Production and characterization of high efficiency bioflocculant isolated from Klebsiella sp. ZZ-3

Deciphering the mechanistic role of Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52) in bio-sorption and phyto-assimilation of Cadmium via Linum usitatissimum L. Seedlings

Three Cd2+ resistant bacterium's minimal inhibition concentrations were assessed and their percentages of Cd2+ accumulation were determined by measurements using an atomic absorption spectrophotometer (AAS). The results revealed that two isolates Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52), identified by 16S rDNA gene sequencing, showed a higher percentage of Cd2+ accumulation i.e., 83.78% and 81.79%, respectively. Moreover, both novel strains can tolerate Cd2+ levels up to 2000 mg/L isolated from district Chakwal. Amplification of the czcD, nifH, and acdS genes was also performed. Batch bio-sorption studies revealed that at pH 7.0, 1 g/L of biomass, and an initial 150 mg/L Cd2+ concentration were the ideal bio-sorption conditions for Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52). The experimental data were fit to Langmuir isotherm measurements and Freundlich isotherm model R2 values of 0.999 for each of these strains. Bio sorption processes showed pseudo-second-order kinetics. The intra-diffusion model showed Xi values for Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52) of 2.26 and 2.23, respectively. Different surface ligands, was investigated through Fourier-transformation infrared spectroscopy (FTIR). The scanning electron microscope SEM images revealed that after Cd2+ adsorption, the cells of both strains became thick, adherent, and deformed. Additionally, both enhanced Linum usitatissimum plant seed germination under varied concentrations of Cd2+ (0 mg/L, 250 mg/L,350 mg/L, and 500 mg/L). Current findings suggest that the selected strains can be used as a sustainable part of bioremediation techniques.

Efficacy of exopolysaccharide in dye-laden wastewater treatment: A comprehensive review

The discharge of dye-laden wastewater into the water streams causes severe water and soil pollution, which poses a global threat to aquatic ecosystems and humans. A diverse array of microorganisms such as bacteria, fungi, and algae produce exopolysaccharides (EPS) of different compositions and exhibit great bioflocculation potency to sustainably eradicate dyes from water bodies. Nanomodified chemical composites of EPS enable their recyclability during dye-laden wastewater treatment. Nevertheless, the selection of potent EPS-producing strains and physiological parameters of microbial growth and the remediation process could influence the removal efficiency of EPS. This review will intrinsically discuss the fundamental importance of EPS from diverse microbial origins and their nanomodified chemical composites, the mechanisms in EPS-mediated bioremediation of dyes, and the parametric influences on EPS-mediated dye removal through sorption/bioflocculation. This review will pave the way for designing and adopting futuristic green and sustainable EPS-based bioremediation strategies for dye-laden wastewater in situ and ex situ.

Lead removal from the aqueous solution by extracellular polymeric substances produced by the marine diatom Navicula salinicola

Microbial extracellular polymeric substances (EPS) have recently emerged as significant contributors in diverse biotechnological applications. Extracellular polymeric substances (EPS), produced by a Navicula salinicola strain, have been studied for potential applications in a specific heavy metal (lead (Pb II)) removal from wastewater. The optimisation of operational parameters, mainly pH, Pb and EPS concentrations, using the Box-Behnken design (BBD) was undertaken to enhance lead uptake. The higher Pb adsorption capacity reached 2211.029 mg/g. Hydroxyl, carbonyl, carboxyl, phosphoric, and sulfhydryl groups were identified quantitatively as potential sites for Pb adsorption. EPS exhibited a notable flocculation rate of 70.20% in kaolin clay at a concentration of 15 mg/L. They demonstrated an emulsifying activity greater than 88%, showcasing their versatile potential for both sedimentation processes and stabilising liquid-liquid systems. EPS could be excellent nonconventional renewable biopolymers for treating water and wastewater.

Perspectives on cultivation and harvesting technologies of microalgae, towards environmental sustainability and life cycle analysis

The development of algae is seen as a potential and ecologically sound approach to address the increasing demands in multiple sectors. However, successful implementation of processes is highly dependent on effective growing and harvesting methods. The present study provides a complete examination of contemporary techniques employed in the production and harvesting of algae, with a particular emphasis on their sustainability. The review begins by examining several culture strategies, encompassing open ponds, closed photobioreactors, and raceway ponds. The analysis of each method is conducted in a systematic manner, with a particular focus on highlighting their advantages, limitations, and potential for expansion. This approach ensures that the conversation is in line with the objectives of sustainability. Moreover, this study explores essential elements of algae harvesting, including the processes of cell separation, dewatering, and biomass extraction. Traditional methods such as centrifugation, filtration, and sedimentation are examined in conjunction with novel, environmentally concerned strategies including flocculation, electro-coagulation, and membrane filtration. It evaluates the impacts on the environment that are caused by the cultivation process, including the usage of water and land, the use of energy, the production of carbon dioxide, and the runoff of nutrients. Furthermore, this study presents a thorough examination of the current body of research pertaining to Life Cycle Analysis (LCA) studies, presenting a perspective that emphasizes sustainability in the context of algae harvesting systems. In conclusion, the analysis ends up with an examination ahead at potential areas for future study in the cultivation and harvesting of algae. This review is an essential guide for scientists, policymakers, and industry experts associated with the advancement and implementation of algae-based technologies.

Coagulation as an effective method for cyanobacterial bloom control: A review

Eutrophication, the over-enrichment with nutrients, for example, nitrogen and phosphorus, of ponds, reservoirs and lakes, is an urgent water quality issue. The most notorious symptom of eutrophication is a massive proliferation of cyanobacteria, which cause aquatic organism death, impair ecosystem and harm human health. The method considered to be most effective to counteract eutrophication is to reduce external nutrient inputs. However, merely controlling external nutrient load is insufficient to mitigate eutrophication. Consequently, a rapid diminishing of cyanobacterial blooms is relied on in-lake intervention, which may encompass a great variety of different approaches. Coagulation/flocculation is the most used and important water purification unit. Since cyanobacterial cells generally carry negative charges, coagulants are added to water to neutralize the negative charges on the surface of cyanobacteria, causing them to destabilize and precipitate. Most of cyanobacteria and their metabolites can be removed simultaneously. However, when cyanobacterial density is high, sticky secretions distribute outside cells because of the small size of cyanobacteria. The sticky secretions are easily to form complex colloids with coagulants, making it difficult for cyanobacteria to destabilize and resulting in unsatisfactory treatment effects of coagulation on cyanobacteria. Therefore, various coagulants and coagulation methods were developed. In this paper, the focus is on the coagulation of cyanobacteria as a promising tool to manage eutrophication. Basic principles, applications, pros and cons of chemical, physical and biological coagulation are reviewed. In addition, the application of coagulation in water treatment is discussed. It is the aim of this review article to provide a significant reference for large-scale governance of cyanobacterial blooms. PRACTITIONER POINTS: Flocculation was a promising tool for controlling cyanobacteria blooms. Basic principles of four kinds of flocculation methods were elucidated. Flocculant was important in the flocculation process.

