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Applying biofloc technology in the intensive and extensive culture of Clarias gariepinus can improve water quality and be used to feed fish. Aeration systems were a critical unit supporting biofloc and water quality. This study's objective was the assessment of various types of diffusers on the growth and water quality in a C. gariepinus culture. Two types of diffuser units were prepared for the experiment, there are air tube diffuser (AT) and air stone diffuser (AS). Growth parameters, water quality, and volume of biofloc were observed within 30 days. The survival rate, weight gain, average body weight, and specific growth rate of C. gariepinus were higher in the tanks that used air tubes (98%, 485.29 %, 7.52 g, 5.89%) than in the tanks that used air stones (92 %, 385.94 %, 5.98 g, 5.23%). The volume of biofloc ranges from 5.40-18.80 ml/L in AT tanks and 4.60-14.00 ml/L in AS tanks. There is no significant difference (p > 0.05) in water quality parameters and FCR value. However, using the air tube diffuser showed better results with the growth performance, survival rate, and formation of biofloc. [ABSTRACT FROM AUTHOR]

Flocculent settling widely exists in various processes of tailings disposal.It bears significance for the accurate calculation of the flocculent settling velocity in engineering, such as tailings backfilling and surface disposal.This paper studied the structural characteristics of tailings flocs from the perspective of the fractal theory, and established the mathematical relationship between tailings particle size, geometry size of floc and fractal dimension.It analyzed the influence of buoyancy effect, reflux effect and viscosity effect on floc settling, and deduced a calculation formula of tailings flocculent settling velocity.This study carried out a tailings flocculent settling test observed the changes in geometric morphology of flocs by focused beam reflectance measurement technology(FBRM), and carried out validation analysis between testing data and model calculation value.The results showed that the settling velocity increased with the equivalent grain size of flocs, which could be divided into three stages, namely accelerated settling, uniform settling and compaction settling.The equivalent grain size of flocs of test tailings were 140~350 μm, and the settling velocity calculated by the formula were 1.3~2.0 mm/s when the fractal dimension was 2.25, which demonstrates significant correlation with the testing value, and had certain practical application value.

Pollutants related to water quality often exist in rivers and form clusters. These pollutants adversely affect river environments and ecosystems. In Korea, the public's interest in water quality has been increasing for decades. Many studies on water quality and pollutants in sewage treatment plants have been conducted; however, studies on the formation of flocs based on the flow characteristics of rivers are insufficient. In general, it is known that floc formation is influenced by hydraulic characteristics, such as velocity and turbulence, and that it combines them with contaminants in the river. However, studies that quantitatively analyze this topic are also insufficient. An analysis of floc formation between sediments must be conducted to understand the formation process of sediments and contaminants. Therefore, in this study, kaolin, which is a cohesive sediment, was used to quantify the floc formation process according to the mixing intensity. Turbidity was analyzed to observe the amount of floc formation, and samples were collected to confirm the concentration. Additionally, the turbidity concentration relationship according to the mixing intensity was quantified using an optical microscope. Regarding the mixing intensity, when the rotation speed was 200 rpm or more, the separation of the flocs was dominant. In contrast, when the rotation speed was 100 rpm or less, turbidity changes due to sedimentation and floc formation were dominant. Analyzing mixing intensities and their association with the flow characteristics of rivers may be useful for the management of contaminants in rivers. [ABSTRACT FROM AUTHOR]

This work deals with the treatment of oily wastewater produced from the washing of oil-contaminated soil. Untreated oily wastewater contains toxic compounds that might be mutagenic or carcinogenic as total petroleum hydrocarbon (TPH) and heavy metals. Based on the water quality analysis, the tested samples contained a high concentration of TPH, chemical oxygen demand (COD) and turbidity with an average value of 67,500 mg/l, 48,240 mg/l and 176 (nephelometric turbidity unit, NTU), respectively. Several technologies were used, such as centrifuging, powdered activated carbon (PAC) and sawdust. The mean values of COD values for sawdust, centrifuging and PAC were 41,067, 25,600 and 13,133 mg/l, respectively. The present study indicated that the coagulation/flocculation processes were more efficient by using aluminium sulphate alum, while the preliminary conclusion derived was that the secondary treatment using an aeration system is capable of lowering the COD values as well as increasing the flocculent mass floc well equal to 4,784 mg/l and 0.69 g, respectively. The microbial seed was able to degrade the biosurfactant, which allows the stability of oil emulsion to be broken down and released easily. HIGHLIGHTS Centrifuging sawdust and PAC were carried out to treat oily wastewater.; The mean values of COD for sawdust, centrifuging and PAC were 41,067, 25,600 and 13,133 mg/L.; The combination of aeration with coagulation/flocculation enhanced the treatment process.; Microbial seed effect on the stability of oil emulsion by degrading saponin in wastewater.;

