Flow-through Electrode System Research Articles

Removal of Chromium ions (Cr6+) and Nickel ions (Ni2+) from Simulated Industrial Wastewater Using Flow-by-Porous Electrode

The quality of water is significantly impacted by the presence of Cr6+ and Ni2+ ions. This study investigates the effectiveness of a flow-by porous graphite electrode cell in removing these contaminants from simulated industrial wastewater. We explore the impact of various factors on the removal process, demonstrating the method's potential for efficient removal. The initial concentration of nickel and chromium ions (20 to 80 mg/l and 20 to 100 mg/l, respectively), the feed flow rate (0.28 to 1.11 ml/s), current density (0.2 to 2.25 mA/cm2) and pH all influence the removal rate and efficiency. A higher feed flow rate negatively affects the removal efficiency of both Ni2+ and Cr6+ ions. Nickel removal efficiency decreased by 34.9% at 20 ppm and 26% at 80 ppm, representing the highest and lowest reductions in efficiency, respectively. Chromium removal efficiency decreased by 19% at 100 ppm and 6.5% at 50 ppm, indicating the highest and lowest reductions in efficiency, respectively, under the same flow rate change. Under optimal conditions, the removal efficiency for Ni2+ was 99.47% after 15 min of operation at a current density of 1.96 mA/cm2, a flow rate of 0.28 ml/s, and a pH of 8 and the removal efficiency for Cr6+ was 99.97% after 10 min of operation at a current density of 2.25 mA/cm2, a flow rate of 0.28 ml/s, and a pH of 2. The flow-through porous electrode system achieves efficient heavy metal removal with operating costs of 0.24 USD/m3 for nickel and 0.38 USD/m3 for chromium at optimal conditions.

Flow-through electrode system (FES): An effective approach for biofouling control of reverse osmosis membranes for municipal wastewater reclamation

Emerging electrochemical disinfection techniques provide a promising pathway to the biofouling control of reverse osmosis (RO) process. However, the comparative effectiveness and mechanism of it under flow-through conditions with low voltage remains unclear. This study investigated the effect of a flow-through electrode system (FES) with both direct current (DC) and alternating pulse current (AC) on RO biofouling control compared with chlorine disinfection. At the initial stage of biofouling development, the normalized flux of AC-FES (67% on Day 5) was saliently higher than the control group (56% on Day 5). Subsequently, the normalized fluxes of each group tended similarity in their differences until the 20th day. After mild chemical cleaning, the RO membrane in the AC-FES group reached the highest chemical cleaning efficiency of 58%, implying its foulant was more readily removable and the biofouling was more reversible. The biofouling layer in the DC-FES group was also found to be easily cleanable. Morphological analysis suggested that the thickness and compactness of the fouling layers were the major reasons for the fouling behavior difference. The abundance of 4 fouling-related abundant genera (>1%), which were Pseudomonas, Thiobacillus, Sphingopyxis, and Mycobacterium exhibited a salient correlation with the biofouling degree. The operating cost of FES was also lower than that of chlorine disinfection. In summary, AC-FES is a promising alternative to chlorine disinfection in RO biofouling control, as it caused less and easy-cleaning biofouling layer mainly due to two advantages: a) reducing the regrowth potential after disinfection of the bacteria, leading to alleviated initial fouling, (b) reshaping the microbial community to those with weaker biofilm formation capacity.

High-efficiency and low-carbon inactivation of UV resistant bacteria in reclaimed water by flow-through electrode system (FES)

