Flocculation by cationic polyelectrolytes: Relating efficiency with polyelectrolyte characteristics

A series of acrylamide/dimethylaminoethylacrylate methyl chloride copolymers (AM‐co‐DMAEA) was evaluated as flocculants for model Precipitated Calcium Carbonate (PCC) in distilled water. These cationic polyelectrolytes (PEL) differed by their AM/DMAEA ratio, i.e., their charge density, chain architecture (linear and branched), their intrinsic viscosity (IV), and zeta potential of their aqueous solutions. The IV being directly related to the hydrodynamic volume of the PEL and the zeta potential reflecting the effective charges in suspension were selected for practically useful correlations with flocculation performance. The fractal dimension (d_F) and the scattering exponent (SE) of the flocs, analyzed by the laser diffraction method, were taken as indication of primary particle and aggregate assembly. For the optimum PEL dosage, SE and d_F varied with the IV and zeta potential. It was observable that floc size, floc resistance, and floc reorganization correlate with the PEL characteristics. Copolymers with lower IV, which is here associated with PEL of similar molar mass but lower charge density, yielded larger and less resistant flocs. Copolymers with higher IV originated smaller more compact flocs being more resistant. In high shear situations, where floc breakage should be avoided, as it is the case in papermaking, polymers with high IV yielding large SE are advantageous. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of Recycling-Sludge Operation on the Structure and Moisture Content of Floc in Water Treatment Plant

Abstract

Recycling-sludge operation is applied in the Feng-Yuan Water Treatment Facility to treat low turbidity source water. By employing fractal dimension analysis and the dilatometry technique, the effects of recycling-sludge operation on the structure and moisture content of sludge flocs are studied. As the results show, the recycling-sludge operation can decrease the average bound water content by nearly 13–24% and increase the effective floc density, thereby forming a compact structure with a high fractal dimension and low floc porosity. The results also indicate that a significant correlation arises between the fractal dimensions and the bound water content of the sludge flocs.     

Characterization of floc size, strength and structure under various coagulation mechanisms

Flocs generated by various coagulation mechanisms exhibit different size, strength and structure. The properties and fractal dimensions of flocs formed under three common coagulation mechanisms, i.e. charge neutralization, sweep and bridging, were investigated at various hydraulic conditions. The results showed that the floc size decreased with the increasing average velocity gradient G and the stable floc size exponent γ was of the following hierarchy: charge neutralization (0.6107) > sweep (0.5618) > bridging (0.3674). Furthermore, fractal dimensions of flocs were the highest when formed by sweep and the lowest when generated by bridging flocculation. The mass fractal dimensions measured by light scattering were between 2.0 and 3.0 and the floc strength was between 0.01 and 0.58 N m^− 2. An intrinsic unity of the relationship among floc size, fractal dimensions, floc strength under the three coagulation mechanisms was demonstrated.     

壳聚糖絮凝剂的投加量对污泥脱水性能的影响

通过污泥比阻的测定,分析絮凝剂剂量对污泥脱水性能的影响。同时对三氯化铝、阳离子聚丙烯酰胺、壳聚糖以及复合絮凝剂的絮凝效果进行比较。结果表明,无论是无机絮凝剂和有机絮凝剂都存在最佳剂量,小于或大于最佳投加量,絮凝效果都不好。阳离子聚丙烯酰胺(CPAM)、壳聚糖、三氯化铝的最佳投加质量浓度分别为0．2g/L、10g/L、35g/L。与三氯化铝相比,阳离子聚丙烯酰胺的药剂消耗量要低得多。壳聚糖与CPAM相比,在达到相同的絮凝效果时,壳聚糖的用量大于CPAM的用量。将壳聚糖与氯化铝复合,用两段法应用于污泥调理,研究这种复合絮凝剂的脱水性能,实验表明壳聚糖和三氯化铝复合,能大大提高污泥的脱水性能。     

