Behavior Of Flocs Research Articles

Inhibiting effects of humic acid on iron flocculation hindered As removal by electro-flocculation on air cathode iron anode

Activated carbon air cathode combined with iron anode oxidation-flocculation synergistic Arsenic (As) removal was a new groundwater purification technology with low energy consumption and high efficiency for groundwater with high As concentration. The presence of organic matter such as humic acid (HA) had ambiguous effects on formation of organic colloids in the system. The effects of the particle size distribution characteristics of these colloids on the formation characteristics of flocs and the efficiency of As purification was not clear. In this work, we used five different pore size alumina filter membranes to separate mixed phase solutions and studied the corresponding changes in iron and arsenic concentrations in the presence and absence of humic acid conditions. In the presence of HA, the arsenic concentration of < 0.05 µm particle size components was 1.01, 1.28, 3.07, 7.69, 2.85 and 1.24 times of that in the absence of HA. At the same time, the arsenic content in 0.05–0.1 µm and 0.1–0.45 µm particle size components was also higher than that in the system without HA, which revealed that the presence of HA hindered the flocculation behavior of As distribution to higher particle sizes in the early stage of the reaction. The presence of HA affected the flocculation rate of iron flocs from small to large particle size fractions and it had limited effect on the behavior of large-size flocs in adsorption of As. These results provide a theoretical basis for targeted, rapid, and low consumption synergistic removal of arsenic and organic compounds in high arsenic groundwater.

Functional behaviour of flocs explained by observed 3D structure and porosity

Clay-rich flocculated suspended sediments are an important constituent of estuarine and coastal systems globally. They are responsible for the host, movement and deposition of a variety of pollutants, contaminants and sediment itself. Accurate modelling of the movement of these sediments is crucial for a number of industries including fisheries, aquaculture, shipping and waste management. This requires an accurate and reliable measurements of the physical properties of flocs and their behaviour. Porosity is a key element in floc structures, and this research provides updated 3D quantified porosity and pore space morphological data in relation to influences on floc settling behaviour. We report the questionable relationship between floc size and settling velocity, and explore alternative influences such as floc composition, porosity and pore morphology. These outcomes suggest that a shift in focus from floc size to a combination of factors is necessitated to understand the complex movement behaviour of flocculated suspended sediments.

Numerical Analysis of Merging Flows of Floc-Forming Fluids in a T-Junction Channel Using a Non-Newtonian Viscous Model Based on a Population

The flow of a floc-forming fluid in a T-junction channel was numerically analyzed using a non-Newtonian viscous model based on the population balance equation (PBE) of the floc size. The finite element method was applied to solve the velocity and pressure fields, and the PBE of the floc size distribution was computed to obtain the effective volume fraction of flocs. The Krieger-Dougherty model was used to evaluate the viscosity of suspension of flocs using the effective volume fraction. The numerical simulation captured the characteristic aggregation-breakage behavior of flocs in the flow. In the region where flows from two entrances merge, the effective volume fraction decreases because the breakage of flocs progresses. In the downstream channel, re-aggregation of flocs occurs near the channel centerline, and the effective volume fraction increases. This aggregation-breakage behavior of flocs was confirmed by the analysis of the floc size distribution.

Study on the characteristics and mechanism of the flocculation behaviour in a novel fluidized bed flocculator

Fluidized bed flocculator is a novel and efficient flocculation reactor. It has an efficiency that directly affected by flow field parameters. However, the structural characteristics of flocs and their influence on subsequent settling performance in fluidized bed flocculators are not clear. In this study, a multi-stage velocity gradient fluidized bed flocculator (MGF) was constructed for the continuous flocculation-sedimentation of kaolinite to investigate the growth and sedimentation behaviour of flocs. Additionally, MGF was compared with traditional mechanical stirring flocculation (MSF). Results showed that MGF achieved a higher removal efficiency (97.6 ± 0.7 %) with less coagulant and flocculant than MSF. Moreover, flocs generated in the MGF yielded a faster settling performance, which can reduce the sedimentation time by 60 times. Comparative analysis of floc structural characteristics, as well as their relationship with the settling velocity, demonstrated that flocs in MGF were more compacted than those in MSFs and thus achieved higher settling velocity. The settling velocity was collaboratively dominated by the size and fractal dimension of flocs. A modified Stokes’ settling velocity equation introducing the structural characteristics of flocs was derived, and verified by actual data to accurately and quantitatively describe the settling velocity of irregular flocs. These results indicated that MGFs have a better flocculation and sedimentation performance than MSFs for solid–liquid separation, and may lay a theoretical foundation for the design of efficient fluidized bed flocculators and popularize their application in practical engineering.

