Boron-doped Diamond Anode System Research Articles

Electrochemical regeneration of granular activated carbon saturated by p-nitrophenol in BDD anode system

Phenolic compounds have been widely used in metallurgy, petroleum, chemicals, textiles, dye printing and pharmaceuticals. These compounds are persistent, non-biodegradable and harmful for human healthy, whose emission should be restricted before their efficient treatment. Electrochemical regeneration of granular activated carbon (GAC) saturated with p-nitrophenol (p-NO2) has been investigated in Boron-doped Diamond (BDD) anode system. The dominated regeneration mechanism was mainly due to the electrostatic repulsion between negative polarized GAC located at cathode and deprotonated p-NO2 ions. Operating parameters including current density, regeneration time, pH value, electrolyte concentration and flow rate have been investigated systematically. Under the optimized experimental conditions, regeneration efficiency of GAC was as high as 81.6%, without significant declination after five-times adsorption-regeneration cycles. During the regeneration process, organic compounds of p-NO2, which was desorbed from GAC and released into electrolyte, was oxidized at BDD anode surface. Therefore, GAC regeneration and p-NO2 degradation were realized simultaneously. Effects of different anode materials on regeneration process was analyzed and BDD showed superior performance compared with PbO2, SnO2 and Pt anodes, which was attributed to different intermediates formed at anode surface. In summary, GAC saturated with p-NO2 can be regenerated efficiently in BDD anode system with p-NO2 removed simultaneously. All these results demonstrated that electrochemical regeneration in BDD anode system has great potential for practical application.

Enhanced degradation of sulfamethazine in boron-doped diamond anode system via utilization of by-product oxygen and pyrite: Mechanism and pharmaceutical activity removal assessment

Treatment of antibiotic contaminants from water has become an urgent problem due to that antibiotic pollution may threaten the ecosystem. This study explored the feasibility of enhancement of boron-doped diamond (BDD) anode system for antibiotic removal by utilization of by-product oxygen and natural pyrite catalyst. Sulfamethazine (SMZ), one of commonly detected antibiotics in the aquatic environment, was selected. Completed degradation of SMZ was achieved within 60 min, when 3 g/L pyrite was added into BDD-nickel foam (NiF) electrochemical system. The pseudo first-order reaction rate constant for SMZ degradation in BDD-NiF-pyrite electrochemical system was approximately 9 times higher than that in BDD-NiF electrochemical system. The optimal conditions of BDD-NiF-pyrite electrochemical system for SMZ degradation were: current intensity of 50 mA, pyrite dosage of 3 g/L, initial pH = 3, and reaction time of 60 min at room temperature (25 ± 1 ℃). The OH and O2− radicals were responsible for SMZ degradation. SMZ degradation intermediates were identified. Possible SMZ degradation pathways were also proposed. Furthermore, in vivo pharmaceutical activity removal of SMZ was assessed by zebrafish inflammation model. SMZ before treatment exhibited anti-inflammatory activity while lost it after treatment. This study offered an alternative approach to boost the BDD electrochemical oxidation of antibiotic-contaminated water.

Electrochemical oxidation of sulfamethoxazole in BDD anode system: Degradation kinetics, mechanisms and toxicity evaluation

In the present study, electrochemical oxidation of sulfamethoxazole (SMX) with Boron-doped Diamond (BDD) anode and Stainless Steel (SS) cathode was investigated systematically. The effects of current density, initial pH, supporting electrolyte and natural organic matter (NOM) on SMX degradation were explored. Under the conditions of current density 30 mA cm−2, 0.1 M Na2SO4 used as supporting electrolyte, pH of 7 and without NOM affect, SMX was completely removed after 3 h electrolysis. COD removal efficiency, current efficiency and energy consumption were 65.6%, 40.1%, 72 kWh kg COD−1, respectively. Degradation mechanism was analyzed based on the active sites of SMX identified by density functional theory (DFT) calculation and intermediates analysis by HPLC-Q-TOF-MS/MS. Three possible degradation pathways were proposed, with the replacement of -NH2 at aromatic ring by -OH, the oxidation of -NH2 to -NO2 and the addition of -OH on isoxazole ring observed. The active sites detected in reaction matched the DFT calculation results exactly. The toxicity of intermediates produced during electrolysis process was evaluated by Escherichia coli experiment. Results showed that, after 2 h electrolysis, the inhibition ratio was decreased from the initial value of 22.8% to 10%, which has already achieved the safety boundary. After 4 h electrolysis, the toxicity was almost zero even with still 60% COD remained in the solution. This phenomenon demonstrated that the toxicity of SMX and its intermediate products was reduced significantly during electrolysis process.

