Floc Aggregation Research Articles

Fine sediment and nutrient dynamics related to particle size and floc formation in a Burdekin River flood plume, Australia

The extreme 2010–2011 wet season resulted in highly elevated Burdekin River discharge into the Great Barrier Reef lagoon for a period of 200days, resulting in a large flood plume extending >50km offshore and >100km north during peak conditions. Export of suspended sediment was dominated by clay and fine silt fractions and most sediment initially settled within ∼10km of the river mouth. Biologically-mediated flocculation of these particles enhanced deposition in the initial low salinity zone. Fine silt and clay particles and nutrients remaining in suspension, were carried as far as 100km northward from the mouth, binding with planktonic and transparent exopolymer particulate matter to form large floc aggregates (muddy marine snow). These aggregates, due to their sticky nature, likely pose a risk to benthic organisms e.g. coral and seagrass through smothering, and also by contributing to increased turbidity during wind-induced resuspension events.

Use of Continuous Aeration Respirometry Method for the Prediction of Slightly Saline Waste Water Biodegradation

The microorganisms growth kinetics is determined by the physical and chemical characteristics of the environment in which they find themselves and multiply; It is therefore essential to understand the effect of these environmental factors to master cell multiplication and hence the pollution biodegradation. Respirometry has been used in recent years in the laboratory as an assessment technique of microbial activity and an effect detector of the contamination (presence of toxic, stress, increase or decrease in pH, temperature variation .) on bacterial respiration and hence on the biological waste water treatment plant. In this study respirometry has been used as a relatively quick and efficient means to detect the effect of the presence of a salt of up to 5g/l (low salt stress) on the degradation of carbon and nitrogen pollution and on bacterial floc aggregation.

Removal of acid and direct dye by epichlorohydrin–dimethylamine: Flocculation performance and floc aggregation properties

A cationic organic flocculant epichlorohydrin–dimethylamine (EPI–DMA) was employed for the treatment of acid and direct dye. The study aims at investigating the flocculation performance of EPI–DMA for the model dye, and corresponding floc aggregation properties, which were determined by jar test and photometric dispersion analysis, respectively. The interactions between cationic flocculant and anionic dye were investigated through spectra analysis. The results showed that EPI–DMA effectively decolorized the tested acid and direct dye. The viscosity and cationicity of EPI–DMA had different influence on the removal of different dye. Chemical interaction was observed between quaternary ammonium of EPI–DMA and sulfonic group of dye. The flocculation dynamic process showed that flocs with better aggregation and sedimentation properties were produced by EPI–DMA with higher viscosity and cationicity for acid dye. Contrarily, flocs with the best aggregation and sedimentation properties were produced by EPI–DMA with the lowest viscosity and cationicity for direct dye.

Characteristic analysis on temporal evolution of floc size and structure in low-shear flow

A series of flocculation tests were performed to investigate the effect of low-shear rates ( G = 3–16 s −1) on flocculation of kaolin suspension by polyaluminum chloride (PACl), with the goal of understanding floc growth mechanisms. Results were reported in terms of floc average size ( d p ) and boundary fractal dimension ( D pf ), derived from a non-intrusive optical sampling and digital image analysis technique. As expected, the rate of floc aggregation increased with increasing G, resulting in faster changes in aggregate size and structure in the initial stage of flocculation. Nevertheless, steady state was attained faster for D pf than for d p at the same shear rates, possibly due to the self-similarity of fractal aggregates. An interesting finding was that at G = 3 s −1, an obvious plateau was observed for the average-size evolution at steady state; for shear rates of 6 and 7 s −1, the flocs exhibited some decrease after reaching the peak of size, mainly as a result of floc settling at steady state; and for G = 11–16 s −1, a decrease in floc size was possibly attributed to the irreversibility of PACl-floc breakage. The process of floc growth was described using a fractal growth model, which defined flocculation as the result of the combined processes of aggregation and restructuring. The conceptual model could effectively characterize temporal changes in floc size and structure, and found that fragmentation followed by reformation seemed to be more effective in forming larger and more compact aggregates than the restructuring process due to erosion and reformation, which may provide useful insights for the design of flocculation reactors.

