Electrochemical Wastewater Treatment Research Articles

Membrane-separated electrochemical latrine wastewater treatment

Membrane electrolysis is shown to be durable over one month of continuous operation.

The Nature of the Electro‐Oxidative Catalytic Response of Mixed Metal Oxides: Pt‐ and Ru‐Doped SnO2 Anodes

AbstractThe catalytic behavior of metal oxides for oxidative reactions is generally classified into active or non‐active, depending on whether surface redox species participate or not. In the case of mixed metal oxides, however, this simplified scenario may be more complex. Non‐active oxides containing electroactive metal species, like Pt‐ and/or Ru‐doped SnO2 electrodes, are promising anode materials for the electrochemical treatment of wastewaters. This work analyzes the effect of Pt and Ru species on the nature of the electro‐oxidative catalytic response of Ti/SnO2 anodes. For this purpose, the electro‐oxidation of phenol and the competing oxygen evolution reaction (OER) in NaOH have been chosen as model reactions. The different electrodes and reactions were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel measurements. The obtained results reveal that both Pt and Ru introduce solid‐state redox processes and catalyze the OER and the phenol oxidation onto Ti/SnO2‐based electrodes. Nevertheless, the dopants induce quite different active behaviors in the mixed oxides. Pt practically does not affect the OER mechanism, but enhances its kinetics, so its electrocatalytic activity is associated with a specific adsorption of hydroxyl anions or phenolate on Pt sites, without participation of the irreversible Pt/PtOx couple (i. e. a “non‐redox‐active” behavior). On the contrary, Ru species involve various and highly reversible redox processes that accelerate and modify the rate‐determining step of the OER, and that actively mediate in the phenol oxidation.

Electrochemical treatment of pharmaceutical wastewater through electrosynthesis of iron hydroxides for practical removal of metronidazole

Antibiotics as the severe contaminants of aqueous environments were received growing attention during the last decades. The current work is the first report on investigating the potency and efficiency of electrocoagulation process in the successful removal of metronidazole (MNZ) from pharmaceutical wastewater using response surface methodology based on central composite design. The applied method by optimizing the independent and combined effects of significant variables which affecting the EC process enhanced the removal efficiency of MNZ. Analysis of variance was applied to verify the significance of independent variables solely and their interactions. The best removal efficiency of 100% found under the optimal operating condition of initial MNZ concentration 21.6 mg L−1, pH 8.2, current density 6.0 mA cm−2, inter-electrode distance 3 cm, and reaction time of 14.6 min. Isotherm investigations revealed that the Langmuir model with the R2 of 0.994 best fitted to the obtained experimental equilibrium results. The fast adsorption of MNZ on the surface of Fe(OH)3 and [Fe(OH)2]+ with the equilibrium time of 15 min confirmed that the kinetics of the electrocoagulation process follow the pseudo-second-order model (R2 = 0.962). The electrocoagulation process under the optimal operating condition revealed that the electrical energy consumption per each m3 of treated pharmaceutical wastewater, per each g of MNZ, removed, and per each kg of Fe electrode consumed, were found to be 0.516 kWh m−3, 0.0234 kWh g−1, and 0.0436 kWh kg−1, respectively.

Highly Tunable and Facile Synthesis of Uniform Carbon Flower Particles.

Three-dimensional hierarchical porous carbon materials with flower-like superstructures are of great interest for energy applications since their unique shape not only provides high accessible surface area and consequently more exposed active sites but also facilitates ion transport for high-rate capability. However, finding a controllable way to make porous carbons with such specific shapes has been challenging. Herein, we report a tunable and simple method for one-pot synthesis of polyacrylonitrile and its copolymer nanostructured particles with various superstructures (flower, pompom, hairy leave, and petal shapes) controlled by employing various solvents or by the incorporation of different co-monomers. The correlation between polymer particle shapes and solvent properties has been identified through Hansen solubility parameters analysis. The obtained uniform polyacrylonitrile particles could be readily converted into porous carbons by high-temperature gas treatment while maintaining the original shape of the polymer precursor structures. The resulting carbon materials have high nitrogen-doping concentration (7-15 at%) and tunable porous structures. This novel synthetic method provides a simple way to make porous carbons with controllable morphology and potentially advantageous properties for a variety of potential energy and environmental applications, such as electrochemical energy conversion and wastewater treatment.