Bioflocculation characteristics of bound extracellular polymers substances from Pseudomonas sp. XD-3 and behavior of polysaccharides

This study aimed to investigate the bioflocculation characteristics of bound extracellular polymers substances (B-EPS), which were extracted from Pseudomonas sp. XD-3. The flocculation efficiency of B-EPS achieved about 80%- 95% with an initial pH of 4-7, kaolin concentrations of 3-7 g L-1, temperature of 25-100 ℃ and B-EPS dosage of 9-105 mg L-1. The bioflocculation process of B-EPS conformed to pseudo-second-order kinetic mode, suggesting that the bioflocculation belonged to chemical adsorption process. Enzymatic hydrolysis experiments demonstrated that both polysaccharides and proteins were active components for bioflocculation. The polysaccharides were irregular aggregates with rough and porous surfaces and contained hydroxyl and carboxyl groups, which helped to promote bridging effect. Ribose, glucose and galactose were the main monosaccharides of polysaccharides. The molecular weight of the polysaccharides was relatively small, but the relatively loose configuration exposed more ion bridging sites, thus promoting the bioflocculation. Optimizing the ingredients of culture medium and culture time for B-EPS were effective strategies to increase the yield of flocculation active components. When the conditions were 10% of 2 g L-1 KH2PO4 + 5 g L-1 K2HPO4, 0.05% of Tween-80, citrate as carbon source and 32-48 h of culture time, both proteins and polysaccharides in B-EPS were significantly improved. This study gives an in-deep understanding on the flocculation characteristics of a novel bioflocculant from Pseudomonas sp. XD-3, which is conducive to the widespread application of bioflocculation.

Commercial Seaweed Liquid Extract as Strawberry Biostimulants and Bioethanol Production

Seaweeds are increasingly intriguing as a sustainable source of bioactive compounds. They have applications in agriculture, fuels, feed, and food products. To become a cost-competitive product with zero waste, a biorefinery approach is applied, where several products are valorized at the same time. True-Algae-Max (TAM^®) has been investigated for its ability to improve the yield and nutritional facts of a strawberry plant. Three concentrations of TAM (0, 50, and 100%) were examined by foliar spray in 2017 with 50% NPK chemical fertilizer. Results indicated that growth, yield, chlorophyll, and potassium content were significantly improved by TAM treatments. TAM50 % resulted in maximum root length, leaf area, plant fresh weight, fruit weight, and yield with an increase ranging from 10 to 110% compared to control. Compared to the NPK control, strawberries grown with TAM50% improved total soluble solids (TSS) from 7.58 to 10.12% and anthocyanin from 23.08 to 29.42 mg CGE 100 g^-1. Noteworthily, this reduced total sugar, and total phenolics were boosted by TAM applications, while non-reducing sugar was reduced compared to control. On the other hand, whole seaweed biomass and TAM residuals were used for bioethanol production by acid scarification. The maximum bioethanol yield was observed in residual biomass (0.34 g g^-1 dw), while the whole seaweed biomass showed only 0.20 g g^-1 dw. These results proved the biorefinery concept of using seaweed extract as a biostimulator and bioethanol production.

A Functionalized Polysaccharide from Sphingomonas sp. HL-1 for High-Performance Flocculation

The characterization and flocculation mechanism of a biopolymer flocculant produced by Sphingomonas sp. HL-1, were investigated. The bio-flocculant HL1 was identified as an acidic polysaccharide, mainly composed of glucose, and also contained a small amount of mannose, galacturonic acid and guluronic acid. The flocculating activity of the purified HL1 polysaccharide could be activated by trivalent cations, and its flocculation mechanism was mainly charge neutralization and bridging. The working concentration of fermentation broth HL1 in a kaolin suspension was only 1/10,000 (v/v), in which the polysaccharide concentration was about 2 mg/L. The bio-flocculant HL1 maintained high efficiency at a wide range of pH (pH 3-10). It also exhibited good flocculating activity at a temperature range of 20-40 °C; it could even tolerate high salinity and kept activity at a mineralization degree of 50,000 mg/L. Therefore, the bio-flocculant HL1 has a good application prospect in the treatment of wastewater over a broad pH range and in high salinity.

The last 25 years of research on bioflocculants for kaolin flocculation with recent trends and technical challenges for the future

The generation of kaolin-containing wastewater is an inevitable consequence in a number of industries including mining, wastewater treatment, and bitumen processing. In some cases, the production of kaolin tailings waste during the production of bitumen or phosphate is as high as 3 times greater than the actual produced product. The existing inventory of nearly five billion barrels of oil sands tailings alone represents a massive storage and reclamation challenge, as well as a significant economic and environmental liability. Current reclamation options like inorganic coagulants and organic synthetic polymers may settle kaolin effectively, but may themselves pose an additional environmental hazard. Bioflocculants are an emerging alternative, given the inherent safety and biodegradability of their bio-based compositions. This review summarizes the different research attempts towards a better bioflocculant of kaolin, with a focus on the bioflocculant source, composition, and effective flocculating conditions. Bacillus bacteria were the most prevalent single species for bioflocculant production, with wastewater also hosting a large number of bioflocculant-producing microorganisms while serving as an inexpensive nutrient. Effective kaolin flocculation could be obtained over a broad range of pH values (1-12) and temperatures (5-95°C). Uronic acid and glutamic acid were predominant sugars and amino acids, respectively, in a number of effective bioflocculants, potentially due to their structural and charge similarities to effective synthetic polymers like polyacrylamide. Overall, these results demonstrate that bioflocculants can be produced from a wide range of microorganisms, can be composed of polysaccharides, protein or glycoproteins and can serve as effective treatment options for kaolin. In some cases, the next obstacle to their wide-spread application is scaling to industrially relevant volumes and their deployment strategies.