The impact of pH on floc structure characteristic of polyferric chloride in a low DOC and high alkalinity surface water treatment

The adjustment of pH is an important way to enhance removal efficiency in coagulation units, and in this process, the floc size, strength and structure can be changed, influencing the subsequent solid/liquid separation effect. In this study, an inorganic polymer coagulant, polyferric chloride (PFC) was used in a low dissolved organic carbon (DOC) and high alkalinity surface water treatment. The influence of coagulation pH on removal efficiency, floc growth, strength, re-growth capability and fractal dimension was examined. The optimum dosage was predetermined as 0.150 mmol/L, and excellent particle and organic matter removal appeared in the pH range of 5.50–5.75. The structure characteristics of flocs formed under four pH conditions were investigated through the analysis of floc size, effect of shear and particle scattering properties by a laser scattering instrument. The results indicated that flocs formed at neutral pH condition gave the largest floc size and the highest growth rate. During the coagulation period, the fractal dimension of floc aggregates increased in the first minutes and then decreased and larger flocs generally had smaller fractal dimensions. The floc strength, which was assessed by the relationship of floc diameter and velocity gradient, decreased with the increase of coagulation pH. Flocs formed at pH 4.00 had better recovery capability when exposed to lower shear forces, while flocs formed at neutral and alkaline conditions had better performance under higher shear forces.

Fouling layer formation by flocs in inside-out driven, horizontal aligned capillary ultrafiltration membranes

The hybrid process coagulation and low pressure membrane filtration for the direct treatment of surface water became a generally accepted rule of technology in recent years. The objective of this work was to contribute to the understanding of fouling layer formation by porous floc aggregates in inside-out driven capillaries. A computational fluid dynamics (CFD) model was developed for the description of a complete fluid flow field in capillaries of arbitrary cylindrical geometries and alignments. It covers user-defined physical properties of flocs and membrane materials and is valid for different chosen operation conditions. This was done by numerical calculations of the Navier–Stokes and continuity equations. Floc velocities and trajectories were derived by balancing the forces and torques acting on the flocs, determining places of preferential deposition, based on numerical calculations of the convection and diffusion equation and the influence of the membrane wall. The models were coupled and eventually used to account for the growing fouling layer height and its influence on the resulting fluid flow field and floc trajectories, delivering a dynamic fouling layer formation over time. New aspects could be derived qualitatively to understand the formation of fouling layers from which recommendations for appropriate operation conditions were concluded.

Effect of polyelectrolyte mixtures on the electrokinetic potential and kinetics of flocculation of clay mineral particles

The effect of binary mixtures of cationic and anionic electrolytes on the kinetics of aggregation, size and strength of flocs formed from kaolin and bentonite particles as a function of the polymer dose, mixture composition, sequence of the components addition and intensity of stirring the system has been studied. A synergism in the flocculation capacity in mixtures of moderate and weakly charged polyelectrolytes was observed; the biggest aggregates have been found at condition of adding first the cationic polymer then the anionic one. An initial intensive short stirring the suspension accelerates the aggregation process and increases the size of flocs independently of the sequence of polymers addition. In mixtures of cationic and anionic polyelectrolytes, the ζ-potential of particles is determined by the adsorbed anionic polymer independently of the charge density of polyelectrolytes and sequence of addition of the mixture components to the suspension. The laws observed were explained by features of polyelectrolytes conformation in adsorbed mixed polymer layers.

Coagulation assessment and optimisation with a photometric dispersion analyser and organic characterisation for natural organic matter removal performance

Three South Australian source waters of low, mid and high dissolved organic carbon (DOC) levels were evaluated for coagulation efficiency in terms of natural organic matter (NOM) interaction and floc behaviour. Experiments were conducted using aluminium chlorohydrate (ACH) and aluminium sulphate (alum) at different mixing conditions with continuous monitoring of formation and breakage of flocs using a flow-through optical measurement device known as photometric dispersion analyser (PDA). A positive correlation of floc growth against coagulant dosage was found for ACH based on a limiting growth function. Floc structure was assessed by analysis of PDA derived parameters showing promise for more rapid coagulation condition optimisation than subjective visual criteria. Removal of NOM and growth of flocs are influenced more by the hydrophobicity of the NOM than the choice of coagulant. A higher hydrophobic fraction resulted in slower aggregation of flocs with both coagulants and better removal when using alum at controlled pH.

