Floc Morphology Research Articles

Asphaltene Deposition

Although asphaltenes are always present in crude oils, they create problems only when they become insoluble in the remainder of the oil. A change in asphaltene solubility can occur because of changes in pressure, composition, or temperature. Whether asphaltene insolubility constitutes a problem, however, depends primarily on when and where in the oil production, transportation, and processing stream it occurs. Instability leading to deposition in a deepwater well is high on the list of potentially problematic situations. While insolubility is a necessary condition, it is not sufficient to predict the buildup of an asphaltene deposit in a production well. Flocculated asphaltenes may deposit or be carried out of the well in the flowing oil phase. To improve understanding and, hence, prediction of asphaltene deposition, several tests have been reported. A capillary deposition test in long stainless steel capillaries has been used to investigate the tendency of a wide variety of oils to create deposits. Observations, in addition to pressure increases during flow through a capillary, include changes in morphology of asphaltene flocs as they slowly separate from unstable oils, the amount of asphaltene produced as a function of time, and chemical analysis of deposits recovered from capillary tests. Other tests have used glass capillaries and a Taylor–Couette cell. As insight grows, the data produced are being used to develop simulators to predict the rate of growth of arterial asphaltene deposits under wellbore conditions.

Characteristic analysis on morphological evolution of suspended particles in water during dynamic flocculation process

The evolution of floc morphology during constant-speed and variable-speed flocculation was examined to understand floc growth mechanisms. Flocculation-test results were reported in terms of floc average size and fractal dimension, derived from in situ optical sampling and image analysis. The morphological evolution was also described using a fractal growth model, which defined flocculation as the combined processes of aggregation and restructuring. During constant-speed flocculation, aggregation rate increased with increasing shear, but breakage became significant. Also, a decrease was observed after reaching the peak of size, possibly due to floc settling in low shear and the irreversibility of breakage in high shear. The development of floc morphology in variable-speed flocculation indicated that the surface nature of initial flocs was critical to form larger final flocs, because aggregates with irregular shape had more connection spots than those with smooth surface, thus producing a higher aggregation...

Study on Effect and Mechanism of Chitosan Coagulation Aid in Flocculation Treatment of Water Supply

The aim of this work is to remove residual turbidity and index of Potassium permanganate of the drinking water by PAC/Chitosan coagulation treatment. The experiments were performd the efficiency of coagulation by PAC/Chitosan at different chitosan dosages , molecular weight and pH value. Zeta potential instrument and Nikon electron microscope were used to test Zeta potential and observe flocs morphology. It turn out that Chitosan enhance the flocculation treatment of the surface water of raw water of Yellow River by polymeric aluminum chloride (PAC)when PAC dosage is 35 mg•l-1 and Chitosan is 0.15 mg•l-1 and infer coagulation aid mechanism was interpartical bridging rather than the electrical neutralization. Microscope and image analysis system of flocs morphology show that fractal dimension of morphology of PAC and PAC/Chitosan were 1.294,1.385, respectively.

Study of Flocs Morphology of Chitosan Coagulation Aid Treatment and Fractal Dimensions

Flocculation water treatment is one of the important aspects of water treatment .The aim of this work is to use PFS for treating Yellow River surface water and different molecular weights of chitosan as coagulant aid. Electron microscope was used to observe flocs morphology and study CTS coagulation aid morphological change, floc image with microscope camera system analysis, calculation of floc fractal dimension. The results show that the different molecular weights of CTS in dealing with surface raw water to play a good coagulation aid effect. Microscope and image analysis system of flocs morphology show that fractal dimension of morphology of PFS / CTS were significantly higher ,Among them，high molecular weight of CTS as coagulant aid，and fractal dimension of morphology of PFS/ CTS were 1.1026,1.5593 , low molecular weight of CTS as coagulant aid，and fractal dimension of morphology of PFS/ CTS were 1.0904,1.5440 respectively. Floc fractal dimension changes to better reflect the flocculation level and treatment effect for the establishment of floc fractal dimension number of changes in the coagulation control is provided for reference.

