Floc Particles Research Articles

Elucidating the formation pattern and mechanism of biofouling layer regulated by pre-deposition of powdered activated carbon in gravity-driven membrane systems

Powdered activated carbon (PAC) pre-deposition promotes pollutant removal in gravity driven membrane (GDM) but diversely affects flux. This study evaluated the effects of one-time deposition (GDM 1), batch deposition (GDM 2) and no deposition (GDM 3) of PAC on the biofouling layer formation mechanism and the GDM performance. The results showed that PAC particles effectively promoted the removal of dissolved organic carbon, ammonia nitrogen and fluorescent pollutants, while also significantly reducing the concentration of extracellular polymeric substances in the biofouling layer. The stable flux in GDM 1–3 were 6.58, 7.88 and 8.61 LMH respectively. One-time deposition of PAC compromised the structure of the biofouling layer and prevented its reverse relaxation. Pollutant floc particles continuously accumulated in the space between the PAC particles, forming a dense layer with low porosity and roughness. In GDM 2, the limited amount of PAC deposited each time helped to partially maintain the intact structure of the biofouling layer, which alleviated the decline in flux. The reverse relaxation of the intact biofouling layer in GDM 3 resulted in increased porosity, which positively influenced the flux. Additionally, the abundance of Bdelloidea significantly decreased in GDM 1 and GDM 2, and more predators with low agility showed limited modification on the biofouling layer, resulting in a dense biofouling layer. In conclusion, batch deposition of PAC is more recommended as the continuously renewed PAC promote pollutant removal, and compared with one-time deposition of PAC, the reduction in biofouling layer disturbance mitigates the flux decline.

Study on the morphological characteristics of coal particle flocs under fractal theory

Based on fractal theory, the geometric size, surface morphology, and spatial structure of flocs in the hydrophobic flocculation process of coal particles were examined via particle size distribution detection, image analysis technology, and numerical simulation. The floc size distribution curve was classified and discussed via the dual-domain fractal rule, and the variation law of the composition and distribution of the coarse- and fine-grained coal particle flocs with the flocculation process was clarified. The various levels and characteristics of the floc growth geometry were explained by the analysis of the fractal dimension of the individual floc surface and the multiple spectra of the floc groups in the metallographic microscopy image. The hydrophobic flocculation process of coal particles was simulated via the diffusion-limited cluster aggregation model. The gyration fractal dimension was used to examine floc fragmentation and reconstruction and clarify the growth law of the floc spatial structure during the hydrophobic flocculation process.

Research on image segmentation processing of coal particle flocs combined with clarity detection

ABSTRACT In the image analysis of the hydrophobic flocculation process of coal particles, the recognition accuracy of floc characteristic parameters is affected by bubbles, floc superposition, and floc morphology. An image processing method was studied and designed based on the PyCharm Community platform for clarity recognition and floc segmentation of coal particle floc characteristics. Firstly, the critical value of image clarity was determined to be 1.31 by using the Laplace convolution accounting method after the average gray level correction, and the fuzzy flocs whose clarity was less than the critical value were eliminated. Then, by comparing the segmentation effect of the threshold, edge, and region segmentation algorithm on the flocs, the histogram bimodal method was determined to be the best image processing segmentation method for fine coal floc collection. The fractal theory was used to verify the effect of image processing. The results showed that the surface fractal dimension of the floc image after deblurring and segmentation was maintained near 2.05, indicating that the processed image can obtain more stable and reliable floc characteristic parameters.

Solidification of concentrated zero-valent iron slurry: A microrheology study using diffusing wave spectroscopy

Concentrated zero-valent iron (ZVI) slurries (CIS) are commonly encountered during the water treatment using ZVI, in the processes such as delivery, settling, and pumping of the ZVI slurry; about the CIS, knowledge about their rheology is critical to the operation of these processes, but little is known about this aspect so far. Herein, microrheology of the CIS of four different ZVI is studied using diffuse wave spectroscopy (DWS). Results show that the CIS of two iron nanoparticles solidify immediately after their separation from water (<3 h), with a fast growth of macroscopic viscosity and a rapid weakening of the fluidity; the CIS of the microscale ZVI (mZVI) is nearly pure viscous or liquid-like and solidifies slower than the nanoparticle CIS; CIS of the floc modified ZVI (mZVI(floc)) is viscoelastic and remains stable in rheology over an extended period up to four days. Such differences in CIS rheology are explained by the coarse surface of the nanoparticle aggregates, the smooth surface of mZVI particles, the intertwined floc coating of mZVI(floc) particles, and the corresponding disparity in surface friction between the particles or aggregates. The solidification of CIS is explained by the binding effect of the oxidation products of the ZVI-water reaction. This study provides information about CIS rheology and offers guidance for process operations in the water treatment using ZVI. This study also shows that the DWS technique is informative in characterizing CIS and the method may be equally applicable for studying other concentrated particle slurries in water treatment.

