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Extracellular cellular adhesins facilitate microbial aggregation; however, most of the information about extracellular adhesins is based on pure culture studies. In this study, we characterized the hydrophobic characteristics and distribution of the extracellular adhesins in environmental biofilms and flocs. The hydrophobic characteristics of the extracellular adhesins were studied by sonicating the microbial aggregates to disperse the cells and by fractionating them using the microbial adhesion to the hydrocarbon method. Furthermore, we probed environmental biofilms and flocs using immunohistochemistry coupled with confocal laser scanning microscopy for reimaging the microbial aggregates based on extracellular adhesins. Small flocs have a relatively dispersed distribution of extracellular adhesins (flagella, fimbriae, pili, and amyloid adhesins). The stratified distribution of extracellular adhesins was observed in environmental biofilms. It was observed that the pili and amyloid adhesins were predominantly present in the core of biofilms, whereas flagella and fimbriae were present in the outer layer of the microbial aggregates. The dispersion of microbial aggregates is one of the limiting factors that challenge the sustainable application of wastewater treatment processes. Greater attention to the components of extracellular protein (such as the adhesins) is required to understand the aggregation of dispersible environmental microbial aggregates. [Display omitted] • Environmental microbial aggregates reimagined incorporating extracellular adhesins. • Adhesins are dispersed in floc, whereas adhesins in biofilms are stratified. • Flagella and fimbriae were relatively predominant in the outer layer of biofilms. • Amyloid adhesins and pili were relatively predominant in the core of biofilms. • Adhesins were differentially distributed in hydrophobic and hydrophilic regions. [ABSTRACT FROM AUTHOR]

Environmental mobility of anthropogenic heavy metal releases is governed by site-specific hydrobiogeochemical factors. Uranium (U) releases from 1965 to 1988 resulted in contamination of the Tims Branch wetland at the United States Department of Energy Savannah River Site (SRS) near Aiken, South Carolina. Today, 80% of the 43,000 kg released remain sequestered in soils of two former ponds, Beaver Pond and Steed Pond. The objective of this study was to understand U partitioning from contaminated wetland sediments to aqueous and particulate iron-floc phases. The approach was to correlate U, iron (Fe), and organic matter (OM) in soil cores at key depositional areas; determine U and Fe concentrations in aqueous- and solid-phases in the stream; and compare these stream water data following two storm events. Uranium was released into an outfall canal leading away from the SRS M-Area and first deposited in a topographically low area where a beaver pond is frequently in place. Uranium soil concentrations in Beaver Pond exceed 14,000 µg/g and a second deposition area 1 km downgradient in a former farm pond (Steed Pond) has U soil concentrations near 300 µg/g. Uranium releases to the stream are minimal at Beaver Pond, but U incorporation into Fe-OM colloids, or flocs, at Steed Pond results in appreciable fluxes of U from the wetland. This work yields four key conclusions. At the kilometer and meter scales, geochemistry cannot be the sole predictor of U mobility, as the anthropogenic U deposition is geologically young relative to Fe and OM. Storm intensity and duration do not appear to be directly proportional to U releases from the wetland, as flooding decreases U inclusion in mobile flocs. The mass of suspended solids present in a stream reach often governs how much U moves. The solid-bound U inventory at Beaver Pond does not enter the mobile aqueous phase as easily as Steed Pond U, resulting in U sequestration amid wetland metal cycling in Tims Branch. This work expands upon studies conducted in the 1990′s and early 2000′s, improving our understanding of the geochemical controls of uranium migration through Tims Branch, particularly with respect to the changes over the last 30+ years. Current wetland conditions do not favor significant U movement, but long-term changes in local and regional hydrology may alter this delicate biogeochemical balance. [ABSTRACT FROM AUTHOR]

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

• A binary structure of sludge was proposed to guide dewaterability sensors design. • Advanced tools including optical tweezers characterized binary gel-like structure. • Shear rheology favored stressing supra-flocs level's interaction networks of sludge. • Shear rheology can't cover sufficient information on flocs' gel-like structure. • Flocs' gel-like properties were vital for the sludge dewaterability determination. The digital transformation of sludge treatment processes requires online sensing of dewaterability. This topic has been attempted for many years based on macroscopic shear rheology. However, the relationship between rheological behavior and dewaterability remains noncommittal, and the reason is unclear. Herein, a binary gel-like structure model was proposed including the interactions network at the supra-flocs level and the gel-like structure at the flocs level. Multiple advanced techniques including optical tweezers were employed to precisely understand the binary gel-like structure and to classify the correlation mechanism between this gel-like structure, rheological behavior, and dewaterability. The analysis of sludge from eight wastewater treatment plants showed the binary gel-like structures at both supra-flocs and flocs levels have significant relationships with sludge dewaterability (p < 0.05). Further deconstruction of the sludge viscoelastic behavior illustrated that the gel-like structure at the supra-flocs level dominates the rheological behavior of sludge. Moreover, the direct description of the binary gel-like structure in four typical sludge treatment processes highlighted the importance of the flocs level's structure in determining the dewaterability. Overall, this study revealed that shear rheology may prefer to stress the interactions network at the supra-flocs level but mask the flocs level's structure, although the latter is important. This observation may provide a general guideline for the design of robust sensors for dewaterability. [Display omitted] [ABSTRACT FROM AUTHOR]

Electrocoagulation has been widely studied in oily wastewater treatment because of its high demulsification efficiency and no secondary reagent is required. Oil removal largely depends on the properties of the aggregates. This study aimed to explore the growth process of aggregates and oil removal near the anode by electrocoagulation. Four factors, current density, solution temperature, initial pH value, and electrode structure, were investigated. According to the findings, the current density and temperature have the most significant influence on the growth process of aggregates. The oil removal rate depends more on the average particle size than the fractal dimension. The results showed that the current density and solution temperature have the most significant influence on the parameters of the electrocoagulation process. With increasing current density, the aggregate growth rate and average particle size entering the stable period were accelerated, and the oil removal efficiency was promoted. The growth of aggregates was retarded at high temperatures. The change in the scope of the fractal dimension was minor, ranging from 1.65 to 1.84, during the growth process of the aggregates. Foamed aluminium electrodes were beneficial for accelerating aggregate growth instead of aluminium plates, but the energy consumption was obviously increased. The relationship between the mean particle size and mean fractal dimension of aggregates is consistent with the power function. From the point of view of aggregate growth, this study forms the basis for an in-depth understanding of the demulsification mechanism. • The influence of aggregate growth near the anode on oil removal was studied. • The relationship between average particle size and fractal dimension was explored. • High temperature (>35 °C) is not conducive to aggregates growth. • The growth of aggregates dissolved from foamed aluminium electrodes and aluminium plates were compared. [ABSTRACT FROM AUTHOR]

Slurries containing fine particles are widely dewatered by flocculation combined with filtration. Understanding the microscopic filtration process of a flocculated slurry is helpful in designing flocculation and filtration schemes; however, there is currently limited research. In this study, the Lattice Boltzmann method–Discrete Element method–DLVO coupling method (LBM–DEM–DLVO) was used to conduct numerical experiments on the pore characteristics of cake by filtration. The numerical results demonstrate that the cake formed by filtration of the flocculated slurry contains two types of pores: interfloc and intrafloc pores. The diameter of the interfloc pores, which are the dominant channels for water seepage in the cake, is relatively large. The pore properties of the cake were significantly influenced by the interaction force between the particles in the floc and the filtration pressure; the mechanism was analyzed. Engineering proposals for dewatering are also presented. A multi-stage pressure treatment process and increased F inter during flocculation are recommended. [Display omitted] • The microscopic filtration process of flocculated slurry was revealed. • Microcosmic interaction forces such as the bridging force were considered. • The key mechanism affecting the pore characteristics of the cake was proposed. • Engineering proposals for dewatering were presented. [ABSTRACT FROM AUTHOR]

Coagulation-based separation has been increasingly applied to microalgal harvesting because of its competitive cost and high scalability. The characteristics of flocs formed during coagulation/flocculation are critical for efficient harvesting. However, few studies have been devoted to systematically investigating the structural characteristics of microalgal flocs and their influences on subsequent settling performance. In this paper, the dynamic mean size and fractal dimension, strength, regrowth and settling performance of Al3+ coagulated Chlorella vulgaris flocs were characterized at various flocculation shear rates. The influence of shear rate on floc characteristics was revealed. An appropriate shear rate (9 s−1) produced more desirable microalgal flocs (in terms of size and compactness), with better settling performance and a higher concentration factor, than higher or lower shear rates, favoring their separation and subsequent harvesting. At this condition, the concentration factor reached 13.50, which was a 177.21% improvement over the 4.87 reached at a low shear rate. Unlabelled Image • Size and structure of Al3+ coagulated Chlorella vulgaris floc were characterized. • The influence of shear rate on the floc characteristics was revealed. • Shear rate was optimized for the improvement of floc settling and concentration factor. [ABSTRACT FROM AUTHOR]