Design and Preliminary Implementation of Onsite Electrochemical Wastewater Treatment and Recycling Toilets for the Developing World

Self-contained toilet wastewater treatment system prototypes based on electrochemical oxidation of feces and urine using bi-layered semiconductor anodes ([Bi2O3]z[TiO2]1-z/IrxTayO2/Ti) have been designed, constructed, and implemented in regions where access to proper and sufficient sanitation is limited. Prototypes were designed to fit in shipping containers in order to provide toilets and onsite wastewater treatment with clean water recycling. Units were designed to handle the waste of 25 users per day (or 130 L of toilet wastewater). The first prototype was tested on the Caltech campus (Pasadena, California) followed by improved second-generation prototypes that were subsequently installed in India (Ahmedabad, Gujarat and Kottayam, Kerala) and China (Yixing, Jiangsu) for open use in various public settings. The prototypes were able to provide for the disinfection of pathogens (<10 MPN Total coliforms and <1 MPN Fecal coliform indicator organisms per 100 mL), reduction of chemical oxygen demand (<100 mg O2 L-1), ammonia (<10 mg N L-1), and color at an average energy consumption of 35 Wh L-1. The treated wastewater was recycled for use as toilet flushing water. Figure 1

Optimized Fabrication of TiO2 Nanotubes Array/SnO2-Sb/Fe-Doped PbO2 Electrode and Application in Electrochemical Treatment of Dye Wastewater

A TiO2 nanotubes array/SnO2-Sb/Fe-doped PbO2 electrode with high oxygen evolution potential and enhanced electrochemical oxidation performance was successfully manufactured. The surface morphology and electrochemical performance of the electrode were characterized by a field emission scanning electron microscope, linear sweep voltammetry, and electrochemical impedance spectroscopy experiments. The effect of Fe doping concentration on the electrode performance was also investigated. This study shows the doping of Fe on a PbO2 electrode improved the micro-morphology and the conductivity of the electrode. The oxygen evolution potential was also increased to 1.95 V [versus a saturated calomel electrode (SCE)] via Fe doping. The optimal condition of Fe doping concentration was 0.02 M. The optimized electrode showed that the decoloration rate and total organic carbon removal ratio of methylene blue approached 98% and 96% after 30 min of electrochemical treatment, respectively. The accelerated lifetime of the optimized Fe-doped electrode was approximately 4.3 times larger than that of the undoped PbO2 electrode. A Ti/TiO2 nanotubes array/SnO2-Sb/Fe-doped PbO2 anode shows potential application in the electrochemical treatment of organic dye wastewater.

Electrochemical degradation of azo dye methyl orange by anodic oxidation on Ti4O7 electrodes

Magneli-phase Ti4O7 has been used in a diverse range of electrochemical applications due to its high electrical conductivity and great corrosion resistance. However, there are relatively few researches on the application of water treatment. In this paper, high density Ti4O7 ceramic electrode was successfully fabricated by the spark plasma sintering (SPS) and used as the anode for the electrochemical degradation of azo dye methyl orange. The phase, morphology and electrochemical properties of Ti4O7 electrode were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and cyclic voltammetry (CV), respectively. The experimental results revealed that the dye degradation was achieved by indirect electrochemical oxidation, mediated by electrogenerated ·OH radicals and active chlorine. Both of the slot voltage and supporting electrolyte concentration had positive effects on color removal of methyl orange whereas the decolorization rate decreased with the increasing initial concentration. The complete removal of color was achieved within a short period of electrolysis for almost all the experiments, and 98.1% of chemical oxygen demand (COD) was removed after 6 h electrolysis under the optimum conditions. This study would provide important significance for achieving efficient and sustainable electrochemical wastewater treatment using Ti4O7 electrode material.