Settling velocity and effective density analysis for aquaculture floc particles: An approach through bivariate parametric copula

The study of flocs' characteristics in aquaculture tanks remains challenging due to their complex composition. Nevertheless, the application of experimental methods, such as particle tracking velocimetry (PTV), has made it possible to measure particle diameters and settling velocities. With the experimental data, bivariate distribution functions through copula modelling were employed to provide a more accurate estimation of the effective density of flocs through the empirical model proposed by Lau and Krishnappan. It was observed that the primary particle density constituting the flocs varied between 1051 kg/m³ and 1426 kg/m³. Moreover, when considering a variable primary particle density, effective floc density values ranging from 980 kg/m³ to 1500 kg/m³ were obtained for floc diameters ranging from 0.068 mm to 1.9 mm, respectively. This variation confirms that the b and c parameters of the Lau-Krishnappan model change for each floc diameter range following the quantiles associated with the conditional probability of diameter and settling velocity. Thus, employing copula approximation, a more accurate fit of the Lau-Krishnappan model was achieved, considering a wide range of particle diameters at the tails. This approach offers better estimates of floc effective density and settling velocity, essential for enhancing the selection and design of aquaculture tanks and settlers to ensure efficient solids removal.

Evaluation an anionic polyacrylamide flocculant with microblock structure in the hematite wastewater treatment: Characterization and flocculation performance

In this study, a template polymer with anionic microblock structure was successfully synthesized through ultrasonic initiated template copolymerization (USTP) by using sodium allylsulfonate (SAS) and acrylamide (AM) as monomers, poly diallyl dimethyl ammonium chloride (polyDADMAC) as template, and 2,2′-azobis [2-(2-imidazolin-2-yl) propane] dihydrochloride (VA-044) as initiator. The anionic polyacrylamide (APAM-T) flocculant was characterized by Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance spectroscopy (1H NMR), and scanning electron microscopy (SEM). Furthermore, the X-ray photoelectron spectroscopy (XPS) was conducted to measure the elemental composition. The results of XPS and 1H NMR spectroscopy analysis indicated the existence of anionic microblock structure in APAM-T. Besides, the copolymerization was revealed to follow the self-assembly mechanism by analyzing the association constant (KM). The flocculation performance was evaluated by turbidity and zeta potential in the flocculation tests. The results indicated that the APAM-T with microblock structure enhanced the charge neutralization and bridging adsorption capacity, thus improving the flocculation performance. In the floc particle size distribution and fragmentation and reflocculation experiments, the floc corresponding to APAM-T had the strongest regeneration ability after fragmentation, which further confirmed the criticality of the microblock structure in enhancing the flocculation performance. Compared with existing studies, this study not only demonstrated a novel synthesis method, but also found that the microblock structure could significantly improve its treatment efficiency and effectiveness, providing a new theoretical basis and practical application path for wastewater treatment technology.

Microbially mediated rock fine fracture mineralization sealing: Evolution of flow channels and the resulting transmissivity reduction

The sealing of fine aperture fractures in geological repositories is an important consideration for long-term sealing integrity. Common grouting materials have some disadvantages, such as low sealing efficiency, environmental pollution, etc. Microbially induced calcium carbonate precipitation (MICP) has been proposed as a potential solution for sealing fine fractures. In this paper, the microbially mediated fine fracture mineralization sealing process was investigated by using a designed visual test device. The flow channel evolution and fracture transmissivity reduction during the sealing process were systematically monitored and analysed. Based on the experimental results, a sealing pattern of microbially mediated rock fracture mineralization was proposed. In addition, the influence of biomineralized floc particles formed by different bacterial concentrations on the critical sealing threshold of fracture was discussed. The results show that the sealing pattern can be divided into four stages: (a) flow channel formation; (b) preferred channel blocking; (c) finer channel blocking; (d) filtration zone formation. The four sealing stages correspond to different fracture transmissivity reduction trends, and the majority of transmissivity reduction occurs in stage III. However, the transmissivity decreases rapidly only after the preferred channels are blocked, which indicates that the critical threshold of sealing fracture is reached. The critical sealing threshold is mainly attributed to two factors: biomineralized floc particle size and fracture aperture. Larger floc particles and finer aperture are more likely to reach the critical sealing threshold, improving the sealing efficiency of fractures. It is crucial to further study the interaction between the biomineralized floc particle sizes and the fracture aperture at the critical sealing threshold to optimize the application of MICP-grouting in rock fine fractures.