In order to improve the removal efficiencies of SS and Fe3+ in anaerobic digestion reject water for the subsequent biological treatment process, on the basis of the single factor test in the early stage, the response surface method was used, and the structure of the formed floc was analyzed by magnetic flocculation. The optimum amounts of magnetic powder, polyaluminum chloride (PAC) and polyacrylamide (PAM) were 40.51 mg/L, 31.31 mg/L and 4.05 mg/L, respectively. At this time, the removal efficiencies of SS and Fe3+ were 97.84% and 98.35%. The effects of floc particle size, scanning electron microscopy, infrared spectroscopy and two-dimensional fractal dimension of flocs on the flocculation ability showed that: compared with conventional coagulation, the average particle size of flocs treated by magnetic flocculation was 76.56 μm, the Fe-O-Al absorption peak appeared at 984 cm−1, the flocculation ability was significantly improved, the surface of the floc was rough and porous, and the structure was dense, and the sedimentation performance was significantly improved also. [ABSTRACT FROM AUTHOR]

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]

This work deals with the treatment of oily wastewater produced from the washing of oil-contaminated soil. Untreated oily wastewater contains toxic compounds that might be mutagenic or carcinogenic as total petroleum hydrocarbon (TPH) and heavy metals. Based on the water quality analysis, the tested samples contained a high concentration of TPH, chemical oxygen demand (COD) and turbidity with an average value of 67,500 mg/l, 48,240 mg/l and 176 (nephelometric turbidity unit, NTU), respectively. Several technologies were used, such as centrifuging, powdered activated carbon (PAC) and sawdust. The mean values of COD values for sawdust, centrifuging and PAC were 41,067, 25,600 and 13,133 mg/l, respectively. The present study indicated that the coagulation/flocculation processes were more efficient by using aluminium sulphate alum, while the preliminary conclusion derived was that the secondary treatment using an aeration system is capable of lowering the COD values as well as increasing the flocculent mass floc well equal to 4,784 mg/l and 0.69 g, respectively. The microbial seed was able to degrade the biosurfactant, which allows the stability of oil emulsion to be broken down and released easily. [ABSTRACT FROM AUTHOR]

How climate and habitat drive variation in aquatic metabolism in wetlands remains uncertain. To quantify differences in seasonal aquatic metabolism among wetlands, we estimated aquatic ecosystem metabolism (gross primary productivity, GPP; ecosystem respiration, ER; net aquatic productivity, NAP) in subtropical ridge and slough wetlands of the Florida Everglades from more than 2 yr of continuously measured water column dissolved oxygen, photosynthetically active radiation (PAR), water temperature, and water depth. Gross primary productivity and ER were modeled from light, temperature, and water depth using non‐linear minimization and maximum likelihood. Reaeration rates were estimated from wind speed. Dissolved oxygen was below saturation at all sites during both wet and dry seasons. Water depth interacted with vegetation to influence PAR, water temperature, and spatiotemporal patterns in aquatic metabolism. Gross primary productivity and ER were highest at the slough with lowest submerged aquatic vegetation (low‐SAV slough), intermediate in the sawgrass (Cladium jamaicense) ridge site, and lowest at the slough with highest submerged aquatic vegetation (high‐SAV slough). Ecosystem respiration was strongly positively correlated with GPP at the sawgrass ridge and low‐SAV slough sites. Gross primary productivity increased with water temperature and PAR across all habitat types, whereas ER decreased (more respiration) with water temperature and PAR. Net aquatic productivity was negatively correlated with water temperature and positively correlated with PAR, suggesting that ER was more sensitive than GPP to water temperature. Aquatic metabolism was largely net heterotrophic in all wetlands, and high‐SAV appeared to buffer seasonal variation in PAR and water temperatures that drive NAP in subtropical wetlands. Our results suggest that aquatic ecosystem metabolism in wetlands with seasonal hydrology is sensitive to changes in water depth and vegetation density that influence temperature and light. Expanding our understanding of how metabolic processes and carbon cycling in wetland ecosystems vary across gradients in hydrology, vegetation, and organic matter could enhance our understanding and protection of conditions that maximize carbon storage. [ABSTRACT FROM AUTHOR]