Is There a Precipitation Sequence in Municipal Wastewater Induced by Electrolysis?

Electrochemical wastewater treatment can induce calcium phosphate precipitation on the cathode surface. This provides a simple yet efficient way for extracting phosphorus from municipal wastewater without dosing chemicals. However, the precipitation of amorphous calcium phosphate (ACP) is accompanied by the precipitation of calcite (CaCO3) and brucite (Mg(OH)2). To increase the content of ACP in the products, it is essential to understand the precipitation sequence of ACP, calcite, and brucite in electrochemical wastewater treatment. Given the fact that calcium phosphate (i.e., hydroxyapatite) has the lowest thermodynamic solubility product and highest saturation index in the wastewater, it has the potential to precipitate first. However, this is not observed in electrochemical phosphate recovery from raw wastewater, which is probably because of the very high Ca/P molar ratio (7.5) and high bicarbonate concentration in the wastewater resulting in formation of calcite. In the case of decreased Ca/P molar ratio (1.77) by spiking external phosphate, most of the removed Ca in the wastewater was used for ACP formation instead of calcite. The formation of of brucite, however, was only affected when the current density was decreased or the size of cathode was changed. Overall, the removal of Ca and Mg is much more affected by current density than the surface area of cathode, whereas for P removal, the reverse is true. Because of these dependencies, though there is no definite precipitation sequence among ACP, calcite, and brucite, it is still possible to influence the precipitation degree of these species by relatively low current density and high surface area or by targeting phosphorus-rich wastewaters.

Electrochemical treatment of flutriafol wastewater using a novel 3D macroporous PbO2 filter: Operating parameters, mechanism and toxicity assessment

In order to break the high operating cost bottleneck of electrochemical treatment of aqueous flutriafol (FTF), an emerging fungicide, a novel three-dimensional ordered macroporous PbO2 (3DOM-PbO2) filter was designed to facilitate mass transfer. The effects of operating parameters, including current density, flow rate and initial concentration on FTF electrooxidation performance were investigated using conventional flat Ti/PbO2 (F-Ti/PbO2) and 3DOM-PbO2 filters, with primary objective being the development of appropriate parameters for FTF treatment. The results indicated that the FTF removal efficiency on 3DOM-PbO2 filter was improved by 2.8 times compared to that on F-Ti/PbO2 at 5 mA cm−2, 10 ml s−1 and 100 mg L−1 FTF. The corresponding electrical energy consumption was reduced by 2.7 times, ` TOC removal and mineralization current efficiency were enhanced by 4.9 and 4.8 times, respectively. Furthermore, aromatic intermediates, nitrogenous compounds and carboxylic acids were identified as main byproducts using experimental method combined with quantum chemical calculations. Then, a possible pathway of FTF degradation on 3DOM-PbO2 was proposed. Finally, the acute toxicity results showed that toxicity of the byproducts first increases and then decreases through the proposed route. LC50,48 h value of FTF wastewater increased 35%–70% on the 3DOM-PbO2 filter, indicating a significant biodegradability enhancement.

Electrochemical treatment of sugar industry wastewater: process optimization by response surface methodology

Wastewater from sugar industry has multiple combinations of organic and inorganic contaminants. It has an adverse impact on nearby environment and requires specific type of treatment to minimize the effect. To treat the sugar industry wastewater, an attempt has been made with the electrochemical process by using aluminum electrode. Four process parameters were selected, namely initial pH (pH 4–10), current density (44.5–133.5 A/m2), electrode spacing (10–20 mm), and experimental time (20–100 min) to optimize the condition with surface response methodology. At optimum condition maximum, 69.2% chemical oxygen demand and 88.6% color reduction were archived at pH 7, current 1 A, electrode distance 1.5 cm and treatment time 60 min. The coefficient of the model predicted (R2) value of 0.87 and 0.48, and adjusted (R2) value of 0.64 and 0.45 for chemical oxygen demand and color reduction were obtained. The physicochemical characteristic indicates that settling sludge has more inorganic material as compared to floating sludge; hence, settling sludge has low calorific value than floating sludge.