Dynamics in Flocculation and Settling Properties Studied at a Full‐Scale Activated Sludge Plant

A comprehensive study of the dynamics in settling and flocculation properties at a full-scale activated sludge treatment plant with secondary settlers operated at their maximum capacity is presented. An extensive set of process data was analyzed to assess physical parameters affecting the capacity and performance of the secondary settlers. There was a large variation in the settling and compaction properties, and they changed quickly, as a result of the short sludge age. Even though the flocculation properties changed throughout the year, they were generally improved during the summer, with lower values of effluent turbidity and effluent suspended solids concentration. The shear sensitivity, which is a measure of floc stability, was higher during the winter, when the water temperatures were lower. The sludge floc morphology had, in general, a different internal structure, with more round microbial colonies during the warmer summer months and a more net-like open structure during the winter.

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.

Fibre floc morphology and dewaterability of a pulp suspension: Role of flocculations kinetics and characteristics of flocculation agents

The aim of this investigation was to find out how properties of a flocculation agent and flocculation kinetics affect the morphology of fibre flocs and how dewatering of a fibre suspension may be attributed to floc morphology. Fibre flocculation, analysed in terms of floc size, mass fractal dimension, floc strength, and the kinetic constant of flocculation, was measured with a digital image analysis system using cationic polyacrylamides as flocculants and NaCl as a coagulant. The results suggest that the kinetics of fibre flocculation is not a key factor determining floc properties but follows from the high bonding ability of the flocculation agent, which also lies behind the high floc density and size, i.e., the factors that lead to fast flocculation and improved floc properties are partly the same. In addition to interfibre bonding strength, the structure of the bonding layer of polymeric flocculants was found to be a significant factor describing floc morphology. Dewaterability of the fibre suspension was improved by increased floc density, which promotes fast water flow through the large voids around the dense flocs, while large, irregular flocs induced loose floc packing, which further improved dewatering by creating larger voids. Increased floc strength seemed to reduce the sealing of fluid passageways, particularly on the surface of the wire, where fibre squeezing could blind the filter fabric.

Hydrolysis and coagulation behavior of polyferric sulfate and ferric sulfate

The hydrolysis behaviors of polyferric sulfate (PFS) and ferric sulfate (FS) under conditions similar to raw wastewater were investigated and the coagulation of biologically pretreated molasses wastewater using PFS and FS was evaluated by studying coagulation efficiency, zeta potential and microscopic surface morphology of flocs. Experimental results show that the hydrolysis behavior of PFS is different from that of FS on the basis of ferron assay. In the case of FS, fast-reacting Fe(III) polymers were the dominant polynuclear species while large fraction of slow-reacting iron polymers is present in PFS. Despite slightly fewer dosages of PFS required as compared to FS, there is no marked difference in the coagulation of molasses effluent between PFS and FS, especially at the optimum dosages. Both coagulants destabilize organic compounds predominantly through charge neutralization-precipitation mechanism. Hydrolysis rate of PFS in synthetic solution is appreciably different from that in raw wastewater. This may due to the effect of sulfate anion introduced as counter-ion as well as depolymerization of larger polymeric Fe(III) species by the organic ligands present in molasses effluent.

The effect of bed age and shear stress on the particle morphology of eroded cohesive river sediment in an annular flume

Erosion experiments were conducted in an annular flume to determine the effect of bed age and shear stress on the particle morphology (fractal dimensions D, D 1, and D k) of eroded cohesive river sediment. Sediment beds were deposited under low shear and left to consolidate for one, two and seven days. Fractal data and photomicrographs show particle morphology changed with shear stress and bed age. During the one-day experiment, flocs were highly branched and particle geometry became more complex with increasing shear. Microflocs present in suspension at low shear, formed larger more loosely bound flocs at moderate shear due to flocculation. At higher shear, larger flocs were less prevalent due to particle breakup. As bed age increased, less sediment was eroded and particles appeared less porous and more angular in shape for a given shear stress. Changes in floc morphology and eroded sediment mass at various shear stresses may be related to bed age-associated biostabilization of bed deposits.