Effect of aging period on the characteristics and coagulation behavior of polyferric chloride and polyferric chloride–polyamine composite coagulant for synthetic dying wastewater treatment

In this paper, a new composite inorganic–organic coagulant (PFC–EPI–DMA) was prepared by polyferric chloride (PFC) and epichlorohydrin–dimethylamine (EPI–DMA) under a given EPI–DMA/Fe and OH/Fe molar ratio. In comparison with PFC, the Fe (III) species and zeta potential of PFC–EPI–DMA were measured. Then their coagulation performance and coagulation kinetics for treating synthetic reactive dying wastewater were investigated. The results showed that the content of Fea and Feb in PFC–EPI–DMA and PFC coagulants decreased with increasing aging period. Compared to PFC, PFC–EPI–DMA had higher content of Fea but lower content of Feb and Fec. The zeta potentials of two coagulants decreased with increasing aging period within all tested pH range. For the treatment of reactive red 24, the color removal efficiency treated by PFC–EPI–DMA decreased, while that treated by PFC remained almost constant with increasing aging period. However, the color removal efficiencies of reactive blue 14 treated by two coagulants both decreased with increasing aging period. The results of floc aggregation process confirmed that with increasing aging period, the orders of floc growth rate, ratio and TWV treated by two coagulants were complicated.

Coagulation enhancement of exopolysaccharide secreted by an Antarctic sea-ice bacterium on dye wastewater

The purpose of this paper is to study the enhancement of Bsi20310 exopolysaccharide (Bsi20310 EPS, secreted by an Antarctic sea-ice bacterium Pseudoalteromonas sp. Bsi20310), on coagulation of reactive brilliant red X-3B (RX-3B) by ferric chloride. The effect of solution pH, EPS addition timing and NaCl concentration for coagulation of RX-3B was investigated. The results showed that at pH 10, Fe(III) dosage of 55 mg/L, adding 150 mg/L Bsi20310 EPS enhanced the decolorization effectively. NaCl had little effect on the enhancement of Bsi20310 EPS. The EPS had negative surface charge and could combine with positive Fe(III)–dye flocs to form neutralized settleable Fe(III)–dye–EPS flocs. Results of residual Fe(III) concentration and ferric–ferron reaction kinetics indicated that EPS addition led not only more Fe(III) to participate in coagulation but also to form more Fe b (the most effective ferric hydrolysis species) in coagulation. Bsi20310 EPS enhanced Fe(III) coagulation performance by neutralization, bridging and sweeping to improve the floc aggregation.

Non-equilibrium flocculation characteristics of fine-grained sediments in grid-generated turbulent flow

Results are presented from a series of settling column experiments investigating temporal variations in the flocculation characteristics of purely cohesive (kaolin clay) sediment suspensions and cohesive (kaolin) and non-cohesive (fine sand) sediment fraction mixtures. Experimental runs were conducted under controlled hydrodynamic conditions generated by a rigid array of in-phase oscillating grids. The results indicated that rapid initial floc aggregation occurred under low turbulent shear rates, with peak maximal and root-mean-square (r.m.s.) floc sizes (∼ 400 μm and ∼ 200 μm, respectively) attained after relatively short time periods, before reducing with time. By contrast, lower aggregation rates and smaller floc sizes were observed under higher shear conditions, with flocs retaining suspended in the settling column for longer time scales due to the increased turbulence. The mud input concentration displayed some correlation with maximal and r.m.s. floc sizes at higher shear rates but no correlation was apparent at low shear rates. This observed floc behaviour may be attributed to the differences in concentration gradients at high and low shear rates that affect both floc settling rate and time required for flocs to attain equilibrium size. The addition of the fine sand fraction to the kaolin clay suspension reduced both the initial floc formation (i.e. aggregation) rate and the maximal and r.m.s. floc sizes attained throughout the experiments. The reduction in maximal floc sizes appeared to be enhanced by an increase in the ratio of fine sand to kaolin clay content within the mixture.