A Comparative Study on Electrochemical Treatment of Wastewater By Using BDD Electrodes with Different Sizes of Crystals

Boron doped diamond (BDD) electrode has been widely used in wastewater treatment, due to its wide potential windows, low background current, high stability and corrosion resistance [1]. Typical BDD electrode is always referred to microcrystalline diamond, which is mainly composed of sp3 carbon and has little sp2 carbon in the film [2]. Thus the electrochemical oxidation ability of this type of BDD electrode can be attributed to the effect of sp3 carbon. When the diamond grain size reduces to the degree of nanometer, its characteristics will certainly change. Nanocrystalline diamond film can be divided into two parts, named grain and grain boundary, grain is made of sp3 diamond, while grain boundary is mainly consist of sp2 carbon, including graphite, hydrocarbon and amorphous carbon et al [3]. The unique structure of the nanocrystalline diamond film makes it has many excellent properties, including high hardness, low surface roughness, high thermal conductivity and electron emission et al. Recently, many researchers try to focus on the study of the role of sp3/sp2 ratio on the influence of electrochemical oxidation efficiency. And they do have some discoveries. Araújo et al. studied the influence of sp3/sp2 ratio on the performance of electrochemical oxidation of Rhodamine B [4]. They found that higher diamond content in the film favored the greater TOC and COD removal rates as well as the oxidation of organic compounds to CO2. Souza et al. studied the effect of the sp3/sp2 ratio on the electrochemical oxidation of 2,4-dichlorophenoxyacetic acid [5]. They found that higher sp3/sp2 ratio would lead to a more rapid and efficient oxidation. Besides, they also found that with the increase of sp3 content in the film, the maximum concentration of chlorinated compounds would decrease. It has shown that sp2 content in the diamond film has significant influence on the performance of electrochemical oxidation. Thus, in this paper, comparative study of electrochemical oxidation of artificial humidity condensate and artificial human urine using boron doped nanocrystalline diamond electrode (BDNCD) and boron doped microcrystalline diamond electrode (BDMCD) respectively was carried out. TOC removal efficiency as well as the variation of the organic and inorganic compounds are investigated. Finally, the accelerated lifetime test was measured to comparison the lifetime of both electrodes. The results showed that the degradation rates were in good agreement with the pseudo first order kinetic model, with the degradation rate constant of 1.33h-1 and 1.02h-1 for BDMCD and BDNCD anode respectively. The degradation rate in BDMCD anode was 1.3 times faster than BDNCD anode, this was mainly due to different carbon phases in BDMCD and BDNCD electrode. BDMCD film was mostly composed of sp3 carbon, the concentration of sp2 carbon was negligible, while BDNCD film had a relatively large amount of sp2 carbon in grain boundary together with sp3 carbon in grain. It was found that NO2- and NO3- were the main intermediate products, and NO3- was the final product for two kinds of electrodes. Compared with BDMCD system, the oxidation of nitrogen compounds also show a lagging behind. In summary, both electrode had the same mineralization efficiency in the enough treatment time, but BDMCD anode has a higher degradation rate. That means high sp3 content in the film favors high degradation rate. The comparative study of the accelerated lifetime test of both electrodes showed that the lifetime of BDNCD electrode was 32.8% higher than BDMCD electrode. So it means high sp2 content in the film will lead to a higher lifetime of diamond electrode due the low surface roughness of electrode. Reference [1] Panizza M, Cerisola G., Journal of Electroanalytical Chemistry, 2010, 638(1): 28–32. [2] Guo L, Chen G., Diamond and Related Materials, 2007, 16(8): 1530–1540. [3] Williams O A., Diamond and Related Materials, 2011, 20(5-6): 621–640 [4] De Araújo D M, Cañizares P, Martínez-Huitle C A, et al., Electrochemistry Communications, 2014, 47: 37–40. [5] Souza F L, Saéz C, Lanza M R V, et al., Electrochimica Acta, 2016, 187: 119–124.

