Floc Fractal Dimension Research Articles

Unveiling the role of cake layer in coagulation-ultrafiltration on membrane fouling and emerging application as dynamic membrane before ultrafiltration

Cake layer is considered to play a crucial role in membrane fouling during the coagulation-ultrafiltration process. However, the contribution of the cake layer on membrane fouling and probable natural organic matter (NOM) removal in this process is unclear, leading to a limited understanding of cake layer and potential secondary utilization. Here, ultrafiltration (UF) membrane fouling contribution, NOM removal, and dynamic membrane application of the cake layer were investigated. Results showed reversible fouling was dominated by cake layer, whereas irreversible fouling was determined by both cake layer and residual NOM in coagulation effluent. Compared with direct UF, the cake layer improved approximately by 15 % of HA removal with molecular weight (MW) of 2000–4000 Da. By optimizing membrane material, HA removal and membrane fouling alleviation were synchronously achieved by cake layer deposition-UF. According to mechanisms analysis, HA removal was attributed to the adsorption or interception of HA with larger MW by the cake layer. Zeta potential and fractal dimension of flocs, and contact angle of the cake layer were closely related to HA removal by cake layer, whereas reversible and irreversible fouling were positively correlated with cake layer thickness and floc fractal dimension respectively. Compared with other dynamic membranes, the cake layer had the best economic performance, which provided application potential on NOM removal in micro-polluted surface water.

Combining Optical and Acoustic Backscatter Measurements for Monitoring of Fine Suspended‐Sediment Concentration Under Changes in Particle Size and Density

AbstractOptical and acoustic backscatter measurements are routinely utilized to monitor suspended‐sediment concentration (M); however, both measurements are affected by changes in particle size and density. In this study, optical and acoustic backscatter measurements are combined to a single parameter, the sediment composition index (SCI), to quantify M, mean particle radius by number (ao), the fraction of sediment <20 μm by diameter (), and particle bulk apparent density (ρbulk). Data are analyzed from Chesapeake Bay and five rivers of Queensland, Australia. SCI is utilized to predict the ratio of M to acoustic backscatter under changes in ao and ρbulk (R2 ranged from 0.6 to 0.98 across all data sets) and combined with acoustic backscatter to predict estimates of M that are independent of changes in ao and ρbulk. SCI is proportional to log10(ao) and for SCI from acoustic backscatter measured at 6 MHz (R2 = 0.8 and 0.74, respectively, p‐value < 0.001, n = 133), while SCI(log10(ao)) and SCI() from acoustic backscatter measured at 2 MHz or lower are sensitive to changes in floc fractal dimension. Estimates of ρbulk from SCI are biased by changes in particle size (R2 is 0.1–0.5 across all datasets). This study builds upon recent work that derived SCI to quantify composition of sand and mud in suspension and demonstrates the utility of the approach in systems transporting flocculated silt and clay. Future research directions are discussed.

Removal of ultrafine colloidal particles from shale gas fracturing flowback fluid by microbubble-intensified flocculation: Effect of microbubble size

Shale gas fracturing flowback fluid (FFF) is characterized as the hazardous wastewater with high viscosity, large displacement, and complex components, which is difficult to deal with. Flocculation has been proven to be the most extensively applied treatment process considering its effortless operation, low energy consumption, and comparatively high efficiency. However, efficient removal of ultrafine colloidal particles (<10 μm) from FFF still remains a big challenge since their extremely stable properties. Herein, microbubbles (MBs) were introduced into the flocculation reaction to enhance the flocculation performance. When the median particle diameter (d50) of MBs reached 0.97 μm (which matched the size of selected colloidal particles), the turbidity removal rate was as high as 91.93 % at 0.70 g/L flocculant dosage, which was superior to traditional stir flocculation without MBs (66.67 %). Under this condition, the mean floc size reached the maximum value of 64.77 μm at 30 s after adding the flocculant. Meanwhile, the floc fractal dimension was significantly improved and the flocs held more resilient, which was beneficial for solid-liquid separation. The MBs worked by the trapping and bridging functions. Consequently, microbubble-intensified flocculation provided an advantageous way for the effective removal of ultrafine colloidal particles in FFF by controlling the bubble size appropriately.