Enhanced remediation of fracturing flowback fluids by the combined application of a bioflocculant/biosurfactant-producing Bacillus sp. SS15 and its metabolites

Fracturing flowback fluids (FFFs), which is generated from the process of oil and gas exploitation, is one of the major environmental concerns. In this study, a bacterial strain, Bacillus sp. SS15, capable of producing both bioflocculant (BF) and biosurfactant (BS), was isolated from oil-contaminated mudflat sediment. The BS produced by SS15 was identified as lipopeptide, which could reduce the surface tension of water from 74.2 mN/m to 36.6 mN/m with a critical micelle concentration of 44.4 mg/L. It also exhibited strong tolerance against a wide range of pH (2-12), temperature (4-60 °C), and salinity (0-100 g/L). Meanwhile, the BF produced by SS15 exhibited high flocculating activity (84.9%) for kaolin suspension, and was confirmed to be thermostable, salt-tolerant, and alkaliphilic. The combined treatment of bioremediation (introducing SS15 and BS) followed by flocculation (introducing BF) greatly promoted the removal of chroma (85.7% reduction), suspended solids (94.4% reduction), chemical oxygen demand (84.9% reduction), n-alkanes (50.0% reduction), and polycyclic aromatic hydrocarbons (66.5% reduction), respectively. The genome analysis showed that strain SS15 possessed abundant genes related to the synthesis of carbohydrate, protein, and lipid, which might play an important role in BF and BS synthesis. The findings in this study demonstrated that Bacillus sp. SS15 has promising prospect in the remediation of FFFs.

Isolation and Optimisation of Culture Conditions for a Marine Bioflocculant-Producing Bacterium and Application of Its Bioflocculant in Wastewater Treatment

The application of bioflocculants has become an alternative to that of chemical flocculants in wastewater treatment due to their environmental friendliness and non-toxic effects. This study aimed at isolating a bioflocculant-producing bacterium from marine water, optimisation of its culture conditions, and investigation of the removal efficiency of its bioflocculant on pollutants in wastewater. The bacterium was identified by 16S rRNA gene analysis. Optimal carbon and nitrogen sources, inoculum size, temperature, pH, and time were determined by the one-factor-at-a-time assay. The cytotoxicity of the bioflocculant was assessed on African green monkey kidney and bovine dermis cells using a tetrazolium-based columetric (MTT) method. Its removal efficiencies on chemical oxygen demand (COD), biological oxygen demand (BOD) and sulphur were determined using the Jar test method. The bacterial isolate was identified as Ochrobactrum oryzae AB84113. A maximum flocculating activity of 92% and a yield of 3.768 g/L were obtained when a 1% (v/v) inoculum size was used in the presence of starch and yeast extract at pH 7, 30 °C, and after 72 h of cultivation. The bioflocculant demonstrated non-cytotoxic effects on bovine dermis and African green monkey kidney cells. The bioflocculant removed 98% COD, 91% BOD and 86% of Sulphur. The bioflocculant has potential for pollutant removal from industrial wastewater.

The role of microplastics biofilm in accumulation of trace metals in aquatic environments

Microplastics are one of the major contaminants of aquatic nature where they can interact with organic and inorganic pollutants, including trace metals, and adsorb them. At the same time, after the microplastics have entered the aquatic environments, they are quickly covered with a biofilm - microorganisms which are able to produce extracellular polymeric substances (EPS) that can facilitate sorption of trace metals from surrounding water. The microbial community of biofilm contains bacteria which synthesizes EPS with antimicrobial activity making them more competitive than other microbial inhabitants. The trace metal trapping by bacterial EPS can inhibit the development of certain microorganisms, therefore, a single microparticle participates in complex interactions of the diverse elements surrounding it. The presented review aims to consider the variety of interactions associated with the adsorption of trace metal ions on the surface of microplastics covered with biofilm, the fate of such microplastics and the ever-increasing risk to the environment caused by the combination of these large-scale pollutants - microplastics and trace metals. Since aquatic pollution problems affect the entire planet, strict regulation of the production, use, and disposal of plastic materials is needed to mitigate the effects of this emerging pollutant and its complexes could have on the environment and human health.

A polysaccharide-based bioflocculant BP50-2 from banana peel waste: Purification, structure and flocculation performance

In this study, the purification and characterization of a polysaccharide-based bioflocculant BP50-2 of banana peel waste were investigated. BP50-2 was purified and identified through HPLC, XPS, TG, SEM, AFM, etc. The results showed that BP50-2 was a heteropolysaccharide composed of Mannose, Rhamnose, Glucuronic acid, Galacturonic acid, Glucose, Galactose, and Fucose at a molar ratio of 8.97:5.36:1.92:1.00:32.52:8.30:2.64, respectively. The MW of BP50-2 was 1.47 × 10 3 KDa. BP50-2 had high pH stability that maintained flocculation activity on kaolin suspension for a pH range from 3 to 11, and high-temperature stability ranged from room temperature to 90 °C. BP50-2 was non-sensitive to cation and affected by HCl, EDTA, little affected by urea, which showed that the BP50-2 was non-cation dependent and its main binding mode with kaolin was ionic bond and contained a small amount of hydrogen bond. And flocculation mechanisms were discussed, which indicated that adsorption bridging was the main mechanism of the flocculation process of BP50-2-Kaolin or BP50-2-Mg²⁺-Kaolin. Moreover, BP50-2 had decolorization activity on RhB and removal activity of heavy metal ion, of which removal rate of Pb²⁺ was the highest. In brief, BP50-2 showed good performance on the removal of pigment, adsorption of heavy metals, and flocculation of particles.

A novel polysaccharides-based bioflocculant produced by Bacillus subtilis ZHX3 and its application in the treatment of multiple pollutants

A high bioflocculant-producing bacterial strain was identified and named Bacillus subtilis ZHX3. Single-factor experiments suggested that 10 g/L starch and 5 g/L yeast extract were optimal for strain ZHX3 to produce bioflocculant MBF-ZHX3. The maximum flocculating rate reached 95.5%, and 3.14 g/L product was extracted after 3 days of cultivation. MBF-ZHX3 was mainly composed of polysaccharides (77.2%) and protein (14.8%). The polysaccharides contained 28.9% uronic acid and 3.7% amino sugar. Rhamnose, arabinose, galactose, glucose, mannose, and galacturonic acid in a molar ratio of 0.35:1.83:3.09:12.66:0.46:3.81 were detected. MBF-ZHX3 had a molecular weight of 10,028 Da and contained abundant groups (-OH, CO, >PO, C-O-C) contributing to flocculation. Adsorption and bridging was considered as the main flocculation mechanism. MBF-ZHX3 was more effective in decolorizing dyes, removing heavy metals and flotation reagents compared to polyacrylamide. The results implied that MBF-ZHX3 has the potential to substitute polyacrylamide in wastewater treatment because of its excellent biological and environmental benefits.