Effect of dosing method and pH on color removal performance and floc aggregation of polyferric chloride–polyamine dual-coagulant in synthetic dyeing wastewater treatment

Two polyferric chloride–polyamine (PFC–EPI–DMA) dual-coagulants with different dosing methods were comparatively investigated in terms of color removal performance and floc aggregation in the treatment of synthetic disperse yellow and reactive red wastewater, and in comparison with PFC and EPI–DMA. The coagulation efficiency was studied by Jar-test, and Photometric Dispersion Analyzer 2000 (PDA 2000) was used to investigate floc aggregation process. The results showed that in two dual-coagulants treatment, PFC dosing followed by EPI–DMA dosing (PFC/EPI–DMA) achieved higher color removal rate for synthetic disperse yellow 201 wastewater, whereas reverse dosing order compared to the former (EPI–DMA/PFC) obtained better color removal performance for synthetic reactive red 24 wastewater. The optimal color removal efficiencies for treating disperse yellow 201 by PFC/EPI–DMA and reactive red 24 by EPI–DMA/PFC were both 97.5% at pH 6.0. The floc aggregation process showed that the floc growth rate of PFC/EPI–DMA was higher than that of EPI–DMA/PFC at the same dosage, whereas both Ratio and the time-weighted ratio variance (TWV) of PFC/EPI–DMA were almost lower than those of EPI–DMA/PFC in the treatment of disperse yellow 201. For reactive red 24 treatment, both floc growth rate and Ratio of EPI–DMA/PFC were higher than those of PFC/EPI–DMA, whereas TWV of EPI–DMA/PFC was lower than that of PFC/EPI–DMA. For disperse yellow 201 treated by PFC/EPI–DMA, the maximums of floc growth rate and Ratio were both reached at pH 6.0, whereas TWV was decreased as the increase of pH. For reactive red 24 treated by EPI–DMA/PFC, the maximums of three parameters were all reached at pH 4.5.

Effect of temperature and pH on droplet aggregation and phase separation characteristics of flocs formed in oil–water emulsions after coagulation

Coagulation process is used for destabilization of emulsions to promote aggregation of oil droplets on flocs which can be subsequently removed by sedimentation or flotation. The objectives of this study were to investigate the effect of temperature and pH on the effectiveness of destabilization of olive oil–water emulsions in relation to floc morphology and aggregation characteristics of oil droplets, and to quantify the ability of flocs to capture and separate oil. A cationic polyelectrolyte was used for the coagulation of oil droplets in edible olive oil–water emulsions using a jar test apparatus. The flocs formed in olive oil–water emulsions after coagulant addition were analyzed using microscopic image analysis techniques. Fractal dimension, radius of captured oil droplets on flocs, number of oil droplets aggregated on flocs, and floc size were used to quantitatively characterize and compared the effectiveness of the coagulation process at different conditions (pH and temperature) and the ability of flocs to remove oil from water. Analysis of microscopic images showed that floc size was not always the best measure of effectiveness of coagulation process in oil–water emulsions. The flocs forming at different pH levels and temperatures had significant morphological differences in their ability to aggregate different sizes and numbers of oil droplets, resulting in significant differences in their ability for separating oil. Fractal dimension did not correlate with the ability of flocs to aggregate oil droplets nor the total amount of oil captured on flocs. Temperature had a significant effect on droplet size and number of droplets captured on flocs. The differences in floc sizes at different temperatures were not significant. However, the flocs forming at 20 °C had fewer but larger droplets aggregating larger amounts of oil than flocs formed at 30 °C and 40 °C. The size of droplets at different pH levels was similar, however, there were significant differences in number of droplets aggregating on flocs and floc sizes. The amount of oil captured on flocs at pH 7 and pH 9 was significantly higher than those at pH 5 and pH 11. The calculated fractal dimensions of the flocs (all less than 1.8) indicated that the coagulation process was diffusion limited implying that there was no repulsion between the colliding particles (i.e., droplets and flocs); hence, each collision between flocs and droplets resulted in attachment.