Enhanced Microcystis Aeruginosa removal and novel flocculation mechanisms using a novel continuous co-coagulation flotation (CCF)

Co-coagulation flotation (CCF) is a novel flotation technology that renders more efficient algal removal compared to traditional mechanical coagulation flotation (MCF) due to a short residence time (< 30 s) and fast rising behavior of algal flocs (> 250 m·h−1). This study compared the algal removal performance using continuous CCF and MCF using water samples taken from Lake Dianchi with severe Microcystis aeruginosa blooms. Removal efficiency, dosage of coagulant/flocculant, rising velocity and structural characteristics of the resulting flocs in the two processes were systematically compared. The results show that CCF could save >50 % polyaluminum chloride (PAC) and polyacrylamide (PAM) compared with MCF when the removal efficiency was both over 95 %. The average rising velocity of flocs in CCF could reach 254.3 m·h−1, much higher than that in MCF (154.5 m·h−1). In the respective optimal coagulation conditions, the flocs formed in CCF (G = 164.8 s−1) were larger (1843 ± 128 μm) and more spherical with a higher fractal dimension (Df = 1.85 ± 0.01) than those generated in MCF (G = 34.1 s−1). The Stokes's Law was found to correctly predict the rising velocity of spherical flocs with large fractal dimensions (Df > 1.7). In contrast, the Haarhoff and Edzwald's extended equation was more suitable for calculating the rising velocity of irregular flocs with small fractal dimension. This study provides new insights into the mechanisms of the enhanced algal removal by CCF and lays foundation for developing cost-efficient algal mitigation processes.

Quantification of 3-dimensional structure and properties of flocculated natural suspended sediment

Natural sediment flocs are fragile and highly heterogeneous aggregates of biogenic and minerogenic material typically with high porosity and low density. In aquatic environments dominated by fine, cohesive or mixed sediments they can dominate suspended sediment flux. Consequently, monitoring and modelling the behaviour, transport and distribution of flocs is very important for many aquatic industries, maintenance of waterways and conservation and management of aquatic waterbodies. Mathematical models that predict the behaviour of flocs rely on the accurate assessments of the size, shape, density, porosity and fractal dimension of flocs. These inherently 3-dimensional (3D) characteristics are typically derived from 2-dimensional (2D) data, largely due to the challenges associated with sampling, capturing, imaging and quantifying these fragile aggregates. We have developed new volumetric microscopy techniques which can quantify 3D internal and external structures and characteristics of sediment flocs. Here, these techniques were applied to quantify the 3D size (volume), shape and fractal dimension of natural and artificial sediment flocs and compare them to standard 2D approaches. Our study demonstrates that 2D approaches are under-estimating shape complexity and over-estimating the size and mass settling flux of flocs by up to two orders of magnitude, and the discrepancy between 2D and 3D is most marked for natural, organic rich macroflocs. Our study has significant implications for estimations of sediment flux at local to global scales within in aquatic environments. These new data and approaches offer the potential to improve the current parameterisation of sediment transport models and to improve the accuracy of current field-monitoring techniques.