In order to improve the removal efficiencies of SS and Fe3+ in anaerobic digestion reject water for the subsequent biological treatment process, on the basis of the single factor test in the early stage, the response surface method was used, and the structure of the formed floc was analyzed by magnetic flocculation. The optimum amounts of magnetic powder, polyaluminum chloride (PAC) and polyacrylamide (PAM) were 40.51 mg/L, 31.31 mg/L and 4.05 mg/L, respectively. At this time, the removal efficiencies of SS and Fe3+ were 97.84% and 98.35%. The effects of floc particle size, scanning electron microscopy, infrared spectroscopy and two-dimensional fractal dimension of flocs on the flocculation ability showed that: compared with conventional coagulation, the average particle size of flocs treated by magnetic flocculation was 76.56 μm, the Fe-O-Al absorption peak appeared at 984 cm−1, the flocculation ability was significantly improved, the surface of the floc was rough and porous, and the structure was dense, and the sedimentation performance was significantly improved also.

Optical gas refractometry has enabled new pressure standards to be developed based on a dual Fixed Length Optical Cavity (FLOC) system. NIST in CRADA (collaboration research and development agreement) partnership with MKS Instruments has created a portable FLOC pressure standard based on gas refractivity. A key challenge for accurate measurements is the characterization of cavity distortions when pressurized. A method for determination of the distortion constants is presented based on using two gases of known refractive index. Using this two-gas technique, the distortions on the portable FLOC pressure standard are corrected so that this correction contributes no more than 1 μPa/Pa of uncertainty (k = 1).

Abstract How climate and habitat drive variation in aquatic metabolism in wetlands remains uncertain. To quantify differences in seasonal aquatic metabolism among wetlands, we estimated aquatic ecosystem metabolism (gross primary productivity, GPP; ecosystem respiration, ER; net aquatic productivity, NAP) in subtropical ridge and slough wetlands of the Florida Everglades from more than 2 yr of continuously measured water column dissolved oxygen, photosynthetically active radiation (PAR), water temperature, and water depth. Gross primary productivity and ER were modeled from light, temperature, and water depth using non‐linear minimization and maximum likelihood. Reaeration rates were estimated from wind speed. Dissolved oxygen was below saturation at all sites during both wet and dry seasons. Water depth interacted with vegetation to influence PAR, water temperature, and spatiotemporal patterns in aquatic metabolism. Gross primary productivity and ER were highest at the slough with lowest submerged aquatic vegetation (low‐SAV slough), intermediate in the sawgrass (Cladium jamaicense) ridge site, and lowest at the slough with highest submerged aquatic vegetation (high‐SAV slough). Ecosystem respiration was strongly positively correlated with GPP at the sawgrass ridge and low‐SAV slough sites. Gross primary productivity increased with water temperature and PAR across all habitat types, whereas ER decreased (more respiration) with water temperature and PAR. Net aquatic productivity was negatively correlated with water temperature and positively correlated with PAR, suggesting that ER was more sensitive than GPP to water temperature. Aquatic metabolism was largely net heterotrophic in all wetlands, and high‐SAV appeared to buffer seasonal variation in PAR and water temperatures that drive NAP in subtropical wetlands. Our results suggest that aquatic ecosystem metabolism in wetlands with seasonal hydrology is sensitive to changes in water depth and vegetation density that influence temperature and light. Expanding our understanding of how metabolic processes and carbon cycling in wetland ecosystems vary across gradients in hydrology, vegetation, and organic matter could enhance our understanding and protection of conditions that maximize carbon storage.