Transcriptome analysis of potential flocculation-related genes in Streptomyces sp. hsn06 with flocculation activity on Chlorella vulgaris biomass

Chlorella vulgaris is a biomass energy provider with promising potential to help alleviate the energy crisis. Streptomyces sp. hsn06, as an actinomycete, can harvest C. vulgaris biomass safely and efficiently through flocculation activity, and proteins contribute greatly to the flocculation effect. However, potential flocculation protein-related genes are unclear. The mycelia of strain hsn06 after culture with glucose as the sole carbon source exhibited significantly higher flocculation activity as well as higher protein contents than those cultured with starch as the carbon source. To further explore the flocculation mechanism, the mycelia of strain hsn06 with distinct flocculation activities after culture with different carbon sources were examined by transcriptome analysis. We found that 403 genes were differentially up-regulated in mycelia cultured with glucose, compared to those cultured with starch as the carbon source. Five significantly differentially expressed protein-related genes were determined and confirmed by qRT-PCR, which indicated that three of the selected genes were potential flocculation-related genes. These results advance our understanding of potential flocculation-related genes during the harvesting of microalgal biomass.

Enlightening the characteristics of bioflocculant of endophytic actinomycetes from marine algae and its biosorption of heavy metal removal

The removal of toxic heavy metal ions from contaminated environments is a great challenge and requires an alternative rapid, efficient, economical bioremediation approach. Henceforth, bioflocculant producing endophytic actinobacterial sp. was isolated from heavy metal contaminated marine environments for heavy metal biosorption process. After molecular characterization, the isolated actinomycete starin was Nocardiopsis sp. GRG 3 (KT235642). It was indicated that the maximum flocculating activity of 80.90% with glucose, and yield is 4.52 g L¹. The optimum flocculating activity was reached at pH 7 in the presence of CaCl₂ ions. Further, the bioflocculent produced Nocardiopsis sp. GRG 3 (KT235642) was characterized by fourier transform infrared analysis spectra (FTIR) and displayed the presence of carboxyl, hydroxyl, amino groups and characteristic of more polysaccharide and protein. The heavy metal sorption by bioflocculant Nocardiopsis sp. GRG 3 (KT235642) was effectively removed 55.90% Cd, 85.90% Cr, 74.7% Pb, and 51.90% Hg. Therefore, this study was proved that the bioflocculant derived from endophytic actinobacteria, Nocardiopsis sp. GRG 3 (KT235642) as a effective alternative method for decreasing the heavy metals towards sustainable environmental management.

Recent advances and perspectives in efforts to reduce the production and application cost of microbial flocculants

Microbial flocculants are macromolecular substances produced by microorganisms. Due to its non-toxic, harmless, and biodegradable advantages, microbial flocculants have been widely used in various industrial fields, such as wastewater treatment, microalgae harvest, activated sludge dewatering, heavy metal ion adsorption, and nanoparticle synthesis, especially in the post-treatment process of fermentation with high safety requirement. However, compared with the traditional inorganic flocculants and organic polymeric flocculants, the high production cost is the main bottleneck that restricts the large-scale production and application of microbial flocculants. To reduce the production cost of microbial flocculant, a series of efforts have been carried out and some exciting research progresses have been achieved. This paper summarized the research advances in the last decade, including the screening of high-yield strains and the construction of genetically engineered strains, search of cheap alternative medium, the extraction and preservation methods, microbial flocculants production as an incidental product of other biological processes, combined use of traditional flocculant and microbial flocculant, and the production of microbial flocculant promoted by inducer. Moreover, this paper prospects the future research directions to further reduce the production cost of microbial flocculants, thereby promoting the industrial production and large-scale application of microbial flocculants.

Optimized production and characterization of cation-independent bioflocculant produced by Klebsiella sp. 59L

The cation-independent bioflocculant (59LF) extracted from Klebsiella sp. 59L was characterized. 59LF consisted of protein (4.8%) and total sugar (85.2%) with high molecular weight (93.82% of 2120 kDa), and total sugar was composed of 76.45% of neutral sugar, 3.65% of uronic acid, and 1.43% of amino sugar. Results indicated that 59LF was pH tolerant and thermally stable, and the maximum yield of 59LF was 4.078 g/L after 48 h culture. The optimal flocculating activity for Kaolin particles was obtained when the dosage of 59LF was 7.0 mg/L without additional metal ions as coagulant aids. Furthermore, the surface properties of 59LF were observed using a Fourier-transform infrared spectrophotometer and X-ray photoelectron spectroscopy, whereas a porous structure was detected by a scanning electron microscope. Thus, a primary flocculation mechanism of 59LF was proposed. This study provided a potential cation-independent bioflocculant with high productivity and low dosage in future application.

Rapid Production of a Novel Al(III) Dependent Bioflocculant Isolated From Raoultella ornithinolytica 160-1 and Its Application Combined With Inorganic Salts

An efficient bioflocculant-producing strain, Raoultella ornithinolytica 160-1, was identified by 16S rRNA and mass spectrometry analyses. Rapid production of bioflocculant EPS-160 was obtained with 10.01 g/(L⋅d) after optimized by response surface methodology. With the aid of Al(III), more than 90% flocculation activity of EPS-160 at 8 mg/L dosage was achieved in 5 min. Thus, this novel Al(III) dependent bioflocculant was used in combined with chemical coagulants AlCl₃ to remove kaolin suspensions and wastewater treatment. The results indicated that the addition of EPS-160 in aggregation system not only largely improved the flocculation ability than the individual use of chemical flocculant (over 30 percent), but also overcome the decrease of flocculation activity due to the overdose of AlCl₃ and maintained the optimum dosage of AlCl₃ in a wide range (11–23 mg/L). The zeta potentials and EPS-160 structure indicated that both charge neutralization and bridging were the flocculation mechanism with kaolin. During the wastewater treatment, this composite flocculants consisted of EPS-160 and AlCl₃ also had great performance for turbidity elimination. Moreover, with the properties of high flocculation activity, hyperthermal stability, pH tolerance and non-toxicity, EPS-160 shows great potential applications.

Marine Actinobacteria Bioflocculant: A Storehouse of Unique Biotechnological Resources for Wastewater Treatment and Other Applications

The bioactive compounds produced by actinobacteria have played a major role in antimicrobials, bioremediation, biofuels, enzymes, and anti-cancer activities. Biodegradable microbial flocculants have been produced by bacteria, algae, and fungi. Microbial bioflocculants have also attracted biotechnology importance over chemical flocculants as a result of degradability and environmentally friendly attributes they possess. Though, freshwater actinobacteria flocculants have been explored in bioflocculation. Yet, there is a paucity of information on the application of actinobacteria flocculants isolated from the marine environment. Similarly, marine habitats that supported the biodiversity of actinobacteria strains in the field of biotechnology have been underexplored in bioflocculation. Hence, this review reiterates the need to optimize culture conditions and other parameters that affect bioflocculant production by using a response surface model or artificial neural network.