With the increasingly serious shortage of water resources globally, it has been paid more attention on how to secure the biosafety of reclaimed water and other non-traditional water sources. However, the 3 most applied disinfection technics, which are chlorine, ultraviolet (UV), and ozone disinfection, all have their disadvantages of selecting undesired bacteria and low energy utilization efficiency. Electrode disinfection is a promising solution, but the current electrode disinfection process still needs to be optimized in terms of the use conditions of the configuration reactivation. In this paper, we built a flow electrode system (FES). To evaluate the disinfection techniques more precisely, we isolated ultraviolet-resistant bacteria (URB) bacteria from the water of the full-scale water plant and tested the disinfection performance of FES and UV. The inactivation rate, reactivation potential, and energy consumption were analyzed. FES could inactivate 99.99 % of the URB and cause irreversible damage to the residual bacteria. FES could make all bacteria strains apoptosis in the subsequent 24 h of storage after alternating pulse current (APC) treatment, 3 V, within 27.7 s. Besides, the energy consumption of FES is about 2 orders lower than that of UV disinfection under the same inactivation rate. In summary, APC-FES is an efficient and low-carbon alternative for future water disinfection, which could achieve the ideal disinfection effect of a high inactivation rate, no reactivation, and low energy consumption.

Biofouling characteristics of reverse osmosis membranes by disinfection-residual-bacteria post seven water disinfection techniques

Reverse osmosis (RO) is widely used in wastewater reclamation to alleviate the increasingly global water shortage. However, it has an inconvenient defect of biofouling. Some disinfection processes have been reported to select certain undesirable disinfection-residual bacteria (DRB), leading to severe long-term biofouling potential. To provide constructive guidance on biofouling prevention in RO systems, this study performed a 32-day experiment to parallelly compared the biofouling characteristics of RO membranes of DRB after five mature water disinfection methods (NaClO, NH2Cl, ClO2, UV, and O3) and two recently developed water disinfection methods (K2FeO4 and flow-through electrode system). As a result, the DRB biofilm of K2FeO4 and O3 caused a slight normalised flux drop (22.4 ± 2.4% and 23.9 ± 1.7%) of RO membrane compared to the control group (non-disinfected, ~27% normalised flux drop). FES, UV, NaClO and ClO2 caused aggravated membrane flux drop (29.1 ± 0.3%, 33.3 ± 7.8%, 34.6 ± 6.4%, and 35.5 ± 4.0%, respectively). The biofouling behaviour showed no relationship with bacterial concentration or metabolic activity (p > 0.05). The thickness and compactness of the biofilms and the organics/bacterial number ratio in the biofilm, helped explain the difference in the fouling degree between each group. Moreover, microbial community analysis showed that the relative abundance of typical highly EPS-secretory and biofouling-related genera, such as Pseudomonas, Sphingomonas, Acinetobacter, Methylobacterium, Sphingobium, and Ralstonia, were the main reasons for the high EPS secreting ability of the total bacteria, resulting in aggravation of biofouling degree (p < 0.05). All types of disinfection except for NaClO and ClO2 effectively prevented pathogen reproduction in the DRB biofilm.

Comparison of disinfection-residual-bacteria (DRB) after seven different kinds of disinfection: Biofilm formation, membrane fouling and mechanisms

Membrane fouling is the Achilles' heel of the reverse osmosis (RO) system for high-quality reclaimed water production. Previous studies have found that after the significant selection effect of traditional disinfection, the remaining disinfection-residual bacteria (DRB) may possess more severe biofouling potentials. To provide more constructive advice for the prevention of biofouling, we compared the RO membrane fouling characteristics of DRB after using five commonly used disinfection methods (NaClO, NH2Cl, ClO2, UV, and O3) and two novel disinfection methods (K2FeO4 and the flow-through electrode system (FES)). Compared with the control group (undisinfected, 21.1 % flux drop), the UV-DRB biofilm aggravated biofouling of the RO membrane (23.4 % flux drop), while the FES, K2FeO4, and NH2Cl treatments showed less severe biofouling, with final flux drops of 6.9 %, 8.1 %, and 8.1 %, respectively. Adenosine triphosphate (ATP) was found to be a capable indicator for predicting the biofouling potential of DRB. Systematic analysis showed that the thickness and density of the DRB biofilms were most closely related to the different fouling degree of RO membranes. Moreover, the relative abundance of bacteria with higher extracellular polymeric substance (EPS) secretion levels, such as Pseudomonas and Sphingomonas, was found closely related with the biofouling degree of RO membranes.