Submergible digital holographic camera can measure the in situ size and shape of suspended particles, such as complex flocs and biological organisms, without disturbance. As the number of particles in the water column increases, overlapping concentric rings (interference patterns) can contaminate the holographic images. Using light intensity (LI), this study proposes a practical method to assess the degree of contamination and screen out contaminated images. The outcomes from image processing support that LI normalized on a gray scale of 0 (black) to 255 (white) can be a reliable criterion for defining the contamination boundary. Results found that as LI increased, the shape of the particle size distribution shifted from a positively skewed to a normal distribution. When LI was lower than approximately 80, owing to the distortion of particle properties, the settling velocities derived from the contaminated holograms with mosaic patterns were underestimated compared to those from the uncontaminated holograms. The proposed method can contribute to a more accurate estimation of the transport and behavior of cohesive sediments in shallow estuarine environments.

The scheme of DLVO theory and the concept of fractal structure of flocs applied to the suspension of montmorillonite have revealed out the unique nature of this clay dispersion. In this context, two major regimes are recognized. The first is the electrostatically dispersed regime. And the second is the coagulated regime. In the former, the formation of a diffusive electric double layer (EDL) characterized by reciprocal Debye length measured from the surface of the particle is distinctively important. Intrinsic viscosity with electroviscous effects and yield stress are interpreted by the steric presence of EDL. In the latter, the unit of transportation is a coagulated floc with finite cohesive strength. Sedimentation process reflecting these factors is carefully observed to recognize the turbulence generation by the formation of large flocs at the moment of gel collapse. Waiting time prior to gel collapse was found to be determined reflecting the pH-dependent charging behavior. By taking into account the effect pH-dependent charge, the DLVO based two regimes are further categorized into five. The developed tools can be extensively used for the system involved with different ionic species, pH, volume fraction and organic substances.

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]

The presence of contaminants in the paint industry effluent confirms the necessity of its treatment before disposal. This study aims to assess the potentiality of green coagulant Cassia fistula by treating it against the synthetic paint industry wastewater. The process of coagulation was done using standard jar test apparatus. The operational variables like solvent type (NaCl, KCl, and distilled water), solvent concentration (1-5 N), coagulant dosage (1-10 g/L), coagulant-extract volume (40-240 mL/L), initial pH (5-11), and initial concentration (1,200; 1,350; 1,850; 2,200; and 2,700 mg/L) had been varied. The recommended condition to treat a liter of effluent was 160 mL of coagulant extract prepared using 5 g of C. fistula and 2 N NaCl, at its initial pH (7.8-8.4). The settling studies were conducted to evaluate the sludge volume index, hindered settling velocity, and sludge weight. The obtained results of C. fistula is compared with the chemical coagulant ferrous sulfate. The results acknowledged that C. fistula, a natural, eco-friendly, green coagulant, could be a strong alternative to the chemical coagulant in the treatment of paint industry wastewater. [ABSTRACT FROM AUTHOR]

The scheme of DLVO theory and the concept of fractal structure of flocs applied to the suspension of montmorillonite have revealed out the unique nature of this clay dispersion. In this context, two major regimes are recognized. The first is the electrostatically dispersed regime. And the second is the coagulated regime. In the former, the formation of a diffusive electric double layer (EDL) characterized by reciprocal Debye length measured from the surface of the particle is distinctively important. Intrinsic viscosity with electroviscous effects and yield stress are interpreted by the steric presence of EDL. In the latter, the unit of transportation is a coagulated floc with finite cohesive strength. Sedimentation process reflecting these factors is carefully observed to recognize the turbulence generation by the formation of large flocs at the moment of gel collapse. Waiting time prior to gel collapse was found to be determined reflecting the pH-dependent charging behavior. By taking into account the effect pH-dependent charge, the DLVO based two regimes are further categorized into five. The developed tools can be extensively used for the system involved with different ionic species, pH, volume fraction and organic substances. [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]