A novel insight into energy conservation and efficiency enhancement in wastewater treatment process: Low-frequency mechanical vibration induced

One important way to break the bottleneck of energy conservation and consumption reduction in sewage treatment process is to attenuate the mass transfer resistance, which is thought as one of key factors to determine the efficiency of activated sludge treatment system. Thus, in this study, two independent Anacrobic/Oxic reactors were operated under low dissolved oxygen (DO) condition to evaluate the effects of low-frequency mechanical vibrations on the removal efficiency of pollutants. Results indicate that 40 Hz low-frequency mechanical vibration could greatly strengthen the efficiency of pollutants removal. Microelectrode-mass transfer efficiency test platform revealed that 40 Hz low-frequency mechanical vibration could increase the oxygen transfer coefficient from gas to liquid by approximately 145.19 %, and oxygen diffusion coefficient from liquid to solid by 75.2 %. Fractal dimension of flocs, particle size and zeta potential analyses jointly suggested that low-frequency mechanical vibrations treatment can form more adsorption points and mass transfer channels to enhance mass transfer efficiency of oxygen in floc. In addition, low-frequency mechanical vibrations treatment further stimulated the biological activities associated with nitrogen metabolism (i.e., specific metabolism rate, metabolism enzyme activities), but slightly alerted the overall microbial community. The findings in this study suggest that low-frequency mechanical vibrations could effectively accelerate the pollutants removal under low-DO condition by enhancing oxygen transfer coefficient and stimulating the associated biological activities. Collectively, this study provides a new technical strategy for efficiency enhancement and energy conservation in the global sewage treatment industry.

Uncovering the optimal structural characteristics of flocs for microalgae flotation using Python-OpenCV

Coagulation-based dissolved air flotation is generally recognized as an efficient and economical method for removal of algae from eutrophicated water, whose efficiency is directly affected by the structural characteristics of flocs. However, it is not clear which floc structures are suitable for microalgal floatation, whether large and compact flocs or small and loose flocs have good rising performance. In this study, a novel technology for dynamically tracking the growth and rising behaviors of flocs was developed based on Python-OpenCV to visually uncover the optimal structural characteristics of flocs for Microcysts aeruginosa coagulation-flotation. Different coagulation flow fields (velocity gradient, G) were adopted to artificially create flocs with various structural characteristics and floatation kinetics. Results showed that G value had significant effects on the growth and rising behaviors of flocs, thus achieving intuitively different flotation kinetics. An idea rising velocity of 91.5 m h−1 was achieved by flocs with optimal structural characteristics generated at a suitable G of 34.1 s−1, which was 29–75% higher than that of flocs at other G. The rising velocity of floc was synergistically determined by the size and fractal dimension of floc. The structural characteristics (size and fractal dimension) of flocs were introduced into the calculation model of rising velocity, which guided the principle of optimal floc structure characteristics (large and compact) suitable for Microcysts aeruginosa removal using DAF. These may provide new technology for the studies of the growth and settling/rising behaviors of flocs, and lay a theoretical foundation for the design of DAF system with high load rate and the selection of optimal operating conditions applied to cyanobacteria blooms prevention and control.

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.

Estimation of Fractal Dimension of Suspended Sediments from Two Mexican Rivers

Sampling programs for suspended sediment were carried out in the Usumacinta River and its tributary Grijalva River in Mexico during the years 2016 and 2017. Suspended sediment samples collected during these sampling programs were analyzed in the laboratory using a Rotating Annular Flume (RAF) fitted with a Particle Tracking Velocimetry (PTV) to obtain the 2D images of the suspended sediment particles as they were undergoing floc reconstruction, and subsequently using a glass settling column fitted with inline digital holography set up to obtain 3D holograms of the fully flocculated sediment particles. From these high-resolution hologram images, the fractal dimension of the flocculated sediment particles was obtained using the classical box-counting method and an improved Triangular box-counting method. The estimated fractal dimension of flocculated sediment, which is a measure of floc compactness and structure that control the settling velocity of flocculated sediment was used to validate two empirical models to estimate the fractal dimension in terms of the floc sizes of suspended sediments of these two rivers. It is shown in this study that the floc characteristic can be analyzed in laboratory experiments after floc reconstruction with the use of an RAF and it offers a viable alternative to the costly in-situ sampling that is often carried out in ocean research. The digital holography method employed in this research offers an efficient methodology to obtain the floc fractal dimension. Regarding the innovative aspects and new contribution to science, we can say that we have developed a laboratory protocol to test river waters to establish floc properties such as fractal dimensions of flocs in this research which will help to test river waters on a routine basis with manageable costs. We can also say that we have developed models to predict the relationship between floc fractal dimension and floc size, which did not exist before.