Effects of cations on biofilms in gravity-driven membrane system: Filtration performance and mechanism investigation

The gravity-driven membrane (GDM) system is desirable for energy-efficient water treatment. However, little is known about the influence of cations on biofilm properties and GDM performance. In this study, typical cations (Ca2+ and Na+) were used to reveal the combined fouling behavior and mechanisms. Results showed that Ca2+ improved the stable flux and pollutant removal efficiency, while Na+ adversely affected the flux. Compared with GDM control, the concentration of pollutants was lower in Ca-GDM, as indicated by the low biomass, proteins, and polysaccharides. A heterogeneous and loose biofilm was observed in the Ca-GDM system, with roughness and porosity increasing by 43.06 % and 32.60 %, respectively. However, Na+ induced a homogeneous and dense biofilm, with porosity and roughness respectively reduced by 17.48 % and 22.04 %. The richness of bacterial communities increased in Ca-GDM systems, while it decreased in Na-GDM systems. High adenosine triphosphate (ATP) concentration in Ca-GDM system was consistent with the abundant bacteria and their high biological activity, which was helpful for the efficient removal of pollutants. The abundance of Apicomplexa, Platyhelminthes, Annelida and Nematoda increased after adding Ca2+, which was related to the formation of loose biofilms. Computational simulations indicated that the free volumes of the biofilms in Ca-GDM and Na-GDM were 13.7 and 13.2 nm3, respectively. The addition of cations changed intermolecular forces, Ca2+ induced bridging effects led to large and loose floc particles, while the significant dehydration of hydrated molecules in the Na-GDM caused obvious aggregation. Overall, microbiological characteristics and contaminant molecular interactions were the main reasons for differences in GDM systems.

Influences of magnesium ions in water on gelatinization characteristics of starch and its flocculation behaviors on particles

It is inevitable for the occurrence or built-ups of disturbing cations, especially Ca&lt;sup&gt;2+&lt;/sup&gt; or Mg&lt;sup&gt;2+&lt;/sup&gt; ions, in process water during the flotation of iron oxides by using starch as flocculants. In addition to alkali concentrations and temperature, water quality could have an essential role in changing the physicochemical properties of the starch solution and consequently disturbing its flocculation performance on particles. This study aims to identify the effects of magnesium ions on the gelatinization characteristics of starch and its flocculation properties on particles through a series of tests, such as flotation tests, settling tests, size analyses, zeta potentials, powder contact angle, Fourier Transform Infra-Red (FTIR) and X-ray Photoelectron Spectroscopy (XPS) measurement. All results show that magnesium ions at ≤ 4 mmol/L have a positive role due to enlarging the sizes of the particle flocs and accelerating their settling rates. The occurrence of Mg&lt;sup&gt;2+&lt;/sup&gt; ions at higher concentrations during starch gelatinization only obtains a starch sol-gel with entangled configurations and preoccupied active sites, resulting in the slower settling rate of the particle flocs and less hydrophilicity on mineral surfaces. It could be attributed to the cross-link interactions of magnesium-based precipitates with the acidic groups, especially carboxyl groups on the starch remnants. The suitable acid/base interactions between Mg(OH)&lt;sub&gt;2&lt;/sub&gt;/MgCO&lt;sub&gt;3&lt;/sub&gt; compounds with these groups in the starch suspension could be beneficial for enhancing the flocculation of hematite as they could build bridges among the pieces and enlarge their sizes as a “load carrier” for aggregation with minerals. However, too much cross-linking could re-entangle the remnants, block their adsorption sites on mineral surfaces, and eventually, weaken the flocculation capacity of starch.

