This approach utilizes a novel flocculant (self-branched chitosan) integrated with flotation function (induced by CaO2@PEG). CP-SBC exhibited better flocculation performance than commercial flocculants, which is attributed to the enhanced bridging and sweeping effect of branched chitosan. CP-SBC demonstrated outstanding biocompatibility, which was verified by zebrafish test and algae activity test. CaO2@PEG-loaded self-branched chitosan can serve as an "Air flotation system" to spontaneous float the flocs after flocculation by sustainably released O2. Furthermore, CP-SBC can improve water quality through minimizing dissolved oxygen depletion and reducing total phosphorus concentrations.

Enhanced floc formation by degP-deficient Escherichia coli cells in the presence of glycerol.

Flocculation is an aggregation phenomenon of microbial cells in which they form flocs or flakes. In this study, it was found that addition of glycerol to a complex glucose medium promoted spontaneous floc formation by an Escherichia coli degP-deficient mutant strain (ΔdegP) in a dose-dependent manner. In the presence of 10% (v/v) glycerol, the amount of floc formation (quantified as floc protein) reached its maximum value (230 mg/L), five times that in its absence. 10% (v/v) glycerol was the limit concentration that does not inhibit cell growth of ΔdegP strain. Glycerol was not consumed by ΔdegP cells during floc formation. To provide media having nearly the same viscosity as that containing 10% (v/v) glycerol, carboxymethyl cellulose (CMC) or polyvinylpyrrolidone (PVP) were added to medium as viscosifying agents. Floc formation was not promoted by increasing the medium viscosity with CMC or PVP. However, addition of ethylene glycol also significantly promoted floc formation in the same manner as glycerol. Addition of short-chain polyols decreased the number of viable ΔdegP cells in the floc structure and enhanced outer membrane vesicle (OMV) production by ΔdegP cells; polyols-induced damage on the outer membrane of ΔdegP cells may contribute to the promoted floc formation.

Temperature sensitive self-assembling hydroxybutyl chitosan nanoparticles with cationic enhancement effect for multi-functional applications.

Hydroxybutyl chitosan (HBC) with different degree of substitution (DS) were prepared using a homogeneous reaction system (KOH/urea), which could achieve temperature-dependent reversible morphological transition in aqueous solution. During hydrophobic assembly, amino groups on HBC chains exposed on the surface of nanoparticles formed a poly-cationic structure. The structure of HBCs was characterized by FTIR, 13C NMR, XRD, TGA and rheology. The morphology and assembly mechanism of HBC nanoparticles were studied by TEM, AFM and DLS. Also, the results of coagulation, bacteriostatic, superoxide anion clearance and anionic contaminant removal tests suggested that HBC nanoparticles had excellent flocculation and removal effect of anionic composites. Moreover, the cytocompatibility test indicated that HBC could effectively promote proliferation and division of mouse fibroblast, mouse embryonic fibroblast and rat bone marrow mesenchymal stem cells. These cationic HBC nanoparticles exhibited great potential in multi-functional applications.

Synthesis of montmorillonite/chitosan/ammonium acrylate composite and its potential application in river water flocculation.

Composites based on montmorillonite/chitosan-grafted-ammonium polyacrylate (MMT/CS-g-APA) were synthesized by gamma irradiation (3-7 kGy) induced polymerization. The composites were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). FTIR results revealed the emergence of vibrational bands in the range of 1622 to 1606 cm-1 in the composites spectra indicating the grafting of APA to CS. The shift in the MMT band at 1030 cm-1 to lower wavenumber indicated a strong interchelation interaction in the composite. XRD results showed a shift in the MMT diffraction peak from 2θ = 7° to 5.3° with an increased interplanar spacing from 13.36 Å to 16.61 Å, which indicated the interchelated-exfoliated nanostructure of MMT by CS-APA chains. The thermal stability of the composite increased at lower irradiation dose and higher content of APA. TEM images indicated that MMT particles were completely covered with CS-g-APA matrix and the DLS revealed the swelling of the composite particles. SEM showed the imperfect microsphere morphology of the composite due to the soft nature of CS-g-APA. The flocculation performance of the composites on river water was tested by jar test and compared with alum. The composite prepared with equal ratios of CS and APA and irradiated at 3 kGy approached the flocculation efficiency of alum with a remaining turbidity % of 9 and 8% for the composite and alum respectively. Furthermore, the composite was used for the removal of methylene blue (MB) from water. A dose of 20 mg/50 ml of the composite was sufficient to completely remove MB from a solution with an initial concentration of 50 mg/l.

Using a novel polysaccharide BM2 produced by Bacillus megaterium strain PL8 as an efficient bioflocculant for wastewater treatment.