Efficiencies and mechanism of enhanced coagulation pre-treatment on domestic sewage with PAC-HCA compound.

Poly dimethyl diallyl propyl ammonium chloride (HCA) and poly aluminum chloride (PAC) were used to prepare complex coagulants for the enhanced coagulation (EC) pretreatment of domestic sewage. The influences of hydraulic conditions, the dosage ratio of PAC-HCA complex coagulants, initial pH value, and dosage on the removal efficiency of SS, COD, and TP in domestic sewage were investigated. The fractal dimension and Zeta potential were used to verify and characterize the experimental results. The results showed that the optimum coagulant conditions were as follows: G1 = 200.0-265.0 s-1, T1 = 1.5 min, G2 = 40.0 s-1, T2 = 5 min, PAC: HCA = 25:1, dosage = 15 mL/L, pH = 8. At the mentioned point, the removal rates of SS, COD, and TP are 98.74%, 44.63%, and 89.85%, respectively. In addition, through comparative tests, PAC-HCA compound coagulants show better treatment efficiency than PAC and HCA used alone. When the HCA dosage was 15 mg/L, Zeta potential and flocs fractal dimension was 2.29 mv and 0.9844, respectively. This indicates that PAC-HCA has a good treatment effect on domestic sewage, and the mechanism of enhanced coagulation to remove nutrients is mainly electrical neutralization.

Comparative evaluation of pilot-scale reactors based on pulsating floc blanket clarification and conventional clariflocculation technologies in simultaneous treatment of natural organic matter and turbidity

Abstract Simultaneous treatment of synthetic raw water containing natural organic matter (6 mg L−1) and clayey turbidity (0–20 NTU) was carried out with PACl on continuous upflow type pilot-scale models of pulsating floc blanket clarifier (PFBC) and conventional clariflocculator (CC) each designed for a capacity to treat about 8,000 liters per day, to understand mechanistic differences in their functioning. Fluidized bed of pre-flocculated particles prompted contact flocculation and enmeshment which lowered the residual turbidity for PFBC (0.07 ± 0.09 NTU) compared to CC (2.48 ± 1.71 NTU). Fine particles suspended in water clarified from PFBC and CC were hetero-disperse with Zavg as 2,341 nm and 5,693 nm respectively. On average, total residual aluminum was found to be 147 ± 33 ppb and 141 ± 51 ppb, while dissolved residual aluminum was found to be 31 ppb and 59 ppb for PFBC and CC respectively. Average total organic carbon reduction by PFBC and CC was 70.4% and 67.7% respectively. Size, structure and fractal dimensions of flocs were studied and average settling velocity of PFBC flocs was calculated to be 37% higher than CC flocs. Distinctness in characteristics of sludge formed in the two reactors has been highlighted by means of SEM micrographs and FT-IR spectra.

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.

Moringa oleifera-derived coagulants for water treatment: Floc structure, residual organics, and performance trade-offs.

The study explored the suitability of unfractionated extracts from the seeds of the Moringa oleifera tree as a coagulant for water treatment. The coagulant was obtained by soaking crushed and sieved seeds in a low salinity aqueous solution: a simple and inexpensive alternative to conventional coagulants in settings where specialized expertise and equipment are lacking. The performance of M. oleifera-derived coagulants was quantified in terms of turbidity removal, bacteriophage clearance, concentration of residual organics, as well as meta-parameters such as floc size and fractal dimension. Treating high turbidity clay suspensions at the optimal coagulant dosage (14.7mg(DOC)/L) and flocculation mixing conditions ([Formula: see text]= 22.4s-1) removed > 94% of turbidity, similar to that recorded in reference tests with alum. Floc size distribution shifted to larger sizes during the first 10min of flocculation with no change afterwards, while the floc fractal dimension, [Formula: see text], continued to increase, pointing to the gradual formation of denser ([Formula: see text]= 2.1 to 2.2), more settleable flocs. Preliminary tests with MS2 bacteriophage showed that coagulation with M. oleifera decreased the viable MS2 titre by ~ 1.3log, which was significantly above the turbidity removal (~ 1log). The extraction process, however, allowed a large amount of residual organics (> 78% of extracted DOC) into the treated water. Combining the coagulants with downstream filtration and adsorption, employing UV or solar disinfection, or limiting applications to non-potable reuse is suggested for mitigating the concerns related to residual DOC.