A structure\u2013function based approach to floc hierarchy and evidence for the non-fractal nature of natural sediment flocs

Natural sediment flocs are fragile, highly irregular, loosely bound aggregates comprising minerogenic and organic material. They contribute a major component of suspended sediment load and are critical for the fate and flux of sediment, carbon and pollutants in aquatic environments. Understanding their behaviour is essential to the sustainable management of waterways, fisheries and marine industries. For several decades, modelling approaches have utilised fractal mathematics and observations of two dimensional (2D) floc size distributions to infer levels of aggregation and predict their behaviour. Whilst this is a computationally simple solution, it is highly unlikely to reflect the complexity of natural sediment flocs and current models predicting fine sediment hydrodynamics are not efficient. Here, we show how new observations of fragile floc structures in three dimensions (3D) demonstrate unequivocally that natural flocs are non-fractal. We propose that floc hierarchy is based on observations of 3D structure and function rather than 2D size distribution. In contrast to fractal theory, our data indicate that flocs possess characteristics of emergent systems including non-linearity and scale-dependent feedbacks. These concepts and new data to quantify floc structures offer the opportunity to explore new emergence-based floc frameworks which better represent natural floc behaviour and could advance our predictive capacity.

Development of novel 2D and 3D correlative microscopy to characterise the composition and multiscale structure of suspended sediment aggregates

Suspended cohesive sediments form aggregates or ‘flocs’ and are often closely associated with carbon, nutrients, pathogens and pollutants, which makes understanding their composition, transport and fate highly desirable. Accurate prediction of floc behaviour requires the quantification of 3-dimensional (3D) properties (size, shape and internal structure) that span several scales (i.e. nanometre [nm] to millimetre [mm]-scale). Traditional techniques (optical cameras and electron microscopy [EM]), however, can only provide 2-dimensional (2D) simplifications of 3D floc geometries. Additionally, the existence of a resolution gap between conventional optical microscopy (COM) and transmission EM (TEM) prevents an understanding of how floc nm-scale constituents and internal structure influence mm-scale floc properties. Here, we develop a novel correlative imaging workflow combining 3D X-ray micro-computed tomography (μCT), 3D focused ion beam nanotomography (FIB-nt) and 2D scanning EM (SEM) and TEM (STEM) which allows us to stabilise, visualise and quantify the composition and multi-scale structure of sediment flocs for the first time. This new technique allowed the quantification of 3D floc geometries, the identification of individual floc components (e.g., clays, non-clay minerals and bacteria), and characterisation of particle-particle and structural associations across scales. This novel dataset demonstrates the truly complex structure of natural flocs at multiple scales. The integration of multi scale, state-of-the-art instrumentation/techniques offers the potential to generate fundamental new understanding of floc composition, structure and behaviour.

Model For Mixing Process Improvement at Water Treatment Plant by Integrating Lean Manufacturing and Parameter Design

The aim of integrating lean manufacturing and parameter design is to minimize seven non-value wastes in addition to the traditional waste in clean water production. These additional wastes to be considered are overproduction, waiting, motion, transportation, inventory, overprocessing, and defects. Information obtained from each waste is the input for the parameter design of the mixing process. The result of interaction between these seven types of waste in the lean production of clean water reveals that overprocessing waste is the most influential input in the parameter design of the Taguchi method. In the process of adding the level of concentration of poly aluminium chloride coagulant in the mixing process, a turbidity level below 5 nephelometric turbidity units is obtained, which in fact is in accordance with the health standard for clean water. An observation was also made on the behavior of flocs as the effect of Brownian motion due to the attractive force of poly aluminium chloride coagulant and colloid particle. The particle was then examined using a scanning electron microscope to find out the dimension of grain-sized flocs as the result of sedimentation in the mixing process. By properly integrating lean manufacturing and parameter design to minimize waste, a quality water meeting the set standard would be produced.

Size, orientation, and strength of Na-montmorillonite flocs flowing in a laminar shear flow

