Steven K. Dentel

Sorption of tannic acid, phenol, and 2,4,5-trichlorophenol on organoclays

Sorption of the organic pollutants phenol, 2,4,5-trichlorophenol, and tannic acid (Fluka) onto montmorillonite-based sorbents was studied. The sorbents were homoionic Na- or Ca-montmorillonite, montmorillonite completely exchanged with the cationic organic surfactant dimethyldistearylammonium chloride (or DDA-M), and DDA-M partially re-exchanged with Ca2+ (Ca-DDA-M). The influence of pH on sorption of phenol and trichlorophenol was also investigated. The sorption capacities for phenol, trichlorophenol, and tannic acid were significantly enhanced by surfactant treatment of the homoionic clay. Uptake onto the organoclays increased in the order phenol < tannic acid < trichlorophenol, which corresponds to the order of increasing hydrophobicity. The significant role played by hydrophobicity was also observed in pH effects which generally favored sorption when the pH was low enough to assure that the uncharged (protonated) species was predominant. In the case of trichlorophenol, sorption could be shown to be quantitatively attributable to the neutral species. The results of X-ray diffraction measurements showed increased d001 spacings when the DDA was intercalated into the interlamellar spaces, increasing the available sorbent porosity. This, and the linkage of uptake to solute hydrophobicity, indicates that uptake is by a partitioning mechanism, though non-linear isotherms may be caused by site limitations. Surprisingly, if a portion of the intercalated DDA is removed by exchange with Ca2+, the d001 spacing decreases but the sorption capacity of the organoclays is improved. One possible mechanism is improved elementary sheets cohesion due to calcium ions, imparting molecular sieve characteristics to the solid. The extent and possible selectivity of sorption using these organoclays suggests that they may provide an alternative to activated carbon sorbents in water treatment.

Sorption of Pentachlorophenol to HDTMA-Clay as a Function of Ionic Strength and pH.

We investigated the sorption of pentachlorophenol (PCP) to a surfactant-modified clay and the solubility of PCP as a function of pH and ionic strength. Pentachlorophenol is a hydrophobic ionizable organic composed; therefore, it can exist as either a protonated or a deprotonated species. The objectives of this study were to determine differences in the sorption and solubility of the two species and to model the sorption as a function of pH. We developed a model that described the sorption across the experimental pH range (4-8.5). The model represented the sorption of the deprotonated species by a Langmuir-type isotherm and the sorption of the protonated species by a linear isotherm

Application of the precipitation-charge neutralization model of coagulation

A quantitative model is considered that develops predictions of suspension stability on the basis of electrokinetic characteristics of colloidal material prior to and following coagulation. The model is applied in this paper to coagulation with aluminum sulfate and other aluminum salts. The effect of increasing particle surface area on coagulation is first modeled for a system containing particulate silica, but of varying size and concentration. Experimental results show a correlation of turbidity removal to attainment of near neutral f potential in “zone 2” coagulation, and the calibrated model successfully predicts this zone. The model is then used to describe the coagulation of waters containing humic substances by considering them as small colloids with a substantial contribution to surface area in the system. Finally, it is shown that the model can be employed to describe the performance of polyaluminum coagulants as well.

Optimization of slurry flocculation and dewatering based on electrokinetic and rheological phenomena

The use of chemical additives known as conditioners or flocculants is crucial in assuring the proper functioning of many solid-liquid separation processes, and dewatering in particular. The additive used is often a water soluble polymer with high molecular mass, strong adsorptive properties, and often a large amount of ionic charge. The type of polymer used, and its exact dose, may change with process or flow conditions, and these changes may lead to poor operation. However, advances in the understanding of conditioning and flocculation of slurries and sludges now make it possible to develop scientifically-based strategies for optimizing these processes. These advances have utilized new characterization methods that allow insight into fundamental aspects of the process. In several cases the analyses employed are also amenable to continuous reading, and therefore to automatic feedback control of the process. This paper describes these advances and suggests conditioning and flocculation control strategies that will allow optimization of subsequent dewatering processes. The research advances described are: (1) use of the streaming current detector for monitoring and controlling dewaterability; (2) evaluation of floc strength by streaming current and rheological and methods; (3) use of rheological characteristics of conditioned residuals for dose control; (4) application of liquid-stream viscosity for polymer dose monitoring and control; and (5) quantification and verification of mixing conditions in conditioning processes, and use for mixing similitude. These developments should aid in the proper initial selection of a conditioner product (flocculant) and its dose, and allow optimization based on continuous monitoring if the sludge conditions vary significantly over time.

Evaluation of the streaming current detector. I: Use in jar tests

Abstract The streaming current detector, or SCD, was evaluated as a means of characterizing coagulation performance. Jar tests utilized buffered water, kaolinite suspensions, or suspensions containing kaolinite plus activated carbon. Alum dose and pH were controlled parameters. Electrophoretic mobility measured for suspensions as a function of pH or alum addition was found to be well correlated to SCD readings, though less significantly after alum dosages. An offset was also observed such that a negative SCD output corresponded with zero electrophoretic mobility. This was attributed to incomplete converage of the negatively charged probe surfaces of the SCD. Salt additions decreased the magnitude of SCD readings as a result of double layer compression and weak adsorption. Alum doses which led to near-neutral SCD readings corresponded to conditions of decreased jar test turbidities, and the nature of the relationship suggests that dose control with an SCD is practicable. However, some experimental conditions were located where this was not the case. Carbon addition to kaolinite suspensions improved settleability and increased alum requirements at high pH, but did not affect the correlation between streaming current and supernatant turbidity.