Dewatering of coal plant tailings: Flocculation followed by filtration

A sustainable alternative to tailings dam disposal of coal refuse is mechanical dewatering of tailings, which provides fast production of dry solids and water reuse. In this study, flocculation followed by filtration of coal plant tailings, a new concept in tailings dewatering is investigated in detail. This paper focuses on the effect of preconditioning tailings with varying flocculants and dosages on filtration kinetics and the resultant moisture content of the filter cake. The results show that the cationic flocculant, MAGNAFLOC LT 425, requires a high dosage to produce a low moisture content filter cake and clear filtrate. Optimal sized flocs were produced with the anionic flocculant, MAGNAFLOC 5250, even though the particles are negatively charged. The kinetics of the filtration was dependent on the composition of process water as indicated by supporting sedimentation tests. The concentration of divalent alkali earth metals such as Ca²⁺ and Mg²⁺ allow for large floc growth by a bridging mechanism, which involves binding of the polymer and the negativity charged particle. Filtration and settling curves at this dosage were also supported by filter cake analysis using Darcy plots. It was found that the large floc size significantly increases the permeability of the filter cake. Floc size measurements and fractal dimension showed that while the large flocs were produced with anionic flocculant, the flocs produced with the cationic flocculant were small and weak. The results indicate that the optimum dosage and flocculant type for effective and efficient filtration of coal plant tailings is approximately 350 g/t of anionic flocculant at a 35% solids content and 40 kPa filtration pressure.     

磷矿酸解料浆与高分子絮凝剂形成的絮团特性研究

用光学连续摄像技术研究了不同絮凝条件下磷矿酸解渣与聚丙烯酰胺形成的絮团特性。实验结果表明酸解料浆与聚丙烯酰胺絮凝剂形成的絮团具有分形几何特征。应用分形理论得到絮团降落速度与絮团孔隙度和絮团密度的关系式。用激光粒度分布仪在线测定了流体力学条件对该体系团强度的影响。在湍流情况下絮团最大平均粒径取决于酸解渣原始平均粒径和体系的能量耗散。较大的絮团破坏主要以裂解为主,在最小的湍流漩涡区也存在相当程度的剥离破坏。试验发现絮团强度随聚合物分子量的增加而提高,对于获得最大平均粒径的稳定絮团存在最佳的絮凝剂加入量。．     

The Practical Application of Fractal Dimension in Water Treatment Practice–the Impact of Polymer Dosing

Abstract

The application of floc fractal dimension has been investigated in this work to determine if this parameter can have operational significance in water treatment. Natural organic matter suspensions were coagulated with aluminium sulphate and varying concentrations of a non‐ionic polymer. The fractal dimensions of the flocs formed were measured using light scattering and settling combined with image analysis. By using the correct methodology, optimum floc properties could be determined using the floc fractal dimension combined with the floc size and strength data.     

污泥调理剂与有机高分子絮凝剂联合作用对污泥脱水性能影响的研究

结合污泥调理剂和有机高分子絮凝剂在调理活性污泥中体现出的优缺点,将两者联合用于活性污泥的调理。先后投加不同量的调理剂和絮凝剂于活性污泥中,研究其对污泥絮体特征和脱水性能的影响。结果表明,当两者投加量分别为1%和0.5%时,污泥泥饼含水率降到最低,为75.41%,且污泥过滤性能得到较好的改善。这是由于调理剂的投加改变了污泥絮体结构,导致胞外聚合物（EPS）的分布发生变化,改善了污泥的脱水性能,絮体颗粒粒径减小,而投加有机高分子絮凝剂使得污泥絮体重新絮凝,从而提高脱水速度。     

Floc model and intrafloc flow

The three-dimensional pore structures in waste activated sludge floc were identified using the fluorescence in situ hybridization (FISH) and confocal laser scanning microscope (CLSM) images. The meshes of the three-dimensional porous configuration of a sludge floc were constructed from the CLSM series images. The intrafloc flow field was simulated for the constructed floc model when it was subjected to a uniform flow field, based on which the Darcy's permeability was estimated. The permeability (k_DL) of original floc was estimated as . Flocculated flocs had higher k_DL due to their large pore size, while the corresponding values of k_DL of the freeze/thawed flocs were lower. The calculated results indicate that a few large pores in the floc determine the permeability. The fractal dimension and compactness, however, are not correlated with the permeability of the flocs.     