The flowing behavior of montmorillonite flocs coagulated in NaCl solution was visualized using a device called Couette chamber which was designed to analyze the strength of floc against breakup in a laminar shear flow generated in the gap between two concentric cylinders. The rotation ax of cylinders was oriented horizontally to avoid the effect of sedimentation during measurement. Observation of the morphology of flowing flocs was performed with a high-speed camera under sufficiently high salt concentration to induce rapid coagulation of montmorillonite as a function of shear rate. The recorded image of flocs demonstrated that the average flowing flocs is approximated by an ellipsoid of equivalent inertial moment with a length ratio of two principal axes being around 2. The most probable orientation of the major axis was found to be the flow direction. Assuming flocs are ellipsoids and will be disrupted by the effect of extensional component of the flow field, the cohesive strength supporting the disintegrating clusters was calculated on the basis of the simple model of floc strength proposed previously for the breakup of a floc under turbulent flow. The tendency of structural enforcement by the rearrangement of internal clusters was recorded with an increase in size of floc irrespective of ionic strength. In addition, the enforcement of cohesive strength by the effect of dehydration of proximately adsorbed sodium ions at extremely high ionic strength was confirmed.

Experimental validation of a cohesive suspended sediment transport model for two Mexican rivers

BackgroundThe south of Mexico is the least developed part of the country but its basins generate more than 60% of the country’s available water. Though disturbances to the rivers caused by development are still low, there is concern about the environmental health of the rivers. The calculation of the sediment load with a focus in fine fraction, where nutrients are found, is a priority. However, models for suspended sediment transport in large rivers are difficult to formulate because they carry a large amount of cohesive sediments, those cohesive sediments form aggregates or flocs with primary particles that are less than 65 μm. The hydrodynamic behavior of flocs depends on their size, density and shape, which differs from that of non-cohesive sediments as theirs depends on their interaction with the water column. A classical model to calculate suspended sediment concentration profiles for steady flow conditions is the Rouse equation, which has been extensively validated for non-cohesive suspended sediment. Some authors have demonstrated that when applied in some large rivers in conjunction with non-cohesive settling velocity models it does not perform very well. The difficulty comes from the fact that most of the suspended sediment charge in large rivers is constituted by cohesive sediments.ResultsSuspended sediments from Mexico’s two largest rivers Usumacinta and Grijalva, with a mean flow rate near river mouth of 2020 m3/s and 1150 m3/s respectively, were analyzed in a rotating annular flume (RAF). The shear velocity obtained in the field by ADCP was reproduced in the annular flume, the size and shape of flocs were obtained by means of PTV. Settling velocity was also obtained to calibrate a settling velocity model appropriate for cohesive sediments.ConclusionsThe settling velocity model developed for cohesive sediments in conjunction with the Rouse equation allowed the reproduction of suspended sediment concentration profiles for the rivers Usumacinta and Grijalva. The estimated concentration profiles were compared and validated with the measured concentration profiles in the field. Thus, the model obtained through this research can be used to estimate nutrient delivery to the sea from the largest rivers in Mexico.

Studies on kinetics and settling behavior of flocs formed using a sustainable coagulant in sewage water treatment

Studies on kinetics and settling behavior of flocs formed using a sustainable coagulant in sewage water treatment

Floc behavior and removal mechanisms of cross-linked Durio zibethinus seed starch as a natural flocculant for landfill leachate coagulation-flocculation treatment

This study investigated the behavior and mechanisms of cross-linked Durio zibethinus seed starch (CDSS) flocculants for landfill leachate treatment. A physical-chemical treatment method of coagulation-flocculation process and starch modification were implemented in treating stabilized leachate from Matang Landfill, Perak, Malaysia. In practical, the removal performance of color, COD, suspended solid and turbidity for CDSS flocculants were evaluated by combining with primary coagulant of polyaluminium chloride (PAC). In this study, the application of crosslinking modification for Durio zibethinus seed waste starch flocculants showed good improvement. The impurities removal for colour, COD, suspended solid and turbidity were increased by the addition of CDSS flocculants. Furthermore, the average size of the floc was also increased from 60.24 µm to 89.5 µm. Despite, the addition of CDSS flocculants produced a reduction of PAC coagulant from 2700 mg/L to 2200 mg/L, with 500 mg/L reduction on the PAC dosage dependency. Therefore, these results affirmed the potentials of crosslinked modification for Durio zibethinus seed waste starch flocculants in landfill leachate treatment.