Fractal simulation of hydrophobic flocculation fragmentation and reconstruction of coal particles

Based on a diffusion limited cluster aggregation model, this study analyzed the fragmentation and reconstruction of flocs during the hydrophobic flocculation process of coal particles. The flocs gyration radius and gyration fractal dimension calculated by the program characterize the geometric size and spatial structure of the coal particle flocs, respectively. With advancing step length, the distributions of gyration radius first increased and then decreased and finally basically stabilized at approximately 1.70 ± 0.2, indicating that the reconstruction of flocs is reversible in geometric size. However, the gyration fractal dimensions first decreased and then increased and finally stabilized at 1.49, 1.63, 1.60 and 1.51 with increasing step length, showing variability. This indicated that the spatial structure of the flocs is irreversible. The above conclusions of the simulation analysis were confirmed by the floc particle size distribution curves and the image analysis of surface fractal dimensions. The study clarifies the morphological changes and fragmentation-reconstruction changes of flocs and improves the hydrophobic flocculation mechanism of coal particles.

Beyond filterability: Understanding the complexities of sludge dewatering through typical coagulation and advanced oxidation

Coagulation and advanced oxidation process (AOP) are the two most significant conditioning methods in sludge dewatering. However, previous studies mainly focus on their differences and overlook their similarities in dewatering mechanisms. In this study, PAC and Fe3+ were selected as typical coagulants, and Fenton and Fenton-like reactions as typical AOP. By regulating the reagent dosage to achieve basically the CST-based filterability (CST = 22.9 ± 1.5 s), AOP had superior dewatering efficiency (59.54–63.04 wt%) compared to coagulation (68.84–69.16 wt%). Obviously, the filterability of sludge could not accurately reflect its dewatering performance. The mechanism revealed that AOP had both “extracellular oxidation” and “intracellular oxidation”, whereas coagulation mainly affected the properties of extracellular organic matter. Both processes improved the sludge's relative hydrophobicity and reduced its interfacial free energy. AOP was superior to coagulation in improving sludge fluidity, hydrophobicity, permeability, cell disintegration and reducing bound water content. While coagulation had a better effect on electric neutralization, floc particle size growth and colloidal structure strength. Moreover, this study emphasized the significance of considering the vector-based relationship between sludge dewatering performance and various influencing factors for analyzing the dewatering mechanism. These findings are expected to deepen our understanding of the similarities and disparities in dewatering efficacy and the related mechanisms between the these two pretreatments.

Effect of ionic surfactants on the settling behavior of silt

Ionic surfactants are easily adsorbed by silt and clay particles, thus affecting the flocculation characteristics and settling behavior. The settling velocity, typical size, Zeta potential and surface tension of silt flocs were measured in the presence of two different kinds of ionic surfactants. The results indicated that the cetyltrimethylammonium bromide (CTAB, a typical cationic surfactant) can dramatically accelerate the settling of slit particles, while the linear alkylbenzene sulfonate (LAS, a typical anionic surfactant) slightly retarded silt sedimentation to some extent. In still water, the representative settling velocity dramatically increased from 0.36 cm s−1 to 0.43 cm s−1 with the increase of CTAB concentration, which increased by more than 20%. Oppositely, the sedimentation rate decreased from 0.36 cm s−1 to 0.33 cm s−1 with the increase of LAS concentration. In flowing water, as the flow rate increased from 0 to 20 cm s−1 and the ionic surfactant concentration increased from 0 to 10 mg L−1, the sedimentation rate decreased to 57% and 89% in the presence of CTAB and LAS respectively, which was due to an enhanced dispersion of silt particles and a breaking of flocs. The SEM image test shows that the floc particle size increased 1.5 times of the primary particle size under the high CTAB concentration. The flocculation induced by ionic surfactants greatly influences the sediment size as well as the law of settling velocity. The intrinsic influence mechanism was also discussed based on the variations of silt particle properties. This systematic study can be used for further development of flocculation models and particle size distribution of fine-grained soil.

Response Surface Optimization and Floc Structure Analysis of Magnetic Flocculation Technology for Anaerobic Digestion Reject Water

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.