Laboratory and full-scale studies of liquid stream viscosity and streaming current for characterization and monitoring of dewaterability

Abstract Many laboratory tests are available to evaluate the dewaterability of a given sludge with a specific type of conditioner. However, most of these are empirical and shed little light on dewaterability mechanisms. The most common laboratory measurements are also not amenable to continuous or flow-through use for actual process application. Viscosity and streaming current are two methods of characterizing the effectiveness of sludge conditioning which may be advantageous in these aspects. Both can be used as measurements characterizing the liquid stream—centrate or filtrate—from the dewatering process. Thus, this study assessed the utility of determining the liquid stream viscosity or streaming current using both lab and full scale experiments. Results were compared to other laboratory measurements of dewaterability, such as the capillary suction time (CST), the conditioned sludge streaming current (SC), and centrate total solids. They were also compared to CST, cake solids content, filtrate turbidity, and percent solids recovery in full-scale dewaterability evaluations. A significant correlation between the centrate viscosity and CST was established, with both related to dewaterability as shown by other parameters. There was also a clear relationship between the CST, the filtrate SC, and these with other dewaterability measures, such as the solids recovery, in the full-scale testing. A minimum CST, SC values near-zero for both centrate and conditioning sludge, and minimum centrate or filtrate viscosity all correlate with maximum solids recovery. These results are of significance both in explaining conditioning and dewatering mechanisms and for possible application in feedback control of polymer dose.

NMR spectroscopy for determination of cationic polymer concentrations.

Organic polyelectrolytes are utilized extensively in wastewater treatment, but their fate after use is poorly understood. Analytical methods used for polymer determination in less complex systems appear to fail in application to wastewater systems, contributing to the lack of knowledge. Thus, the development of 1H NMR spectroscopy is reported here for specifically quantitating certain cationic flocculant polymers in environmental samples. Proton observe frequencies of 250 or 400 MHz proton were used. A copolymer of acrylamide and acryloyloxyethyltrimethylammonium chloride was used, representative of cationic flocculant polymers possessing quaternary ammonium groups with terminal methyls that provide a sharp singlet at a chemical shift of approximately 3.06 ppm. A strong linear relationship was demonstrated between polymer concentration and either height or area of this peak. Recoveries were up to 96% at higher concentrations (250 mg/L), and were greater than when using viscosity or charge titration methods for polymer determination. Lesser recoveries at lower concentrations (70% at 5 mg/L) were attributed to adsorptive losses. The detection limit of this method was determined to be <0.5 mg/L. Use of the method was exemplified by analysis of anaerobically digested sludges for residual polymer following a range of dosages, showing the resulting isotherm.

Modified method for the analysis of anionic surfactants as Methylene Blue active substances

Determination of anionic surfactants as Methylene Blue active substances (MBAS) in water, waste water and sludge samples is of increasing importance because of the rapidly growing use of different types of anionic surfactants in household and industrial applications. We have developed a modified method for MBAS measurement, using sodium dodecyl sulfate (SDS), an alkyl sulfate anionic surfactant compound, as the reference anionic surfactant compound for the MBAS analysis. The modified method has achieved a reduction in sample size, elimination of the use of expensive glassware, and a decrease in the quantity of chloroform used compared with the standard method. The theoretical relationship between the modified method and the standard method was confirmed by the experimental calibration curves. The linear calibration curves had r2 values between 0.994 and 0.999. On the basis of the statistical analysis on the MBAS recoveries from standard addition and spiked samples, the modified method is equally capable of extracting anionic surfactant compounds from the samples, when compared with the standard method.

Theoretical Principles of Streaming Current Detection

In spite of the increased use of streaming current detectors (SCDs) as a means of monitoring and/or controlling coagulant dosage, knowledge regarding fundamental workings is incomplete. This paper provides an initial attempt at predicting and verifying functioning compared to electrophoretic mobility. The instruments components -the sensor and the signal processor -are first described. Equations modelling electro-double layer behavior in its sensor are then developed. Simplifying assumptions include the use of a capacitance model of the double layer and a triangular velocity profile for fluid within the sensors annulus. More complex modelling approaches are also suggested which incorporate the Gouy-Chapman electro-double layer model and an exact solution for the velocity profile. Experimental results confirm predictions of the simplified model under conditions of low potential. A monotonic relationship exists between streaming current electrophoretic mobility, which is required for its use as a control parameter. Deviations from model predictions are suggested to be due to charge characteristics of the sensor surfaces themselves.

Chemical Conditioning for Solid–Liquid Separation Processes

Particularly for suspensions and slurries of biological origin, efficient solid–liquid separation is highly dependent on proper chemical conditioning. This review first describes the material properties that may be sought through chemical conditioning and then it reviews the nature of colloidal stability, considering whether classical theory can be successfully related to practical application or whether newer models of suspension slurry behavior are required. Finally, the chemical agents used as conditioners are described, with important attributes explained.