Enhancement of Conductive Coated Polymer Networks Utilizing Guest-Host Inclusion Complexes for the Electrotreatment of Heavy Metal Ion Effluent

As water pollution continues to be a global concern, there is a demand for cost effective remediation technologies. A large contribution of water scarcity can be traced back to heavy metal ion contamination which current technologies, such as ion exchange or ‘softening’ have proven to be ineffective. This work focuses on the remediation of heavy metal ion pollutants using the incorporation of β-Cyclodextrin (β-CD), and conductive polymers into an adsorbent, cellulosic nanocomposite. Previous results have shown that β-CD can enhance the adsorption capability allowing the removal of 75% Cadmium (Cd) ions from solution. To further increase the yield of metal ion removal, the chemical polymerization of a conductive polymer, such as polyaniline (PANI) introduces electrochemical properties to the cellulosic film. Initial results have indicated that with the application of voltage these conductive nanocomposites have the ability to be used for the electrochemical treatment of simulated wastewater as Copper (Cu) ions were shown to be successfully removed from solution.

Cobalt-Doped Black TiO2 Nanotube Array as a Stable Anode for Oxygen Evolution and Electrochemical Wastewater Treatment.

TiO2 has long been recognized as a stable and reusable photocatalyst for water splitting and pollution control. However, it is an inefficient anode material in the absence of photoactivation due to its low electron conductivity. To overcome this limitation, a series of conductive TiO2 nanotube array electrodes have been developed. Even though nanotube arrays are effective for electrochemical oxidation initially, deactivation is often observed within a few hours. To overcome the problem of deactivation, we have synthesized cobalt-doped Black-TiO2 nanotube array (Co-Black NTA) electrodes that are stable for more than 200 h of continuous operation in a NaClO4 electrolyte at 10 mA cm–2. Using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, electron paramagnetic resonance spectroscopy, and DFT simulations, we are able to show that bulk oxygen vacancies (Ov) are the primary source of the enhanced conductivity of Co-Black. Cobalt doping both creates and stabilizes surficial oxygen vacancies, Ov, and thus prevents surface passivation. The Co-Black electrodes outperform dimensionally stable IrO2 anodes (DSA) in the electrolytic oxidation of organic-rich wastewater. Increasing the loading of Co leads to the formation of a CoOx film on top of Co-Black electrode. The CoOx/Co-Black composite electrode was found to have a lower OER overpotential (352 mV) in comparison to a DSA IrO2 (434 mV) electrode and a stability that is greater than 200 h in a 1.0 M KOH electrolyte at a current density of 10 mA cm–2.

Electrochemical treatment of wastewater from a bakery industry: Experimental and modeling study

Abstract The typical treatment of wastewater from the bakery industry in skimming tanks and bioreactors has some limitations, such as low removal of grease, and partial degradation of organic matter. The primary aim of this investigation was to evaluate the use of electrocoagulation as an alternative/complementary method to treat efficiently such an effluent, with focus on the determination of the best operating conditions, and on the kinetics of electrocoagulation at the optimal defined set of process variables. To search for the optimal, a 23 factorial design of electrocoagulation experiments with iron and aluminum electrodes was applied in the pH range from 4.6 to 7.0, at 6 and 12 V for 1200 s and 2400 s. A reliable statistical model revealed that the results of removal of chemical oxygen demand (6–8%) and turbidity (32–98%) by using aluminum electrodes, which were in average about twice as high as those with iron electrodes, were influenced by almost all the considered factors (p ≤ 0.05). At the best determined values of pH (7.0) and voltage (12 V), kinetic experiments of electrocoagulation with aluminum electrodes were performed by monitoring periodically the pH, turbidity, apparent color, concentration of oil/grease, chemical oxygen demand, concentration of chloride anion and electric conductivity of the wastewater for 2400 s. Almost all the examined pollutant parameters, and in particular the content of oil/grease (traditionally poorly removed in fat traps) were reduced to negligible values in a short treatment time. A reliable semi-empirical kinetic model described properly the high rates of disappearance of turbidity and apparent color.

