Electrosteric stabilization of concentrated cement suspensions imparted by a strong anionic polyelectrolyte and a non-ionic polymer

Strong polyelectrolytes, known as superplasticizers, improve the initial fluidity of concentrated cement suspensions through electrostatic stabilization. These polyelectrolytes do not maintain the initial fluidity, however, primarily due to an increase in the ionic strength of the cementitious suspension. Consequently, non-ionic polymers are often used in conjunction with polyelectrolytes to provide steric stabilization and hence to sustain the desired fluidity over a longer time, and this has lead to the development of copolymers with both electrostatic and steric (electrosteric) functionalities. To design such polymers, it is necessary to optimize the balance between electrostatic and steric stabilization to maximize suspension fluidity. We have quantified the effects of a strong anionic polyelectrolyte, melamine formaldehyde sulfonate (MFS), and a non-ionic polymer, hydroxypropylmethylcellulose (HPMC), on the zeta potential of cement particles and the steady shear and low-amplitude rheological properties of concentrated cement suspensions. While the adsorption of MFS onto the cement particle surfaces leads to a sign inversion in the zeta potential, the adsorption of the non-ionic HPMC has no significant effect on the potential. The addition of HPMC to the suspensions substantially reduces the steady shear viscosity and the storage modulus at constant MFS concentration; in addition, there exists an intermediate HPMC concentration that minimizes fluidity. The resulting suspension fluidity is also maintained over a longer time than in the absence of HPMC. This improvement in the stability and fluidity of cement suspensions is attributed to “complementary electrosteric dispersion/stabilization”, and provides insight to the design of polymers with electrosteric functionality.     

Understanding the role of restructuring in flocculation: The application of a population balance model

The effect of shear on floc properties was observed through population balance to comprehend the mechanisms of flocculation, in particular the role of restructuring. Little fundamental attention has been given before to the shear influence responsible for creating compact aggregates, while the floc characteristics might differ in other conditions. It is crucial to understand how aggregates evolve to steady state, if their properties are to be ‘tailored’ to suit subsequent solid-liquid separation. From a previous experimental study (Langmuir 18(6) (2002) 1974), restructuring was observed to occur extensively in the flocculation of latex particles in couette-flow, and was proposed to be responsible for the decrease in floc size on their transition to equilibrium. On the other hand, flocs of larger primary particles were more susceptible to breakage, with densification occurring as a result of fragmentation and re-aggregation. Denser flocs were found when structural deformation dominated, particularly in the initial stage of the process, while comparatively tenuous ones were observed when formation and breakage kinetics were the governing mechanisms. The distinct manners in which aggregates of different primary particle sizes evolved with time, were replicated with a population balance that incorporated the floc structural variation; verifying that restructuring indeed played a crucial role under certain flocculation conditions.     

Reuse of carwash water with a cellulose acetate ultrafiltration membrane aided by flocculation and activated carbon treatments

A reuse system for carwash water with a cellulose acetate (CA), hollow-fiber-type ultrafiltration membrane with the aid of flocculation and activated carbon treatments was proposed. The multi-blended flocculating agent containing bentonite, Al₂(SO₄)₃, sodium alginic acid and a cationic polyacrylamide showed higher removals of COD and turbidity for carwash wastewater compared with Al₂(SO₄)₃ or a water-soluble polymer individually. The effect of pure water permeability of the membrane on permeation flux in pretreated carwash wastewater by this agent was examined using three kinds of CA membranes whose molecular weight cut-offs were 150,000 Dalton. Permeation flux showed a higher value in the case of the membrane with higher pure water permeability. Practical scale experiments with a membrane area of 32 m² and 48 m² were conducted under a membrane pressure of 20 kPa. When carwash wastewater was pretreated with 50 mg/L of this multi-blended flocculating agent, permeation flux through the CA membrane with pure water permeability of 0.78 m³/(m²/h) at 100 kPa showed 1.0 m³/(m²/d) for more than 6 months. The COD, BOD and extract by n-hexane values of reuse water were 3.7-15.7 mg/L, 2.5-14.0 mg/L and below 0.5 mg/L, respectively.     

Effects of a strong polyelectrolyte on the rheological properties of concentrated cementitious suspensions

Strong polyelectrolytes, referred to as superplasticizers, are known to improve the initial fluidity of concentrated cement suspensions. To quantify how the polyelectrolytes affect the fluidity, we have studied the effect of a strong anionic polyelectrolyte, melamine formaldehyde sulfonate (MFS), on the zeta potential of cement particles and on the steady-shear and low-amplitude rheological properties of cement suspensions. Adsorption of low concentrations of MFS onto the cement particles leads to an inversion in the sign of the surface potential, causing the electrostatically flocculated particles to become electrostatically dispersed and giving rise to a corresponding decrease in the steady-shear viscosity and storage modulus. At an intermediate MFS concentration, the steady-shear viscosity and the storage modulus each display a minimum. This concentration corresponds to that at which the zeta potential becomes constant. Larger concentrations of MFS result in an increase in the viscosity and storage modulus, which is attributed to depletion flocculation. These results thus relate the interaction between particles to the suspension fluidity through the analysis on the surface potential of particles and microstructure of suspension.     