Abstract Estrogenic compounds can cause human and ecological health issues and have been detected in surface and drinking water. In this research a reactor analysis determined the impact of operational parameters, the best fit kinetic model for the removal of estrone (E1), 17β-estradiol (E2), estriol (E3), and 17α-ethynylestradiol (EE2) using a bench-top iron electrocoagulation reactor, and characterized the floc generated in-situ. The parameters investigated were current density, conductivity, stir rate, and polarity reversal. Estrogen removal correlated well with an increase in current density, while conductivity did not impact removal but did reduce potentials. High stir rates and frequent polarity reversal demonstrated greater removal. The operating parameters that achieved the greatest estrogen removal were a current density of 16.7 mA cm−2, conductivity of 1000 μS cm−1, stir rate of 500 rpm, and a polarity reversal time of 30 s. These parameters led to average removal efficiencies of 81%, 87%, 85%, and 97% for E1, E2, E3, and EE2, respectively. The removal data for all estrogenic compounds best fit a pseudo-first order relationship with kinetic rate constants of 0.015 min−1 for E1 and E2, 0.016 min−1 for E3 and 0.040 min−1 for EE2. The floc formed in-situ were characterized by determining the crystalline phases with X-ray diffraction, the size and zeta potential, and the shape and major components using scanning electron microscope with energy-dispersive X-ray spectrometer. The iron coagulant generated during electrocoagulation was lepidocrocite with a point of zero charge of 5.67 and an average floc diameter of 2255 nm. Highlights • Iron electrocoagulation was effective in removing >80% of estrogens. • Increased current density, stir rate, and decreased polarity reversal times increased estrogen removal. • Estrogen removal using iron electrocoagulation followed pseudo-first order kinetics. [ABSTRACT FROM AUTHOR]

Abstract Because of the eminent adsorptive capacity and rate for dissolved organic molecules compared to conventionally-sized powdered activated carbon (PAC), super-fine powdered activated carbon (SPAC) is gathering momentum for use in not only the pretreatment for membrane filtration for drinking water purification but also the conventional water purification process consisting of coagulation-flocculation, sedimentation, and rapid sand-filtration (CSF). However, the probability of SPAC particles to leak through a sand bed is higher than that of PAC, and their strict leakage control is an issue to be challenged when applying SPAC to CSF. However, study focusing on very high particle removal, which yield residual concentrations down to around 100 particles/mL, has been very limited. A previous study mentioned that the tendency of SPAC leakage is related to its low destabilization. In response to this, the present study focused on the two key components of coagulation (mixing intensity and coagulants) and investigated how to effectively reduce the residual SPAC after CSF. Astonishingly, the flash mixing (the first process of CSF), especially its G (velocity gradient) value, played the most important role in determining the residual SPAC in the filtrate of sand filter (the fourth process). Even if the slow mixing time was short, a sufficiently large G value but short T (mixing time) value in flash mixing effectively reduced the residual SPAC. When the total GT value of flash and slow mixing was fixed at a constant, priority should be given to flash mixing to reduce the residual SPAC. Among 23 PACl (poly-aluminum chloride) coagulants, PACl with a high-basicity (basicity 70%) and with sulfate ion (0.14 of sulfate/aluminum in molar ratio), produced by Al(OH) 3 -dissolution, were the most effective to reduce the residual SPAC after CSF. PACls produced by base-titration, which have been intensively investigated in previous researches, were not effective due to lack of floc-formation ability. However, their Al species composition determined by the ferron method were almost the same as those of PACl by Al(OH) 3 -dissolution, and their charge-neutralization capacities were higher. PACls produced by Al(OH) 3 -dissolution possessed both charge-neutralization and floc-formation abilities, but the former ability was more important to minimize the residual of SPAC. Graphical abstract Image 1 Highlights • Removal of superfine PAC (SPAC) by conventional water treatment was examined. • Residual SPAC in sand filtrate was strongly influenced by coagulation performance. • G value in flash mixing was key for the SPAC removal but not in slow mixing. • High-basicity sulfated PACl by Al(OH)3-dissolution removed SPAC efficiently. • PACl by base-titration was ineffective despite a high charge-neutralization capacity. [ABSTRACT FROM AUTHOR]

• There is little research on the effect of floc morphology change on flotation. In this work, we mainly focuses on the influence of floc morphology on flotation. • Using the agglomeration of flocs as an entry point, the morphology of flocs was investigated in multiple dimensions through the fractal dimension and AFM characterization of flocs. • The adsorption of flocculants on the surface of different morphologies of flocs was investigated using XPS tests, revealing the correlation between flocculant adsorption and floc morphology. • The induction time and encapsulation angle of different forms of flocs and bubbles were investigated to reveal the flotation mechanism of flocs from the unmicroscopic level. This study investigates the impact of floc morphology on flotation by preparing two types of flocs with similar apparent particle sizes but different aggregation degrees through varying the stirring speed. Flotation tests were conducted on the two flocs, revealing that flocs with higher aggregation degrees demonstrated superior floatability and higher flotation rate constants. Fractal dimension and AFM analysis indicated that flocs with higher aggregation degrees exhibited higher fractal dimensions, displaying a more circular and compact overall morphology, as well as a more regular and uniform surface morphology. XPS and contact angle tests showed that, for flocs with comparable particle sizes, an increase in fractal dimension led to increased adsorption of flocculant (PEO) on the surface, accompanied by enhanced hydrophobicity. Further analysis of the induction time for particle-bubble attachment and coverage angle demonstrated that flocs with higher fractal dimensions had shorter induction times and larger coverage angles, indicating faster attachment between flocs and bubbles. These findings suggest that flocs with higher fractal dimensions can acquire greater kinetic energy in a flow field, enabling them to more effectively disrupt the hydration film on the bubble surface and adhere to the bubble surface, thereby enhancing floatability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Granule-EPS exhibited more complex texture than Floc-EPS. • Floc-EPS formed looser adhered structure on abiotic surfaces than Granule-EPS. • The intensity of granules was mainly contributed by non-extractable structure EPS. • The difference in adhesion properties led to the segregation of flocs and granules. Granules and flocs have been widely found co-existing in anammox granular systems, but the segregation mechanism of granules and flocs is still largely unknown. Here, the chemical composition, physical properties, spectral characteristics, and adherence properties of extracellular polymeric substances (EPS) extracted from anammox granules (Granule-EPS) and flocs (Floc-EPS), which were closely related to sludge aggregation, were tested and compared. Granule-EPS exhibited more complex texture with larger biomolecule size and higher molecular weight than Floc-EPS. Moreover, Floc-EPS showed weaker co-aggregation ability, which might be due to its lower proteins/polysaccharides ratio, more compact protein secondary structure, stronger hydrophilicity, and lower intermolecular hydrogen bond proportion, than Granule-EPS. Besides, due to the looser connection between Floc-EPS biomolecules compared to Granule-EPS biomolecules, the structure of adhered Floc-EPS layer was looser than that of the adhered Granule-EPS, which was in accordance with the lower sludge intensity of anammox flocs compared to granules (595.2 ± 36.8 Pa vs. 315.3 ± 13.8 Pa; p = 0.001). More importantly, during the process of anammox flocs aggregation, a portion of EPS formed structure EPS that was difficult to extract, to maintain a tight structure of the granules. We therefore assumed that biomass segregation between anammox granules and flocs was due to the difference in the tightness of the adhered layer structure they formed. Overall, the results improve our understanding of anammox granular system, especially for the segregation phenomenon between granules and flocs. [ABSTRACT FROM AUTHOR]

