Streaming Current Detector Research Articles

Evaluation of Streaming Current Detector (SCD) and Charge Analyzing System (CAS) for automation of coagulant dosage determination

Evaluation of Streaming Current Detector (SCD) and Charge Analyzing System (CAS) for automation of coagulant dosage determination

How to use alum with cationic dispersed rosin size

Retention of cationic dispersed rosin size was studied via turbidity measurements on stock filtrate with different alum and dispersed rosin size dosages. Stock charge characteristics were analyzed using both an analysis of charge demand determined via a streaming current detector and an evaluation of zeta potential of the fibers by streaming potential measurement. The results indicated that an optimum amount of alum existed such that good sizing retention was maintained throughout a wide range of dispersed rosin size dosages. However, when an excessive amount of alum was used and fines and colloidal particles were transitioned from anionic to cationic, the cationic size retention was reduced. Laboratory results were confirmed with a paper machine trial. All data suggested that a stock charge study was necessary to identify optimal alum dosage for a cationic dispersed rosin sizing program.

Evaluation of the Streaming Current Detector (SCD) for Coagulation Control

A streaming current detector (SCD) is an instrument for measuring the charge that exists on small, suspended particles in water. The SCD is the instrument that can be used to measure coagulated particle stability for the feedback control of coagulant dosage. This report discusses the application of SCD as an instrument for coagulation dosage control. The SCD with automatic control of coagulant dosage consistently produced acceptable water quality, even during periods of changing raw water turbidity and varying flow rates. It minimizes under and overdosing of coagulant. It requires regular cleaning and maintenance to ensure optimum operation. The SCD is no substitute for efficient water treatment management.

Chemical feed control using coagulation computer models and a streaming current detector

This paper describes the use of both the streaming current detector (SCD) and coagulation computer models to provide real-time data for required coagulant feed rates. The method for computer modeling of coagulation and other water treatment processes/operations was originally developed for Lake Michigan Filtration Plant in Grand Rapids, Michigan (MI). Since the initial implementation, a number of water treatment plants (WTPs) in the United States have begun routinely utilizing computer models for chemical feed control and process performance optimization. One plant, Holland WTP in Holland, MI, currently employs both an SCD and a coagulation computer model for chemical feed control. Case studies presented in this paper compare the performance of coagulation computer models and the SCD in full-scale operation.

β-Lactoglobulin–sodium alginate interaction as affected by polysaccharide depolymerization using high intensity ultrasound

The purpose of this study was to provide insights into the interaction between β-lactoglobulin (BLG) and sodium alginate (ALG, before and after sonication) using isothermal titration calorimetry (ITC), streaming current detector (SCD), turbidity measurement, dynamic light scattering and electrophoretic mobility methods. High intensity ultrasound could effectively decrease the intrinsic viscosity of the ALG solution. Time and amplitude of the sonication treatment had a direct effect on the viscosity depression, while the sonication temperature had an inverse effect. ITC measurements indicated that the sonication decreased the interaction strength between ALG and BLG. The isoenthalpic plateau was obtained at higher ALG (US)/BLG weight ratio compared to ALG (IN)/BLG weight ratio. The zeta-potential of the nanoparticles produced from ALG (US)–BLG attractive interaction was lower than of those produced from ALG (IN)–BLG interaction. These differences were attributed to the lower charge density of the ALG (US) as a result of sonochemical interactions. Particle size measurements showed that the effect of the sonication treatment was the homogenization of the nanoparticles in the mixed dispersion. The biopolymeric nanoparticles formed may therefore be useful as a delivery system for fortification purposes of transparent liquid food products.

Streaming current titration for coagulation of high turbidity water

A jar test is commonly used to determine the chemical coagulation conditions in water treatment plants (WTPs). However, due to the frequent and intermittent turbidity measurements, and time-consuming determination for achieving optimal coagulation conditions, the jar test is not appropriate for the samples which are rapidly changing water turbidities. As an alternative, a streaming current detector (SCD) can be used by achieving electrically neutral conditions. A SCD can quantify the negatively charged particles by measuring the current of water samples. In this study, SCD titration was conducted to rapidly determine the optimal coagulation dosage for highly turbid waters (50∽600NTU) prepared with suspensions of kaolin (100∽1000mg/L). Polyaluminum chloride (PAC) and poly-diallyldimethylammonium chloride (poly-DADMAC) were added as coagulants. To estimate the optimal dose, a SCD titration-coagulation model was constructed, and its suitability was verified statistically by multiple linear regression analysis. In both homogeneous (PAC-PAC) and heterogeneous (poly-DADMAC-PAC) titration-coagulation models, the residual turbidity of highly turbid kaolin samples was successfully lowered to less than 1NTU. The homogeneous model and the jar test showed a maximum difference of 3mg/L for the suggested coagulant dose. Our results suggest that SCD can be applied to rapidly and accurately determine the coagulation dosage for highly turbid waters in water treatment plant even during rainy season.