In this study, the purification and characterization of a novel polysaccharide-based bioflocculant BM2 produced by a bacterium Bacillus megaterium strain PL8 with self-flocculating property were investigated. The results showed that BM2 was an acidic polysaccharide composed of Gal, GalUA, Glc, GlcUA and Man at a molar ratio of 45.1: 33.8:9.3:9.2:2.4, respectively. The molecular weight of BM2 was 4.55 × 106 Da. BM2 had high flocculation efficiencies across a wide pH ranged from 4 to 11 and a wide temperature ranged from 20 to 100 °C towards kaolin clay. BM2 was a cation-independent bioflocculant which could achieve high flocculation activity without the addition of other cations. Adsorption bridging was the main mechanism in the flocculation process of BM2 towards kaolin clay. The BM2 also displayed a high removal efficiency in terms of Congo red (88.14%) and Pb2+ ions (82.64%). These results suggested that BM2 had a great potential as an efficient bioflocculant candidate in wastewater treatment.

Capture of Environmental DNA (eDNA) from Water Samples by Flocculation.

The analysis of environmental DNA (eDNA) has become a widely used approach to problem solving in species management. The detection of cryptic species including invasive and (or) species at risk is the goal, typically accomplished by testing water and sediment for the presence of characteristic DNA signatures. Reliable and efficient procedures for the capture of eDNA are required, especially those that can be performed easily in the field by personnel with limited training and citizen scientists. The capture of eDNA using membrane filtration is widely used currently. This approach has inherent issues that include the choice of filter material and porosity, filter fouling, and time required on site for the process to be performed. Flocculation offers an alternative that can be easily implemented and applied to sampling regimes that strive to cover broad territories in limited time.

Comprehensive investigation of the relationship between organic content and waste activated sludge dewaterability.

The relationship between sludge organic fraction and its dewaterability is well known in practice. However, the formal study to reveal the underlying reason is limited. To improve understanding of the nature of organic content on sludge dewatering process, this study systematically evaluated the effects of sludge organic content on its dewaterability and revealed the underlying mechanism. Analysis of 10 waste activated sludge (WAS) samples with varying organic contents showed that capillary suction time (CST) increased linearly from 34.90 ± 0.10 s to 104.90 ± 0.30 s (R2 = 0.92, p < 0.01), whereas the solid content of centrifuge cake decreased from 21.23 %±0.45 % to 12.52 %±0.14 % (R2 = 0.89, p < 0.01) when organic fractionincreased from 35.72 % to 61.11 %. These results first confirmed that WAS dewatering performance was negatively correlated to its organic content. Then, the underlying mechanism was revealed by studying the basic physicochemical properties of WAS with various organic content. The results showed that sludge with a higher organic content generally had greater extracellular polymeric substances (EPS) content, lower density and higher negative zeta potential, which hinder the aggregation and flocculation of floc particles. These properties endow the WAS with a higher organic content generally possessed more bound water content, small pores, poorer fluidity, and stronger network strength. These characteristics can hamper the separation of water from sludge cake during dewatering. Based on which, this study discussed the potential of organic fraction as a surrogate of EPS for evaluating WAS dewaterability and indicated the organic fraction can be a useful and strong indicator of WAS dewaterability.

Floc properties and membrane fouling in coagulation/ultrafiltration process for the treatment of Xiaoqing River: The role of polymeric aluminum-polymer dual-coagulants.

In this study, novel lignin-based flocculant (LBF) was prepared in recycling of papermaking sludge. And LBF combined with polyaluminum chloride (PAC) was used in the coagulation/ultrafiltration combined process. Effects of polymer types, pH and ultrafiltration time on the membrane fouling mechanism and resistance distribution were studied based on blocking model and resistance-in-series model. Results showed that strongly-attached external fouling was the primary fouling mechanism in PAC coagulation and dual-coagulation systems. Dual-coagulation achieved the slighter fouling due to the formation of poriferous cake layer. In the PAC system, the fouling mechanism transformed from intermediate fouling to cake layer with the ultrafiltration process. Addition of LBF could accelerate cake layer formation and further control internal fouling. PAC + LBF mainly decreased external fouling resistance and reversible internal fouling resistance to enhance permeation flux. And the total resistance (expect intrinsic membrane resistance) was lowered by more than 50% compared with PAC. The primary combined models in PAC and PAC + LBF systems were cake-standard blocking and cake-intermediate blocking, respectively. Initial pH showed a significant effect on membrane fouling. The slighter membrane fouling was acquired at pH 5.5. Addition of LBF could decrease the influence of pH on the fouling index and distribution.

Effects of powdered activated carbon on the coagulation-flocculation process in humic acid and humic acid-kaolin water treatment.