Production of a bioflocculant from Enterobacter sp. P3 using brewery wastewater as substrate and its application in fracturing flowback water treatment

A novel bioflocculant (BW-P3) was produced by a strain of Enterobacter sp. P3 using brewery wastewater as substrate and was further applied to remove the colored substance of fracturing flowback water. The optimum conditions for bioflocculant production were specified by the response surface methodology as COD of brewery wastewater 1487.77 mg/L, glucose 8.94 g/L and initial pH 7.09, under which a bioflocculant yield of 1.274 g/L could be reached. The BW-P3 consists of 79.12% polysaccharides and 15.63% protein. Results show that BW-P3 has a high molecular weight (921 kDa) and contains functional groups (hydroxyl, amino, carbonyl, and acylamino) that likely contribute to flocculation. When using the BW-P3 to flocculate fracturing flowback water, the optimal dosage was 1 g/L BW-P3 with addition of 100 mg/L polymeric aluminum chloride as coagulant aid, and treated under 50 °C at pH 7. Under the optimal condition, the removal rates of chroma and suspended solids (SS) of the fracturing flowback water could reach 85% and 52%, respectively.

Simultaneous nitriles degradation and bioflocculant production by immobilized K. oxytoca strain in a continuous flow reactor

High cost is one of the limiting factors in the industrial production of bioflocculant. Simultaneous preparation of bioflocculant from the contaminants in wastewater was considered as a potential approach to reduce the production cost. In this study, butyronitrile and succinonitrile were verified as sole nitrogen sources for the growth of strain K. oxytoca GS-4-08 in batch experiments. Moreover, more than 90 % of the mixed nitriles could be degraded in a continuous flow reactor, and the bioflocculant could be prepared simultaneously in the effluent. All the as-prepared bioflocculants exhibited high flocculation efficiencies of over 90 % toward Kaolin solution. FTIR and XPS results further unveiled that, the bioflocculant samples with abundance of carboxyl, amine and hydroxyl groups may play an important role on adsorption of Pd²⁺. The adsorption process could be well simulated by Freundlich model, and the K_f values were as high as 452.8 mg^1-1/n l^1/n g^-1. The results obtained in this study not only confirm the technical feasibility for preparation of bioflocculant from various single nitrile and/or mixed nitriles, but also promise its economic feasibility.

Demonstration of the ability of the bacterial polysaccharide FucoPol to flocculate kaolin suspensions

In this study, the flocculation properties of FucoPol, a bacterial extracellular polysaccharide, were investigated. FucoPol is a high molecular weight polymer and negatively charged due to the presence of glucuronic acid and the acyl groups succinyl and pyruvyl. High flocculation rate values (>70%) were achieved with a low bioflocculant dosage of 1 mg/L, for pH values in the range 3-5 and temperature within 15-20°C. The bioflocculant was also shown to be stable after freezing/thawing and heating up to 100°C. Given the polymer's anionic character, the size of flocs formed and their surface profile, bridging seems to be the main flocculation mechanism of FucoPol. This study demonstrated that FucoPol is a promising natural, biodegradable and biocompatible alternative to the currently used synthetic or inorganic hazardous products, with potential to be used as a novel flocculation agent in several applications, such as water treatment, food or mining. Further studies will involve evaluating the reduction of cation dosage on flocculation efficiency, as well as testing the applicability of FucoPol to flocculate different types of suspended solids, such as, for example, activated carbons, soil solids or yeast cells.

Bioflocculant production and heavy metal sorption by metal resistant bacterial isolates from gold mining soil

Two bioflocculant producing bacterial isolates from mining soil samples were investigated for their application in heavy metal removal. The bacterial isolates were identified as Pseudomonas koreensis and Pantoea sp. using 16S rRNA gene. Cadmium resistant genes cadA and CzcD were detected in Pantoea sp. while P. koreensis harbor CzcD and chrA responsible for Cd and Cr resistance respectively. The isolates showed maximum flocculating activity of 71.3% and 51.7% with glucose and yield of 2.98 g L^-1 and 3.26 g L^-1 for Pantoea sp. and P. koreensis respectively. The optimum flocculating activity was achieved at pH 7.5 and temperature of 30 °C. Fourier transform infrared analysis of the bioflocculants produced by the two isolates showed the presence of carboxyl, hydroxyl and amino groups characteristic of polysaccharide and protein. Heavy metal sorption by bioflocculant of Pantoea sp. removed 51.2% Cd, 52.5% Cr and 80.5% Pb while that of P. koreensis removed 48.5% Cd, 42.5% Cr and 73.7% Pb. The bioflocculants produced have potential in metal removal from industrial wastes.

Exploration of Performance Kinetics and Mechanism of Action of a Potential Novel Bioflocculant BF-VB2 on Clay and Dye Wastewater Flocculation

This study explores production of an efficient bioflocculant; BF-VB2, by strain Bacillus sp. TERI VB2 and proposes its potential application in wastewater treatment. One milligram of BF-VB2 can effectively flocculate 1980.0 mg ± 5.0 mg of kaolin particles leading to 99.0% ± 0.5% enhancement in flocculation activity and 99.6% ± 1.0% reduction in turbidity; in less time. BF-VB2 when applied for treatment of textile dyeing industrial wastewater revealed reduction in dye color (82.78% ± 3.03%), COD (92.54% ± 0.24%), TSS (73.59% ± 0.71%), and chloride ions (81.90% ± 0.716%). The best-fit kinetic model (for both COD removal, and dye decolorization) was pseudo-first order with regression coefficient of 0.98 and 0.95, and rate constant of 4.33 × 10^-2 and 1.83 × 10², respectively. Bridging due to presence of surface charges have been proposed as flocculation mechanism. From results obtained during test-tube studies, flocculation in larger volumes (0.01–5.0 L) was also performed to intend taking up BF-VB2 for in situ industrial wastewater treatment. This eco-friendly polysaccharide bioflocculant had longer shelf-life, stability to pH and temperature, cation-independence, and emerged to be more efficient than other flocculants assessed. This study proposed BF-VB2 as a potential natural flocculant candidate for industrial application.

Preparation of a bioflocculant by using acetonitrile as sole nitrogen source and its application in heavy metals removal

A novel bioflocculant, A-GS408, produced by Klebsiella oxytoca GS-4-08 cultured in acetonitrile (ACN) as sole nitrogen source was investigated in this study. A complete degradation of 1 g l^-1 of ACN was achieved in 350 h, and 4.6 g of crude A-GS408 can be obtained in one litter of synthetic medium. The as-prepared bioflocculant exhibits good flocculation efficiency (over 90%) toward Kaolin solution with the aid of Fe³⁺. Chemical analysis showed that the bioflocculant was mainly composed of polysaccharides (46.3%) and proteins (20.6%). FTIR and XPS results indicated the abundant carboxyl, amine and hydroxyl groups in A-GS408 s, which play an important role on Pd²⁺ and Cu²⁺ adsorption. The adsorption of heavy metals can be well stimulated by Freundlich isotherm equation, and the K_f was up to 439.2 mg^1-1/n l^1/n g^-1 and 112.2 mg^1-1/n l^1/n g^-1 for Pb²⁺ and Cu²⁺, respectively. The kinetic fitting results proved that the adsorption of heavy metals by A-GS408 was chemisorption. This study may provide a new method for preparation of bioflocculant, which can not only degrade toxic compound i.e., acetonitrile, but also can reuse considerable nitrogen source from nitrile-containing wastewater.