Square-Wave Alternating Voltage for Enhancing Cr(VI) Reduction in a Carbon Fiber-Based Flow-Through Electrode System

Electrochemical reduction with a flow-through electrode system (FES) has been regarded as an effective method for water decontamination. However, under a direct voltage (DV) power supply, the reduction efficiencies were strongly limited by the gas bubbles generated in porous electrodes and the electrostatic repulsion between the negatively charged pollutants and cathode. Herein, square-wave alternating voltages (SWAV) were applied to regulate the anodic–cathodic polarities of electrodes for eliminating the gas accumulation in porous electrodes and enhancing the mass transfer efficiency. Under the optimized SWAV parameters, the Cr(VI) reduction and energy efficiency were increased obviously to ∼86 and 84% as compared with the 20%–30% Cr(VI) reduction and 30%–50% energy efficiency under the DV power supply. With periodically altering the anode to cathode, localized H+ and Cr(VI) species were formed on the anodic interface via H2O oxidation and Cr(VI) adsorption, which were further in situ reduced for enhancing the Cr(VI) mass transfer and reduction efficiencies. In addition, O2 species generated via H2O oxidation was also in situ reduced to H2O2 species, hence promoting the Cr(VI) reduction and operation stability for most Cr(VI) reduction with a stable energy efficiency (∼82%) over a 10 day operation (8 mg/L Cr(VI) and 500 L/m2/h flux). The successful application of SWAV may derive similar decontamination strategies, especially for electrically charged pollutants with the H+ or OH– ions as reactants.

Electroporation-coupled electrochemical oxidation for rapid and efficient water disinfection with Co3O4 nanowire arrays-modified graphite felt electrodes

Biologically unsafe drinking water occurs in developing regions lack of centralized water treatment plants. Herein, Co3O4 nanowire electrodes with Co3O4 nanowire arrays grown on graphite felt were fabricated and employed to construct a flow-through electrode system (FES) for rapid and efficient water disinfection, which achieved over 6.7-log E. coli removal under applied voltage of 2.5 V and flow rate of 65 mL/min (HRT ∼ 4.5 s) with energy consumption of 2.3 Wh/m3. The FES also achieved over 6.7-log removal at 2.5 V for the Gram-negative P. aeruginosa under ∼ 60 mL/min and for Gram-positive bacteria (E. faecalis and S. aureus) under ∼ 40 mL/min, and the Gram-negative bacteria were more vulnerable to FES disinfection than Gram-positive ones due to their larger sizes and thinner cell walls. In-situ sampling and live/dead backlight staining experiments revealed that pathogen inactivation mainly occurred on anode via the sequential adsorption, inactivation and desorption processes under the mass transfer forces of electric field attraction and flow scouring effect in porous electrodes. The disinfection mechanisms on the Co3O4 nanowire anode were recognized to be electroporation and electrochemical oxidation, and the pores generated by electroporation can provide diffusion channels for reactive species into the pathogen cells, promoting the disinfection performance.

Enhancement of Cr(VI) reduction by polyaniline nanorod-modified cathode in flow-through electrode system

Cr(VI) reduction to Cr(III) has been demonstrated to be an effective method for Cr(VI) detoxification. Herein, we fabricated polyaniline (PANI) nanorod forests-modified Carbon fiber felt (CFF) as CFF-PANI cathode in a Flow-through electrode system (FES) with the counter CFF anode for enhancing Cr(VI) reduction. The CFF-PANI was synthetized via in-situ polymerization under different aniline concentration to investigate the effect of PANI nano-structures on Cr(VI) reduction. It was revealed that BET and electrochemical surface area of PANI nanorods significantly affected the Cr(VI) reduction, and CFF-PANI cathode with the largest BET and electrochemical surface area exhibited ∼ 45% higher Cr(VI) removal and ∼ 35% lower specific energy consumption than the CFF cathode. A decrease-then-stable Cr(VI) removal was observed within 120 min operation time, which was attributed to the electro-adsorption of Cr(VI) species on CFF anode. In-situ sampling experiments revealed that the electrochemical oxidation on CFF anode inhibited the Cr(VI) electro-adsorption, and at applied voltage above 0.7 V, the Cr(VI) reduction on cathode was the main mechanism for Cr(VI) removal. The operation of FES at 0.8 V had the lowest specific energy consumption (48.5 Wh/mol) and maintained ∼ 95% energy efficiency for Cr(VI) reduction with minor competitive reduction of H2O or O2 species. The results suggested that CFF-PANI can be a promising cathode for Cr(VI) reduction from aqueous solutions.