The flocs generated by different coagulants under various coagulation mechanisms produce fundamentally different floc characteristics. In this investigation, the fractal dimensions of aggregates produced by the different types of coagulants and coagulation mechanisms to drilling wastewater were described with image-based techniques. The flocs properties, which were evaluated in terms of floc strength, size and structure, formed by non-composite, polyferric chloride (PFC), and by a novel composite coagulant, polyferric chloride −polydimethyldiallylammonium chloride (PFC-PDM), were comparatively investigated. Besides, an intrinsic unity of relation among the floc properties under various coagulation mechanisms was also reported. It was found that the composite coagulant could exhibit better bridging capacity during coagulation process. Fractal dimension analysis revealed that PFC-PDM tended to form more regular and compact flocs with larger D pf value than PFC formed. The results clearly demonstrated that the size of PFC-PDM-floc was larger than that of PFC-floc. Additionally, the PFC-PDM-flocs strength were higher than PFC-flocs, indicating that the aggregated flocs induced by the composite coagulant could be more resistant to shear and more recoverable than those induced by the non-composite coagulant. Those presented above results indicate that PFC-PDM may be used as alternative coagulant during wastewater treatment process with some capacities exceeding that of PFC, providing there is an economic and practical method to improve floc properties from its application. [ABSTRACT FROM AUTHOR]

The particle size distributions (PSD) of four clay minerals from the US Clay Minerals Society, kaolinite, illite, Ca 2 + -montmorillonite, and Na + -montmorillonite, were analyzed using different dispersion techniques to evaluate their PSD variability and intrinsic particle sizes. Both dry dispersion in pressurized air and wet dispersion in water and ethyl alcohol with and without an interlayer expanding agent, glycerol, were employed, along with mechanical ultrasound disaggregation and chemical dispersion. Results show that all four clay minerals exhibit multimodal PSD consisting of superimposed subordinate lognormal distributions from submicron and 1–2 μm primary particles, 10–20 μm flocculi (and trace impurities). Microflocs of 50–500 μm occur only in the dry dispersion mode. Owing to the presence of relatively strong flocculi that are not prone to breakdown to smaller primary particles, the intrinsic PSD of these clay minerals cannot be readily obtained by the adopted dispersion methods. The two swelling clay minerals, Na + -montmorillonite and Ca 2 + -montmorillonite, are more sensitive than the non-swelling ones, kaolinite and illite, to different dispersion solvents. The variability of these clay minerals' PSD is further discussed in terms of the complex interactions among clay mineral particles, polar or less polar solvent, and dispersant, such as swelling, cation exchange, exfoliation, and electrical double layer repulsion. A significant practical implication is that most existing dispersion methods for PSD analysis tend to overestimate the silt-sized fraction but underestimate the clay-sized fraction, which may yield misleading classification for clay mineral-rich soils. For expansive clay minerals, appropriate dispersants should be selected to avoid cation exchange between the sample and dispersants, which can change their intrinsic PSD. [ABSTRACT FROM AUTHOR]

• Hydrolysis explains the dependence of coagulation on type of PACl and raw water. • Hydrolysis and coagulation depend on type of PACl and the anions in the raw water. • Effects of sulfate, bicarbonate, and NOM in raw water on PACl hydrolysis are additive. • Hydrolysis of high-basicity PACl by bicarbonate is slow and hence needs sulfate ions. • Large hydrolysis power of sulfate is due to its divalency and tetrahedral structure. Application of poly-aluminum chloride (PACl) coagulant is a popular mode of water treatment worldwide because of the high capacity of PACl to neutralize charge. The manufacture and use of PACls with various basicities in different regions around the world suggest that the characteristics of the raw water are important determinants of the efficacy of PACl application. However, attention has not been fully paid to the effects of water quality other than the substances to be removed. In this study, two typical PACls with different basicities were used to investigate why the performance of PACls depends on the characteristics of the raw water. We focused on the concentrations of inorganic ions in the raw water. Use of high-basicity PACl (HB-PACl) with a high content of polymeric-colloidal species (Al b +Al c) resulted in very slow floc formation and little turbidity removal in raw water with low concentrations of sulfate ions. The performance of the HB-PACl was inferior to that of normal-basicity PACl (NB-PACl), although the charge-neutralization capacity of the HB-PACl was higher. Rates of floc formation were strongly correlated with the rate of aluminum precipitation by hydrolysis reaction, which was identified as an indicator for evaluating the compatibility of raw water with PACl treatment. Among the common ions in natural water, the sulfate ion had the greatest ability to hydrolyze and precipitate PACl because of its divalency and tetrahedral structure. This conclusion followed from experimental results showing similar effects for selenate and chromate ions as for sulfate ions and somewhat smaller effects for thiosulfate ions. Bicarbonate ions and natural organic matter affected PACl hydrolysis-precipitation, but chloride ions, nitrate ions, and cations had little effect on PACl hydrolysis-precipitation. Interestingly, the abilities of sulfate ions to hydrolyze HB-PACl and NB-PACl were very similar, but bicarbonate ions were less effective in hydrolyzing HB-PACl than NB-PACl, and bicarbonate ions contributed little to the hydrolysis-precipitation of HB-PACl in raw water with normal alkalinity. Therefore, sufficient coagulation with HB-PACl therefore usually requires a certain concentration of sulfate ions in water to be treated. The implication is that which anions are most influential to the hydrolysis-precipitation of PACl, and thus to PACl's coagulation ability depends on the constituents of the PACl. [Display omitted] [ABSTRACT FROM AUTHOR]

In most aquatic environments, suspended sediment is composed of loosely packed particle aggregates, termed flocs that have variable apparent densities. The apparent density of flocs, which is defined as particle dry mass over wet volume, is an important variable because it affects settling velocity and vertical sediment flux. Two established methods exist for measuring apparent density. One method uses physical measurements of sediment mass concentration combined with measurements of particle volume concentration from optical instruments to estimate apparent density. This method is laborious because it requires the collection of water samples, so it is not conducive to construction of high-resolution time series of density. Another method uses video observations of particles in a settling column to measure particle size and settling velocity. These measurements are used to solve for apparent density according to Stokes Law. The goal of this study is to develop a new method that uses the ratio of particulate beam attenuation to particle volume to estimate apparent density of sediment in suspension. Data from five studies are used to compare density estimates with the new method to the previous methods. The new optical method produces apparent densities that are correlated linearly with measurements of the ratio of dry mass to wet volume. However, the new optical method produces density estimates that do not correlate with video estimates of apparent density. This lack of correlation is due to sampling bias of the video method, which has a relatively large lower limit of resolution in particle size. Development of a higher resolution camera would eliminate the current bias in particle size and would enable further assessment of the new optical method as an accurate proxy for apparent density. [ABSTRACT FROM AUTHOR]

The sedimentation behavior of semi-dilute suspensions of sodium montmorillonite in the flocculation regime was studied as a function of ionic strength at pH 4.0 and 9.5 to elucidate the response of variation of macroscopic sedimentation behavior with microscopic particle association. The maximum velocity of the boundary between the supernatant and sediment and ultimate sediment height were chosen as indexes to evaluate the sedimentation behavior. Increment ratio of effective volume fraction of the particles (α) caused by the formation of flocs and hydrodynamic floc diameter were evaluated by Michaels and Bolger method on the basis of the Richardson–Zaki formula. The results clearly demonstrate that the maximum velocity of the boundary is strongly affected by both pH and salt concentration. The two observed patterns of variation of maximum sedimentation rate and ultimate sediment height can be clearly defined using 0.25–0.5 M NaCl as an inflection range. This range is consistent with the transition point at 0.3 M NaCl for the swelling behavior of sodium montmorillonite reported by Norrish. Below 0.25 M NaCl, the effect of pH on the sedimentation rate is remarkably enhanced compared with that at higher salt concentration. This effect is ascribed to the dominant appearance of edge–face (EF) particle interactions, which can be regarded as negligible at higher salt concentration. The reason for this is that the breakage of weak EF bonds is induced by the dominant appearance of face–face particle interactions at higher salt concentrations. That is, the decrease of repulsion strengthening the attraction between neighboring particles is responsible for EF bond breakage. The small influence of pH on ultimate sediment height at high salt concentration can be ascribed to the residual strong EF bonds. The Michaels and Bolger method can be used qualitatively at range of NaCl greater than 0.5 M. [ABSTRACT FROM AUTHOR]

Sedimentation and electrophoresis of porous colloid complex; a colloidal floc and a colloidal particle covered with adsorbed polyelectrolytes are visited to examine the characteristic length of the transport phenomena. In the sedimentation, the overall size of a floc is dominative in the determination of Stokes drag, while the permeability is determined by the largest pore in the floc. This picture is important when break-up of flocs in a turbulent flow is considered. When a colloidal particles is coated with polyelectrolytes, the characteristic length for diffusion is that of the diameter of colloidal particle plus protruding part of polymer chain adsorbed onto the particle. On the other hand, when the porous colloid complex is placed in the electric field, fluid surrounding the complex can easily penetrate into the complex by means of electro-osmosis. The diffusive part of electric double layer located inside of the complex is the source of strong driving force of this osmotic flow. Flow generated in this regime can be treated as a sort of shear driven. The characteristic length scale for transport phenomena is the Debye length or the distance between charged segments. These lengths are much shorter than the case of sedimentation and Brownian diffusion. [ABSTRACT FROM AUTHOR]