Dispersions of acid hydrophobized hydrolysis lignin in light crude oil, industrial oil, and diesel fuel were found to demonstrate the transition from Newtonian to non-Newtonian behavior with shear-thinning and thixotropy within the increase in lignin concentration. Lignin-in-diesel fuel dispersions were shown to have the smallest apparent viscosity while lignin-in-industrial oil dispersions have the highest one and the sharpest drop of viscosity with shear rate increasing. At the same time, relative viscosity demonstrates the inverse dependence: It is highest for lignin-in-diesel fuel suspensions. Calculation of parameters based on microrheological model of elastic flocs with generalized Casson equation allowed determining of the parameters k and A that describe hydrodynamic interaction between separated particles and their aggregates under flow, parameter FA, characterizing the force impeding the break of aggregates and numbers of particles in the floc for different systems as the dependence of shear stress. The explanation based on a higher affinity of diesel fuel to lignin unlike industrial oil and light crude oil as dispersing medium has been given.

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]

In this study, the decolourisation of Palm Oil Mill Effluent (POME) was investigated by electrocoagulation (EC) batch reactor utilizing aluminium plate electrodes. POME was characterized physicochemically for colour, chemical oxygen demand (COD), pH, conductivity and turbidity. The colour of POME was observed to be dark brown of 2707 PtCo with a high organic content of COD at 3909 mg/L and high turbidity at 755 NTU. The electrical conductivity was at 12.82 mS. The influence of various operating parameters such as pH (3 to 11), applied voltage (5 V to 20 V) and plate gap (7.5 to 11.5 cm) to the POME colour removal were investigated as well. The highest colour removal was spotted at pH 5, applied voltage of 20 V and plate gap of 9.5 cm with corresponding colour removal percentage of 89, 79 and 78%, respectively. The EC flocs examined using FESEM exhibited the amorphous spherical and rod-like shape structure. [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]

Over the past several decades, major hydro-sedimentary changes have occurred in both continental and coastal regions of the Mekong Delta, and this has severely impacted coastal erosion. A good characterization of floc properties and of their changes over time is necessary to gain comprehensive understanding and modelling of hydrodynamics and of the associated geomorphological changes. This paper quantifies the influence of sediment concentration, turbulence and differential particle settling on flocculation through field and laboratory investigations of the Mekong estuary. For concentrations lower than 200 mg·L −1 , the particles do not exhibit a dynamic response to their environment, while for higher concentrations (up to 3–4 g·L −1 ), particle size and settling velocity increased by more than one order of magnitude. Flocculation by differential settling has not been sufficiently investigated yet, but this study reveals it as a predominant factor for siltation in quiescent environments such as the ones existing in the inner mangrove fringe. Such results are important to provide realistic simulations of the coastal evolution. [ABSTRACT FROM AUTHOR]

The survival of microorganisms within a cementitious geological disposal facility for radioactive wastes heavily depends on their ability to survive the calciumdominated, hyperalkaline conditions resulting from the dissolution of the cementitious materials. The results from this study show that the formation of flocs, composed of a complex mixture of extracellular polymeric substances (EPS), provides protection against alkaline pH values up to 13.0. The flocs were dominated by Alishewanella and Dietzia spp., producing a mannose-rich carbohydrate fraction incorporating extracellular DNA, resulting in Ca2+ sequestration. EPS provided a ~10-μm thick layer around the cells within the center of the flocs, which were capable of growth at pH values of 11.0 and 11.5, maintaining internal pH values of 10.4 and 10.7, respectively. Microorganisms survived at a pH of 12.0, where an internal floc pH of 11.6 was observed, as was a reduced associated biomass. We observed limited floc survival (<2 weeks) at a pH of 13.0. This study demonstrates that flocs maintain lower internal pHs in response to the hyperalkaline conditions expected to occur within a cementitious geological disposal facility for radioactive wastes and indicates that floc communities within such a facility can survive at pHs up to 12.0. IMPORTANCE: The role of extracellular polymeric substances (EPS) in the survival of microorganisms in hyperalkaline conditions is poorly understood. Here, we present the taxonomy, morphology, and chemical characteristics of an EPS-based microbial floc, formed by a consortium isolated from an anthropogenic hyperalkaline site. Short-term (<2 weeks) survival of the flocs at a pH of 13 was observed, with indefinite survival observed at a pH of 12.0. Measurements from micro-pH electrodes (10-m-diameter tip) demonstrated that flocs maintain lower internal pHs in response to hyperalkaline conditions (pH 11.0, 11.5, and 12.0), demonstrating that floc formation and EPS production are survival strategies under hyperalkaline conditions. The results indicate how microbial communities may survive and propagate within the hyperalkaline environment that is expected to prevail in a cementitious geological disposal facility for radioactive wastes; the results are also relevant to the wider extremophile community. [ABSTRACT FROM AUTHOR]