The addition of powdered activated carbon (PAC) to remove micropollutants is a commonly used technology to improve drinking water quality. However, the effects of PAC dosing strategy on the coagulation-flocculation process of water treatment have not been well understood, especially for water with low amounts of inorganic particles. Therefore, the current research aimed to comprehensively study the effects of simultaneous addition of PAC and aluminum sulfate (AS) coagulants (denoted as PAC-AS) or adding PAC 2 h before coagulation (denoted as PAC2h-AS) on the coagulation behavior in humic acid (HA) and HA-kaolin water treatment. The results showed that the floc size, growth rate, breakage factor, and fractal dimension were all enhanced by PAC-AS and PAC2h-AS for HA but not for HA-kaolin water treatment. In HA water treatment, PAC-AS reached a larger floc size and faster growth rate, while PAC2h-AS achieved a larger floc breakage factor and fractal dimension value. For PAC2h-AS, the pre-adsorption of HA onto PAC would lower the initial particle concentration and reduce the collision probability during HA water coagulation process; thus, the DOC removal efficiency, floc size, and growth rate of PAC2h-AS were relatively smaller than those of PAC-AS. For the floc strength and floc fractal dimension, the pre-adsorption of HA onto PAC contributed to formation of stronger inter-particle bonds; thus, stronger and more compact flocs were formed by PAC2h-AS compared with those of PAC-AS. The addition of PAC had a smaller impact on the floc properties in HA-kaolin water treatment owing to its higher initial particle concentration.

Role of silica coated magnetic nanoparticle on cell flocculation, lipid extraction and linoleic acid production from Chlorella pyrenoidosa.

In the present work, it has been observed that magnetic (Fe3O4) - silica core- shell nanoparticles helps in flocculation of Chlorella pyrenoidosa cells with simultaneous production of linoleic acid. The mean particle size in Dynamic light scattering (DLS) of the silica coated magnetic nanoparticle was estimated 444.7 nm. The characterization of nanoparticles was also performed by X-ray diffraction technique (XRD). Apart from flocculation, it has been observed that in presence of magnetic silica core- shell nanoparticles the amount of lipid obtained was four times than that of control. On the contrary, in presence of these nanoparticles, linoleic acid (18:2) has been produced in Chlorella pyrenoidosa cells almost by 80% whereas, it has been noticed only 8.73% in control. This is the first report where the linoleic acid has been obtained as major component of microalgal fatty acid methyl esters (FAME) having important application in nutraceuticals and pharmaceutical sectors.

Histone chaperones and the Rrm3p helicase regulate flocculation in S. cerevisiae.

BACKGROUND: Biofilm formation or flocculation is a major phenotype in wild type budding yeasts but rarely seen in laboratory yeast strains. Here, we analysed flocculation phenotypes and the expression of FLO genes in laboratory strains with various genetic backgrounds. RESULTS: We show that mutations in histone chaperones, the helicase RRM3 and the Histone Deacetylase HDA1 de-repress the FLO genes and partially reconstitute flocculation. We demonstrate that the loss of repression correlates to elevated expression of several FLO genes, to increased acetylation of histones at the promoter of FLO1 and to variegated expression of FLO11. We show that these effects are related to the activity of CAF-1 at the replication forks. We also demonstrate that nitrogen starvation or inhibition of histone deacetylases do not produce flocculation in W303 and BY4742 strains but do so in strains compromised for chromatin maintenance. Finally, we correlate the de-repression of FLO genes to the loss of silencing at the subtelomeric and mating type gene loci. CONCLUSIONS: We conclude that the deregulation of chromatin maintenance and transmission is sufficient to reconstitute flocculation in laboratory yeast strains. Consequently, we propose that a gain in epigenetic silencing is a major contributing factor for the loss of flocculation phenotypes in these strains. We suggest that flocculation in yeasts provides an excellent model for addressing the challenging issue of how epigenetic mechanisms contribute to evolution.

Using Moringa oleifera Lamarck seed extract for controlling microbial contamination when producing organic cachaça.

This study investigated the use of seed extract from Moringa oleifera Lamark (MO) for both clarifying the sugarcane juice and removing fermentation contaminants that originated during the 24 h storage of the freshly cut stalks. The addition of the MO seed extract during the juice clarification step decreased the total microbial population by 41.66% compared to the other treatments. The non-stored raw material had less lactic acid bacteria and yeasts counts in the fermentation process, resulting in 8.8% lower glycerol content compared to the stored raw material. The concentrations of congeners in both raw materials decreased by 5.27% after liming and by 10% after using the natural extract with flocculation activity. It can be concluded that the clarification process combined with the use of the seed extract from Moringa oleifera Lamarck can potentially control microbial contaminating during fermentation and increase the alcohol content in the cachaça.