Settling, dewatering and filtration of flocs are important steps in industry to remove suspended solids and improve subsequent processing of the aqueous system. The influence of non-sucrose impurities (Ca 2+ , Mg 2+ , phosphate and aconitic acid) on the calcium phosphate floc structure (scattering exponent, S f ), size and shape were examined in synthetic and authentic sugar juices using X-ray diffraction techniques. In synthetic juices, S f decreases with increasing phosphate concentration to values where loosely bound and branched flocs are formed. These types of flocs are effective for the removal of suspended colloidal particles. Ca 2+ and Mg 2+ ions, and aconitic acid did not affect S f increasing concentration, although the floc size significantly decreased with increasing aconitic acid concentration, thereby reducing the ability of the flocs to remove particles. In authentic juices, the flocs structures were marginally affected by increasing proportions of non-sucrose impurities. However, optical microscopy indicated the formation of well-formed macro-floc network structures in sugar cane juices containing lower proportions of non-sucrose impurities. These structures are better placed to remove suspended particles in sugar solutions. [ABSTRACT FROM AUTHOR]

This study focused on the application of polyacrylamide (PAM) as a coagulant aid of polytitanium sulfate (PTS) in humic acid-kaolin water treatment. Coagulation performance and floc properties were all measured in terms of dose amount and dose sequence of PAM and PTS which is meaningful for the practical application. Results showed that PTS-PAM (PTS dosed firstly) attained better natural organic matter (NOM) removal and PAM-PTS (PAM dosed firstly) attained better turbidity removal. Floc size was significantly enhanced by the PTS-PAM, while floc size of PAM-PTS attained similar size as that of PTS alone. Floc strength and recovery ability were also significantly improved by PTS-PAM. Moreover, PTS-PAM floc had a looser structure than that of PTS, while PAM-PTS floc and PTS floc had similar and more compact structure. The effect of PAM on the sludge reuse process was also studied. Results showed that the addition of PAM had a positive effect on the photocatalytic activity of sludge prepared TiO 2 . [ABSTRACT FROM AUTHOR]

This study was carried out to evaluate the efficiency of Guar gum in removing Persistent Organic Pollutants (POPs), viz. phenol,2,4-bis(1,1-dimethylethyl) and bis(2-ethylhexyl) phthalate (DEHP), from farm effluent. The removal efficiency was compared with alum. The results indicated that 4.0 mg L −1 of Guar gum at pH 7 could remove 99.70% and 99.99% of phenol,2,4-bis(1,1-dimethylethyl) and DEHP, respectively. Box Behnken design was used for optimization of the operating parameters for optimal POPs removal. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR) spectroscopy studies were conducted on the flocs. SEM micrographs showed numerous void spaces in the flocs produced by Guar gum as opposed to those produced by alum. This indicated why Guar gum was more effective in capturing and removal of suspended particles and POPs as compared to alum. FTIR spectra indicated a shift in the bonding of functional groups in the flocs produced by Guar gum as compared to raw Guar gum powder signifying chemical attachment of the organics present in the effluent to the coagulant resulting in their removal. Guar gum is highly recommended as a substitute to chemical coagulant in treating POPs due to its non-toxic and biodegradable characteristics. [ABSTRACT FROM AUTHOR]

Methylated arsenic can be found in virtually all earth surface environments. So far, however, little information has been collected regarding their removal by coagulation. In this study, the removal of monomethylarsenate (MMA) and dimethylarsenate (DMA) from drinking water by coagulation was investigated from the viewpoint of methyl substitution. Results indicated that FeCl 3 was more efficient than AlCl 3 and polyaluminum chloride (PACl) in methylated As removal. For the initial arsenic concentration of 200 μg/L, an FeCl 3 dosage of 0.2 mmol Fe/L was sufficient to attain about 95% removal of MMA, while a dosage of 0.6 mmol Fe/L achieved about 57% removal of DMA. Arsenic removal efficiency was negatively correlated with the degree of methyl substitution. With the increase in methyl group number, the quantity of negatively charged arsenic species decreased and molecular size increased, leading to the decrease of methylated As removal by coagulation. Adsorption on preformed hydroxide flocs was the major mechanism during coagulation. Both FTIR and XPS results indicated that the As O group of As might substitute the O H group of Fe/Al hydroxide to form a Fe/Al O As complex. Furthermore, the use of traditional oxidants and coagulation aids exhibited limited help for improving coagulation removal of DMA. [ABSTRACT FROM AUTHOR]

Coagulation is effective, simple to operate, and widely used in treatment of industrial effluent. However, commonly used inorganic coagulants pose detrimental effects on human health and living organisms in long run, and generate large amount of toxic sludge. Thus, this study investigated the optimized use of Cassia obtusifolia alone or combination of alum with lower dosages in treatment of industrial effluent. In this study, raw pulp and paper mill effluent (PPME) was used as a model wastewater in confirming the potential use of C . obtusifolia seed gum as a plant-based coagulant or coagulant aid together with the alum. Response surface methodology (RSM) enabled the study of interactive effects between operating treatment conditions, and to determine the optimal treatment conditions. The analysis of variance results obtained in the present study reflected significant quadratic models and strong correlations between operating conditions and treatment performance. In addition, current findings suggested that the coagulation mechanisms using C . obtusifolia seed gum together with the alum were most likely based on adsorption with inter-particle bridging and charge neutralization. Floc characterization also showed distinctive results, indicating the presence of active functional groups and the thermal stability of floc formed using C . obtusifolia seed gum and alum. Using RSM, optimal dosages of 0.17 and 0.09 g/L of C . obtusifolia seed gum and alum, respectively were required to achieve maximum total suspended solids and chemical oxygen demand removals (89.6 and 55.4%, respectively) under natural pH of raw PPME and slow-mixing time of 3.40 min. By combining the use of both coagulants, coagulant dosages of C. obtusifolia seed gum and alum could be reduced up to 90.5 and 62.5%, respectively. The present study revealed C . obtusifolia seed gum could be used as a potential plant-based coagulant or coagulant aid in treatment of raw and complex industrial effluent together with reduced dosage of alum. [ABSTRACT FROM AUTHOR]

The aerobic respiration of flocculent detrital organic material (floc) from Everglades National Park was found to be dependent on phosphorus limitation and carbon quality and is likely influenced by substrate age, hydrology, and local biomass productivity. Floc was collected at four sites along the Shark River and Taylor Sloughs of Everglades National Park and incubated for up to one week at room temperature in the dark. Floc respiration was determined by measuring the total amount of CO 2 evolved and CO 2 generation rates. To investigate the effect of hydrological conditions, samples were collected in a typical dry (April) and wet (October) season and from short- and long-hydroperiod sites. Floc from the short-hydroperiod freshwater site generated more CO 2 compared to the long-hydroperiod site due to the labile nature of the periphyton-derived organic matter at the former and the presence of more degraded and aged material at the latter. The tidally-influenced Shark River Slough mangrove site generated more CO 2 compared to the Taylor Slough mangrove site, likely as a result of phosphorus inputs from the adjacent Gulf of Mexico at the former and reduced phosphorus inputs and prolonged inundation at the latter. Generally, more CO 2 was generated during the dry season. Floc respiration rates were faster in the wet season, suggesting that fresh vegetation inputs to the floc can influence this process. Phosphorus and glucose additions enhanced CO 2 generation suggesting that phosphorus limitation and carbon quality are important factors regulating floc decomposition. [ABSTRACT FROM AUTHOR]

[Display omitted] • TXC was more effective than PFS for Sb(V) removal from RO concentrates. • Electrostatic interaction played a major role in Sb(V) removal by PFS. • Sweep flocculation was the dominant mechanism in Sb(V) removal by TXC. • TXC was less sensitive to pH and organic matter than PFS. • TXC coagulation is a robust approach for treatment of RO concentrates. Reverse osmosis (RO) is a useful process for water purification or water reuse. Nevertheless, the generated RO concentrate may adversely affect the environment if not properly treated. Coagulation with polymeric ferric sulfate (PFS) is a widely used method for the treatment of antimony (Sb)-containing RO concentrate. However, the PFS coagulation is still suffering from high residual metal and turbidity. Herein, a titanium xerogel coagulant (TXC) was evaluated as an alternative for PFS to remove Sb from RO concentrate. The RO concentrate collected from a local textile factory had an initial Sb concentration of 806 μg/L, a turbidity <1 NTU, and a high conductivity (5.3 mS/cm). With TXC as the coagulant, the residual Sb concentrations met the direct discharge limit (50 μg/L) at all the tested conditions (pH: 3.0–9.0, dosage: 40–100 mg/L). Based on the analyses with potentiometric titrations, X-ray photoelectron spectroscopy, and X-ray diffraction pattern, the binding states between Sb and the flocs of TXC and PFS were investigated. The results reveal that sweep flocculation dominated in the removal of Sb by TXC, whereas charge neutralization played a major role in Sb removal by PFS. As a result, TXC coagulation was robust in a wide pH range and was less sensitive to organic matter. The work here provides a promising approach for the treatment of RO concentrate. [ABSTRACT FROM AUTHOR]

