Flocculation Of Suspensions Research Articles

Preparation of octopus-like lignin-grafted cationic polyacrylamide flocculant and its application for water flocculation

High efficiency lignin-grafted cationic polyacrylamide (L-CPA) flocculant was synthesized via “grafting to” method using acrylamide (AM), methylacryloyloxyethyltrimethyl ammonium chloride (DMC) and enzymatic hydrolysis lignin (EHL) as raw materials. The linear pre-polymer of cationic polyacrylamide (CPA) terminated with chlorine was first synthesized and then grafted onto EHL via reactions of chlorine with phenolic hydroxyl groups in lignin molecules. The synthesized L-CPA could self-assemble into octopus-like nanospheres with CPA segments dissolved in water and hydrophobic lignin skeletons concentrated in the core, which endowed the L-CPA with excellent flocculation efficiency for kaolin suspension under faintly acid, neutral or alkalescent conditions (pH = 5–9). Only a small dosage between 4.0–4.5 mg/L of L-CPA was needed for flocculation of the kaolin suspension. The charge neutralization and bridging effect was proposed for the flocculation mechanism of the lignin-grafted cationic polyacrylamide. The octopus-like L-CPA was cheap, environmentally friendly and technically feasible, showing a great prospect in wastewater treatment.

Enhancement of flocculation and shear resistivity of bentonite suspension using a hybrid system of organic coagulants and anionic polyelectrolytes

In this study, the influence of the hybrid coagulation-flocculation system on the flocculation and shear resistivity of bentonite suspension has been investigated. Two short-chained coagulants, polyamine and polyDADMAC, accompanied with low and high Molecular Weight (Mw) long-chained anionic Polyacrylamide (PAM) flocculants have been used to enhance the size and mechanical properties of the produced flocs. Four characterization techniques were used as evaluation criteria of degree of flocculation including turbidity, zeta potential (ζ), floc size analysis and rheology. Optimum dosages between 5 and 10 mg/L were obtained for flocculants and between 20 and 30 mg/L for coagulants in hybrid systems. Compared to single systems, hybrid systems performed exceptionally well. Removal efficiency of 99% was achieved using hybrid systems producing water with turbidity as low as 1.05 NTU. Although differences were insignificant in the treatment quality, significant improvement was achieved in floc size and rheological behavior. Hybrid systems were able to produce large flocs of more than 400 µm, five times bigger than flocs from the single cationic coagulant systems. Most importantly, rheological testing of produced slurries revealed the remarkable advancement achieved by hybrid systems. Hybrid systems were able to increase the elastic modulus (G′) by more than ten times resulting from the compacted flocs present in the system. Furthermore, resistivity toward shear and oscillations were improved. Ultimately, hybrid systems have surpassed the single cationic systems by achieving slightly better treatment besides producing larger, denser and more resistive flocs. Generally, polyDADMAC performed better than polyamine in hybrid systems. The combination of polyDADMAC with high Mw PAM gave the best separation as well as the largest flocs, while the combination with low Mw PAM resulted in the best rheological properties.

Evaluation of the structural factors for the flocculation performance of a co-graft cationic starch-based flocculant

Three series of co-graft cationic starch (St)-based flocculants with distinct structural characteristics, namely, charge density (CD), graft-chain length (L), and graft-chain distribution (N), were successfully synthesized through graft copolymerization of [(2-methacryloyloxyethyl) trimethyl ammonium chloride] and acrylamide. These St-based flocculants with different molecular structures were used to flocculate various kaolin suspensions with different initial turbidities and a sodium humate (NaHA) aqueous solution. The experimental results indicated that CD contributed to flocculation evidently, whereas average L and its N were insignificant in experimentally measured ranges. On the basis of phenomenological theory, a second-order polynomial equation was used to further quantitatively analyze the effects of the three structural factors on the flocculation performance of these St-based flocculants, which were fully consistent with the experimental results. Besides, the optimal dose and its corresponding removal rate could be predicted exactly, and the flocculation mechanisms were discussed in detail according to the established models. With the combination of floc properties and zeta potentials, the flocculation mechanisms of these St-based flocculants for flocculation of kaolin suspensions and NaHA aqueous solution were mainly ascribed to charge patching and simple charge neutralization, respectively. These results improve the understanding of the structure–activity relationship of these graft St-based flocculants, which is of significant guidance for the utilization and design of novel flocculants.