Enhancing disinfection performance of the carbon fiber-based flow-through electrode system (FES) by alternating pulse current (APC) with low-frequency square wave

This study was aimed to investigate the influence of low-frequency alternative pulse current (APC) with square wave on the disinfection performance of carbon fiber-based flow-through electrode system (FES) towards a model bacterium (Escherichia coli). The FES disinfection under direct current (DC) supply was limited by the weak disinfection efficiency of cathode. Compared with DC supply (less than 1 log removal), FES under APC supply achieved superior disinfection performance (over 6 log removal) at the voltage of 3 V and flow rate of 125 mL/min. The optimum condition was acquired when pulse cycle time (T) equaled to hydraulic retention time (HRT), i.e. HRT/T = 1, corresponding to the low frequency (less than 1 Hz), under which the disinfection performance was improved by alternating of anode and cathode. In-situ sampling experiments revealed that redox reactions were carried out alternatively in each electrode, and both electrodes made great contributions to disinfection under APC supply, which was significantly different from DC supply. In addition, FES disinfection under APC supply also caused irreversible damage to bacterial cells, resulting in no bacterial regrowth/reactivation during storage, and guaranteed low energy consumption (11.4 ~ 12.1 Wh/m3) with high flow rate (100 ~ 125 mL/min). Therefore, the development of a novel FES under APC supply provided exciting possibilities for future application of electrochemical disinfection to achieve superior disinfection performance with no bacterial regrowth and low energy consumption.

Carbon fiber-based flow-through electrode system (FES) for Cr(VI) removal at near neutral pHs via Cr(VI) reduction and in-situ adsorption of Cr(III) precipitates

Cr(VI) reduction to Cr(III) and subsequent Cr(III) precipitation is an extensively employed strategy to treat Cr(VI)-contaminated wastewater, which generally generates large volumes of sludge that need expensive disposal, and requires high chemical cost for pH adjustment. Herein, flow-through electrode system (FES) with a sequential oxidation-reduction process was employed to simultaneously reduce Cr(VI) and in-situ precipitate Cr(III), thereby simplifying the treatment processes and providing potentials to recollect Cr resource. The influent (10 mg/L Cr(VI)) with near neutral pHs (6–8) was first oxidized by the anode with H+ ions generation via H2O oxidation, leading to the anode-treated effluent turned into strong acidic with pH below 3.5. Subsequently, under acidic condition, the Cr(VI) species were prone to reduce to Cr(III) on the cathode. The multi-cathode FESs (1A + nC) equipped with one counter anode (1A) and multiple cathodes (nC) were constructed to enhance the Cr(VI) reduction by providing more cathode reactive sites and in-situ Cr(III) precipitation by maintaining near neutral effluent pHs. The flow-through flux and applied voltage were optimized to be 500 L/h/m2 and 2.6 V, under which Cr species were undetectable in effluent of 1A + 4C FES within continuous operation time of 30 min. Regenerating the Cr(OH)3-passivated CFF electrodes and recollecting the Cr waste resource were easily accomplished by using a small volume of acidic solution with reversed applied voltage. This study suggested that carbon fiber-based FES with a sequential oxidation-reduction process can be a feasible approach for remediation and recovery of Cr(VI) contamination.