Extracellular polymeric substances (EPS) play a crucial role in the formation of activated sludge flocs. However, until now, the EPS are rather classified by the method used for extraction than by a theoretical consideration of their function and composition. In this paper, a new classification paradigm of EPS was proposed, which offered a novel approach to identify the role of EPS in the formation of activated sludge flocs. The current study gave an exploration to distinguish the EPS in the floc level (extra-microcolony polymers, EMPS) and in the microcolony level (extra-cellular polymers, ECPS). It was found that cation exchange resin treatment is efficient to disintegrate the flocs for EMPS extraction, however, inefficient to disaggregate the microcolonies for ECPS harvesting. A two-steps extraction strategy (cation exchange resin treatment followed by ultrasonication-high speed centrifugation treatment) was suggested to separate these two types of EPS in activated sludge flocs and the physicochemical characteristics of EMPS and ECPS were compared. The protein/polysaccharide ratio of ECPS was higher than that of EMPS and the molecular weight of proteins in EMPS and ECPS were found to be different. The ECPS contained higher molecular weight proteins and more hydrophobic substances than the EMPS contained. The result of excitation-emission matrix fluorescence spectroscopy analysis also showed that the EMPS and the ECPS have different fluorescent expressions and the components of EMPS were more diverse than that of ECPS. All results reported herein demonstrated that two different types of exopolymers exist in the activated sludge flocs and the inter-particle forces for aggregation of activated sludge flocs are not identical between the floc level and the microcolony level. It suggested that cation bridging interactions are more crucial in floc level flocculation, while the entanglement and hydrophobic interactions are more important in microcolony level cohesion. [ABSTRACT FROM AUTHOR]

Abstract: The advantages of FLOC over clear water (CW) in rearing juvenile Litopenaeus vannamei and its effects on Vibrio communities were evaluated. Survival rate in FLOC and clear water was recorded and a probiotic was tested under both conditions. Daily growth rate (DGR) was higher in FLOC (p<0.05) than in CW. Survival in each system increased significantly when a probiotic was included in the diet (p<0.05). The Vibrionaceae community from the hepatopancreas (HP) and the culture medium did not differ between the two culture media. Nevertheless, a novel group of Vibrio strains was found to be unique to FLOC. No high level of lesions was observed in shrimp tissues from the FLOC+probiotic treatment; it suggests that the probiotic contributed to homeostasis and prevented outbreak of opportunistic pathogenic species. [Copyright &y& Elsevier]

Abstract: Although the antimicrobial capabilities of silver nanoparticles (AgNPs) are widely reported, their impacts on ecologically important microbial communities are not well understood. AgNPs released from consumer products will likely enter sewer systems and wastewater treatment plants, where they would encounter (and potentially upset) activated sludge (AS), a complex ecosystem containing a variety of bacteria. Herein we address the effects of AgNPs and Ag+ ions on the microbial community structure of AS, using pyrosequencing technology. Compared to Ag+ amendment, a lower AgNP concentration resulted in a more pronounced effect on AS community structure, possibly reflecting a higher propensity of Ag+ than AgNPs to be scavenged by inorganic ligands and organic matter. Furthermore, AgNPs decreased the abundance of nitrifying bacteria, which would hinder N removal, and damaged AS floc structure, which could affect sludge clarification and recycling. Overall, although released Ag+ is known to be the critical effector of the antimicrobial activity of AgNPs, the nanoparticles apparently delivered Ag+ to bacteria more effectively and exerted more pronounced microbial population shifts that would hinder some wastewater treatment processes. [Copyright &y& Elsevier]

The acoustic return from a flocculated suspension recorded with a mono-static transducer was computed considering that the small distances among the primary particles that form the floc increased the backscatter coherent component, which otherwise would be neglected. Using this approach the floc backscatter form function was computed and it was found not only to depend on floc size and fractal dimension, but also on size distribution of the primary particles. Sound attenuation was found to be dominated by the primary particle total scattering cross section, with no deviations that could be clearly associated with the occurrence of flocculation. The proposed theory accurately represented the detailed experimental data of MacDonald et al. (2013). • Acoustic return from a flocculated suspension is studied. • Floc form function considers the coherent contribution of primary particles. • Form function depends on floc size, fractal dimension, and particle size distribution. • Sound attenuation is dominated by primary particle scattering cross section. • Proposed theory captures existing experimental data (Mac Donald et al. 2013). [ABSTRACT FROM AUTHOR]

Highlights: [•] Chitosan hydrochloride produced bigger, stronger and better recoverability flocs. [•] Chitosan hydrochloride provides better flocculation performance than chitosan. [•] Fast-mixing speed had greater effect on chitosan hydrochloride flocs than chitosan. [•] Fast-mixing speed had slight influence on chlorogenic acid for both flocculants. [Copyright &y& Elsevier]

Abstract: Integrated fixed-film activated sludge systems (IFFAS) may achieve year-round nitrification or gain additional treatment capacity due to the presence of both flocs and biofilms, and the potential for multiple redox states and long solids retention time. Flocs and biofilms are distinctive microbial structures and characterization of the physicochemical and structural properties of these may provide insight into their respective roles in wastewater treatment and contaminant removal in IFFAS. Flocs and biofilms were examined from five different pilot media systems being evaluated for potential full scale implementation at a large municipal wastewater treatment plant. Flocs and biofilms within the same system possessed different surface characteristics; flocs were found to have a higher negative surface charge (−0.35 to −0.65 meq./g VSS) and are more hydrophobic (60%–75%) than biofilms (−0.05 to −0.07 meq/g VSS; 19–34%). The EPS content of flocs was significantly higher (range of 2.1–4.5 folds) than that of biofilms. In floc-derived extracellular polymeric substances (EPS), protein (PN) was clearly dominant; whereas in biofilm-derived EPS, PN and polysaccharide (PS) were present in approximately equal proportions. Biofilm EPS had a higher proportion of DNA when compared to flocs. Biofilm growth was preferential on the protected internal surfaces of the media. Colonization of the external surfaces of the media was evident by the presence of small microcolonies. The structural heterogeneity of the biofilms examined was supported by observed differences in biomass content, thickness and roughness of biofilm surface. The biofilm on the interior surface of media was found to be patchy with clusters of cells connected by an irregular arrangement of interconnecting EPS projections. Biofilm thickness ranged between 139 μm and 253 μm. The pattern of oxygen penetration is expected to be complex. Nitrifiers and denitrifiers were predominantly associated with the biofilms, and the latter were found to be dispersed throughout the film and arranged in micro-clusters, suggesting partial oxygen penetration. [Copyright &y& Elsevier]

Abstract: A double-stage velocity gradient conical fluidized bed flocculator (DG-FBF) was employed to investigate the issue of floc breakage that occurred in a single-stage velocity gradient conical fluidized bed flocculator (SG-FBF), using 150mg/L Kaolin clay suspension as the influent and 60mg/L polymer aluminum chloride as the flocculant dosage. Two kinds of particles with significant differences in effective weight (i.e. silica gel beads and resin beads) were packed into the DG-FBF; these particles separated into two grades along the axial direction due to the fluid shearing force. The back-mixing problem, which lead to floc breakage in the SG-FBF was apparently solved, as confirmed by both the observed flow patterns and the floc size distributions. The two-stage velocity gradient and voidage observed in the DG-FBF created a more suitable environment for growth of the aggregates. The flocs formed in the DG-FBF tended to be denser and presented an advanced self-similarity as evidenced by the results of fractal dimensioning. In addition, the abatement efficiencies of Kaolin suspensions in the DG-FBF increased by about 10% at most of the loading rates investigated (at superficial velocities of 6.7–17.9mm/s) and became more stable compared with those from the SG-FBF. [Copyright &y& Elsevier]