Cationic starch-grafted-cationic polyacrylamide based graphene oxide ternary composite flocculant for the enhanced flocculation of oil sludge suspension

In this study, a novel, highly efficient and environmentally friendly ternary composites flocculant, namely, cationic starch-grafted-cationic polyacrylamide/graphene oxide (CS-g-CPAM/GO), was synthesized by ammonium persulfate initiation polymerization and condensation reaction. First, CS-g-CPAM was polymerized with cationic starch (CS), acrylamide (AM) and diallyl dimethyl ammonium chloride (DMDAAC), and CS-g-CPAM/GO was then synthesized by condensation reaction. The influence factors of graft polymerization were investigated, including total monomer concentration, initiator dosage, monomer mass ratio of mAM: mCS: mDMDAAC, post-polymerization temperature and post-polymerization time. The chemical structures and morphologies of the samples were characterized by Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermo-gravimetric and differential scanning calorimetry (TG-DSC), and scanning electron microscope (SEM). The CS-g-CPAM/GO was used to flocculate the oil sludge suspension, the effects of CS-g-CPAM/GO dosage, temperature and pH value on the flocculation performance were investigated, and the flocculation mechanism of CS-g-CPAM/GO was also analyzed. The results show that CS-g-CPAM/GO has outstanding flocculation effect, and CS-g-CPAM/GO flocculates oil sludge particles by adsorption bridging and charge neutralization in acidic and alkaline conditions.

Solid-State Microwave Modification of Flocculants for Wastewater Treatment

Presents the results of research on the creation of effective technical preparations – flocculants based on polyacrylamide, modified by the physical action of microwaves with frequency 4.5 GHz on their solid phase. The change in the basic physical properties of the working solutions of flocculants was established (dissolution rate, shear stress values, efficiency and sedimentation rate). Mechanisms of microwave solid phase modification and features of dissolution of pretreated batches of solid polyelectrolyte fractions are proposed. On the basis of rheological studies of prepared working solutions of flocculants and test experiments on the flocculation of suspension a comparative evaluation of effectiveness of the action of microwaves on polyectrolyte during its preliminary preparation using solid phase and liquid phase modifications.

Electrocoagulation/flocculation of cyanobacteria from surface waters

Abstract Cyanobacterial blooming episodes in surface waters used for drinking purposes are increasing due to eutrophication of water ecosystems. Water treatments should be optimised to remove phytoplankton cells as well as their associated toxins. The performance of a multicell electrocoagulation reactor operating under a continuous flow and coupled with flocculation for cyanobacteria removal was examined. Electrocoagulation of a suspension of the unicellular cyanobacteria Microcystis aeruginosa and its related toxin microcystin-LR, as a model of toxic cyanobacterium and cyanotoxin, respectively, showed that cell removal occurred through charge neutralisation with the Al hydroxides generated in the system, whereas the toxin did not undergo electrolytical processes. Cell inactivation was a function of the charge loading and the cell population. Inactivation of a 105 cells/mL suspension was 34% for a charge loading of 50 C/L whereas only 3% was achieved by increasing cyanobacteria concentration by one-order of magnitude. Flocculation of the electrocoagulated suspensions with anionic polyelectrolytes revealed a bridging mechanism, whereas an electrostatic patch aggregation was involved with cationic flocculants. Electrocoagulation/flocculation of a cyanobacterial blooming surface water (about 106 cells/mL) showed quite good concordance of cell inactivation values (9.7–10.7%) with those detected previously with Microcystis aeruginosa (5.4%). However, the performance of the flocculants was slightly worse as determined from the residual turbidity values (17% vs. 7% in pure cultures of M. aeruginosa) due to the different compositions of the extracellular organic matter.

Long-range, selective, on-demand suspension interactions: Combining and triggering soluto-inertial beacons.