Insights into kaolin clay flocculation by cationic tapioca starch by analysis of variance and floc fractal dimension

The flocculation performance of two cationic starches with different charge densities with kaolin clay was investigated by a statistically designed set of small angle light scattering experiments. The analysis of variance of the results showed that shear and starch concentration were important factors affecting the floc size for both starches. The temperature was found to be a significant factor only for the higher charge density cationic starch S880. The combination effect of NaCl and starch concentration and that of temperature and starch were found to be significant for the floc size of the S880 system. The combination effect of shear rate and NaCl was found to be significant for the floc size induced by the low charge density S858.

The reinforcement of sludge-recycling enhanced flocculation by the acid activation of settled sludge

ABSTRACT Sludge-recycling enhanced flocculation (SEF) is an effective method for enhancing flocculation. In the conventional SEF process, the settled sludge is recirculated into the flocculation process without any further treatment. However, studies have shown that the efficacy of the SEF process could be improved by pre-treating the sludge. In this work, the acid activation of sludge was performed using a range of pH values (1.0–6.0) and charge states, with and without long-chain bridging. The resulting residual turbidities, floc fractal dimensions and floc morphologies were then analyzed, to examine the effects of sludge activation on the efficacy of SEF. In the absence of long-chain bridging, it was found that flocculation was enhanced by pH values between 2.0 and 5.0 in the electrostatic patch (EP) and near charge neutrality (NCN) states. In the EP state, the optimal pH for SEF enhancement was pH = 2.0; in the NCN state, the optimal pH was pH = 3.0. In terms of floc morphology, pH values between 2.0 and 5.0 resulted in larger average floc sizes and lower floc fractal dimensions than conventional SEF. However, in the presence of long-chain bridging, sludge activation did not enhance flocculation; residual turbidity increased with decreases in pH, in both the EP and NCN states. Based on these results, it may be surmised that the acid activation of sludge is suitable for cases without long-chain bridging.

A quantitative lab examination of floc fractal property considering influences of turbulence, salinity and sediment concentration

Flocculation is an important dynamic process for fine sediment transport. A number of physical and biochemical factors affecting flocculation have been identified, but quantitative examination of floc structure and fractal property under varying physical conditions is still needed. In this contribution, we conducted lab experiments using an annular flume and natural sediment to evaluate changes in floc size distributions and fractal dimensions under varying turbulent shear G, salinity and suspended sediment concentration (SSC). The low-intrusive optical instrument of LabSFLOC-2 was deployed to capture images of flocs which enables calculation of floc sizes and settling velocities. Observations showed that the mean floc size in freshwater first increased with increasing G below a threshold of G = 40 s−1, followed by a decrease with further increases in shear. The shear threshold was smaller for saline water (salinity of 7 PSU), i.e., G = 20–30 s−1, than that in freshwater. The fractal dimension of flocs decreased with an increase in size, suggesting more fragile structure for macro-flocs. Turbulent shear appeared to play a dominant role in controlling floc structure. Flocs formed under large shear force were more compacted, and had larger fractal dimensions. The floc fractal dimension was 28–37% greater in freshwater than in saline water. An improved method considering both floc size and variable fractal dimension is proposed for better simulation of floc effective density. The improved understanding of flocculation dynamics and floc structure in this work have implications for fine sediment and adherent nutrients management in varying natural water environments.

Interactions between magnetic particles and polyaluminum chloride on the coagulation behavior in humic acid-kaolin synthetic water treatment

Understanding the interactions between magnetic particles (MPs) and polyaluminum chloride (PACl) is essential to elucidate the magnetic seeding coagulation (MSC) process. However, little is known about how MPs interact with the different Al species coexisting in the PACl. Here, the relationships among pollutants removal, residual Al distribution, and floc properties were comparatively studied in the MSC and traditional coagulation (TC) processes to address this issue. The response surface analysis indicated that the interaction between PACl and MPs dosages exhibited significant effects on turbidity and DOC removal. Negligible changes of dissolved Al after MPs addition indicated the weak connection between Ala and MPs. The formation of MPs-Alb-HA complexes resulted in the increase of turbidity removal from 90.2% to 96.0% and the reduction of colloidal Al from 0.67 to 0.30 mg L−1. Humic-like components could be adsorbed on MPs forming MPs-HA complexes, which enhanced the DOC removal from 55% to 58.5%. MPs addition produced loose flocs with a small floc fractal dimension value (1.74), so the average size and strength of flocs in the MSC process (425 μm and 49.7%) were lower than that in the TC process (464 μm and 58.3%). The cumulative volume percentage of large flocs (>700 μm) was decreased from 29.7% to 20.7% with MPs addition, indicating the disruption of large flocs and the reproduction of more fragments. The effective separation of these fragments by magnetic attraction maintained the efficient coagulation performance. This study provides new insights into the interaction mechanism of MPs and PACl in the MSC process.