Abstract: Here we introduce a distribution of floc fractal dimensions as opposed to a single fractal dimension value into the floc settling velocity model developed in earlier studies. The distribution of fractal dimensions for a single floc size was assumed to cover a range from 1.9 to 3.0. This range was selected based on the theoretically determined fractal dimensions for diffusion-limited and cluster–cluster aggregation. These two aggregation mechanisms are involved in the formation of the lime softening flocs analyzed in this study. Fractal dimensions were generated under the assumption that a floc can have any value of normally distributed fractal dimensions ranging from 1.9–3.0. A range of settling velocities for a single floc size was calculated based on the distribution of fractal dimensions. The assumption of multiple fractal dimensions for a single floc size resulted in a non-unique relationship between the floc size and the floc settling velocity, i.e., several different settling velocities were calculated for one floc size. The settling velocities calculated according to the model ranged from 0 to 10 mm/s (average 2.22 mm/s) for the majority of flocs in the size range of 1–250 μm (average 125 μm). The experimentally measured settling velocities of flocs ranged from 0.1 to 7.1 mm/s (average 2.37 mm/s) for the flocs with equivalent diameters from 10 μm to 260 μm (average 124 μm). Experimentally determined floc settling velocities were predicted well by the floc settling model incorporating distributions of floc fractal dimensions calculated based on the knowledge of the mechanisms of aggregation, i.e., cluster–cluster aggregation and diffusion-limited aggregation. [Copyright &y& Elsevier]

Abstract: Electrocoagulation (EC) and chemical coagulation (CC) are employed in water treatment for particle removal. Although both are used for similar purposes, they differ in their dosing method – in EC the coagulant is added by electrolytic oxidation of an appropriate anode material, while in CC dissolution of a chemical coagulant is used. These different methods in fact induce different chemical environments, which should impact coagulation/flocculation mechanisms and subsequent floc formation. Hence, the process implications when choosing which to apply should be significant. This study elucidates differences in coagulation/flocculation mechanisms in EC versus CC and their subsequent effect on floc growth kinetics and structural evolution. A buffered kaolin suspension served as a representative solution that underwent EC and CC by applying aluminum via additive dosing regime in batch mode. In EC an aluminum anode generated the active species while in CC, commercial alum was used. Aluminum equivalent doses were applied, at initial pH values of 5, 6.5 and 8, while samples were taken over pre-determined time intervals, and analyzed for pH, particle size distribution, ζ potential, and structural properties. EC generated fragile flocs, compared to CC, over a wider pH range, at a substantially higher growth rate, that were prone to restructuring and compaction. The results suggest that the flocculation mechanism governing EC in sweep floc conditions is of Diffusion Limited Cluster Aggregation (DCLA) nature, versus a Reaction Limited Cluster Aggregation (RLCA) type in CC. The implications of these differences are discussed. [Copyright &y& Elsevier]

Abstract: Natural organic matter (NOM) is shown to be an important determinant of Pb dynamics across nine highly variable freshwater (wetland, stream, lake) ecosystems of Ontario, Canada. Soluble organic–Pb complexes emerged as the dominant Pb aqueous species (68–99%) in NOM-rich ecosystems; while distinct surficial sediment and suspended floc Pb sequestration and solid-solution partitioning patterns were observed across sites, driven by differential roles of living versus refractory NOM respectively within these two compartments. Field results suggest organo-Pb complexes dominate bed sediment Pb solid-solution partitioning, as sites with the highest pH values showed the greatest Pb mobilization, despite site-specific solid-phase Pb sequestration patterns. Contrasting bed sediment results, amorphous Fe oxyhydroxides (FeOOH) collected by floc microbes and extracellular polymeric substances, were the best predictor of floc Pb solid-solution partitioning, more consistent with cationic Pb behavior, as well as the key floc Pb sequestration phase (43–82%) across systems. Laboratory batch experiments assessed Pb solid-solution dynamics as a function of pH (5, 6, 6.5, 7 and 8) for surficial bed sediments (wetland, stream and lake) and limnetic floc (pH 5 and 8) varying in NOM concentrations. Results confirmed the occurrence of stable organo-Pb complexes in NOM-rich sediments, as mobilization of dissolved organic carbon (DOC) and Pb occurred with increasing pH, while Pb release decreased with increasing pH from NOM-poor sediment. The most organic rich, wetland surficial sediments showed the greatest mobilization rate of organo-Pb complexes, indicating dynamic DOC and Pb export is likely from such NOM-rich ecosystems under changing pH conditions. In contrast, experimental floc pH dependent Pb mobilization showed no correlation to DOC concentrations and was consistent with FeOOH-cationic Pb solid-solution behavior, rather than anionic organo-Pb complexes, as suggested in field observations. Results of this combined field and laboratory study demonstrate that establishing the nature of NOM and differential processes impacting NOM abundance/reactivity in each aquatic compartment across intrinsically connected aquatic ecosystems is fundamental to understanding Pb migration in freshwater catchments from upstream NOM-rich wetlands through to downstream NOM-poor littoral lake environments. [Copyright &y& Elsevier]

Abstract: Presence of particles is known to decrease the effectiveness of ultraviolet (UV) disinfection by shielding the targeted microorganisms from UV light. This study aims to provide an in-depth understanding on the effect of particles and flocs on UV disinfection by using a stable, well-defined and well-controlled synthetic system that can simulate the bioflocculation of particles and microorganisms in water and wastewater samples. The synthetic system was created by using Escherichia coli, latex particles (1, 3.2, 11, 25, and 45 μm), alginate, and divalent cations; and the bioflocculation of particles was achieved naturally, as it would occur in the environment, without using chemical coagulants. E. coli was quantified before and after UV disinfection using membrane filtration. Even in the absence of particles, some of the self-aggregated E. coli could survive a UV dose of 90 mJ/cm2. E. coli inactivation levels measured in the presence of particles were lower than the inactivation levels measured in the absence of particles. At low UV doses (<9 mJ/cm2), neither particle size nor degree of flocculation had a significant effect on the inactivation of E. coli. Particle size had a significant effect on the inactivation of E. coli only at high UV doses (80 mJ/cm2), and larger particles (e.g., 25 μm) protected bacteria more compared to smaller particles (e.g., 3.2 and 11 μm). What size of particles flocs were made of (3.2, 11, and 25 μm) did not make a significant difference on the inactivation levels of E. coli. For 3.2 μm particles, there was no significant difference in E. coli inactivation between non-flocculated and flocculated samples at any UV dose. For 11 and 25 μm particles, there was a significant difference in E. coli inactivation between non-flocculated and flocculated samples at 80 mJ/cm2. Degree of flocculation became a significant factor in determining the number of surviving bacteria only at high UV doses and only for larger particles. [Copyright &y& Elsevier]

Abstract: Electroflocculation (EF) is gaining recognition as an alternative process to conventional coagulation/flocculation. The electrical current applied in EF that generates the active coagulant species creates a unique chemical/physical environment in which competing redox reactions occur, primarily water electrolysis. This causes a transient rise in pH, due to cathodic formation of hydroxyl ions, which, in turn, causes a continuous shift in coagulation/flocculation mechanisms throughout the process. This highly impacts the formation of a sweep floc regime that relies on precipitation of metal hydroxide and its growth into floc. The size and structural evolution of kaolin–Al(OH)3 flocs was examined using static light scattering techniques, in aim of elucidating kinetic aspects of the process. An EF cell was operated in batch mode and comprised of two concentric electrodes – a stainless steel cathode (inner electrode) and an aluminum anode (outer electrode). The cell was run at constant current between 0.042A and 0.22A, and analyses performed at pre-determined time intervals. The results demonstrate that EF is able to generate a range of flocs, exhibiting different growth rates and structural characteristics, depending on the conditions of operation. Growth patterns were sigmoidal and a linear correlation between growth rate and current applied was observed. The dependency of growth rate on current can be related to initial pH and aluminum dosing, with a stronger dependency apparent for initial optimal sweep floc regime. All flocs exhibited a fragile nature and undergo compaction and structural fluctuations during growth. This is the first time size and structural evolution of flocs formed in the EF process is reported. [Copyright &y& Elsevier]