Treatment with chemical coagulants at different dosing levels changes ecotoxicity of stormwater from the Tahoe basin, California, USA

In recent decades, the transport of stormwater-associated fine particles and phosphorus into Lake Tahoe has led to decreased water clarity and related ecological changes. Polyaluminum chloride coagulants (PACs) have shown great promise in removing these constituents from stormwater before it enters the lake. However, the potential risks of coagulant treatment to aquatic organisms are not well understood. This study investigated stormwater and coagulant toxicity under non-dosed, optimally-dosed, and over-dosed conditions using the US EPA 3-species test through growth of green algae (Selenastrum capricornutum), zooplankton (waterflea, Ceriodaphnia dubia) mortality and reproduction, and larval fish (fathead minnow, Pimephales promelas) mortality and biomass. Stormwater samples were collected during a 2005 spring snowmelt runoff event from three sites representing various forms of developed regions around Lake Tahoe. Samples were dosed with two different coagulants (a chitosan and a PAC) at levels optimized with a streaming current detector (SCD). Non-treated highway runoff was toxic to zooplankton and fish. Optimal coagulant dosing increased algal growth and reduced zooplankton toxicity. Overdosing at two and three times the optimal level of a PAC decreased zooplankton reproduction and increased fish mortality. PAC-related toxicity was correlated with increasing total unfiltered aluminum and decreasing alkalinity, pH, and DOC. Because of toxicity risks, we recommend keeping PAC coagulant dosing at or below optimal levels in practice.

Shapes of Polyelectrolyte Titration Curves. 1. Well-Behaved Strong Polyelectrolytes

The charge content of aqueous polymers is measured routinely by polyelectrolyte titrations in which an unknown polymer is titrated with an oppositely charged standard polymer solution, usually poly(diallyldimethyl ammonium chloride) or potassium poly(vinyl sulfate). Polyelectrolyte titration end points are frequently determined with a streaming current detector (SCD). The shapes of polyelectrolyte titration curves from polyelectrolytes with fixed electrical charges were simulated by a diffuse electrical double layer model. Well-behaved titration curves obtained with fixed charged polyelectrolytes were fit by the modeling, giving support for the basic hypothesis that the net charge of material adsorbed on the SCD wall is a linear function of the volume of added titrant. The shapes of titration curves from deviant systems such as poly(vinyl alcohol)-borate cannot be predicted by the model.

Ultrafiltration of surface water with coagulation pretreatment by streaming current control

Due to unfit soil and water conservancy in some regions of China, conventional water treatment has showed some defects for the poor quality of water resource. Ultrafiltration (UF) by hollow-fiber membranes is in increasing development in the fields of drinking water purification. Coagulation/UF process can be used to treat poor quality surface water: the permeate quality is increased and membrane fouling is reduced. In this research, a streaming current detector (SCD) method was introduced to asses how coagulation affects membrane performance. Results showed that membrane performance was improved with the coagulant added to get the positive streaming current (SC) value, since with the positive SC coagulation removed more organic matters. In the coagulation/UF process, coagulation unit does not need to be controlled to get complete charge neutralization, the point of zero charge, because the ultrafiltration membrane has an excellent ability to remove particles and colloids.

Enhancement of coagulation control using the streaming current detector

In water treatment processes, the individual unit operations are complex, highly non-linear and poorly understood. Whilst many models have been developed to improve process understanding, these are rarely in a form easily exploited by the control engineer. Attempts to improve the performance of water treatment works through the application of improved control and measurement have had variable success. This paper discusses investigations into the application of feedback control on the clarification process of a large-scale pilot plant using a streaming current detector (SCD). The application is aimed towards maximising the efficiency of the chemical coagulation process. To achieve this, a simple model of the interactions of process operating conditions on the SCD measurements must be made.