The influence of protruding filamentous bacteria on floc stability and solid-liquid separation in the activated sludge process

Filamentous bacteria can impact on the physical properties of flocs in the activated sludge process assisting solid-liquid separation or inducing problems when bacteria are overabundant. While filamentous bacteria within the flocs are understood to increase floc tensile strength, the relationship between protruding external filaments, dewatering characteristics and floc stability is unclear. Here, a quantitative methodology was applied to determine the abundance of filamentous bacteria in activated sludge samples from four wastewater treatment plants. An automated image analysis procedure was applied to identify filaments and flocs and calculate the length of the protruding filamentous bacteria (PFB) relative to the floc size. The correlation between PFB and floc behavior was then assessed. Increased filament abundance was found to increase interphase drag on the settling flocs, as quantified by the hindered settling function. Additionally, increased filament abundance was correlated with a lower gel point concentration leading to poorer sludge compactability. The floc strength factor, defined as the relative change in floc size upon shearing, correlated positively with filament abundance. This influence of external protruding filamentous bacteria on floc stability is consistent with the filamentous backbone theory, where filamentous bacteria within flocs increase floc resistance to shear-induced breakup. A qualitative correlation was also observed between protruding and internal filamentous structure. This study confirms that filamentous bacteria are necessary to enhance floc stability but if excessively abundant will adversely affect solid-liquid separation. The tools developed here will allow quantitative analysis of filament abundance, which is an improvement on current qualitative methods and the improved method could be used to assist and optimize the operation of waste water treatment plants.

Multi-scale features including water content of polymer induced kaolinite floc structures

Despite their many uses, fine clay particles, such as kaolinite, present a problem in the management of tailings in various mineral industries such as the oil sands and phosphate processing industries. The effective flocculation, sedimentation and consolidation of these fine particles are major challenges. The structure of the flocs and the water entrapped within the flocs determine floc behavior and settling characteristics. The quantification of water entrapped within the kaolinite flocs has not been reported previously.In this research, a new technique was developed for water content and size analysis of sedimented kaolinite flocs using High Resolution X-ray Microtomography (HRXMT). The results suggest a normal distribution of water content for these flocs, with mean water content of 53.9% by volume and a standard deviation of 11.8%. About 98% of the flocs were found to have water content in the range 30–80%. The size analysis revealed that about 90% of the flocs are less than 1.5mm in size. The water content was found to decrease with an increase in size of the floc. The floc shape analysis was done for selected flocs. The flocs were found to be fairly irregular, with sphericity values around 0.1.In addition to macroscopic analysis of individual flocs, flocs were also analyzed for their microstructure by cryo-SEM. Visualization of floc microstructure and polymer chains revealed the stabilization of kaolinite microflocs in the web formed by polymer chains. The structure of the polymer chains as well as the interaction between microflocs and polymer chains is a key to understanding floc growth and stability.

Effective energy controls on flocculation under various wave-current regimes

Transport of sediments is a critical process in the coastal zone because of its relation with coastal erosion, productivity and pollution. Of particular interest are the dynamics of suspended cohesive sediments, known as flocs, which can aggregate and break-up during the flocculation process. This changes their size, density, settling velocity and overall transport. Even though turbulence is widely accepted to be an important control on floc aggregation and break-up, specific and detailed floc behaviour is still not fully understood. The present study seeks to help in the understanding of the intra-tidal turbulence-induced flocculation under different current-wave regimes. Observations of floc size and currents at high sample rates are used to investigate the changes throughout a fortnightly cycle. The occurrence of waves at different stages during the sampling period enabled determination of three regimes of currents dominant, combined waves and currents, and wave dominant. The first two regimes showed quarter-diurnal floc size variability with aggregation during low turbulence (slack waters) and higher floc aggregation magnitude on low water slack. Break-up occurred with high turbulence (flood and ebb) with higher magnitude after ebb. During the “currents-waves” regime, waves were tidally modulated and led to enhanced aggregation and break-up, with larger floc size range than during the “current dominant” regime. Wave tidal modulation and quarter-diurnal variability of floc size were lost when waves were dominant. Flocs sizes exhibited a low range related to wave height. Inverse relationships between turbulent properties and median floc size were found for the three regimes, with higher scatter of data for the Kolmogorov microscale and shear rate due to different floc behaviour during flood and ebb phases. Effective kinetic energy obtained from the combined effect of both currents and waves seems to have a better relationship with floc size, which suggests its use as a floc size predictor instead of shear stress.