Abstract: Flow interactions with aquatic vegetation and effects on sediment transport and nutrient redistribution are uncertain in shallow aquatic ecosystems. Here we quantified sediment transport in the Everglades by progressively increasing flow velocity in a field flume constructed around undisturbed bed sediment and emergent macrophytes. Suspended sediment <100μm was dominant in the lower range of laminar flow and was supplied by detachment from epiphyton. Sediment flux increased by a factor of four and coarse flocculent sediment >100μm became dominant at higher velocity steps after a threshold shear stress for bed floc entrainment was exceeded. Shedding of vortices that had formed downstream of plant stems also occurred on that velocity step which promoted additional sediment detachment from epiphyton. Modeling determined that the potentially entrainable sediment reservoir, 46gm−2, was similar to the reservoir of epiphyton (66gm−2) but smaller than the reservoir of flocculent bed sediment (330gm−2). All suspended sediment was enriched in phosphorus (by approximately twenty times) compared with bulk sediment on the bed surface and on plant stems, indicating that the most easily entrainable sediment is also the most nutrient rich (and likely the most biologically active). [Copyright &y& Elsevier]

To conduct the micro-environment study of flocs in an enhanced biological phosphorus removal (EBPR) process, a phosphate ion-selective microelectrode was developed. The cobalt-based microelectrodes have tip diameters of 5–20μm and respond to all the three forms of phosphate ions, namely, H2PO4 −, HPO4 2−, and PO4 3−. The calibration curve at pH 7.5 had a slope of 31.5mV per decade change of concentration and a R 2 value of 0.99. Other characteristics of this microelectrode, such as response time, interferences from pH, ion strength, DO and other anions were also evaluated. [Copyright &y& Elsevier]

Abstract: This paper introduces a new method to estimate in-situ floc density and porosity of three particle-size classes: 0.45–10, 10–63 and, 63–250μm. LISST-100 and CatNet (a novel on-board filtration system of nested filters) were used to measure suspended particle volume and mass concentrations of 32 and 3 size-classes, respectively. Two field experiments were conducted in 2004 and 2006 in the head region of Gaoping Submarine Canyon (GPSC) to test this method. In each experiment CTD and LISST-100 profiling and simultaneous water sampling were carried out on board R/V Ocean Research III. In 2004, the water samples were filtered in the laboratory after the cruise using traditional methods. CatNet was used in 2006 and the seawater filtration was done on board. Assuming the observed suspended particles were all flocs composed of primary particles (with assumed density of 2.65g/cm3) and interstitial water (with assumed density of 1.025g/cm3) we estimated the volume of primary particles. The volume difference between flocs (measured from LISST-100) and primary particles is the interstitial pore space in flocs. Subsequently, the porosity of a floc particle is the ratio of the volume of the interstitial pore space to that of the floc particle. Results for 2004 show erroneous values of estimated floc porosities, which do not appear in 2006. The major difference is that the seawater was filtered immediately on board using CatNet in 2006. After removing erroneous data related to after-cruise filtering, the averaged floc porosity and density in the three grain-size classes were 47.0, 64.0, 85.9% and 1.89, 1.61, 1.25g/cm3, respectively. There is a trend that larger particles have lower density, which is supported by literature. The temporal variations of floc density and porosity of all three particle-size groups were larger in the surface than near the bottom of the submarine canyon. This vertical variability resulted from flocculation and biogenic processes in the surface of the coastal ocean, and the terrestrial source of the Gaoping River. Floc density is an important physical parameter to evaluate the settling flux of suspended sediments in estuarine and marine environments. This approach provides direct in-situ floc bulk densities of different grain-size classes, which has advantages over conventional methods. [Copyright &y& Elsevier]

As a pretreatment for membrane microfiltration (MF), the use of powdered activated carbon (PAC) with a particle size much smaller than that of conventional PAC (super-powdered PAC, or S-PAC) has been proposed to enhance the removal of dissolved substances. In this paper, another advantage of S-PAC as a pretreatment for MF is described: the use of S-PAC attenuates trans-membrane pressure increases during the filtration operation. The floc particles that formed during coagulation preceded by S-PAC pretreatment were larger and more porous than the floc particles formed during coagulation preceded by PAC pretreatment and those formed during coagulation without pretreatment. This result was due to increased particle–particle collision frequency and better removal of natural organic matter, which inhibits coagulation by consuming coagulant, before the coagulation reaction. The caked fouling layer that built up on the membrane surface was thus more permeable with S-PAC than with normal PAC. Both physically reversible and irreversible membrane foulings were reduced, and more stable filtration was accomplished with S-PAC pretreatment. [Copyright &y& Elsevier]

Abstract: A new formulation for floc yield strength of cohesive sediment is theoretically derived and incorporated into a flocculation model based on variable fractal dimension. The new flocculation model is validated with existing data on the temporal evolution of floc size measured in the laboratory. Comparing with existing flocculation models using a constant yield strength, it is found that new flocculation model based on variable yield strength and variable fractal dimension is superior in predicting the temporal evolution of floc size. It is also demonstrated that the present model results are very similar to that using an empirical formulation of variable yield strength suggested by Sonntag and Russel (1987. Structure and breakup of floccs subjected to fluid stressses. II. Theory. J. Colloid Interface Sci. 115(2), 378–389) when the empirical coefficient is specified according to our theoretical value. Hence, it is concluded that the new variable yield strength formulation derived in this study and the variable fractal dimension are effective in improving the prediction of flocculation process. [Copyright &y& Elsevier]

Although flocculation has been widely applied to improve filtration performance before filtered dry stack tailings storage, it is still a challenge to create flocculated aggregates having desired characteristics which are both conducive to improving the filtration rate and reducing the filter cake moisture content. In this paper, the alternate shear conditions were investigated to enhance flocculant-aided filtration performance of coal tailings. The focused beam reflectance measurement (FBRM) was used as an in-situ monitor to measure the floc size under different shear conditions in the presence of anionic polyacrylamide. Compared with single shear conditions, sequenced flocculation produced stronger flocs. It was also found that the flocs formed under two cycles of high (1192.8 s−1) and low (637.6 s−1) shear rates were the strongest and contained fewer particles and small flocs. The particle vision measurement (PVM) was used to analyze the effects of alternate shear conditions on floc morphological characteristics. It was observed that the floc structure became more compact with the number of cycles. Lastly, the filtration experiments were conducted to determine the filtration performance of coal tailings. The results showed that the coal tailings had the best comprehensive filtration performance under the sequenced flocculation with two cycles of high and low shear rates, the filtration time was 12.17 min, which was very close to the fastest 12.03 min of single low shear rate, and 21.2% of cake moisture content was about the same as the minimum 21.1%. The filtration outcomes were consistent with that given by FBRM and PVM. [Display omitted] • Sequenced flocculation improved the filtration performance of coal tailings. • Alternate shear condition has a profound impact on floc compactness. • The size and shape characteristics of flocs were monitored in situ. [ABSTRACT FROM AUTHOR]

The complexity of natural water made it difficult to remove fluoride. Based on the environmental problems found in the investigation, the fluoride removal research in the water containing algal cells was carried out. In this study, AlCl 3 and [AlO 4 Al 12 (OH) 24 (H 2 O) 12 ]7+ (Al 13) were used to remove fluoride. Additionally, the role of aluminum speciation in fluoride removal and the effect of Microcystis aeruginosa on the fluoride removal by different aluminum species coagulants were elucidated. The results showed that AlCl 3 mainly removed fluoride by physical interactions, surface adsorption and enmeshment. When algal cells were added to the system, the fluoride removal rate increased from 22.75 % to 72.99 % at a dosage of 40.0 mg/L. This was because algal cells greatly increased the distribution of Al(OH) 3 in the flocs. In particular, the specific surface area of the flocs containing algal cells reached 160.77 m2/g, which allowed more fluoride to be adsorbed. However, excessive Al3+ led to serious damage to algal cells and release of intracellular organic matter (IOM), worsening the effect of defluoridation. F− and Al3+ formed AlF2+ and AlF 2 + via complexation in water. These compounds were not conducive to defluoridation. Al 13 removed fluorine mainly through ion exchange, substitution and hydrogen bonding. Algal cells had an inhibitory effect on defluorination, which was observed in the process of coagulation by different Al dosages. Al 13 achieved agglomeration of algal cells and generated small and dense flocs through charge neutralization and electrostatic patch mechanism. Once Al 13 combined with algal cells and algae organic matter (AOM), the reaction between Al 13 and fluoride would be weakened. Al 13 not only maintained the defluoridation performance, but also did not damage the integrity of algal cells, even at high dosages. [Display omitted] • Defluorination by AlCl 3 relied merely on physical actions. • Algal cells promoted the adsorption of F− by changing the distribution of Al(OH) 3. • Algal cells increased F− removal rate by 50.24 % at 40.0 mg/L AlCl 3. • Al 13 removed F− mainly through ion exchange, substitution and hydrogen bonding. • The presence of algal cells impaired the ability of Al 13 to remove F−. [ABSTRACT FROM AUTHOR]