有机絮凝剂对铁矿相沉降性能影响及其吸附机理

通过模拟拜耳法赤泥沉降过程研究了聚丙烯酸铵(PAAA)、阴离子聚丙烯酰胺(APAM)和氧肟酸絮凝剂(HPAM/HCPAM)对赤铁矿和针铁矿沉降性能的影响规律和絮凝后絮体的粒径分布及分形维数,并利用傅里叶变换红外光谱探讨了絮凝剂与铁矿相的吸附机理。在不同类型絮凝剂中,添加氧肟酸絮凝剂铁矿相沉降速度最快,且氧肟酸含量越高,沉降性能越好;聚丙烯酸铵和阴离子聚丙烯酰胺絮凝剂对铁矿相沉降性能影响较小;同等条件下赤铁矿沉降速度要远高于针铁矿,增加絮凝剂添加量有助于提高针铁矿沉降速度。在赤铁矿絮体中,添加PAAA絮体粒径最大,HPAM絮体分形维数最大、致密性最好;在针铁矿絮体中,添加APAM絮体粒径最大,HCPAM絮体分形维数最大、致密性最好。氧肟酸絮凝剂与铁矿相形成结构稳定、吸附能力强的五元环状螯合物,增强了赤铁矿和针铁矿的絮凝效果;PAAA通过双齿桥接配位与赤铁矿表面发生吸附,通过单齿配位与针铁矿表面发生吸附,其吸附能力弱于五元环;APAM与赤铁矿和针铁矿表面发生化学吸附,沉降性能差。     

有机絮凝剂对铁矿相沉降性能影响及其吸附机理

通过模拟拜耳法赤泥沉降过程研究了聚丙烯酸铵(PAAA)、阴离子聚丙烯酰胺(APAM)和氧肟酸絮凝剂(HPAM/HCPAM)对赤铁矿和针铁矿沉降性能的影响规律和絮凝后絮体的粒径分布及分形维数,并利用傅里叶变换红外光谱探讨了絮凝剂与铁矿相的吸附机理。在不同类型絮凝剂中,添加氧肟酸絮凝剂铁矿相沉降速度最快,且氧肟酸含量越高,沉降性能越好;聚丙烯酸铵和阴离子聚丙烯酰胺絮凝剂对铁矿相沉降性能影响较小;同等条件下赤铁矿沉降速度要远高于针铁矿,增加絮凝剂添加量有助于提高针铁矿沉降速度。在赤铁矿絮体中,添加PAAA絮体粒径最大,HPAM絮体分形维数最大、致密性最好;在针铁矿絮体中,添加APAM絮体粒径最大,HCPAM絮体分形维数最大、致密性最好。氧肟酸絮凝剂与铁矿相形成结构稳定、吸附能力强的五元环状螯合物,增强了赤铁矿和针铁矿的絮凝效果;PAAA通过双齿桥接配位与赤铁矿表面发生吸附,通过单齿配位与针铁矿表面发生吸附,其吸附能力弱于五元环;APAM与赤铁矿和针铁矿表面发生化学吸附,沉降性能差。     

Properties of flocs in sludge conditioning by a novel amphoteric polymer with different anionic degrees

This paper aimed to examine how the amphoteric conditioner poly (acrylamide‐′acryloyloxyethyl trimethyl ammonium chloride ?2‐acrylamido‐2‐methyl‐propane sulfonate) (PADA) with different anionic degrees (AD) affected the properties of sludge flocs in the conditioning. The floc properties were characterized by morphological parameters (floc size distribution, fractal dimension, specific surface area, and pore volume), physical properties (floc strength and surface charge density), and chemical constituents (Fe³⁺, Al³⁺ and extracellular polymeric substances (EPS), including the polymeric proteins and carbohydrates). The results of this investigation revealed that (1) morphological properties of flocs were associated with anionic degree, particularly in the range of 0–4%, where the anionic degree led to a shift of the particle size toward groupings of larger diameter, meanwhile better regularity and increased compactness of floc structure formed. (2) The introduction of the anionic groups indeed had bad effects on flocs in terms of its stability and charge neutralization, but the downtrend could be inhibited by adjusting the anionic degree of polymer to a reasonable level. (3) The dissolved EPS for sludge followed a role of decreasing firstly then increasing with increased anionic degree, but the content of bound EPS kept nearly constant. (4) The polymer with anionic groups had apparent effects on enrichment of metal ions. POLYM. ENG. SCI., 57:197–205, 2017. © 2016 Society of Plastics Engineers     

Cellulose nanofibers prepared from TEMPO‐oxidation of kraft pulp and its flocculation effect on kaolin clay