Effect of dye molecules and electrode material on the settling behavior of flocs in an electrocoagulation induced settling tank reactor (EISTR)

A simple electrocoagulation induced settling tank reactor (EISTR) was fabricated to study the dye removal and sedimentation kinetics of Amido Black 10B (AB), Methyl Violet (MV), Eosin Yellow (EY), Malachite Green (MG), Methylene Blue (MB), Rhodamine 6G (R6G), their binary, tertiary mixtures and actual textile effluent. Optimum conditions such as current density, electrolysis time, initial pH and NaCl concentration to achieve high color removal efficiency (CRE) and sludge settling velocity were evaluated for the removal of 100mg/L AB dye. The CRE and chemical oxygen demand (COD) reduction, initial sludge settling velocity, final sludge height and turbidity reduction were measured. These experiments indicate that 81–99% CRE, 54–68% COD reduction and 73–88% turbidity reduction can be achieved for the synthetic as well as textile dye wastewater systems. Around 3.8Ah of charge loading per gram of dye was found to be sufficient for high CRE and satisfactory sedimentation kinetics for most of the dyes. The energy requirement was found to be 24±3Whg−1 of dye molecule. Fe electrodes perform better when compared to Al electrode in similar operating conditions. XRD and SEM studies indicate that relatively large porous low density aluminum hydroxide flocs formed under the induced sedimentation conditions do not settle effectively. Relatively smaller and denser iron hydroxide flocs generated using Fe electrode leads to relatively better performance.

Flocculation Efficiency of Chitosan for Papermaking Applications

There is a large interest in bio-polymers as environment-friendly alternatives to synthetic additives in papermaking. In this work, the behavior of three chitosans with different molecular weights and cationic charges were investigated as flocculation additives in papermaking on two systems: calcium carbonate (GCC) and pulp/GCC suspension. Comparison was made with two traditional cationic polymers used in wet end chemistry (poly-diallyldimethyl-ammonium chloride (PDADMAC) and poly-ethylene imine (PEI)). Flocculation efficiency was evaluated by flocculation parameters (mean floc size and number of counts) and by floc behavior under shear conditions, using a focused beam reflectance measurement (FBRM) technique. Results indicated different behaviors between the three chitosans when they were used for the flocculation of GCC and pulp/GCC suspensions. Chitosans were found to be more efficient over PDADMAC and PEI for flocculating small particles of the GCC suspension, but less efficient for increasing floc sizes, regardless of their MW or CCD. Flocculation parameters for pulp/GCC suspensions suggested the flocculation behavior of chitosan was close to that of PEI, but chitosan had higher efficiency and affinity towards cellulose fibers.

Floc architecture of bioflocculation sediment by ESEM and CLSM

Sediment flocculation is a critical component for the understanding of cohesive sediment dynamics. Traditionally, the referred study has largely been devoted to forming mechanism, influencing factors and physicochemical sediment conditions of all kinds of organic-flocculation and inorganic-flocculation. However, during the last decade, the bioflocculation of sediment by biological activity has been given increasing attention. But most studies have focused on the interrelations between biological and sedimentological variables. With the assistance of a newly developed field kit and correlative microscopy (which includes environmental scanning electron microscopy and confocal laser scanning microscopy), this article begins to bridge the resolution gap between sediment particles and biological activities as well as its metabolic products biofilm, in order to better understand the role of polymeric material biofilm in floc ultrastructure and outward floc behavior of bioflocculation sediment. Results have demonstrated that bioflocculation sediment was observed to be composed of complex networks of biofilm and appeared to be of complicated physical floc structures. The biofilm was found to embed particles and permeate the void space, representing the dominant physical bridging mechanism of the flocs and contributed to the extensive surface area, architecture characteristics, and mechanical properties of bioflocculation sediment.

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

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