Charge determination of synthetic cationic polyelectrolytes by colloid titration

The stoichiometric interaction between oppositely charged polyelectrolytes forms the basis of the technique of colloid titration. This can be used, for instance, to determine the charge density of a cationic polyelectrolyte, using an anionic polyelectrolyte of known charge density, such as potassium polyvinyl sulphate (PPVS). The technique requires a suitable method of end-point detection and there are several possibilities. In this work three methods have been investigated: visual observation of the colour change of a cationic dye ( o-toluidine blue), spectrophotometric determination of the colour change of the same dye, and electrokinetic detection of charge neutralisation, using a streaming current detector. These have been applied to a range of cationic polyelectrolytes, with different charge densities and molecular weights. In all cases, the cationic charge was due to quaternary nitrogen groups. In the case of the cationic dye, it was shown that the sharpness of the colour change depends on the charge density of the cationic polyelectrolyte. With lower charge density materials the binding to PPVS is weaker and binding of the dye to PPVS can occur before all of the polyelectrolyte charge has been neutralised. However, by carrying out titrations at several polyelectrolyte concentrations, good linear relationships were found, from which reliable charge density values could be derived. The streaming current method avoids the problem of competitive interaction of PPVS with o-toluidine blue and gives quite sharp transitions at the isoelectric point, although there was some dependence on polyelectrolyte charge density. This method gave good agreement with charge densities derived from the spectrophotometric technique. Effects of pH and ionic strength were also briefly investigated. For most of the cationic polyelectrolytes, there was some loss of charge at higher pH values, probably as a result of hydrolysis. Increasing ionic strength causes a less distinct colour change of o-toluidine blue, as a result of weaker electrostatic interactions.

Automatic control of polymer dose using the streaming current detector

A previous phase of this study demonstrated that streaming current (SC) measurements taken from the liquid stream after dewatering can be used to adjust and optimize polymer dosages used for conditioning of wastewater solids. Consequently, use of the streaming current detector (SCD) was evaluated for continuous feedback control of polymer dosing in two full‐scale dewatering facilities. Control was implemented using a slightly negative SC setpoint, and the SCD's ability to control the polymer pumps was assessed when the wastewater solids characteristics changed during routine operation and when controlled additions of ferrous chloride were made. Changes in the solids flow rate were also imposed to assess the control system's response at one facility. At the second wastewater treatment plant, an unexpected change in the polymer also occurred during SCD use, and the system's ability to adjust the polymer dose accordingly was assessed during this incident. Results indicated that the SCD adjusted the polymer feed rate appropriately during all changes in solids flow rate and characteristics and polymer concentrations. The device's success indicates that charge neutralization plays a significant role in solids conditioning and can be used as an indicator of polymer performance and for feedback control of dosage. Routine and thorough cleaning of the SCD's probe with a plastic brush may be necessary in certain applications to maintain consistent control.

Polymer dose assessment using the streaming current detector

The streaming current detector(SCD) is an electrokinetic analyzer for characterizing charge properties of particles in aqueous suspension. Its use in water treatment is well established. This research evaluated its use for automatic monitoring of polymer dosage in three wastewater treatment facilities using centrifuges or belt filter presses for dewatering. Continuous SCD readings from the liquid stream (centrate or filtrate) and other process responses were recorded while imposing stepwise changes in the polymer dose. The polymer caused a transition from negative to positive charge in both the conditioned solids and the liquid stream. Near‐zero SCD readings coincided with optimal fullscale dewatering, as indicated by solids measurements and recoveries and by minima in filtrate turbidity, filtrate viscosity, conditioned solids filterability times, and (in some cases) capillary suction times. Thus, charge neutralization is a key mechanism in solids conditioning, and the SCD is suitable for monitoring of polymer dosage. For its use in automatic polymer dose control—evaluated in a subsequent phase of the study—modifications were required to provide more reliable continuous sampling.

Fuzzy control of coagulation reaction through streaming current monitoring

A fuzzy logic controller (FLC) incorporating the streaming current detector (SDC) was utilized in the automatic control of the coagulation reaction. Kaolinite was used to prepare synthetic raw water, and ferric chloride was used as the coagulant. The control set point was decided at a streaming current (SC) of −0.05 and pH of 8.0 from jar tests, zeta potential and streaming current measurements. A bench-scale water treatment plant with rapid mix, flocculation, and sedimentation units, operated in a continuous-flow mode, was utilized to simulate the reaction. Two critical parameters affecting the coagulation reaction, i.e., pH and streaming current, were chosen as process outputs; while coagulant dose and base dose were chosen as control process inputs. They were on-line monitored and transduced through a FLC. With raw water of initial turbidity of 110 NTU, residual turbidity of lower than 10 NTU before filtration was obtained. Results show that this combination functions satisfactorily for coagulation control.

Fuzzy control of coagulation reaction through streaming current monitoring

A fuzzy logic controller (FLC) incorporating the streaming current detector (SDC) was utilized in the automatic control of the coagulation reaction. Kaolinite was used to prepare synthetic raw water and ferric chloride was used as the coagulant. The control set point was decided at a streaming current (SC) of -0.05 and pH of 8.0 from jar tests, zeta potential and streaming current measurements. A bench-scale water treatment plant with rapid mix, flocculation, and sedimentation units, operated in a continuous-flow mode, was utilized to simulate the reaction. Two critical parameters affecting the coagulation reaction, i.e., pH and streaming current, were chosen as process outputs; while coagulant dose and base dose were chosen as control process inputs. They were on-line monitored and transduced through a FLC. With raw water of initial turbidity of 110 NTU, residual turbidity of lower than 10 NTU before filtration was obtained. Results show that this combination functions satisfactorily for coagulation control.