Structures and particles that slowly release solute into solution can attract or repel other particles in suspension via diffusiophoresis, a process we termed "soluto-inertial (SI) interactions." These SI interactions involve "beacons" that establish and sustain nonequilibrium solute fluxes over long durations. Here, we demonstrate the versatility of the SI concept and introduce distinct strategies to manipulate solute gradients and, hence, suspension behavior using beacons with different physicochemical properties. First, we demonstrate on-demand particle migration using beacons that can be actuated with a trigger. We then show the synergy between multiple, distinct beacons that modify solute fluxes in a way that allows directed, yet selective, colloidal migration to specific target sites. Moreover, this multibeacon harmony enhances migration velocities, and delays the equilibration of the SI effect. The different SI techniques highlighted here suggest previously unidentified possibilities for sorting and separating colloidal mixtures, targeting particle delivery, and enhancing rates of suspension flocculation.

Design of a parallel plate shearing device for visualization of concentrated suspensions

A modified version of the commercially available RheOptiCAD® was developed to visualize the microscopic structural changes occurring in concentrated suspensions, such as the break-up of flocs in clay suspensions, under shearing action. This is made possible by replacing the inverted microscope used in the traditional RheOptiCAD® set-up by an upright modular microscope equipped with a CMOS camera and epi-illumination. Our device retains the following features of the previous version of RheOptiCAD®: [i] uniaxial translational motion of two parallel plates, [ii] three modes of shear straining, [iii] controlled thermal environment, and [iv] vacuum joining of microscopy glass slides. The validation of the new design was done using a model system of un-flocculated and flocculated kaolin suspensions and concentrated natural mud suspension. The results showed that the constructed device is a promising tool for studying, from fundamental and industrial perspectives, the microstructural behaviour of complex suspended systems under controlled thermal and mechanical conditions.

ROLE OF SORPTION IN EFFECTIVE OF SUSPENSIONS FLOCCULATION BY COMPOSITIOINS SURFACTANTS AND NATURAL POLYMERS

Natural flocculants as chitosan and sodium alginate has physic-chemical properties: biodegradability, reaction and complexing ability, compatibility with living tissues without toxicity. Researches had shown that chitosan and sodium alginate can be used for flocculation of suspensions, sorption from aqueous solutions of heavy metals. Sorption has a specific role in the flocculation process. Sorption determined by the nature, molecular weight, concentration, charge density of the flocculants, as well as the properties of dispersions. It is necessary to understand the mechanism of processes in these systems in order to select an effective flocculants. The mechanism of action of natural flocculants is different from synthetic. The state of biopolymers depends on the pH of the solution. A positive effect on flocculation exerted by the addition of inorganic substances, surfactants or oppositely charged polyelectrolytes. The aim of our researches was to study the flocculation ability of compositions natural flocculants and surfactants. It was studied sedimentation stability of suspensions ground sediments containing macromolecular substances (flocculants) and cationic surfactants. It was shown that the sedimentation stability defines as flocculants characteristics such as molecular weight, concentration, nature of flocculants, polyelectrolyte’s charge density and nature of the suspensions. It was found that compositions of natural flocculants chitosan and sodium alginate with surfactants are effective. The findings suggest that the studied compositions of natural flocculants have significant potential for use, thanks to a number of advantages: the efficiency of their actions, low reagent consumption, environmental safety.

Flocculation behaviour of bentonite clay-water systems

ABSTRACTThe effect of polyacrylamide (PAM) as flocculant, NaCl electrolyte concentration and pH on the degree of flocculation of bentonite suspension has been investigated. It has been observed that the increase in PAM dosage reduces the residual turbidity and improves the settling rate of the bentonite particles. At higher pH conditions bentonite dispersions are highly flocculated having high settling rates and low supernatant turbidity. The combined effect of salt concentration and PAM dosage improved the overall flocculation efficiency of the system.