Effects of salinity on the performance of bioflocs with activated sludge as inoculum

This study evaluated the feasibility of domesticating the bioflocs with activated sludge as inoculum at high salinity. By using the gradually increase salinity from 0.2 to 4.0%, the study evaluated the effectiveness of bioflocs in sustaining the water quality of aquaculture, the biofloc morphology characteristics and microbial community structure of bioflocs in order to discover the influence of salinity. From the perspective of sustaining the water quality of bioflocs, the COD removal efficiency dropped sharply from 63.9% to 3.7%, the NO3−-N was maintained below 0.5 mg/L but the NH4+-N exceeded the safety threshold of aquaculture at the salinity of 2.5–4.0%. From the pespective of flocculation of flocs, the biofloc volume index and content were maintained at about 30 ml/g and 7 g/L, while the floc particle size (45–200 um) tended to increase cumulatively, showing good agglomeration, sedimentation and stability. From the pespective of floc microbial community structure, Arenibacter, Thauera, Paracoccus and Denitromonas became the dominant genera with relative abundances of 4.8–7.5%, 4.9–17.1%, 3.0–4.7% and 5.3–14.1% at 3.0–4.0% salinity, respectively, however, the relative abundance of Candidatus Competibacter rapidly decreased from 15.0% to 2.5% with the increasing salinity from 1.0% to 4.0%. Furthermore, Redundancy analysis (RDA) indicated that salinity was a key environmental factor affecting floc community, and Functional Annotation of Prokaryotic Taxa (FAPROTAX) confirmed the promoted flocs denitrification as well as inhibited nitrification and hydrocarbon cycling in higher salinity to some extent. This study demonstrated the feasibility of using freshwater activated sludge as a base nucleus for biofloc formation for salinity up to 2% – 2.5%, which provided a useful reference for improving the taste and nutritional value of fish cultured by Biofloc Technology (BFT).

Continuous floc image analyser (C-FIA) for tracking floc particle dynamics during coagulation–flocculation–settling processes

A continuous floc image analyser (C-FIA) was developed for tracking the dynamics of floc particle formation, growth and settling during conventional water treatment. This is based on a new RGB signal for flocculation index determination.

Reducing disinfection byproduct precursors through coagulation enhancement as particle weight and size control using potassium permanganate.

The widespread use of chlorine pre-oxidation in water purification has been limited in several countries owing to the production of carcinogenic byproducts when combined with naturally occurring organic matter. This study investigates the efficient use of potassium permanganate (KMnO4) pretreatment and coagulation enhancement as particle size and molecular weight distribution controlling parameters. KMnO4 pretreatment significantly reduced the apparent molecular weight of humic acid due to KMnO4 reduction and the continuous generation of manganese dioxide (MnO2) formed in situ under neutral and alkaline conditions. The MnO2 formed in situ had adsorption characteristics that enabled it to form large and stable flocs with the hydrolysis products of aluminum sulfate. However, under acidic conditions, KMnO4 pretreatment exhibited strong oxidation characteristics due to Mn(VII) reduction to Mn(II), and the mean particle floc size was the same as without KMnO4 pretreatment. Overall, KMnO4 pretreatment is a useful alternative strategy for traditional pre-oxidation using chlorine and a good coagulant enhancement agent in neutral and basic media.

A novel vortex flocculation reactor for efficient water treatment: Kinetic modeling and experimental verification

We designed a novel vortex flocculation reactor with column-cone-column structure by adding vortex generators to form the micro-vortices to improve the flocculation efficiency. The vortex generators, actually wedge-shaped baffles, act as turbulence components to generate large flow resistance, thus reducing the size of the vortex to approach that of the floc. The inverted cone-cone-inverted cone structure in small-vortex flow flocculation zone prompts the fluid to form boundary layer dissociation phenomenon, thereby enhancing the relative motion of floc particles. The numerical simulation results of flow field structure indicated that the fluid presented a multiphase flow of “swirl flow-vortex flow-plug flow”; hence the fluid characteristic changed step by step. Moreover, the multistage velocity gradient of the fluid in different flow layers enhanced the probability of floc particles collision, thus strengthening the flocculation. Then the lab-scale vortex flocculation reactor was manufactured to conduct flocculation tests. The results revealed that the vortex flocculation reactor took the reaction time of only 10 s to achieve a superior chemical oxygen demand removal rate of 93.7%. The vortex flocculation reactor, based on the multiphase flow and multistage velocity gradient reinforcement flocculation strategy, can offer an effective way to improve the flocculation efficiency.