The drawback of the parameter estimation method for ARMA SαS process based on fractional lower order moments（FLOM） was analyzed,and based on the conception of fractional lower order covariance（FLOC）,a new parameter estimation method of ARMA SαS process was proposed based on FLOC coefficient.Then,the α-spectrum estimation of ARMA SαS process was presented.By estimating the α-spectrum of ARMA SαS process and the sinusoidal signals that embedded in the α-stable noise,the α-spectrum estimation performances of ARMA SαS process based on FLOM and FLOC were compared in detail.Simulation results show that,for small values of alpha,the performance of the proposed α-spectrum estimation method for ARMA SαS process based on FLOC provides better performance than the method based on FLOM.

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]

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]

The gelation of FeOOH rod particles in a glycerin-water mixture under shear flows is investigated using rheological measurements. The average length and the average diameter of the rod particles are 1 μm and 120 nm, respectively. The van der Waals energy is much larger than the Brownian and electrostatic contributions. To examine the effect of shear history on gelation, two different kinds of experimental procedures are used: A strong, but short preshear followed by a creep test and a preshear for a long time followed by a creep test. The rod particle suspension becomes a gel during the creep test showing the plateau in G′ and yield stress. The gelation time during the creep test is dependent on preshear time while it is not affected by the preshear stress for a short time before the creep test. Both the plateau in G′ and the yield stress are larger when the preshear time is longer. The gelation appears to occur by two steps of the formation of flocs by the aggregation of individual particles and then the formation of the sample spanning network by the aggregation of the flocs. Gel strength appears to be dependent on floc size which is determined by the imposed shear stress in the present case of shear induced gelation. [ABSTRACT FROM AUTHOR]

Application of magnesium hydroxide as a coagulant for treating kaolin suspension under high pH was studied. The coagulation performance and magnesium hydroxide–kaolin floc properties were investigated under different dosages and pH values. Flocculation index and turbidity removal were then discussed with controlled experiments using intelligent particle dispersion analyzer. Floc size distributions were derived from microscopy and image analysis. The results showed that floc size decreased with increasing coagulant dose. The optimum magnesium ion dose tended to decrease with the increase of initial turbidity and pH value. Higher pH and higher magnesium dose led to rapid floc formation and relatively small flocs. The experiments showed that magnesium hydroxide coagulation process had two stages including fast floc formation and growth of flocs and then the larger flocs break into relative small particles. All of the flocs under investigation showed a limited capacity to regrowth when they had been previously broken. Based on the changes of zeta potential and floc properties, charge neutralization and precipitate enmeshment were proposed to be the main coagulation mechanisms. [ABSTRACT FROM PUBLISHER]

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]