Impact of filamentous bacteria on properties of activated sludge and membrane-fouling rate in a submerged MBR

This study presents the results from the continuous microfiltration of activated sludge with different filamentous bacteria density (expressed as filament index (FI)) in a submerged membrane bioreactor (MBR). During the entire experimental duration of 120 days, the filamentous bacteria density increased gradually from FI = 2 to 6 in the beginning, thereafter maintained at a plateau of FI = 6 for about 20 days, and decreased to FI = 4 at the end of the experiment. The relationship between FI and other properties of activated sludge were analysed using statistical analysis. It was found that filamentous bacteria density has no significant effect on bound extracellular polymeric substances (bound EPS, r p = −0.343, p = 0.080) and soluble microbial products (SMPs, r p = 0.221, p = 0.267). However, it has an important impact on floc size ( r p = 0.944, p = 0.000) and floc structure ( r p = −0.752, p = 0.000). High FI favored the formation of bigger flocs with a loose structure, and vice versa. Further studies on the impact of the activated sludge properties on membrane-fouling rate indicated that variations of the bound EPS may be the major factor contributing to the membrane-fouling rate. Although filamentous bacteria have the ability to change the floc morphology, the effect on the membrane-fouling rate may be negligible.

Enhanced production of l(+)-lactic acid by floc-form culture of Rhizopus oryzae

A process to optimize l-lactic acid production from glucose by Rhizopus oryzae, based on sustaining floc morphology throughout the fermentation process, is herein performed. During the fermentation, supplementary ammonium sulfate was added intermittently to maintain the ammonia level of the culture medium always higher than 0.1 g/L. With replenish of nitrogen source, mycelia flocs did not aggregate, and the lactic acid production was optimized upon the fermentation being controlled at pH 4.3–4.5 by adding calcium carbonate slurry. In contrast, without supplementary addition of nitrogen source, mycelial clumps formed, resulting in a poor production of lactic acid. In the initial batch fermentation process, the final concentration of lactic acid produced was 109 g/L, with a yield (g lactic acid/g glucose consumed) of 0.87 and a productivity of 2.73 g/L h, using 125 g/L of glucose as substrate. For the first four cycles of repeated-batch fermentation, the average final concentration, the productivity and the yield of lactic acid were 113 g/L, 4.03 g/L h and 0.90, respectively.

Feasibility investigation of oily wastewater treatment by combination of zinc and PAM in coagulation/flocculation

Poly-zinc silicate (PZSS) is a new type of coagulant with cationic polymer synthesized by polysilicic acid and zinc sulfate. It has been used in several sorts of wastewaters treatment, but not used in oily wastewater treatment. In this study, we investigated the coagulation/flocculation of oil and suspended solids in heavy oil wastewater (HOW) by PZSS and anion polyacrylamide (A-PAM). The properties of PZSS cooperated with A-PAM were compared with PAC and PFS in dosages, PAMs amount, settling time, pH value and flocs morphology. The results showed that PZSS was more efficient than PAC and PFS. Under the optimum experimental conditions of coagulation/flocculation (dosage: 100 mg/L, A-PAM dosage: 1.0 mg/L, settling time time: 40 min and pH 6.5–9.5), more than 99% of oil was removed and suspended solid value less than 5 mg/L by using PZSS cooperated with A-PAM, which could satisfy the demands of the pre-treatment process for HOW to be reused in the steam boiler or recycled into the injecting well.

The influence of the selected nonionic surfactants on the activated sludge morphology and kinetics of the organic matter removal in the flow system

Synthetic surfactants are believed to act on the structure of activated sludge flocs and some of them are toxic towards aquatic organisms. Nevertheless, the number of studies concerning their effect on the activity of sludge biomass and flocs morphology is limited. In this work, the removal of two different nonionic surfactants: alcohol ethoxylate and alkyl phenol ethoxylate in the activated sludge wastewater treatment processes was investigated. In contrast to our previous study, in which the influence of anionic surfactants on flocs morphology was the main aim, in this paper also the chosen aspects of the kinetics of the tested processes were included. Moreover, the influence of two most common groups of synthetic surfactants: anionics and nonionics, on the activated sludge flocs and biomass is compared and discussed. The presence of nonionic surfactants in wastewater at the concentration of 50 mg L −1 in the influent causes a decrease of flocs size when the dilution rate is equal to or higher than 0.102 h −1. The removal rate of organic pollutants for both nonionics tested is lower than in the control run for this range of dilution rates and so is the degree of COD removal, which then does not exceed 80%. The affinity of substrate to the biomass, expressed as a COD half-saturation constant, decreases in the presence of synthetic surfactants, as this constant is elevated in all surfactant runs. The strongest effect was exerted by the anionic surfactants: sodium alkyl benzene sulphonate, while nonionics acted moderately on the affinity of the substrate.