Trichosporon fermentans biomass flocculation from soybean oil refinery wastewater using bioflocculant produced from Paecilomyces sp. M2-1

The soybean oil refinery (SOR) wastewater contains a high concentration of chemical oxygen demand (COD) and lipid, so the direct emissions of SOR wastewater will result in environmental pollution and waste of resources. Oleaginous yeast Trichosporon fermentans can consume organic materials in SOR wastewater to synthesize microbial oil, which achieves the purpose of SOR wastewater resource utilization. The effective harvesting technology of oleaginous yeasts can improve the utilization efficiency. In this study, Paecilomyces sp. M2-1 with high flocculating activity was isolated. The flocculants produced by M2-1 (MBF2-1) include 75% (w/w) polysaccharides, rely on cations, and display the flocculation percentage of above 77% in the range of pH 2-11. Especially under alkaline conditions, the flocculation percentage can be kept above 97%. The results of scanning electron microscope observation and zeta potential measurements suggested that the bridging, net trapping, and sweeping were the main flocculation mechanism of MBF2-1. MBF2-1 could flocculate T. fermentans that was used to reduce the organic matter in SOR wastewater and to produce microbial oil. Under the optimum conditions, the flocculation percentage of MBF2-1 against T. fermentans from SOR wastewater can reach 95%. Fatty acid content percent in microbial oil from T. fermentans was not almost affected by flocculation of MBF2-1. Moreover, MBF2-1 can further remove 55% and 53% of COD and oil content in the fermented SOR wastewater, respectively. The properties and high flocculating percentage displayed by MBF2-1 indicated its potential application prospect in oleaginous yeast harvest and food industry wastewater treatment.

Production of a bioflocculant from Klebsiella sp. OS-1 using brewery wastewater as a source

This study evaluated the potential of bioflocculant production from a Klebsiella strain using brewery wastewater as nutrients. The bioflocculant named OS-1B produced by Klebsiella sp. OS-1 exhibited a good flocculating activity to kaolin clay suspension (around 95%), when the diluted brewery wastewater with 7.2 mg/L total nitrogen and 1013 mg/L COD_Cr was used as a nitrogen source. Glucose (15 g/L) is the most favorable carbon source for Klebsiella sp. OS-1 in bioflocculant production from brewery wastewater. The yielded bioflocculant is pH tolerant and thermally stable, suggesting its good industrial potential. OS-1B mainly comprises polysaccharide (69.4%) and protein (24.5%). Fourier-transform infrared spectra indicate the presence of hydroxyl, carboxyl, esters and amino groups in the bioflocculant molecules. Combined with the results of zeta potential measurements, bridging is suggested as the main flocculation mechanism for OS-1B flocculation with kaolin. Overall, brewery wastewater can be used as a substrate to produce bioflocculants.

Microbial Flocculants as an Alternative to Synthetic Polymers for Wastewater Treatment: A Review

Microorganisms such as bacteria, fungi, and microalgae have been used to produce bioflocculants with various structures. These polymers are active substances that are biodegradable, environmentally harmless, and have flocculation characteristics. Most of the developed microbial bioflocculants displayed significant flocculating activity (FA > 70–90%) depending on the strain used and on the operating parameters. These biopolymers have been investigated and successfully used for wastewater depollution in the laboratory. In various cases, selected efficient microbial flocculants could reduce significantly suspended solids (SS), turbidity, chemical oxygen demand (COD), total nitrogen (Nt), dye, and heavy metals, with removal percentages exceeding 90% depending on the bioflocculating materials and on the wastewater characteristics. Moreover, bioflocculants showed acceptable results for sludge conditioning (accepted levels of dry solids, specific resistance to filtration, moisture, etc.) compared to chemicals. This paper explores various bioflocculants produced by numerous microbial strains. Their production procedures and flocculating performance will be included. Furthermore, their efficiency in the depollution of wastewater will be discussed.

Flocculation characteristics of a bioflocculant produced by the actinomycete Streptomyces sp. hsn06 on microalgae biomass

Background

Microbial flocculation is a good choice for harvest of microalgae biomass, which has gained extensive attention. There have been carried out massive studies in bacterial flocculation, many bacterial strains with flocculation activity were isolated and different types of bioflocculants were produced. However, harvest of algal biomass by bioflocculants which produced from actinomycete are deficiency. In this study, the bioflocculant from an actinomycete Streptomyces sp. hsn06 could be used to harvest Chlorella vulgaris biomass.

Results

Consecutive treatment with 20 mg·L^− 1 bioflocculant and 5 mM CaCl₂ for 5 min showed the highest flocculating activity. The bioflocculant was a nonprotein substance with thermal stability and pH stability, which can be used in comprehensive applications. Chemical analysis of the bioflocculant indicated that it is a small molecule substance of moderate polarity with containing triple bond and cumulated double bonds. Algal temperature, pH, and metal ions showed great effects on the flocculation efficiency of the bioflocculant.

Conclusions

The bioflocculant produced by Streptomyces sp. hsn06 possesses the potential to harvest algal biomass with high-efficiency.

Electronic supplementary material

The online version of this article (10.1186/s12896-018-0471-9) contains supplementary material, which is available to authorized users.

Characterization and coagulation-flocculation performance of a composite flocculant in high-turbidity drinking water treatment

Klebsiella variicola B16, a microbial bioflocculant (MBF-B16)-producing bacteria, was isolated and identified by its 16S rRNA sequence, biochemical properties, and physiological characteristics. The effects of culture conditions on MBF-B16 production, including carbon source, nitrogen source, C/N ratio, initial pH, and culture temperature, were investigated in this study. Results showed that 6.96 g of MBF-B16 could be extracted from a 1-L culture broth under optimized conditions. Chemical analysis showed that polysaccharide and protein were the main components. The neutral sugar consisted of galactose only, which was proposed in Klebsiella genus for the first time. In addition, a composite flocculant (CF) that contains polyaluminum ferric chloride (PAFC) and MBF-B16 for the removal of turbidity and SS in drinking water was optimized by response surface methodology. CF could reduce PAFC dosage by about 56.2-72%. Charge neutralization and adsorption bridging effect were the primary flocculation mechanisms.