Inhibitory effect of ochratoxin A on DNMT-mediated flocculation of yeast.

The mycotoxin ochratoxin A (OTA) is considered to be a human carcinogen. However, the mode of its carcinogenetic action has not been elucidated. Recently, it has become evident that epigenetic changes influence the risk of developing cancer. Since it has been revealed that the yeast flocculation displayed by the strains transformed with human DNA methyltransferases (DNMT) can be regulated by epigenetic mechanisms, we examined the effect of OTA on the transcription level of FLO1, which mediates the flocculation phenotype. OTA but not a non-carcinogenetic mycotoxin deoxynivalenol (DON) inhibited the intensity of GFP fluorescence under the transcriptional regulation of FLO1 promoter in a dose-dependent manner. At the same time, OTA had no effect on the reporter activity under the control of modified FLO1 promoter with reduced CpG motifs. In addition, it was confirmed that the flocculation and FLO1 mRNA of DNMT gene-transformed yeast (DNMT yeast) were decreased by OTA. In vitro methylation assay using a bacterial DNMT revealed an inhibitory effect of OTA on the DNMT activity, and OTA treatment reduced the frequency of abnormally shaped nuclei which were often observed in DNMT yeast. These results suggest that the carcinogenicity of OTA may involve inhibition of DNMT-mediated epigenetic regulation.

Coagulation removal of fluoride by zirconium tetrachloride: Performance evaluation and mechanism analysis.

Fluoride (F-) pollution is a worldwide issue. Coagulation with aluminum (Al) salts is an efficient and economical method for the removal of F-. However, due to the strong complexation between Al3+ and F-, the residual F- and Al after coagulation usually exceed the limits. Zirconium (Zr) coagulants have drawn increasing attention due to their excellent flocculation ability for organic matter. In this work, the performance and mechanism of ZrCl4 coagulation for F- removal were investigated with the widely used Al2(SO4)3 as a reference. The optimum pH range is 4.0-6.0 for ZrCl4 and 8.0-10.0 for Al2(SO4)3. ZrCl4 was superior to Al2(SO4)3 for F- removal as the initial F- concentration was less than 30.0 mg L-1. Coexisting substances at environmental concentration levels showed negligible effects on F- removal by ZrCl4. Besides the better F- removal, another advantage of ZrCl4 over Al2(SO4)3 was the much lower residual metal concentration in the pH range of 4.0-11.0. The hydrolysis of Al2(SO4)3 was significantly inhibited due to the formation of Al-F complexes while the hydrolysis of ZrCl4 was not influenced even under strongly acidic conditions. Therefore, F- removal by Al2(SO4)3 was mainly achieved by preliminary complexation between Al3+ and F- and subsequent hydrolysis and polymerization of these complexes, while adsorption onto hydrolysates and ion exchange with surface hydroxyl groups were the main ways of F- removal by ZrCl4. The work here provides a new method for F- removal and may shed light on the application of Zr coagulants for other pollutants.

Auto-flocculation through cultivation of Chlorella vulgaris in seafood wastewater discharge: Influence of culture conditions on microalgae growth and nutrient removal.

Nowadays, the pretreatment of wastewater prior to discharge is very important in various industries as the wastewater without any treatment contains high organic pollution loads that would pollute the receiving waterbody and potentially cause eutrophication and oxygen depletion to aquatic life. The reuse of seafood wastewater discharge in microalgae cultivation offers beneficial purposes such as reduced processing cost for wastewater treatment, replenishing ground water basin as well as financial savings for microalgae cultivation. In this paper, the cultivation of Chlorella vulgaris with an initial concentration of 0.01 ± 0.001 g⋅L-1 using seafood sewage discharge under sunlight and fluorescent illumination was investigated in laboratory-scale without adjusting mineral nutrients and pH. The ability of nutrient removal under different lighting conditions, the metabolism of C. vulgaris and new medium as well as the occurrence of auto-flocculation of microalgae biomass were evaluated for 14 days. The results showed that different illumination sources did not influence the microalgae growth, chemical oxygen demand (COD) and biochemical oxygen demand (BOD) significantly. However, the total nitrogen (total-N) and total phosphorus (total-P) contents of microalgae were sensitive to the illumination mode. The amount of COD, BOD, total-N and total-P were decreased by 88%, 81%, 95%, and 83% under sunlight mode and 81%, 74%, 79%, and 72% under fluorescent illumination, respectively. Furthermore, microalgae were auto-flocculated at the final days of cultivation with maximum biomass concentration of 0.49 ± 0.01 g⋅L-1, and the pH value had increased to pH 9.8 ± 0.1 under sunlight illumination.