Construction and optimization mechanisms of carbon fiber-based flow-through electrode system (FES) with stackable multi-cathode units for water disinfection

The stackable carbon fiber-based flow-through systems (m(nC + 1A)) were constructed, where the multi-cathode units (nC + 1A) were equipped with multiple cathodes (nC) and a counter anode (1A), and the m was the stackable numbers of the nC + 1A units. The configuration of the m(nC + 1A) systems with m and n values from 1 to 6 was optimized by comparing their disinfection performance toward a model pathogen (Escherichia coli) from the aspects of disinfection ability, energy consumption and HRT. For multi-cathode units (nC + 1A), increasing the cathode numbers (n) promoted the E. coli inactivation by the predominant direct oxidation on the anode. Among the stackable m(nC + 1A) modules, the 3(3C + 1A) module was recommended as the best configuration. In the stackable 3(3C + 1A) module with consecutive reduction-oxidation processes, the E. coli inactivation mechanisms were attributed to the direct oxidation on the anodes and H2O2-induced indirect oxidation on the cathodes. The synergistic effect between the stackable 3C + 1A units promoted the electro-redox of the electrodes and their disinfection ability, which was also accompanied by the enhancement of energy consumption for O2/H2O2 mutual transformation on the electrodes. In turn, the modules with excessive stackable unit numbers (m > 3) over-promoted the competitive reaction of O2/H2O2 mutual transformation, restraining the disinfection performance.

Disinfection performance and mechanism of the carbon fiber-based flow-through electrode system (FES) towards Gram-negative and Gram-positive bacteria

The disinfection performance of a carbon fiber-based flow-through electrode system (FES) towards Gram-negative bacteria (Escherichia coli and fecal coliform) and Gram-positive bacteria (Enterococcus faecalis and Bacillus subtilis) in normal saline was systematically investigated over a wide range of applied voltages (1–5 V) and hydraulic retention times (HRTs) (1–10 s). It was revealed that the Gram-negative bacteria were more vulnerable to FES for their thinner cell walls, and over 6.5 log removal (no live bacteria detected) was achieved at the applied voltage of 2 V and HRT of 2 s; while Gram-positive bacteria were inactivated at slightly higher voltages (3 V, 2 s) or longer HRTs (2 V, 5 s). Bacterial inactivation was attributed to the change and rupture of cell membrane mainly by anode direct oxidation without bacterial regrowth/reactivation. In addition, negligible generation of the free chlorine at low voltages (≤2 V) can avoid the formation of potential chlorinated disinfection byproducts (DBPs). Hence, FES can offer a potential alternative to conventional disinfection methods for bacterial inactivation in natural and contaminated water.

Disinfecting Water with the Carbon Fiber-Based Flow-Through Electrode System (FES): Towards Axial Dispersion and Velocity Profile

Electrochemical technology for the killing of pathogens has been largely investigated. Lately, Ni et al. [1] published excellent research on the disinfection efficiency of a carbon fiber-based flow-through electrode system (FES) versus Gram-negative bacteria (Escherichia coli and fecal coliform) and Gram-positive bacteria (Enterococcus faecalis and Bacillus subtilis) in normal saline over a large span of applied voltages (1 - 5 V) and hydraulic retention times (HRTs) (1 - 10 s). They established that the Gram-negative microbes were more susceptible to FES for their thinner cell walls and over 6.5 log reduction (no live bacteria found) was obtained at the applied voltage of 2 V and HRT of 2 s; however, Gram-positive microbes were demobilized at slightly bigger voltages (3 V, 2 s) or longer HRTs (2 V, 5 s). Demobilizing microorganisms was related to the alteration and laceration of cell membranes mostly via anode direct oxidation in the absence of bacterial regrowth. Further, the disregarding formation of the free chlorine at low voltages (≤2 V) could avert the production of possible chlorinated disinfection by-products. Therefore, FES could furnish an undeveloped substitute to traditional disinfection processes for eliminating pathogens in water. This work concludes that focusing on axial dispersion and velocity profile inside anode will be very useful in comprehending the transport phenomena and proposing a fresh model that merges the axial dispersion and velocity profile for the FES. Such a research trend will more encourage the FES implementation at the large industrial level for disinfecting water.