Efficiency of plasma elaborated sub-stoichiometric titanium oxide (Ti4O7) ceramic electrode for advanced electrochemical degradation of paracetamol in different electrolyte media

This paper investigates the behavior of conductive Ti4O7 ceramic anode in different electrolytes during the degradation of the anti-inflammatory drug paracetamol (PCM) by advanced electrochemical oxidation processes mainly anodic oxidation with generation of H2O2 (AO-H2O2) and electro-Fenton (EF). Regardless of the medium, better degradation and mineralization efficiency was always observed with EF compared to AO-H2O2. The degradation of PCM was carried out by hydroxyl radical (OH) produced on the anode surface from water oxidation and mediated oxidation in the solution from oxidant species generated at the anode such as sulfate radicals and active chlorine species depending on the supporting electrolytes used, as well as OH generated homogeneously in the solution by electrochemically assisted Fenton’s reaction. Faster degradation was observed in Cl− compared to other media, but the solution was poorly mineralized. Highest total organic (TOC) removal efficiency with excellent degradation rate was attained in SO42− with either process, thus remain the best medium for advanced electrochemical wastewater treatment. Comparative studies with dimensional stable anode (DSA) and boron-doped diamond anode (BDD) showed similar trend of degradation and TOC removal efficiency with DSA anode achieving low mineralization power compared to Ti4O7 anode, whereas BDD showed slightly better efficiency than Ti4O7 in all electrolytes studied. The analysis of concentration of generated active chlorine species, especially ClO−, during AO-H2O2 decreased in the order: DSA > Ti4O7 > BDD. Therefore, the Ti4O7 electrode was found to be a promising anode material for an efficient treatment of PCM in SO42−, NO3− and ClO4− media but less effective in Cl− medium.

Time and calcination temperature influence on the electrocatalytic efficiency of Ti/SnO2:Sb(5%),Gd(2%) electrodes towards the electrochemical oxidation of naphthalene

Produced water is the largest volume wastewater associated with petroleum and gas production. Due to its diverse composition and large volume, produced water treatment is very challenging in order to avoid permanent or significant damages to the environment. On the other hand, the anodic material stability and the electrocatalytic properties are crucial for improved pollutant degradation efficiencies in electrochemical wastewater treatment. Here, we report the development of Ti/SnO2:Sb(5%),Gd(2%) electrodes by the polymeric precursor method, also known as Pechini method, for use in naphthalene electro-oxidation. The influence of the calcination time and temperature in the electrodes synthesis was investigated focusing on obtain an enhanced material with improved efficiencies in naphthalene oxidation. Thus, the Ti/SnO2:Sb(5%),Gd(2%) electrodes were calcined at 350, 400 and 450 °C during 1, 2 and 3 h for each temperature. Both temperature and time presented influence on the electrode electrocatalytic efficiency during naphthalene degradation, with emphasis on the calcination temperature influence. The most efficient electrodes are those calcined at 400 °C for 2 h, which degrade around 97% of the pollutant and reduce 86% of total organic carbon after 2 h of electrolysis at 2.0 V versus reversible hydrogen electrode. Besides that, they present the greatest rate constant coefficient of k = 1.41 mol−1 L min−1 and the greatest voltammetric charge density (13.75 mC cm−2) according to cyclic voltammetry measurements. Additionally, all the synthetized electrodes show high physical and electrochemical stability.