Cellulose nanofibers were prepared using TEMPO/NaBr/NaClO oxidation of kraft pulp and successive ultrasonic treatment, and the properties were characterized by conductimetric titration, X‐ray diffraction, and atomic force microscopy. The resulting product was then applied as an anionic microparticle to constitute a microparticulate system with cationic polyacrylamide (CPAM), to induce the flocculation of the kaolin clay suspension. The flocculation effect was evaluated by determining the relative turbidity of clay suspension. The results showed that the obtained cellulose nanofibers had cellulose I structure with higher crystallinity than that of the kraft pulp, and their cross‐sectional dimension was in the range of 3–5 nm. They had more negative zeta potential at neutral and alkaline conditions. It was found that the microparticulate system showed high flocculation effect on kaolin clay at a very low level of nanofiber addition, and a high shear level after CPAM addition was helpful for the flocculation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40450.     

The structure and strength of depletion force induced particle aggregates

Aggregating fine particulate matter is common practice in many industrial solid-liquid separation processes. Data obtained in this work on dilute aqueous dispersions of model colloidal polystyrene latex spheres indicate that depletion flocculation, which uses non-adsorbing polymer, can yield very compact aggregates. Flocculation of the negatively charged latex particles was induced by the addition of a poly(acrylic acid) at pH 10. The structural compactness of the latex flocs formed in the dilute dispersions was characterised using small-angle static light scattering in terms of mass fractal dimensions. Rheological measurements on the concentrated latex dispersions in the presence of the non-adsorbing polyacid showed Bingham yield stress behaviour. Both the compactness and strength of the latex flocs were found to be significantly dependent upon the level of the polyacid, as well as the concentration of the initial particles. In particular, as the level of the polyacid was raised the floc compactness decreased, whereas its strength increased. They were both seen to level off at high polymer concentrations. Atomic force microscopy measurements were made at varying concentrations of the polyacid to provide a qualitative explanation of the observed floc structural behaviour of the dilute dispersions. By combining the fractal dimension and the Bingham yield stress we were also able to estimate the energy required to separate the flocs into single units in the concentrated dispersions. It was concluded that the interparticle interaction energy is the key to understanding the dependence of both the floc structure and strength on the polymer concentration.     

A population balance model for flocculation of colloidal suspensions by polymer bridging

A detailed population balance model for flocculation of colloidal suspensions by polymer bridging under quiescent flow conditions is presented. The collision efficiency factor is estimated as a function of interaction forces between polymer coated particles. The total interaction energy is computed as a sum of van der Waals attraction, electrical double layer repulsion and bridging attraction or steric repulsion due to adsorbed polymer. The scaling theory is used to compute the forces due to adsorbed polymer and the van der Waals attraction is modified to account for presence of polymer layer around a particle. The irregular structure of flocs is taken into account by incorporating the mass fractal dimension of flocs. When tested with experimental floc size distribution data published in the literature, the model predicts the experimental behavior adequately. This is the first attempt towards incorporating theories of polymer-induced surface forces into a flocculation model, and as such the model presented here is more general than those proposed previously.     

基于介观尺度模拟的污泥絮凝形态及机理

用介观动力学的方法对胶体颗粒与高分子链的絮凝过程进行了模型研究,并根据模型结果对污泥和阳离子聚丙烯酰胺的絮凝过程和污泥脱水机理进行有针对性的探讨。通过建立粗粒化模型和经验势函数力场有效模拟了负电性的胶体颗粒与阳离子型高分子链的絮凝过程;模拟得出了絮凝的外观形态,证明了高分子链对胶体颗粒的桥接作用以及表面电荷的中和作用对絮凝的影响;并对絮凝反应过程的体系势能变化进行了研究。对实际污泥胶体颗粒和阳离子聚丙烯酰胺溶液拍摄了电镜图片并观察了其吸附过程;最后研究了高分子链离子度对溶液体系絮凝的影响,验证了离子度的增加有利于絮凝体的形成,但同时也由于絮凝体结构的复杂而对污泥脱水造成了一定的不利影响。     

Study of microwave-template initiated copolymerization peculiarity and evaluation on the coal floc distinctive behavior and flocculation performance