Hairy cationic nanocrystalline cellulose as a novel flocculant of clay

HypothesisThe present paper investigates, for the first time, the potential of cationic hairy cellulose nanocrystals (CNCC) to induce the flocculation of a model suspension of kaolinite. CNCC belong to a brand new family of nanocelluloses characterized for presenting a crystalline rod-like body and functionalized amorphous chains at both ends. Given that these chains can be easily tuned, these nanocelluloses present a high potential as fit-to-purpose flocculants. ExperimentsCNCC were produced through periodate oxidation, cationization and thermal treatment of cellulose. Flocculation was monitored by both photometric dispersion analysis and laser reflectance. Flocs were characterized by the determination of zeta potential, supernatant turbidity removal and optical microscopy. A recently developed machine learning random forest regression model was used to estimate fractal dimension (Df) from chord length distribution data. FindingsAlthough a high efficiency was achieved for CNCC dosages between 7.5 and 75 mg/g, the maximum floc size and the fastest flocculation were found near the isoelectric point (10–30 mg/g). Thus, CNCC acted through charge neutralization mechanism. The model used to estimate flocs Df was found very successful to describe the flocculation process. The clay/CNCC flocs Df values suggest a relation between floc conformation and CNCC dosage, presenting an opener structure when closer to the isoelectric point.

Flocculation of a High-Turbidity Kaolin Suspension Using Hydrophobic Modified Quaternary Ammonium Salt Polyacrylamide

In this work, a novel cationic polyacrylamide (PAMD) was synthesized by acrylamide (AM) diallyl dimethyl ammonium chloride (DMD) and dodecyl polyglucoside (DPL) under low-pressure ultraviolet (UV) initiation. The intrinsic viscosity and cationic degree of PAMD were optimized in copolymerization. The optimum synthesis conditions that affect polymerization were determined to be solid content 30%, DPL content 25%, DMD content 30%, illumination time 135 min, and pH 9. The flocculation performance of flocculant PAMD with a high cationic degree was investigated in the purification of high-turbidity water. The flocculation mechanism was correspondingly studied and summarized based on Fourier transform-infrared (FTIR) analysis. Finally, the results of an experimental simulation using the response surface method show that 98.9% supernatant transmittance was achieved under dosage 4 mg/L, fast stirring time 20 min, pH 7, and stirring speed 320 rpm.

Stochastic transient Liquid-Solid Phase Separation reveals multi-level Dispersion States of Particles in Suspension

Abstract Wall slip or, more usually, liquid-solid phase separation at the boundary wall when measuring the rheological properties of particulate suspensions is normally considered an undesirable source of error. However, exclusion of a structure consisting of multiple particulates at a planar boundary can, in turn, reveal the nature of that structure and the way it interacts with other elements in the dispersion. Using a system of surface-treated ground calcite particles, designed to control lyophilicity, dispersed, respectively, in two comparative liquids, hexadecane (dispersive surface tension component only) and linseed oil (both dispersive and polar surface tension components), the relative wettability of the particulate surface can be studied. The static state is viscoelastic, with the elastic component reflecting the network of interacting forces acting to structure the particles together and/or to trap liquid within the long-range particle-particle matrix. As strain is applied under plate-plate geometry, selected aggregate structures become size-excluded at the wall, leading to a loss of shear coupling with the bulk polydisperse suspension. At high strain, given optimal solids content, this results in a stochastic transition between two discrete stress data sets, i.e. that with full shear coupling and that with only partial coupling. Stress recovery is subsequently monitored as strain is step-wise reduced, and the progress toward loss of the stochastic transient phenomenon, together with its parallel change in magnitude, is used to describe the re-formation of primary agglomerates. Cessation of the phase separation indicates re-build of the close-to-static structure. Under certain conditions it is observed that the cessation may be accompanied by a secondary relaxation of state, indicating the build of a secondary but weaker structure, likened to the well-known dual-level flocculation in aqueous colloidal suspension. Rheo-optical observations using small angle light scattering illumination (SALS) are used to confirm a structure model switching from static (uncoupled with shear) to rotating (fully coupled to the boundary-defined shear) and finally uniformly sheared.