Evaluation of coagulation and PAC adsorption pretreatments on membrane filtration for a surface water in Korea: A pilot study

Application of membrane filtration has been significantly expanded throughout the world in two decades. A project was launched to facilitate the application of membrane filtration in drinking water plants in Korea in 2004. Five pilot plants each with a capacity of 500 m3/d were installed in a Gueui Drinking Water Plant. The Han River water was a main raw water source for the plants. Key parameters of the raw water were examined. The raw water characteristics are tremendously varied with seasons and rain fall, especially in terms of turbidity and algae numbers. The operation of pretreatment was of substantial importance due to the variation of the raw water. Coagulation and powdered activated carbon adsorption were performed as pretreatment options of microfiltration. The coagulant doses were optimized with increasing turbidity compared to the conventionally used operational manual. PAC adsorption was applied to overcome fouling by high algae numbers. The addition of PAC relieved the aggravation of fouling. However, the PAC addition could not stop the undergoing fouling. A set of laboratory experiments showed that the removal of floc aggregates after coagulation and PAC was critical to maintain high water flux in the membrane system.

Introducing a slow cross-flow at the capillary outlet in comparison to conventional dead-end mode—a trajectory analysis of the effects

A model has been developed, based on the finite element method (FEM) of computational fluid dynamics (CFD), for the description of the complete flow field and concentration distribution inside a membrane capillary, driven in inside-out and dead-end or ‘slow’ cross-flow mode, sometimes referred to as ‘bleed flow’. Particle or floc transport and deposition have been described by trajectory analysis, i.e. superimposing the calculation of forces and torques acting on the particles or flocs, based on the previously modelled fluid flow field. The model is used to give an overview of deposition behaviour and fouling layer formation of particles and flocs of a certain size in dead-end and cross-flow filtration. Example results are shown for different sized flocs. It is shown that the choice of dead-end or cross-flow operation is more significant if small floc aggregates have to be filtered by the membrane. Small flocs will be deposited more or less homogeneously along the membrane wall after some significant distance to the capillary inlet, leaving the first part of the membrane area unused for deposition. A ‘slow’ cross-flow could be used to transport small flocs out of the capillary which entered the capillary cross section area in the neighbourhood of the axis. The faster the chosen cross-flow velocity, the larger the area. Larger flocs will be ‘accumulated’ in one resulting equilibrium trajectory and are transported to the rear end of the capillary, independent of their starting radial position at the inlet and operation conditions. It was calculated, that larger flocs will not be significantly transported out of the capillary lumen by introducing ‘slow’ cross-flow velocities at the capillaries outlet only.

Investigation of dynamic processing on aluminum floc aggregation: Cyclic shearing recovery and effect of sulfate ion

The floc formation and re-aggregation potential and the effects of sulfate on coagulation by AlCl3, polyaluminum chloride (PAC), and Al13 species using a photometric dispersion analyzer (PDA) are investigated. It is found that the recovery level from shearing is the highest for the Al13 species. This is likely a result of increased collision efficiency due to more effective charge neutralization. The experimental results show that sulfate has a significant effect on coagulation and promoting aggregation of hydrolyzed species for the Al13 species. It results in significant improvement of the coagulation efficiency through an electrostatic patch effect. The results further indicate that zeta potential of the particle suspension is not the only indicator for the coagulant efficiency when precipitate formation significantly improves coagulation.

The size and coagulation behavior of a novel composite inorganic–organic coagulant

In this study, a novel composite inorganic–organic coagulant was prepared by polyferric chloride (PFC) and polydimethyldiallylammonium chloride (PDMDAAC). The variations of size and specific surface area with respect to pH for composite polyferric chloride-polydimethyldiallylammonium chloride (PFC-PDMDAAC) were investigated, and the coagulation efficiency of PFC-PDMDAAC was studied by Jar–test, and Photometric Dispersion Analyzer 2000 (PDA 2000) was used to investigate floc aggregation process of PFC-PDMDAAC. The results show that the average size and specific surface area of PFC-PDMDAAC are larger than that of PFC. The coagulation efficiency of PFC-PDMDAAC is higher than that of PFC and PDMDAAC. The floc aggregation process shows that kaolin particles may be aggregated to micro-flocs by Fe(III) species in PFC-PDMDAAC at first, and then the micro-flocs are bridged together to form large flocs by organic coagulants in PFC-PDMDAAC. The soluble dye is aggregated initially to insoluble dye micro-compound by the reaction of PDMDAAC, and then the insoluble dye micro-compound is aggregated to large flocs by Fe(III) polymers in PFC-PDMDAAC.