Magnetic flocculation of Cu(II) wastewater by chitosan-based magnetic composite flocculants with recyclable properties

In this study, three magnetic flocculants, namely, MC, MC-g-PAM, and MC-g-PAA, were prepared. The structure characteristics, flocculation performance, and floc characteristics of the three magnetic flocculants were systematically studied and compared. SEM, FT-IR, XPS, XRD, TG–DSC, and VSM characterization results show that MC, MC-g-PAM, and MC-g-PAA are successfully prepared and exhibit good magnetic induction. The removal rates of copper ions by MC, MC-g-PAM, and MC-g-PAA under the optimal coagulation conditions are 93.39 %, 88.64 %, and 61.41 %, respectively. Kinetic fitting shows that the flocculation reaction process of MC and MC-g-PAM conforms to pseudo first-order kinetics, while the flocculation reaction process of MC-g-PAA conforms to pseudo second-order kinetics. The flocs produced by MC-g-PAA have larger particle size and fractal dimension than those by MC and MC-g-PAM. At 80 mg/L dosage and pH 6, the floc size and floc fractal dimension obtained by MC-g-PAA reach the maximum values of 48.28 um and 1.468, respectively. Zeta potential studies show that the flocculation functions of the three flocculants are mainly adsorption bridging, adsorption electric neutralization, and chelating precipitation. Recycling experiments show that MC-g-PAA has good recyclability, and the recovery rate after the fifth use is 77.24 % with the Cu(II) removal rate of 67.53 %.

Membrane fouling performance of Fe-based coagulation-ultrafiltration process: Effect of sedimentation time

Pre-coagulation is commonly used with ultrafiltration (UF) to alleviate the membrane fouling. Compared to conventional coagulation-sedimentation-UF (CSUF) processes, the direct coagulation-UF (CUF) processes are widely believed to perform better due to the formation of a looser cake layer. It is however shown in this study that not only the density of a cake layer, but also its thickness as well, can affect the membrane fouling behavior, which therefore are influenced by both the sedimentation time and flocs characteristics. Herein, the membrane fouling performance of Fe-based coagulation-UF process was systematically investigated with different sedimentation times. A critical threshold of 30 min was observed at the lab-scale: if shorter than that, the membrane fouling depended mainly on the cake layer density, and thus CUF outperformed CSUF; but when the sedimentation time was over 30 min, the cake layer thickness turned to be the dominant factor, thereby resulting in CSUF performing better. Furthermore, it was shown that the critical sedimentation time was decided by flocs characteristics. A lower water temperature induced the formation of irregular flocs with a lower fractal dimension, and the corresponding cake layer exhibited an almost identical density with increasing sedimentation time. In this regard, CSUF processes were constantly superior to CUF as the cake layer thickness decreased. On the other hand, a critical sedimentation time reappeared because of the higher floc fractal dimension under acidic conditions. This work showed for the first time that the membrane fouling of CSUF was up to the sedimentation time, and it was possible to outperform CUF if the sedimentation time exceeded a critical threshold. Such a finding is crucial to the future development of coagulation integrated UF processes.

The Importance of Organic Content to Fractal Floc Properties in Estuarine Surface Waters: Insights From Video, LISST, and Pump Sampling