Flocculation of kaolin from aqueous suspension using low dosages of acrylamide‐based cationic flocculants

ABSTRACTFlocculation of kaolin from aqueous streams has become very important in view of its wide range of applications. In this work, cationic flocculants based on copolymers of acrylamide (AM) and 3‐acrylamidopropyltrimethylammonium chloride (APTMAC) were synthesized with two different mole ratios of monomers, 80 mol % of AM (CP‐8020) and 40 mol % of AM (CP‐4060). The chemical structures of copolymers were confirmed by 1H and carbon‐13 nuclear magnetic resonance (13C NMR) spectroscopy. The molecular weight (MW) and zeta potential of the copolymers were determined. High MW was obtained for copolymer with high content of AM (CP‐8020) and high zeta potential was observed for copolymer with high content of APTMAC (CP‐4060). Flocculation of kaolin suspension was performed using both CP‐8020 and CP‐4060 and the flocculation was correlated to the zeta potential and MW of the copolymers. The optimum dosages of flocculants were determined. The mechanism of flocculation was discussed in terms of charge neutralization and bridging. The flocs of kaolin were characterized in terms of moisture content and size. To the best of our knowledge, this copolymer system was used for the first time for kaolin flocculation and found out to be efficient. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47286.

Ammonium persulfate-initiated polymerization of cationic starch-grafted-cationic polyacrylamide flocculant for the enhanced flocculation of oil sludge suspension

In this study, a novel, highly efficient and environmentally friendly flocculant, namely, cationic starch-grafted-cationic polyacrylamide (CS-g-CPAM), was synthesized by initiation polymerization of ammonium persulfate. First, CS-g-CPAM was polymerized with cationic starch(CS), acrylamide(AM) and diallyl dimethyl ammonium chloride (DMDAAC), and then the influence factors of graft polymerization were investigated, including total monomer concentration, initiator dosage, the monomer mass ratio of mAM: mCS: mDMDAAC, post-polymerization temperature and post-polymerization time. And the intrinsic viscosity of the CS-g-CPAM was measured by the one point method accurately. The chemical structures and morphology of the samples were characterized by Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermo-gravimetric and differential scanning calorimetry (TG-DSC), and scanning electron microscope (SEM). The CS-g-CPAM was utilized to flocculate the oil sludge suspension, the effects of CS-g-CPAM dosage, temperature and pH value on the flocculation performance were investigated. The results show that CS-g-CPAM has outstanding flocculation effect.

Effect of sequentially adsorbed multilayers, citric acid(CA)-PEI-CA-PEI and PEI-CA-PEI-CA, on the surface chemistry and rheology of spherical α-alumina suspensions

The yield stress and zeta potential of washed spherical α-Al2O3 suspensions with two to four layers of critic acid(CA) and polyethyleneimine(PEI_Mw1.8and 70 kDa) adsorbed sequentially were characterized. With CA adsorbed as the first layer, pHξ=0 was shifted to a lower pH and the maximum yield stress (τymax) was reduced. With PEI adsorbed as the first layer, the pHξ=0 was moved slightly higher. With the introduction of the second layer, the CA/PEI additive was formed which functioned as a bridging agent. The pH range of yield stress was broadened significantly and increased with the number of layers. This pH ranged from 2.5 to 11. The CA/PEI multilayer additive loses its positive charge at pH >11. There was less adsorption in layer3 and layer4 when lower Mw PEI is applied to the suspension. The CA/PEI multilayer additive formed by PEI of Mw70000 and CA was larger in size than that formed by PEI of Mw 1800 and CA. Lower Mw PEI produced a stronger flocculated network or higher τymax suspension due to a higher concentration of multilayer additive. CA/PEI multilayer additive was participating in bridging and particle bridging interaction was not affected by the adsorption order of CA and PEI.GRAPHICAL ABSTRACT

Chemical and Enzymatic Protein Cross-Linking To Improve Flocculant Properties

Some proteins promote the flocculation of aqueous suspensions, but proteins are much smaller than modern polymeric flocculants, and they are often not as potent. In this study, two globular protein...