Amino acids in cell wall of Gram-positive bacterium Micrococcus sp. hsn08 with flocculation activity on Chlorella vulgaris biomass

The aim of this work was to investigate the flocculation mechanism by Gram-positive bacterium, Micrococcus sp. hsn08 as a means for harvesting Chlorella vulgaris biomass. Bacterial cells of Micrococcus sp. hsn08 were added into algal culture to harvest algal cells through direct contacting with algae to form flocs. Viability dependence test confirmed that flocculation activity does not depend on live bacteria, but on part of the peptidoglycan. The further investigation has determined that amino acids in cell wall play an important role to flocculate algal cells. Positively charged calcium can combine bacterial and algal cells together, and form a bridge between them, thereby forming the flocs, suggesting that ions bridging is the main flocculation mechanism. These results suggest that bacterial cells of Micrococcus sp. hsn08 can be applied to harvest microalgae biomass with the help of amino acids in cell wall.

Isolation, identification, and characterization of an Aspergillus niger bioflocculant-producing strain using potato starch wastewater as nutrilite and its application

A bioflocculant (MBFA18) was produced by Aspergillus niger (A18) using potato starch wastewater (PSW) as nutrients. The cultivation processes and flocculating treatment for PSW purification were systematically studied. The flocculating rate of the MBFA 18 achieved 90.06% (kaolin clay) under the optimal cultivation condition (PSW with 5950 mg/L COD, 20 g/L glucose, 0.2 g/L urea and without phosphorus source addition and pH adjustment). Furthermore, effects of flocculant dosage, initial pH, coagulant aid (CaCl₂) addition and sedimentation time on the PSW treatment were discussed and studied in detail. The optimum flocculation treatment conditions were determined according to the treatment efficiency, cost and flocculation conditions. During the PSW treatment, 2 mL/L bioflocculant (1.89 g/L) dosage and 0.5 mol/L coagulant aid addition were applied without pH adjustment and 91.15% COD and 60.22% turbidity removal rate could be achieved within 20 min. The comparative study between the bioflocculant and conventional chemical flocculants showed excellent flocculating efficiency of MBFA 18 with lower cost (4.7 yuan/t), which indicated that the bioflocculant MBFA 18 produced in PSW substrate has a great potential to be an alternative flocculant in PSW treatment.

Uncovering the flocculating potential of extracellular polymeric substances produced by periphytic biofilms

The aim of this work was to study the characteristics and flocculating properties of extracellular polymeric substances (EPS) extracted from periphytic biofilms. The periphytic EPS, with an extracted yield of 491.8mg/g, were mainly composed of hetero-polysaccharides and proteins, and the elements C1s, N1s, and O1s. Polysaccharides represented 53.28% of the periphytic EPS. Proteins constituted 20.26% of the EPS, and contributed to at least 34.65% of the total flocculating activity. The periphytic EPS showed high turbidity removal capacity (86.76±1.52%, 10min) and efficient aniline blue (AB) removal capacity (56.46±1.41%, 30min). The mechanism of AB removal by the periphytic EPS seemed to be a combined technique of "adsorption-flocculation". This study reveals the flocculating capability of periphytic EPS, and suggests that periphytic biofilms are novel sources for bioflocculants preparation.

Flocculation of coal washing wastewater using polysaccharide produced by Paenibacillus mucilaginosus WL412

Natural polymeric flocculant shows effectiveness in wastewater treatment without increasing the environmental burden. The extracellular substance produced by Paenibacillus mucilaginosus WL412 was identified as an anionic polysaccharide composed of five types of monosaccharides, namely, D-mannose, D-glucuronic acid, D-glucose, D-galactose, and L-fucose with the molar ratio of 2.8:1.2:2.0:1.8:0.8. The purified polysaccharide, POS412, presented high efficiency in flocculating coal washing wastewater and kaolin suspension without the assistance of inorganic coagulants. Addition of POS412 resulted in the polymer bridging phenomenon in suspensions, which was observed by means of scanning electron microscopic imaging, size grading, and ζ-potential analyses. More importantly, POS412 exhibited satisfactory stability after storage in various conditions. The flocculation rate was more than 91% for coal washing wastewater when POS412 was stored for 264 h in the wide range of pH (3-11) and temperature (20-50 °C) before use. Results indicate that POS412 is a competent bioflocculant for wastewater treatment.

Recent advances in polysaccharide bio-based flocculants

Natural polysaccharides, derived from biomass feedstocks, marine resources, and microorganisms, have been attracting considerable attention as benign and environmentally friendly substitutes for synthetic polymeric products. Besides many other applications, these biopolymers are rapidly emerging as viable alternatives to harmful synthetic flocculating agents for the removal of contaminants from water and wastewater. In recent years, a great deal of effort has been devoted to improve the production and performance of polysaccharide bio-based flocculants. In this review, current trends in preparation and chemical modification of polysaccharide bio-based flocculants and their flocculation performance are discussed. Aspects including mechanisms of flocculation, biosynthesis, classification, purification and characterization, chemical modification, the effect of physicochemical factors on flocculating activity, and recent applications of polysaccharide bio-based flocculants are summarized and presented.

Flocculation mechanism of the actinomycete Streptomyces sp. hsn06 on Chlorella vulgaris

In this study, an actinomycete Streptomyces sp. hsn06 with the ability to harvest Chlorella vulgaris biomass was used to investigate the flocculation mechanism. Streptomyces sp. hsn06 exhibited flocculation activity on algal cells through mycelial pellets with adding calcium. Calcium was determined to promote flocculation activity of mycelial pellets as a bridge binding with mycelial pellets and algal cells, which implied that calcium bridging is the main flocculation mechanism for mycelial pellets. Characteristics of flocculation activity confirmed proteins in mycelial pellets involved in flocculation procedure. The morphology and structure of mycelial pellets also caused dramatic effects on flocculation activity of mycelial pellets. According to the results, Streptomyces sp. hsn06 can be used as a novel flocculating microbial resource for high-efficiency harvesting of microalgae biomass.