Better understanding of sediment flocculation will better help to predict fine sediment transport. Multiple advanced instruments were employed to get the field observations in the turbidity maximum of the Changjiang Estuary. Floc pictures were taken by a scanning electron microscope in the laboratory. The sediment flocculation dynamics and the floc characteristics are investigated in this paper. The results show that the morphology and size of flocs show obvious tidal variations. There are diverse flocs in each tidal cycle, mainly including loose, porous and dense flocs, which are mainly comprised of silt and clay. They have indistinct or distinct shapes, rough or less rough surfaces, incompact or compact structures. The floc size is highly related to the tidal processes. The average floc size (94.8 μm) during water slacks is larger than that (24.1 μm) during maximum floods and ebbs, owing to the lower flow velocity during water slacks. The average floc size (105.6 μm) during high water slacks is larger than that (83.9 μm) during low water slacks due to the higher salinity during high water slacks. The average floc size (74.7 μm) during neap tide is larger than that (44.3 μm) during spring tide, which can be attributed to the lower flow velocity, the higher salinity and the finer primary particle during neap tides. Additionally, the floc size increases gradually from the surface to the bottom. The turbulent shear stress is the controlling factor for sediment flocculation. The maximum flocs can be formed under the condition of mid-low flow velocity and the optimal flow velocities for the maximum flocs during neap and spring tides are 0.41 and 0.56 m/s, respectively. The floc size decreases significantly with the increase of turbulent shear when the turbulent shear rate parameters during neap and spring tides are higher than about 3 and 4 s−1, respectively. The conclusions can help to extend our understanding of flocculation dynamics and help to predict the fine sediment transport. • Floc properties are observed in the turbidity maximum of the Changjiang Estuary. • There are diverse flocs, mainly including loose, porous and dense flocs. • Sediment flocculation shows obvious tidal variations over a tidal cycle. • The floc size decreases significantly with the increase of turbulent shear. [ABSTRACT FROM AUTHOR]

[Display omitted] • Natural energy was successfully used to power a water treatment system. • Solar-powered electrocoagulation produced large flocs at a low current density. • The gravity-driven membrane bioreactor achieved a high flux of 25 L/m2h. • Large flocs and membrane rejection facilitated the enrichment of useful microbes. • Nitrogen was largely removed by Nitrospira and Diaphorobacter bacteria. Rural water treatment is generally more challenging than urban water treatment. This study proposed a novel rural water treatment system effectively harnessing solar energy and gravitational hydropower. Influent was initially fed to a solar-driven electrocoagulation unit, in which UV 254 level was reduced (by almost 60%) and large flocs (averaging up to 66.2 μm in diameter) were formed. The effluent was then introduced to a gravity-driven ceramic membrane bioreactor (GDCMBR) at different water head differences (ΔH = 0.5 or 1.0 m). Generally, applying the greater water head difference (ΔH = 1.0 m) did not enhance removal of turbidity and organic matter, but it led to a reasonably high flux (25.9 L/m2/h). The GDCMBR enriched various useful microorganisms such as nitrifiers (Nitrospira bacteria), and denitrifiers (Diaphorobacter bacteria), enabling almost complete elimination of NH 3 -N and NO 2 –-N. Overall, the findings of this study suggest the possibility of sustainable operation during rural water treatment. [ABSTRACT FROM AUTHOR]

Abstract: In this study, coagulation of kaolinite suspensions at low temperatures is compared with that at an ambient temperature of 22°C, and the process is examined with regard to the coagulation rate (CR) and chemical aspects of coagulation. Experiments using a photometric dispersion analyzer (PDA) show that coagulation of kaolinite suspensions can be taken as a two-phase process. Low temperature greatly reduces the CR of the first phase but not that of the second one. On the other hand, results show that low temperature did not serve to impede the hydrolysis of aluminum [Al(III)] within 1min of alum addition. The measurements of electrophoretic mobility (EM) indicate that destabilization of kaolinite particles by hydrolyzed Al species was not hindered by low temperature within 1min of alum addition. Slow coagulation at low temperature is due to the lowered CR but not the altered chemistry aspect of Al(III). Furthermore, the change in settled turbidity after 20-min flocculation as a function of coagulant dosage was more severe in the cold because of the low CR. Elongating floc-growth time, as observed, was able to counterbalance the retarded CR at low temperature and improve turbidity removal efficiency. [Copyright &y& Elsevier]

Abstract: Direct movie analysis of the Brownian motion of single colloidal particles under optical microscope was carried out to determine hydrodynamic diameter. Mean squared displacements of individual particle against time interval of observation were obtained from the trace of Brownian motion. The hydrodynamic diameter is obtained via diffusion coefficient determined on the basis of Einstein relation. The validity of the applied method was statistically confirmed by the comparison of predicted relative error with those obtained from the measurement using uniform polystyrene latex particles of three different diameters. Determination of hydrodynamic diameters with coefficients of variation (CV) less than 6% was achieved when processing 501 frames. Achieved coefficients of variation correspond to those statistically predicted for the Brownian motion. Obtained diameter of doublet was consisted with those reported by other researchers. In the case of flocs composed with primary particle more than three, the value of CV slightly increases up to 7.3%. This increment can be ascribed to deviation of center of mass determined from projected image from true value. However, within this accuracy the hydrodynamic diameters of coagulated flocs being composed of up to six primary particles were determined. The determined hydrodynamic diameters were found to be significantly smaller than the maximum distances in the projection indicating different power law relation against the number of composing particles in flocs. [Copyright &y& Elsevier]

Column and pilot scale experiments for a chemical treatment involving the use of coagulants to remediate heavy metal contaminated groundwater were performed. Granulated lime (Ca(OH)2) and calcium carbonate (CaCO3) were used as coagulants and contaminated groundwater obtained at an abandoned Fe-mine in Korea was used for the experiments. The main removal mechanism of heavy metals in the experiments was “sweep precipitation” by coagulation. Using granulated lime as a coagulant in the column experiment, more than 98% of As and Ni were removed from artificially contaminated water. When granulated calcium carbonate was used in the artificially contaminated water, the removal efficiencies of Ni and Zn were more than 97%, but As removal efficiency was lower than 50%. For the continuous column experiment with mixed lime and calcium carbonate at a 1:1 (v/v) ratio, almost all As was removed and more than 98 % of Ni was removed. For pilot scale experiments (acryl tank: 34cm in length and 24cm in diameter), the removal efficiencies of As and Cd were above 96% for 150l groundwater treatment and their accumulated removal capacities linearly maintained. This suggests that coagulants could treat more than 22 times greater groundwater volume compared with the volume of coagulants used. [Copyright &y& Elsevier]

Abstract: Ultrasonication is an energy intensive process used to enhance organics’ solubilisation and used in promoting methane yield from wastewater sludge. Applying limited ultrasound without full disruption of floc structure or cell walls can significantly enhance methane yield from sludge at reduced energy cost. This work probed the spatial distribution of extracellular polymeric substances, cells in the original wastewater flocs, and the yielded fragments following weak ultrasonication using a process of multiple staining and a confocal laser scanning microscope technique. The stereological information of the three-dimensional architecture of the original wastewater floc and ultrasonicated fragments was extracted and compared. The local structural changes following weak ultrasonication were presented for the first time, which should also correlate with the enhanced methanogenesis thereby produced. [Copyright &y& Elsevier]

Abstract: The present effort is the development of a multiscale modeling, simulation methodology for investigating complex phenomena arising from flowing fiber suspensions. Specific consideration was given to dynamic simulations of viscoelastic fibers in which the fluid flow is predicted by a method that is a hybrid between Direct Numerical Simulations (DNS) and Large Eddy Simulation techniques (LES), and fluid fibrous structure interactions (FSI) will be taken into account. Numerical results are presented for which focus is on fiber floc deformation by hydrodynamic forces in turbulent flows. Dynamics of simple fiber networks in a shearing flow of water in a channel flow illustrate that the shear-induced bending of the fiber network is enhanced near the walls. Fiber–fiber interaction in straight ducts is also investigated and results show that deformations would be expected during the collision when the surfaces of flocs will be at contact. Smaller velocity magnitudes of the separated fibers compare to the velocity before collision implies the occurrence of an inelastic collision. In addition because of separation of vortices interference flows around two flocs become very complicated. The results opening the possibility for developing a meaningful numerical model of the fiber flow at the continuum level where an Eulerian multi-phase flow model can be developed for industrial use. [Copyright &y& Elsevier]