Applicability of electrochemical wastewater treatment system powered by temperature difference energy

In this research, an electrochemical wastewater treatment system, powered through the conversion of temperature difference into energy, was designed. The wastewater treatment system was applied to drainage flowing from two different mines, one contaminated by arsenic (As), the other ferrous iron (Fe2+). Arsenic was adsorbed on, or co-precipitated with, iron hydroxide generated from iron electrodes. A pseudo second order model well described the tendency for As removal. Ferrous iron oxidation occurred directly on graphite electrodes and followed a first order reaction model. The efficiency of As and Fe2+ removal was up to 99.7% and 97.9%, respectively. The rate constants for each model were proportional to given temperature differences, as the relationship between current generation and temperature difference was linear. Economic evaluation of the wastewater treatment system was performed by comparing the predicted cost of the thermocouples under particular environmental conditions. The thermocouple technology currently available could be applied to wastewater treatment for hot springs with high temperatures and high As concentrations. The applicability of the system to low temperature wastewaters will expand as energy production capacity per unit cost of thermocouples increases, as occurred with the photovoltaic and heat pump systems currently in use.

Phosphate Recovery from Human Waste via the Formation of Hydroxyapatite during Electrochemical Wastewater Treatment.

Electrolysis of toilet wastewater with TiO2-coated semiconductor anodes and stainless steel cathodes is a potentially viable onsite sanitation solution in parts of the world without infrastructure for centralized wastewater treatment. In addition to treating toilet wastewater, pilot-scale and bench-scale experiments demonstrated that electrolysis can remove phosphate by cathodic precipitation as hydroxyapatite at no additional energy cost. Phosphate removal could be predicted based on initial phosphate and calcium concentrations, and up to 80% total phosphate removal was achieved. While calcium was critical for phosphate removal, magnesium and bicarbonate had only minor impacts on phosphate removal rates at concentrations typical of toilet wastewater. Optimal conditions for phosphate removal were 3 to 4 h treatment at about 5 mA cm–2 (∼3.4 V), with greater than 20 m2 m–3 electrode surface area to reactor volume ratios. Pilot-scale systems are currently operated under similar conditions, suggesting that phosphate removal can be viewed as an ancillary benefit of electrochemical wastewater treatment, adding utility to the process without requiring additional energy inputs. Further value may be provided by designing reactors to recover precipitated hydroxyapatite for use as a low solubility phosphorus-rich fertilizer.

Principles of a multistack electrochemical wastewater treatment design

Electrolyzer stacks in a bipolar architecture (cells connected in series) are desirable since power provided to a stack can be transferred at high voltages and low currents and thus the losses in the power bus can be reduced. The anode electrodes (active electrodes) considered as part of this study are single sided but there are manufacturing cost advantages to implementing double side anodes in the future. One of the main concerns with a bipolar stack implementation is the existence of leakage currents (bypass currents). The leakage current is associated with current paths that are not between adjacent anode and cathode pairs. This leads to non uniform current density distributions which compromise the electrochemical conversion efficiency of the stack and can also lead to unwanted side reactions. The objective of this paper is to develop modelling tools for a bipolar architecture consisting of two single sided cells that use single sided anodes. It is assumed that chemical reactions are single electron transfer rate limited and that diffusion and convection effects can be ignored. The design process consists of the flowing two steps: development of a large signal model for the stack, and then the extraction of a small signal model from the large signal model. The small signal model facilitates the design of a controller that satisfies current or voltage regulation requirements. A model has been developed for a single cell and two cells in series but can be generalized to more than two cells in series and to incorporate double sided anode configurations in the future. The developed model is able to determine the leakage current and thus provide a quantitative assessment on the performance of the cell.

Study on the effect of electrochemical treatment of nicosulfuron wastewater

Nicosulfuron, a kind of sulfonylurea herbicide, because of its high activity and low dosage, has been widely used in corn planting weeding. Electrochemical method was chosen to treat its simulated waste water and the influence factors such as current intensity, plate spacing and electrolyte pH on electrolysis effect were investigated. A double-coated titanium dioxide titanium plate was chosen as the anode accompanied with a single-coated titanium plate as the cathode. The results showed that the removal efficiency of nicosulfuron was the highest when the electrolyte pH=3, the plate spacing is 1.5cm and the current intensity is 0.8A. Under the optimal condition, the removal rate of nicosulfuron reached 86.6% after 7 hours electrolysis. Thus, electrochemical technology might provide a significant method to remove the synthetic organic compounds.