Screening for Bioflocculant-Producing Bacteria from the Marine Environment of Sodwana Bay, South Africa

Abstract Flocculants are chemicals that mediate flocculation process, by aggregating colloids from suspension to form floc. Chemical flocculants are hazardous to the environment, which inform the search for safer and eco-friendly alternatives from microorganisms. Bacterial strains were isolated from water and sediment samples collected from Sodwana Bay, South Africa, and physiological properties of the bacterial strains were observed. Flocculation test using kaolin clay suspension was done on all isolates and the ones that showed flocculating activity were identified molecularly using 16 rRNA gene sequence analysis. Forty marine bacteria isolates were gotten from sediments and water samples collected from Sodwana Bay. Most of the isolates exhibited a range of colony pigmentation (pink, creamy, yellow, and white). After purification of individual isolates, they were screened for their potential to produce bioflocculant. The result revealed that isolates marked SOD3, SOD10, SOD12, SOD26, SOD27, SOD28, SOD32, SOD33 and SOD34 produced bioflocculants as shown by the flocculating activities from their crude extract. All these isolates showed good flocculation of kaolin clay suspension above 60% (flocculating activity) except SOD12. These bioflocculant producing isolates were identified as Pseudoalteromonas sp, Alcaligenes faecalis, Bacillus subtilis, Bacillus cereus, Bacillus stratosphericus. The results showed Sodwana Bay, South Africa as a reservoir of bacteria with potential to produce flocculants. However, further studies on the optimisation of culture conditions for bioflocculant production, extraction, characterisation and application of isolates is on the way to underscore the biotechnological importance of these microbes as producers of substitutes to harmful chemical flocculants commonly used in water and wastewater treatment.

Natural flocculants from fresh and saline wastewater: Comparative properties and flocculation performances

Natural flocculants, due to their eco-friendliness, have gained increasing attention for (waste) water treatment and are promising alternatives to oil-based synthetic flocculants. We systematically investigated simultaneous industrial wastewater treatment with the production of microbial extracellular polymeric substances (EPS) as natural flocculants. EPS were produced in two membrane bioreactors, respectively treating fresh and saline synthetic wastewater from biodiesel and (bio)ethanol industries. From each reactor, soluble and bound EPS fractions were extracted, purified and characterised for their functionalities, molecular weights and charge densities using Fourier transform infrared (FTIR), size exclusion chromatography and colloid titration, respectively. High removal of chemical oxygen demand (COD) was achieved in both reactors (93–95%), with 5.8–7.6% of the inlet COD recovered as EPS. FTIR spectroscopy reveals these EPS as a mixture of proteins and polysaccharides, possessing carboxyl, hydroxyl and amine groups. These functional groups, which provided a net anionic charge density (1.5–2.9 meq/g at neutral pH), coupled with EPS mixed molecular weight (MW) distribution: high (>1000 kDa), medium (1000–100 kDa) and low (<100 kDa) MW fractions, make them promising flocculants. Extracted EPS showed good flocculation of non-saline kaolin suspension (74–89% turbidity reduction) and excellent flocculation of saline kaolin suspension (88–97%), performances comparable to anionic polyacrylamide. The results show the possibility for wastewater treatment plants to combine wastewater treatment with the production of valuable flocculants.

Partial flocculation for spray drying of spherical mixed metal oxide particles

AbstractParticles are an important design consideration for many proposed solar thermochemical water splitting reactor concepts. These particles must maintain physical integrity and chemical performance at very high temperatures (&gt;900°C) while flowing within a system. Spray drying is a commonly used, scalable method to produce solid spherical particles that have the best opportunity to meet these requirements. Spray drying is used to produce hercynite (FeAl2O4) particles using pH‐modification of a charge‐stabilized sol. This process involves inducing partial flocculation in nanoparticle suspensions to yield larger particles that are spherical and structurally robust. A commercial boehmite suspension is characterized along with a mixture of the boehmite suspension with an iron oxide suspension. Zeta potential near zero and peak yield stress measurements at the same pH indicate flocculation, but associated sedimentation behavior is not observed. The behavior of both the boehmite‐only and mixed suspensions both seem to be driven by the behavior of the boehmite suspension alone. Spray dried particles from the mixed suspension at the critical pH gave significantly larger and more spherical particles, which also indicates flocculation. This relatively simple technique shows promise for new mixed‐metal material formulations and scalable applications.