A new insight into membrane fouling mechanism during membrane filtration of bulking and normal sludge suspension

Membrane bioreactor (MBR) is an important solid–liquid separation technology employed widely in the wastewater treatment. However, membrane fouling is the major problem that hinders the practical application of membrane bioreactor (MBR) systems. A major obstacle for the application of MBRs is the rapid decline of the permeation flux as a result of sludge filamentous bulking. In this paper a series of membrane filtration tests were performed to evaluate the fouling behaviors of bulking sludge and normal sludge. In order to specify the fouling mechanism of bulking sludge, the floc morphology of bulking sludge and normal sludge was studied based on fractal theory and image analysis. The sludge characteristics was also evaluated in terms of extracellular polymeric substances (EPS), relative hydrophobicity (RH) and sludge viscosity. The results showed that the bulking sludge resulted in a greater flux decline rate than normal sludge. The bulking sludge could cause a severe cake fouling, which was induced by the fixing action of filamentous bacteria. The results also showed that the sludge flocs had a good fractal characteristic, and the boundary fractal dimension of bulking sludge flocs was much larger than that of normal sludge. The flocs of bulking sludge had more irregular shape than the flocs of normal sludge. The irregular shape of bulking sludge would do great harm to membrane filtration process. The higher EPS concentration, RH and sludge viscosity of bulking sludge would speed up membrane fouling further.

Effect of Feed Length on Settleability, Substrate Uptake and Storage in a Sequencing Batch Reactor Treating an Industrial Wastewater

The paper compares the performance of two Sequencing Batch Reactors (SBRs) treating the same industrial wastewater (composed of formic acid, ethylene glycol and methanol) operated at two different lengths of the feed. The two SBRs were operated in parallel under the same conditions of organic load (0.85 gCOD l−1 d−1) and sludge age (about 10 d), the only difference being the length of the feed: less than 1 min vs. 5 h. In this way the conditions of a plug flow reactor and of a completely mixed reactor were simulated. The two systems were compared on sludge settleability (related to filaments abundance and floc morphology), substrate uptake rates and polyhydroxyalkanoates (PHAs) storage rates. The main difference between the two systems was in the settling properties of the sludge: both SVI and effluent solids were higher in the system with slow feed. With regard to filamentous microorganisms, even though both reactors were inoculated with the same sludge with high concentration of filaments, they were rapidly washed out from both systems. Microscopic observations showed that the reason for the different settling properties of the two sludges was in the floc structure, which was more compact in the system operated with fast feed. These data support the theory of the role of diffusion inside the flocs in determining the settling properties of the sludge. The maximum substrate uptake rates and PHA storage rates were similar in the two systems, showing that also the microorganisms grown at a constant and low substrate concentration were able to quickly increase their activity and to store PHAs when in the presence of a sudden change in substrate concentration.

Effect of selected anionic surfactants on activated sludge flocs

Results of a comparative study on the removal of anionic surfactants in the activated sludge flow system are presented. Three anionic surfactants: sodium dodecyl sulphate, sodium dodecylbenzene sulphonate and sodium alkyltrioxyethylene sulphate of different chemical structure were studied. All tested anionics strongly influenced the activated sludge flocs morphology and activity at the dilution rate above 0.05 h −1. As a result of saponification processes the sludge flocs became smaller and more circular in comparison to flocs, which had not been exposed to anionic surfactants. Also dehydrogenase activity of the activated sludge decreased with an increase of the dilution rate in all surfactant runs. Among the tested anionics, sodium dodecylbenzene sulphonate, which belongs to linear alkylbenzene sulphonates, exerted the strongest saponificative effect on sludge flocs and dehydrogenase activity of microorganisms.