A novel Fe(III) dependent bioflocculant from Klebsiella oxytoca GS-4-08: culture conditions optimization and flocculation mechanism

In this work, the effect of cultivation factors on the flocculation efficiency (FE) of bioflocculant P-GS408 from Klebsiella oxytoca was optimized by the response surface methodology. The most significant factor, i.e. culture time, was determined by gray relational analysis. A total of 240 mg of purified P-GS408 was prepared from 1 liter of culture solution under the optimal conditions. GC-MS analysis results indicated that the polysaccharide of P-GS408 mainly contains Rhamnose and Galactose, and the existence of abundant hydroxyl, carboxyl and amino groups was evidenced by FTIR and XPS analyses. With the aid of Fe³⁺, the FE of kaolin solution by P-GS408 could achieve 99.48% in ten minutes. Functional groups of polysaccharide were involved in the first adsorption step and the zeta potential of kaolin solution changed from -39.0 mV to 43.4 mV in the presence of Fe³⁺ and P-GS408. Three-dimensional excitation-emission (EEM) fluorescence spectra demonstrates that the trivalent Fe³⁺ and Al³⁺ can bind efficiently with P-GS408, while those univalent and divalent cations cannot. With the help of SEM images, FTIR, zeta potential and EEM spectra, we proposed the P-GS408 flocculation mechanism, which consists of coordination bond combination, charge neutrality, adsorption and bridging, and net catching.

First evidence of bioflocculant from Shinella albus with flocculation activity on harvesting of Chlorella vulgaris biomass

Bioflocculant from Shinella albus xn-1 could be used to harvest energy-producing microalga Chlorella vulgaris biomass for the first time. In this study, we investigated the flocculation activity and mode of strain xn-1, the characteristics of bioflocculant, the effect of flocculation conditions and optimized the flocculation efficiency. The results indicated that strain xn-1 exhibited flocculation activity through secreting bioflocculant; the bioflocculant with high thermal stability, pH stability and low molecular weight was proved to be not protein and polysaccharide, and flocculation active component was confirmed to contain triple bond and cumulated double bonds; algal pH, temperature and metal ions showed great impacts on the flocculation efficiency of bioflocculant; the maximum flocculation activity of bioflocculant reached 85.65% after the response surface optimization. According to the results, the bioflocculant from S. albus xn-1 could be a good potential in applications for high-efficiency harvesting of microalgae.

Production of a bioflocculant from Pseudomonas veronii L918 using the hydrolyzate of peanut hull and its application in the treatment of ash-flushing wastewater generated from coal fired power plant

In this study, bioflocculant produced by Pseudomonas veronii L918 was applied to treat ash-flushing wastewater. The strain L918 could convert the hydrolyzate of peanut hull into bioflocculant, which can effectively reduce the production cost of bioflocculant. The yield of 3.39g/L bioflocculant MBF-L918 was achieved when 300mL/L peanut hull hydrolyzate was used as carbon source. The bioflocculant MBF-L918 contains 77.14% polysaccharides and 4.84% proteins, and the molecular weight (MW) of MBF-L918 is 24.77kDa. Furthermore, MBF-L918 showed good flocculating efficiency of 92.51% to ash-flushing wastewater when 2.83mg/L MBF-L918 was added, and thus achieved the recycling of ash-flushing wastewater. This study reported for the first time that the bioflocculant was produced using peanut hull hydrolyzate and effectively applied in the treatment of coal ash-flushing wastewater.

Implications for public health demands alternatives to inorganic and synthetic flocculants: bioflocculants as important candidates

Chemical flocculants are generally used in drinking water and wastewater treatment due to their efficacy and cost effectiveness. However, the question of their toxicity to human health and environmental pollution has been a major concern. In this article, we review the application of some chemical flocculants utilized in water treatment, and bioflocculants as a potential alternative to these chemical flocculants. To the best of our knowledge, there is no report in the literature that provides an up‐to‐date review of the relevant literature on both chemical flocculants and bioflocculants in one paper. As a result, this review paper comprehensively discussed the various chemical flocculants used in water treatment, including their advantages and disadvantages. It also gave insights into bioflocculants production, challenges, various factors influencing their flocculating efficiency and their industrial applications, as well as future research directions including improvement of bioflocculants yields and flocculating activity, and production of cation‐independent bioflocculants. The molecular biology and synthesis of bioflocculants are also discussed.

Evaluation of flocculating performance of a thermostable bioflocculant produced by marine Bacillus sp

This study assessed the bioflocculant (named MBF-W7) production potential of a bacterial isolate obtained from Algoa Bay, Eastern Cape Province of South Africa. The 16S ribosomal deoxyribonucleic acids gene sequence analysis showed 98% sequence similarity to Bacillus licheniformis strain W7. Optimum culture conditions for MBF-W7 production include 5% (v/v) inoculum size, maltose and NH4NO3 as carbon and nitrogen sources of choice, medium pH of 6 as the initial pH of the growth medium. Under these optimal conditions, maximum flocculating activity of 94.9% was attained after 72 h of cultivation. Chemical composition analyses showed that the purified MBF-W7 was a glycoprotein which was predominantly composed of polysaccharides 73.7% (w/w) and protein 6.2% (w/w). Fourier transform infrared spectroscopy revealed the presence of hydroxyl, carboxyl and amino groups as the main functional groups identified in the bioflocculant molecules. Thermogravimetric analyses showed the thermal decomposition profile of MBF-W7. Scanning electron microscopy imaging revealed that bridging played an important role in flocculation. MBF-W7 exhibited excellent flocculating activity for kaolin clay suspension at 0.2 mg/ml over a wide pH range of 3-11; with the maximal flocculation rate of 85.8% observed at pH 3 in the presence of Mn(2+). It maintained and retained high flocculating activity of over 70% after heating at 100°C for 60 min. MBF-W7 showed good turbidity removal potential (86.9%) and chemical oxygen demand reduction efficiency (75.3%) in Tyume River. The high flocculating rate of MBF-W7 makes it an attractive candidate to replace chemical flocculants utilized in water treatment.

Revealing the characteristics of a novel bioflocculant and its flocculation performance in Microcystis aeruginosa removal

In the present work, a novel bioflocculant, EPS-1, was prepared and used to flocculate the kaolin suspension and Microcystis aeruginosa. We focused on the characteristics and flocculation performance of EPS-1, especially with regard to its protein components. An important attribute of EPS-1 was its protein content, with 18 protein types identified that occupied a total content of 31.70% in the EPS-1. Moreover, the flocculating activity of these protein components was estimated to be no less than 33.93%. Additionally, polysaccharides that occupied 57.12% of the total EPS-1 content consisted of four monosaccharides: maltose, D-xylose, mannose, and D-fructose. In addition, carbonyl, amino, and hydroxyl groups were identified as the main functional groups. Three main elements, namely C1s, N1s, and O1s, were present in EPS-1 with relative atomic percentages of 62.63%, 24.91%, and 10.5%, respectively. Zeta potential analysis indicated that charge neutralization contributed to kaolin flocculation, but was not involved in M. aeruginosa flocculation. The flocculation conditions of EPS-1 were optimized, and the maximum flocculating efficiencies were 93.34% within 2 min for kaolin suspension and 87.98% within 10 min for M. aeruginosa. These results suggest that EPS-1 could be an alternative to chemical flocculants for treating wastewaters and cyanobacterium-polluted freshwater.