Degradation of methylisothiazolinone biocide using a carbon fiber felt-based flow-through electrode system (FES) via anodic oxidation

Methylisothiazolinone (MIT) is one of the most widely used non-oxidizing biocides, however its toxicity may pose a threat to ecosystems. A carbon fiber felt-based flow-through electrode system was used for MIT degradation in an aqueous solution. An excellent degradation rate (~90%) was achieved at a low applied cell voltage (2.5 V) and a high feed water flux (3 m3 h−1 m−2) that corresponds to a short resistance time of ~11 s. In-situ sampling experiments and electrochemical characterization indicated that MIT was degraded via a direct anodic oxidation mechanism. In terms of electrode sequence, anode–cathode system (by placing the anode upstream from the cathode) exhibited an improved MIT degradation performance and energy efficiency compared with a reversed cathode–anode system (by placing the anode downstream from the cathode), because the former arrangement prevented parasitic reactions and provided a higher anode potential. Effluent analysis by time-of-flight mass spectrometry and luminescent bacteria acute toxicity showed that the organic sulfur atom was oxidized to the sulfoxide or sulfone structure and then hydrolyzed to release from the MIT molecule, which led to a significant toxicity reduction. No obvious performance loss was observed over 5 h of continuous operation with a total treated MIT solution up to 1400 times the cell volume and an energy requirement of 0.03 kWh m−3. These promising data make the carbon fiber felt-based flow-through electrode system attractive for effective and low-cost water purification.

Comparison of carbonized and graphitized carbon fiber electrodes under flow-through electrode system (FES) for high-efficiency bacterial inactivation

The disinfection performance of a flow-through electrode system (FES) was systematically evaluated using different carbonized (C1, C2, and C3) and corresponding graphitized (G1, G2, and G3) carbon fiber felt (CFF) electrodes. The physicochemical and electrochemical properties were characterized to identify the differences among CFFs. Graphitized CFFs (gCFFs) can achieve complete inactivation of Escherichia coli (>6 log) at the voltage of 3 V and flux of 120–3600 L/(m2 h) for high conductivity and chemical stability, while carbonized CFFs (cCFFs) only achieved around 1 log removal with obvious carbon corrosion. For the gCFFs, G1 (>6 log removal) with higher conductivity, better graphite structure, and larger surface area (related to fiber diameter and density) presented better disinfection performance at the flow rate of 30 mL/min than G2 (∼3 log) and G3(∼1 log). Furthermore, no regrowth and reactivation of bacteria occurred during the storage under visible light illumination after FES treatment. Three parallel FESs with G1 were operated continuously for one week (24 h per day, 7 days) treating the solution with an E. coli concentration ranging from 106 to 107 CFU/mL at the applied voltage of 3 V and the flow rate of 20 mL/min. No live bacteria were detected in the effluent of any of these three FESs. In-situ sampling experiments demonstrated that the inactivation of bacteria on anode was the dominant mechanism for FES treatment, which can be attributed to the sequential adsorption, direct-oxidation and desorption process on anode, instead of indirect oxidation by generating chemical oxidants. In addition, hydroxide ion generated from cathode reaction enhanced anode adsorption and inactivation of bacteria by providing alkaline environment. Combining the analysis results of material properties and disinfection performance, the gCFF-based FES was suggested to be a low-cost, high-efficiency, and safe alternative for future water disinfection.

Carbon Fiber-Based Flow-Through Electrode System (FES) for Water Disinfection via Direct Oxidation Mechanism with a Sequential Reduction-Oxidation Process.

Flow-through configuration for electrochemical disinfection is considered as a promising approach to minimize the formation of toxic byproducts and energy consumption via the enhanced convective mass transport as compared with conventional flow-by one. Under this hydrodynamic condition, it is essential to ascertain the effect of sequential electro-redox processes with the cathode/anode then anode/cathode arrangements on disinfection performance. Here, carbon fiber felt (CFF) was utilized to construct two flow-through electrode systems (FESs) with sequential reduction-oxidation (cathode-anode) or oxidation-reduction (anode-cathode) processes to systematically compare their disinfection performance toward a model Escherichia coli ( E. coli) pathogen. In-situ sampling and live/dead backlight staining experiments revealed that E. coli inactivation mainly occurred on anode via an adsorption-inactivation-desorption process. In reduction-oxidation system, after the cathode-pretreatment, bulk solution pH increased significantly, leading to the negative charge of E. coli cells. Hence, E. coli cells were adsorbed and inactivated easily on the subsequent anode, finally resulting in its much better disinfection performance and energy efficiency than the oxidation-reduction system. Application of 3.0 V resulted in ∼6.5 log E. coli removal at 1500 L m-2 h-1 (50 mL min-1), suggesting that portable devices can be designed from CFF-based FES with potential application for point-of-use water disinfection.