Effect of filamentous bacteria on membrane fouling in submerged membrane bioreactor

Membrane fouling is the major problem that hinders the practical application of membrane bioreactor (MBR) systems. Since the MBR system includes living microorganisms and their metabolites, the fouling mechanism is even more complex than that of conventional membrane separation processes. This paper provides an improved understanding of the influence of filamentous bacteria on membrane fouling in microfiltration of activated sludge wastewater. In order to make clear the membrane fouling mechanism of filamentous bacteria, the physicochemical characteristics of sludge flocs, including extracellular polymeric substance (EPS), zeta potential, relative hydrophobicity (RH) and floc morphology were systematically investigated. The results showed that the sludge flocs with negligible filamentous bacteria led to severe membrane pore blocking, and the sludge flocs with filamentous bacteria created the formation of a non-porous cake layer on the membrane surface. The excess growth of filamentous bacteria resulted in much more release of EPS, lower zeta potential, higher hydrophobicity of sludge flocs and more irregularly shaped flocs, which did great harm to membrane filtration. The sludge flocs with a small quantity of filamentous bacteria had a positive effect on membrane permeation. It is important to control filamentous bacteria concentration in the operation of MBRs.

Fragmentation of wastewater sludge floc by planar ice front

Floc size has substantial impact on sludge dewaterability, which might be increased or reduced after freezing and thawing. It is commonly assumed that floc size would be increased by low-speed freezing, with a planar ice front rejecting most flocs ahead of it to form large aggregates. We demonstrate in this work that an advancing planar ice front can not only engulf an activated sludge floc of size 3030 μm, but also fragment it. During floc freezing, when the ice engulfed a thin layer of floc, the latter would be pulled apart vertically by the action of the former. This particular portion of floc was then axially elongated and fixed in the frozen layer, with accumulated force pushing upward. In the present test the floc's vertical length was increased by over 92% and its width decreased by 37% over freezing. The force measurement and floc morphology tracking revealed that the force gradient that pulled apart the floc was 0.0027 N/m. The floc under investigation was fragmented at the point where the normal stress acting on the interior network exceeded 8 Pa.

Effects of Fe(III) on floc characteristics of activated sludge

AbstractThe effects of Fe(III) on floc characteristics of activated sludge were investigated in nine parallel sequencing batch reactors (SBRs). The results showed that Fe(III) improved the quality of organic matters in the effluent of reactors. Concentrations of Fe(III) up to 23.8 mg dm−3 decreased suspended solids and turbidity in effluent but overdosage resulted in deterioration of these parameters. Activated sludge floc size measurements indicated that Fe(III) led to a shift in the size distribution from large to small flocs. Concentrations of Fe(III) less than 23.8mg dm−3 did not significantly change the proportion of larger flocs, but overdosage of Fe(III) markedly decreased the fraction of larger flocs and produced a large number of smaller flocs, which may be responsible for the deterioration of effluent suspended solids and turbidity. Scanning electronic microscopic (SEM) observation suggested high Fe(III) concentrations lead to significant changes in floc morphology and reduction of filamentous microorganisms available for the formation of large aggregates. Copyright © 2005 Society of Chemical Industry

Floc morphology and cyclic shearing recovery: comparison of alum and polyaluminum chloride coagulants

This study investigated the floc formation and re-aggregation potential for alum, polyaluminum chloride (PACl) and a blend of these coagulants. Bench-scale testing included floc morphology characterization for well-developed floc, post-shear floc, and non-settleable (filter influent) floc. Different applications of coagulants were observed to produce non-settleable floc that was morphologically different. The alum treatment had a decrease in average floc size from coagulated to non-settleable conditions, whereas the PACl and PACl/alum treatments resulted in similar sized floc between these processes. Zeta potential distribution measurements showed that the alum treatment resulted in a negative shift from coagulated to non-settleable conditions whereas the PACl and PACl/alum treatments had no significant shift. A photometric dispersion analyzer (PDA) was employed to compare the differences between coagulant treatments with respect to shear induced aggregate breakup and recovery. The PDA allowed a dynamic monitoring of initial floc aggregation and measured the degree of recovery from cyclic shearing. The degree of recovery from shearing was greatest for the PACl/alum treatment likely as a result of increased collision efficiency due to more effective charge neutralization.