箭竹1井胶凝酸酸压返排液处理及回注技术

胶凝酸主要由盐酸和胶凝剂配制而成,在低渗透碳酸盐岩地层压裂时,盐酸溶蚀地层,沟通缝隙。胶凝酸与地层岩石的化学反应在2小时内完成,返排液中的残酸用以NaOH为主的碱中和剂处理,通过中和、沉降、过滤、杀菌等一系列处理后回注地层。     

中小河流水质特征及修复方法探讨

考察了上海市几条中小河流的水质特征及生物膜对漕河泾和青春河水的净化效果，对污染河流修复方法作了讨论。结果表明，单靠生化方法难以达到修复中小河流的目的，可采用先生化后混凝或先混凝后生化的方法对其进行修复。     

Dual Polymer Conditioning of Water Treatment Residuals

Conditioning of either wastewater biosolids or water treatment residuals conventionally utilizes a single polymer to improve subsequent dewatering. The sequential addition of two polymers has been reported to enhance biosolids dewaterability, but comparable benefits have not been demonstrated for water treatment residuals. This paper evaluated the use of cationic and nonionic polymers, singly and in combination (dual), to investigate whether dual polymer conditioning of residuals offers any advantages, and to determine whether the results could be accommodated by current mechanistic understandings. For this purpose, lab-scale tests used capillary suction time (CST), supernatant viscosity, zeta potential, streaming current, turbidity, floc size, and rheometric analyses. Comparisons of CST and viscosity results for single and dual polymer additions indicated that dual polymer use gave moderately improved dewaterability, possibly due to the increased mixing utilized for dual polymer addition. Using a cationic polymer produced a less turbid supernatant. Zeta potential and streaming current were not good indicators of conditioning efficacy when a nonionic polymer was used. Rheometric analyses were only meaningful in one selected method for treatment of the data: the area under the rheogram up to a shear rate of 30?inverse?s. Overall, implementation of dual polymer use does not appear warranted.     

Estimating the Removal of Anthropogenic Organic Chemicals from Raw Drinking Water by Coagulation Flocculation

A mathematical model was developed to estimate the efficacy of coagulation–flocculation treatment for removing neutral hydrophobic organic chemicals from raw drinking water. The model assumed that the only significant removal mechanism was the destabilization and settling of organic matter containing sorbed anthropogenic organic compounds. The model was validated with standard jar tests using compounds with a range of hydrophobicities (log?Kow = 1.89?to?5.48), including contaminant candidate list chemicals, pesticides, pharmaceuticals, and endocrine disrupting chemicals. Final concentrations of test compounds after coagulation and flocculation were in good agreement with model estimations for synthetic waters composed of Aldrich (Milwaukee, WI) humic acid solutions. The final compound concentrations in coagulated natural waters from two drinking water reservoirs were about 80% lower than those estimated with the model. Overestimations of treated water concentrations by the model were attributed to an increase in sorption by natural organic matter when coiled in aluminum hydroxide flocs, compared to sorption to dispersed natural organic matter in untreated water.     

Flocculation and mechanism of self-flocculating lipid producer microalga Scenedesmus quadricauda for biomass harvesting

In this study, the extracellular polymeric substance of Scenedesmus quadricauda called EPS-S.q and its bioflocculatoin mechanism were investigated. Results showed EPS-S.q was successfully used as bioflocculating agent for S. quadricauda biomass harvesting and flocculation efficiency of up to 86.7% to S. quadricauda cells could be achieved in presence of Zn²⁺. EPS-S.q was the flocculating agent for self-flocculating microalga S. quadricauda and bioflocculation mechanism was polymer bridging. The sugar and protein mass fraction of dry EPS-S.q was sugar 56.7% and protein 41%. The infrared spectrum further indicated the presence of hydroxyl, carboxyl and amino groups. Moreover, pH decrease induced the flocculation of S. quadricauda and 78.4% of flocculation efficiency was the highest at pH 3. In addition, chemical flocculant FeCl₃ was efficiently used for S. quadricauda harvesting and up to 96.8% of flocculation efficiency could be achieved for S. quadricauda culture with biomass concentration 0.21–0.39 g L⁻¹ at pH 7.     

用赤铁矿制备聚硅酸铁絮凝剂及应用研究

采用酸浸-催化氧化-水解-聚合工艺，进行了以低品位赤铁矿、废硫酸和硅酸钠为原料制备聚硅酸铁（PSF）絮凝剂的试验研究，结果表明，适宜的工艺条件为硫酸浓度5～6 mol/L，液固比4∶1，酸浸温度90 ℃，酸浸时间2～3 h，氧流量40 cm³/（min·L），Fe/Si摩尔比=2，硅酸活化pH值=3，硅酸活化时间25 min，陈化时间2 h。用所制备的PSF处理印染废水，并与聚合硫酸铁（PFS）和聚合氯化铝（PAC）进行比较，结果表明，在90 mg/L用量下，PSF可使废水中浊度、色度、SS和COD_Cr的去除率分别达到91.5%、87.8%、92.2%和78.5%，比相同用量下的PFS和PAC均分别高出10、24、14、18个百分点以上。