Background: We investigated the surface characteristics of two strains of Shewanella sp., S. oneidensis MR-1 and S. putrefaciens 200, that were grown under aerobic conditions as well as under anaerobic conditions with trimethylamine oxide (TMAO) as the electron acceptor. The investigation focused on the experimental determination of electrophoretic mobility (EPM) under a range of pH and ionic strength, as well as by subsequent modeling in which Shewanella cells were considered to be soft particles with water- and ion-permeable outermost layers. Results: The soft layer of p200 is significantly more highly charged (i.e., more negative) than that of MR-1. The effect of electron acceptor on the soft particle characteristics of Shewanella sp. is complex. The fixed charge density, which is a measure of the deionized and deprotonated functional groups in the soft layer polymers, is slightly greater (i.e., more negative) for aerobically grown p200 than for p200 grown with TMAO. On the other hand, the fixed charge density of aerobically grown MR1 is slightly less than that of p200 grown with TMAO. The effect of pH on the soft particle characteristics is also complex, and does not exhibit a clear pH-dependent trend. Conclusions: The Shewanella surface characteristics were attributed to the nature of the outermost soft layer, the extracellular polymeric substances (EPS) in case of p200 and lypopolysaccharides (LPS) in case of MR1 which generally lacks EPS. The growth conditions (i.e., aerobic vs. anaerobic TMAO) have an influence on the soft layer characteristics of Shewanella sp. cells. Meanwhile, the clear pH dependency of the mechanical and morphological characteristics of EPS and LPS layers, observed in previous studies through atomic force microscopy, adhesion tests and spectroscopies, cannot be corroborated by the electrohydrodynamics-based soft particle characteristics which does not exhibited a clear pH dependency in this study. While the electrohydrodynamics-based soft-particle model is a useful tool in understanding bacteria's surface properties, it needs to be supplemented with other characterization methods and models (e.g., chemical and micromechanical) in order to comprehensively address all of the surface-related characteristics important in environmental and other aqueous processes. [ABSTRACT FROM AUTHOR]

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: The hydrodynamic diameter (D h) of cationic polyacrylamides (c-PAM) in water can either decrease or increase dramatically in the presence of small amounts of β-cyclodextrin (β-CD). It is proposed that the CD partially disperses the charge on the polymer thereby promoting associations within or among neighboring polymer strands. Turbidity measurements show that β-CD enhances the c-PAM induced flocculation of wood pulp fibers, which is in keeping with previous observations on sludge dewatering. The CD-polymer combinations that are the most effective for fiber flocculation are also those for which D h of the polymer is reduced the most. In situations where the CD compacts the c-PAM, the fiber network associated with the c-PAM is also compacted giving rise to a tighter floc. [Copyright &y& Elsevier]

The principal aim of this study is to analyze a seawater coagulation process by means of the evaluation of flocculation index and fractal dimension of flocs. Floc size was evaluated by flocculation index (FI) and floc shape by fractal dimension. Two coagulation parameters of the coagulant type and the mixing condition were selected to evaluate a seawater coagulation process. The study results indicate that the coagulant type was important for seawater coagulation. The coagulant type affected the kinetics of floc formation, floc size and floc shape. Floc formed fast at use of ferric chloride, while it formed slowly at use of aluminum salts. Ferric chloride and titanium chloride produced bigger flocs than aluminum salts. Flocs formed by use of ferric chloride and titanium chloride were more spherical than Al floc. Fe floc was more insensitive to a change in the coagulant dose and the seawater pH than Al floc. Slow mixing was more important for seawater coagulation than rapid mixing. Tapered flocculation produced bigger flocs than constant flocculation. Increase in slow mixing speed from 20 rpm to 40 rpm resulted in formation of bigger flocs, which was reflected by lower settled turbidity value. On the base of the study results, it can be stated that the evaluation of floc characteristics could be a useful tool in order to optimize the seawater coagulation process. [ABSTRACT FROM AUTHOR]

Abstract: This paper discussed the coagulation characteristics of BPA with polyaluminum chloride (PACl-Al13) as coagulant, examined the impact of coagulation pH, PACl-Al13 dosage, TOC (total organic carbon) and turbidity on BPA removal, and analyzed the possible dominant mechanisms in water coagulation process. Formation and performance of flocs during coagulation processes were monitored using photometric dispersion analyzer (PDA). When the concentration of humic acid matters and turbidity was low in the solution, the experimental results showed that the removal of BPA experienced increase and subsequently decrease with the PACl-Al13 dosage increasing. The optimal PACl-Al13 dosage was found at BPA/PACl-Al13 =1:2.6(M/M) under our experiment conditions. Results show that the maximum BPA removal efficiency occurred at pH 9.0 due to the adsorption by Al13 aggregates onto BPA rather than charge neutralization mechanism by polynuclear aluminous salts in the solution. The humic acid matters and kaolin in the solution have significant effect on BPA removal with PACl-Al13 in the coagulation. The BPA removal will be weakened at high humic matters. The removal rate of BPA increased and subsequently decreased with the turbidity increasing. [Copyright &y& Elsevier]

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]