AbstractTo better understand the nature of flocs of varying organic content in estuarine surface waters, Laser in situ Scattering and Transmissometry, video settling, and pump sampling were deployed in the York River estuary. A new in situ method was developed to simultaneously solve the floc fractal dimension (F), primary particle size (dp), and primary particle density (ρp) by fitting a simple fractal model to observations of effective floc density (Δρ) as a function of floc diameter (df), while ensuring that the integrated particle size distribution was consistent with measurements of bulk apparent density (ρa). When fractal fits were statistically justified, application of the above methods showed the bulk fraction of organic matter (forg) to be well correlated to multiple floc properties. As forg increased, dp and ρa also increased, while ρp, total suspended solids (TSS), and median floc size decreased. Notably for microflocs, neither F nor Δρ was significantly related to either forg or TSS. This indicates that organic matter may partially displace water content within microflocs without fundamentally changing the flocs' inorganic structure. When pooling multiple samples, a marked decrease in F was seen at the transition to macroflocs, and most strongly for high forg cases. This suggested that settling velocities ≥ ∼1 mm/s may produce turbulent stresses that tend to tear macroflocs apart. This study also found that when the fractal theory held, ρp had a near 1:1 correlation with the bulk dry density of filtered TSS, implying that primary particles are tightly bound aggregates of combined mineral and organic components.

Magnetic seeding coagulation: Effect of Al species and magnetic particles on coagulation efficiency, residual Al, and floc properties

Magnetic seeding coagulation (MSC) process has been used to accelerate flocs sedimentation with an applied magnetic field, offering large handling capacity and low energy consumption. The interactions of three typical Al species, aluminum chloride (AlCl3), Al13O4(OH)247+ polymer (Al13), and (AlO4)2Al28(OH)5618+ polymer (Al30), with magnetic particles (MPs) were examined to clarify the MSC process. In traditional coagulation (TC) process, the aggregation of primary Ala-dissolved organic matter (DOM) complexes with in-situ-formed polynuclear species generated a large average floc size (226 μm), which was proved to be efficient for DOC removal (52.6%). The weak connections between dissolved Ala-DOM complexes and MPs led to the negligible changes of dissolved Al after seeding with MPs in AlCl3. A significant interaction between MPs and Al13 was observed, in which the MPs-Al13-DOM complexes were proposed to be responsible for the significant improvement of DOC removal (from 47% to 52%) and residual total Al reduction (from 1.05 to 0.27 mg Al L−1) with MPs addition. Al30 produced a lower floc fractal dimension (Df = 1.88) than AlCl3 (2.08) and Al13 (1.99) in the TC process, whereas its floc strength (70.9%) and floc recovery (38.5%) were higher than the others. Although more detached fragments were produced with MPs addition, the effective sedimentation of these fragments with the applied magnetic field led to the decrease of residual turbidity and colloidal Al in Al30. The dependence of coagulation behavior to MPs and different Al species can be applied to guide the application of an effective MSC process.

Chitosan Modified Cationic Polyacrylamide Initiated by UV-H2O2 for Sludge Flocculation and New Insight on the Floc Characteristics Study.

In the present study, a novel graft modified flocculant CTS-g-PAMD was synthesized and applied to conduct sludge conditioning and dewatering. CTS-g-PAMD was copolymerized with AM, DMC and chitosan (CTS) under UV-H2O2 initiation. In addition, the effects of single factor experiments on the molecular weight (MW) CTS grafting efficiency (GE) of CTS-g-PAMD were determined and the optimal copolymerization conditions were achieved. The GE of CTS-g-PAMD reached 91.1% and the MW was 4.82 × 106 Da. As revealed from the characterized results of Fourier-transform infrared spectra (FT-IR), 1H/ NMR, X-ray diffraction (XRD), scanning electron microscopic (SEM) and X-ray photoelectron spectroscopy (XPS), the successful synthesis of CTS-g-PAMD was confirmed, which is considered to be conducive to explaining sludge dewatering performance. Under the optimal conditions (pH = 7.0, flocculant dosage = 35 mg/L), the best flocculating performance (FCMC: 73.7%; SRF: 4.7 × 1012 m·kg−1, turbidity: 9.4 NTU) and large and dense sludge flocs (floc size d50 = 379.142 µm, floc fractal dimension Df = 1.58) were formed. The DMC and CTS chain segments exhibiting cationic properties significantly improved the positive charge density and enhanced the electrical patching effect of CTS-g-PAMD. The long molecular chain of CTS-g-PAMD exhibited superior extensibility, which enhanced bridging effect on adsorption. Moreover, the sludge floc after undergoing CTS-g-PAMD conditioning exhibited robust shear resistance and regeneration ability. After the sludge floc was crushed and broken, a large and dense sludge floc was formed, helping significantly reduce the sludge specific resistance (SRF), turbidity and cake moisture content (FCMC) and enhance the sludge dewatering effect. The novel CTS-g-PAMD flocculant shows promising practical applications and high market value.