Sequential injection with lab-at-valve (LAV) approach for potentiometric determination of chloride

Sequential injection with “Lab-at-Valve (LAV)” approach is demonstrated for potentiometric determination of chloride. The LAV flow-through electrode system consists of two Ag/AgCl electrodes: one as a reference electrode, silver chloride activated surface-silver wire soaked in a constant-concentration chloride ion solution in a small tube covered with a polymer-membrane, another as a working electrode (a similar silver chloride activated surface-silver wire) placed in a flow channel. The electrode system is attached at one port of a 10 port multiposition valve. A modified autoburette was used as a propelling device. Using SI operation via a program written in-house, based on LabVIEW ®, a standard/sample is inserted, via the selection valve, in potassium nitrate as an electrolyte and water is used as a carrier. The zones are transported from the holding coil to the flow cell to monitor the difference in potential due to concentration cell behavior. The potential difference is then recorded as a peak. Peak height is proportional to logarithm of chloride concentration. The SI-LAV for chloride determination is very simple, fast, precise, accurate, automatic and economical. Applications to mineral drinking water and surface water have been made. The results agree with those of IC and titrimetric methods.

Continuous analysis in extracorporeally circulating blood--a rat model applying flow-through ion-selective electrodes for the measurement of Ca2+, K+, Na+ and pH.

A rat model is introduced which enables investigations in anticoagulated blood with continuous measurements by a flow-through electrode system. In the present study, a potentiometric ion-selective electrode (ISE)-system was used for measuring Ca2+, K+, Na+ and pH in rats. The setup was adjusted to an extracorporeal blood-volume of 0.750 ml. This permits indirect measurements of the analytes via a dialysis membrane, with electrical separation of the ISE's and the animal. The flow-rates of blood and dialysis-solution were adjusted in such a way that water diffusing from the aqueous dialysis solution into the blood, across the dialysis membrane, does not alter the haematocrit. Polyethyleneglycol-hirudin was used for anticoagulation, since it was superior to heparin. The assembly enables continuous measurements in the living anaesthetized rat over a time period of at least 3 hours.

Analysis of flow-through porous electrode cell with homogeneous chemical reactions: application to bromide oxidation in brine solutions

Electrochemical generation of elemental bromine from bromide-containing brine solutions using a flow-through porous electrode system was modelled and studied. Bromine yield was undermined by the homogeneous reactions taking place in the liquid phase which converted bromine back to bromide as well as other undesirable compounds. The effects of these reactions were characterized and accounted for in a mathematical description of a flow-through porous electrode system. The resulting model was used to analyse and estimate the effects of these reactions on the cell size and the current efficiency. Experimental data obtained support the model predictions.

Determination and distribution of iodide- and total-iodine in the North Pacific Ocean - by using a new automated electrochemical method

A new automated analytical method for determining inorganic iodine species in seawater as iodide- and total-iodine (iodide+iodate), by using a flow-through electrode system, has been applied to the seawater samples collected from the adjacent seas of Japan and the western and central North Pacific Ocean. It was found that a considerable amount of iodide-iodine is distributed not only in the euphotic zone, but also in deep waters of the Japan Sea and the Japan Deep and in directly overlying waters on the sea floor of the open ocean. This fact suggests that the reduction of iodate to iodide by biological activity in seawater occurs when nitrate is consumed by nitrate respiration in the presence of a large amount of easily oxidizable organic matter, which may be in particulate form, rather than when nitrate is deficient, as is generally accepted, because these waters contain the usual amount of nitrate for deep waters.