Klebsiella pneumoniae Flocculation Dynamics

The bacterial pathogen Klebsiella pneumoniae is a cause of community- and hospital-acquired lung, urinary tract and blood stream infections. It is a common contaminant of indwelling catheters and it is theorized in that context that systemic infection follows shedding of aggregates off of surface-adherent biofilm colonies. In an effort to better understand bacterial proliferation in the host bloodstream, we develop a PDE model for the flocculation dynamics of Klebsiella pneumoniae in suspension. Existence and uniqueness results are provided, as well as a brief description of the numerical approximation scheme. We generate artificial data and illustrate the requirements to accurately identify proliferation, aggregation, and fragmentation of flocs in the experimental domain of interest.

Calcium‐Enhanced Ferric Hydroxide Co‐Precipitation of Arsenic in the Presence of Silicate

This study focuses on the effectiveness of calcium (Ca2+) improving ferric (hydro)oxides precipitation and its subsequent effects on arsenic co-precipitation with ferric (hydro)oxides. The effects of Ca2+ on surface charge characteristics and precipitating behavior, which are respectively represented as zeta (zeta) potential and R(PDA), are investigated for ferric (hydro)oxides precipitates. The presence of Ca2+ increases the potential of ferric (hydro)oxides, and a more significant effect is observed at higher pH conditions. Calcium apparently facilitates ferric (hydro)oxide floc aggregation, increasing the maximum R(PDA) from 3.19 to 5.27% (in the presence of 3.5 mg/L silicate as silicon). These positive effects contribute to reduce the adverse effects resulting from the presence of silicate and enhance arsenic removal via ferric (hydro)oxides co-precipitation under different conditions. Furthermore, the effect of Ca2+ facilitating ferric precipitation (and therefore providing more precipitated solids for arsenic) is predominant in favoring arsenic removal compared with that of increasing surface charge. Calcium plays an important role in arsenic co-precipitation with ferric (hydro)oxides in the presence of silicate.

Role of extracellular protein in the formation and stability of aerobic granules

The extracellular proteins extracted from the sludge samples had molecular weights in the range of 31.0–97.4 kDa. Several new protein bands were observed with the aerobic granulation. The quantitative data on extracellular polymeric substances (EPS) indicated the secreted extracellular protein contents increased from 49.4 mg g −1 (VSS) in the seed sludge to 148.3 mg g −1 (VSS) in aerobic granules on day 45, while the extracellular polysaccharides remained almost unchanged. The quantitative data on protein was consistent with the sodium dodecyl sulfonate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. Sludge surfaces were more hydrophobic and less negatively charged after aerobic granulation than the flocculent seed sludge. The ratio of proteins to polysaccharide within the sludge EPS increased with the granulation from 2.3 to 4.9 corresponding to the changes in the surface properties of the sludge. A more hydrophobic and less negatively charged surface corresponded to a higher ratio of the extracellular proteins to polysaccharides. After the complete aerobic granulation, the increase of the influent COD loads from 4 to 12 g L −1 d −1 was accompanied with a decrease of the secreted extracellular protein in types and contents and an increase of polysaccharide concentration in sludge EPS. A less hydrophobicity of sludge surface was associated with the changes in the composition of EPS. This might explain why the disintegration of granules would occur at the high influent COD loads employed (10 and 12 g L −1 d −1) from a standpoint of microbiological surface properties. It was proposed that that extracellular protein might be strongly involved in the aggregation of suspended flocs into granules, and also associate with the stability of the granules through affecting the surface properties of sludge.