The Streaming Current Detector: A Quantitative Model

The streaming current detector (SCD) is an instrument used for continuous characterization of colloidal surface charge. It measures the alternating current generated by mobile countering when charged material momentarily adheres to cylinder and piston walls while the piston reciprocates. The utility of the SCD for coagulant control is generally accepted, as evidenced by the estimated one thousand units in service in North America. However, one drawback to this device has been the lack of an exact quantitative model explaining its functioning. This paper provides such a description, relating the generated current to the zeta potential of the characterized material as a function of instrument parameters and solution chemistry. The model, programed inMathematica,agrees closely with an earlier analytical solution under many conditions. Its inclusion of an inertial term, however, allows behavior of the SCD to be simulated under a more general range of conditions.

Adsorbing Colloid Flotation of As(V)–-Feasibility of Utilizing Streaming Current Detector

Abstract A feasibility study was conducted to assess the application of a streaming current detector (SCD) in flotation processes. The adsorbing colloid flotation (ACF) of As(V) with iron oxide and sodium dodecylsulfate (SDS) was investigated. Both zeta potential and streaming current (SC) reading of each colloidal systems were measured. Results show SC changed with pH values and can be well correlated to zeta potential. The optimum pH range for As(V) removal was found to be ca. 4–5. Removal of As(V) as affected by SDS concentration, colloidal concentration, and gas flow rate were investigated. It is proposed that both free arsenic ox anions and iron-arsenate complex were involved in the process. Preliminary results show it feasible for SCD to be utilized in adsorbing colloid flotation.

Influence of pH adjustment on microcapsules obtained from complex coacervation of gelatin and acacia.

The coacervation behaviour of commercial grade gelatin and acacia mixtures was studied with five different acids to adjust the coacervation pH, i.e. HCl, HNO3, H2SO4, acetic acid, and citric acid. The electrical equivalence pH value (EEP) of the polymer mixture was determined by means of a streaming current detector (SCD). With all acids--except H2SO4--maximum coacervate yield was observed at the EEP. Using H2SO4 the EEP was found at a lower pH value than compared with the point of maximum coacervate yield. The quantity of coacervate at the EEP was significantly reduced in the presence of H2SO4 whereas with all other acids, almost no differences were found. The dependence of the coacervate volume on the added amount of acid did not change in parallel to the dry coacervate yield and there was no coincidence of the maximum coacervate volume and the EEP. The barrier properties of the capsule shells of corresponding microcapsules using indomethacin as a model drug were examined by dissolution studies. Indomethacin microcapsules showed the slowest release rate when the coacervation pH was adjusted to the EEP and not to the pH of maximum coacervate yield. As expected from the coacervation behaviour, dissolution profiles of the microcapsules were quite similar even when different acids were used for pH adjustment.

The streaming current detector: A comparison with conventional electrokinetic techniques

The streaming current detector (SCD) is an instrument showing increasing application for the in-situ monitoring of colloidal flocculation processes. The mechanism of operation of the SCD is examined by the use of well characterized surfaces and dispersed colloidal particles. The response of the instrument in the presence of various electrolytes and with the addition of colloids of known electrokinetic properties indicates that the apparatus is measuring a quantity that shows contributions from the charge on both the walls and piston of the apparatus and from colloidal material associated with the surfaces. Analysis of the output of the instrument in terms of the magnitude of the current is poorly accounted for by theory. The efficiency of adsorption of colloids, polymers and other simple reagents to the walls and/or piston and the ease of removal of these substrates was found to be critical to the response of the instrument. Streaming potential measurements were used to obtain reference zeta potentials.kw]Electrokinetic techniques; Streaming current detector

Development of New Polymer Dosage Control Method for Sludge Dewatering Process

In a sludge dewatering process using polymer, controlling the polymer dosage is an important factor for upgrading performance and achieving a saving on costs. A new automatic polymer dosage control method has been developed by the authors, which features the use of a streaming current detector or a colloid titrator. These detectors detect the colloidal charge of the filtrate from sludge. The said method was used with actual dehydrators and the following advantages were confirmed.(1) The said method is applicable for various types of dehydrators.(2) The said method is effective even when there are changes in sludge characteristics.(3) The said method is more economical than a conventional solids proportional control method in that less polymer is used.