Morphological characteristics of starch sol-gel and its influences on flocculation of fine particles

Pasting starch into sol-gels by alkali is one of the most common methods for its use as flocculants in flotation. Any variation in its gelatinization process, however, could lead to different starch solutions with certain charges, sizes, and configurations of the segments, influencing their flocculating properties onto mineral surfaces. The purpose of this study is to identify the morphological characteristics of the starch sol–gel digested with different concentrations of alkali and their flocculation mechanisms on hematite through a series of tests, such as viscosity, turbidity, adsorption, pasting titration, settling, zeta potential All results pointed out that the gel-sol transition of starch was possibly governed by alkali concentrations or starch to alkali weight ratios. As the sodium hydroxide concentration increases, an increase in viscosity but a decrease in turbidity of the starch solution was obtained, inducing an upwards trend in the settling rates of the particle flocs. A suitable sol–gel by 1.25% sodium hydroxide (a 1.6 wt ratio of starch to NaOH) at turbidity of near 2 NTU and a viscosity of 258 mL/g harvested a maximum adsorption density of 11.5 mg/g hematite at a settling rate of 7.1 × 10−5 m/s. A certain amount of acidic contents on the segment chains resulting from alkali gelatinization play an important role in determining the morphological characteristics of the starch sol–gel at different pH values affecting adsorption density on iron oxides. It is worthy to be noted that the starch remnants at very small sizes produced by high concentrations of NaOH by over 1.50% or at a starch to alkali weight ratio of less than 1.3 were hard to achieve high efficiency on flocculating the particles but occasionally dispersing them instead. It could attribute to the less possibility of “bridging interactions” between the particles and these small segments with negative charges, which may limit the size and compactness of the particle flocs, and, consequently, reduce their settling rates.

Kinetics of flocculated illite suspensions affected by ionic strength, pH, and hydrodynamic shearing

An experimental investigation is presented of the kinetics of particle size distributions (PSDs) of flocculated illite suspensions subject to varying ionic strength, pH, and hydrodynamic shearing. A total of 21 PSD measurements were conducted by analyzing the high-resolution optical images of particle flocs extracted from illite suspensions with a concentration of 0.4 g/L prepared at four ionic strengths (i.e., 0, 0.09, 0.17, 0.60 M NaCl solution), three pHs (i.e., 8.61, 4.51, 2.25), and three vibrational shaking speeds (i.e., 150, 225, 300 oscillation/min) at four shaking durations (i.e., 10, 30, 60, 1440 min). Experimental PSD histograms were constructed using a new bin size index (BSI) data binning method involving the conversion of original multimodal lognormal distributions into regular Gaussian distributions, followed by the probability density function (PDF)-based deconvolution to extract the number, mean, standard deviation, and fraction of different characteristic particle size groups: primary particles, flocculi, microflocs, and macroflocs. Results show that flocculation is enhanced by the high ionic strength and low pH, and more microflocs and macroflocs form at higher ionic strengths (i.e., 0.60 M) and more acidic pHs (i.e., 2.25, 4.51). Moreover, higher hydrodynamic shearing causes more breakdown of weaker flocs, but promotes stronger and smaller ones. The new BSI data binning method can better reveal the smaller-sized particle groups due to the logarithmic conversion. The PSD kinetics of illite suspensions is chiefly controlled by the face-to-face and edge-to-face interparticle interactions, caused by the suppression of the electrical double layer and generation of positive edge charges, respectively. Finally, the implications and significance of PSD kinetics of clay suspensions for engineering practices and environmental processes are discussed.

Physical Clogging Characteristics and Water Quality Variations by Injecting Secondary Effluent into Porous Media: A Laboratory Column Study

Artificial recharge engineering has been widely used to solve the water resource crisis. However, there are still some safety hazards regarding reclaimed water quality. Here, chlorinated secondary effluent (SE) was injected into saturated porous media composed of high–purity quartz sands. The column experiment was conducted and modeled through a developed numerical model to predict the evolution of physical clogging. Some representative inorganic and organic indicators were measured both at different times and in different column sections. The study showed that the relative hydraulic conductivity (K/K0) decreased significantly by approximately 63.5% in 40 h. Especially for the first 3 cm of the column, the clogging was the most serious, with a decrease of approximately 85.8%. The porous media has a certain degree of filtration effect on turbidity, TOC, protein (Pr) and polysaccharide (PS) but has slight removal for other water quality indicators. Pr is the main component of the intercepted TOC, and its content is higher than that of Ps. Moreover, the inorganic and organic parameter variations along the column further verified that the organic floc particles were mainly retained in the first 3 cm. The 3D excitation/emission matrix (3DEEM) fluorescence spectra illustrated that the humic acids and fulvic acids were easy to release and that their injection may be harmful to groundwater quality. The study will lay a theoretical foundation and provide a guiding scheme for optimizing China’s reclaimed water reuse technology, ensuring the safety of reclaimed water quality.