Cationic polyacrylamide (CPAM) contains a large number of acylamino and positively charged methyl ammonium chloride groups. It has the advantages of good water solubility, strong adsorption bridging ability, enhanced charge neutralization and destabilization performance, excellent flocculation effect, and wide application. Therefore, CPAM can be used in the treatment of coal washing wastewater, and the research and development of a new flocculant with high efficiency is a hot topic in this field. Template copolymer (TPADM) of methacryloyloxyethyl trimethyl ammonium chloride (DMC) and acrylamide (AM) was synthesized by microwave-template initiated polymerization with sodium polyacrylate (PAAS) as template. The microwave-template initiated polymerization is abbreviated as MW-TP. By analyzing FTIR, ¹H (¹³C) NMR and TG/DSC of TPADM, it was found that TPADM had obvious cationic fragment structure. In addition, the association constant (K_M) and the kinetics of the template reaction showed that the MW-TP was confirmed to be free radical initiated polymerization and I Zip-up (ZIP) polymerization mechanism, which demonstrated the formation of the cationic fragment structure again. This new cationic fragment structure greatly enhanced the ability of charge neutralization, electrical patching and adsorption bridging, thus improving the flocculation performance. Compared with cationic P(AM-DMC) (CPADM), Commercial cationic polypropanamide (CCPAM-1 and CCPAM-2), TPADM had better flocculation effect on coal washing wastewater. Under the optimum flocculation conditions (dosage = 16 mg/L, pH = 7.5), suspended solid (SS) concentration and turbidity of coal washing wastewater treated by TPADM reached 14.3 mg/L and 8.7 NTU, respectively. The floc formation, breakage, and regeneration analyses showed that the cationic fragment structure in TPADM could contribute to the formation of large and high density flocculation structure (d₅₀ ≥ 245 μm, D_f ≥ 2.05), and these coal flocs can regenerate rapidly after being broken. Finally, these large and compact flocs help to accelerate the flocs sedimentation and reduce the SS concentration and turbidity of coal washing wastewater, and enhance the effect of solid–liquid separation.     

Evaluation of flocs resistance and reflocculation capacity using the LDS technique

In a previous paper we have shown the added value of using LDS to monitor flocculation. It can supply, simultaneously, information on flocs size and structure and enlighten flocculation kinetics and mechanisms. In this paper, LDS is applied to study deflocculation and reflocculation processes of precipitated calcium carbonate (PCC) induced by cationic polyacrylamides, when different types of shear forces are applied. LDS can detect the influence of polymer characteristics and concentration as well as of the type of shearing, on flocs resistance and reflocculation degree, which depend on flocs structure and on the type of bonds between particles. As expected, flocs formed by bridging mechanism reflocculate with difficulty while flocs formed by patching reflocculate to a higher degree. Flocs resulting from reflocculation are more compact than the original ones, as assessed by the mass fractal dimension. Reflocculation is also lower when the flocs are submitted to superficial shearing than when they are submitted to sonication. Shearing induced by sonication is sufficient to break down the flocs in many fragments while the increase of pump speed only detaches particles by erosion, at the flocs surface, where bonds are weaker. Results prove that LDS is useful to monitor deflocculation and reflocculation processes and to predict floc resistance under different conditions. Moreover, the whole study demonstrates the benefit of using LDS for a complete evaluation of flocculants performance in the different stages of flocculation: aggregation, stabilization, deflocculation and reflocculation.     

超声能量密度对污泥脱水性能的影响

<正>引言近年来,生物法在城市污水处理中得到广泛的应用,然而在处理过程中产生了大量的污泥,污泥中含有50%～70%的有机物和较多的氮、磷等营养成分以及致病菌、寄生虫卵等有害物质。其化学     

Weak gels of fat crystals in oils at low temperatures and their fractal nature

The formation of fat crystal gels in soybean oil has been studied by sedimentation in a low concentration region at 10–25°C. At 10°C, weak gels were formed with 1% crystals, and no gels formed at concentrations of 2–5%. At temperatures of 15–25°C, no gels were formed at concentrations of 1–5%, and samples sedimented. Stronger gels of fat crystals were formed with ∼10% fat crystals at all temperatures examined. Formation of weak gels is a consequence of the fractal nature of fat crystal aggregates and sediments. At low temperature, the interaction is weak. The fractal dimension is then high, and the floc size is large for low crystal concentrations. These large flocs form a three-dimensional network that act as a weak gel and withstand gravitational force. When the temperature is increased, the fat crystal interaction becomes stronger, fractal dimension decreases, and floc size decreases. Smaller flocs have a higher density, pack more easily, and sediment. Similar effects are observed when the concentration of fat crystals is increased at low temperature due to a decrease in floc size.