Maximization of current efficiency for organic pollutants oxidation at BDD, Ti/SnO2-Sb/PbO2, and Ti/SnO2-Sb anodes

Whereas electrochemical oxidation is noted for its ability to degrade bio-refractory organics, it has also been incorrectly criticized for excessive energy consumption. The present paper rectifies this misunderstanding by demonstrating that the energy actually consumed in the degradation process is much less than that wasted in the side reaction of oxygen evolution. To minimize the side reaction, the possible highest instantaneous current efficiency (PHICE) for electrochemical oxidation of phenol at Boron-doped Diamond (BDD), Ti/SnO2-Sb/PbO2 (PbO2), and Ti/SnO2-Sb (SnO2) anodes has been investigated systematically, and found to reach almost 100% at the BDD anode compared with 23% at the PbO2 anode and 9% at the SnO2 anode. The significant discrepancy between PHICE values at the various anodes is interpreted in terms of different existing forms of hydroxyl radicals. For each anode system, the PHICEs are maintained experimentally using a computer-controlled exponential decay current mode throughout the electrolysis process. For applications, the minimized energy consumption is predicted by response surface methodology, and demonstrated for the BDD anode system. Consequently, almost 100% current efficiency is achieved (for a relatively meagre energy consumption of 17.2 kWh kgCOD−1) along with excellent COD degradation efficiency by optimizing the initial current density, flow rate, electrolysis time, and exponential decay constant. Compared with galvanostatic conditions, over 70% of the energy is saved in the present study, thus demonstrating the great potential of electrochemical oxidation for practical applications.

The Improvement of Boron-Doped Diamond Anode System in Electrochemical Oxidation and Fenton Coupling System Degradation of p-Nitrophenol By Sensing Electrode of Iron

Boron-doped diamond (BDD) electrodes are promising anode materials in electrochemical oxidation system in degradation of wastewater containing toxic and bio-refractory organic pollutants due to their corrosion resistant ability and strong oxidation ability. In order to further improve the performance of BDD anode system, electrochemical oxidation of p-nitrophenol(PNP) was initially investigated in BDD anode system with the presence of sensing electrode. The results showed that the performance of the synthetic system was improved under neutral conditions with the joint actions of anode oxidation (64.6%) and H2O2 which was produced by oxygen reduction at carbon fiber cathode (11.9%). Under acid conditions, the degradation efficiency of PNP was further improved from 41.8% of the traditional system to 84.5% of the synthetic system. The strong oxidation ability was due to the anode oxidation (24.5%) and Fenton reaction by H2O2 and Fe2+ releasing from sensing electrode (66.7%). Moreover, under alkaline conditions, the results showed that the combined system was also improved by the coagulation of iron flocs formed from sensing electrode besides anode oxidation. Furthermore, hydroxyl radicals and H2O2  which were dominated oxidants were detected and quantified for the oxidation mechanism explanation.

Definitive screening design applied to electrochemical degradation of Chromotrope 2R with BDD anodes

Here, a novel three-level definitive screening design (DSD) was initially employed to investigate the electrochemical degradation of Chromotrope 2R (C2R) with boron-doped diamond (BDD) anodes. Experiments were performed using a synthetic C2R solution containing five supporting electrolytes (Na2SO4, NaCl, Na3PO4, NaNO3 and Na2CO3). The effects of nine quantitative parameters on C2R removal rate: initial C2R concentration (50–100 mg L−1), applied current density (1.29–3.87 mA cm−2), Na2SO4 concentration (0–10 mM), NaCl concentration (0–10 mM), Na3PO4 concentration (0–10 mM), NaNO3 concentration (0–10 mM), Na2CO3 concentration (0–10 mM), flow rate (300–500 mL min−1) and temperature (10–50 °C), were investigated. The model obtained was validated and used to select three most significant variables for further investigation. Interestingly, the differing roles of electrolytes during the electrolysis revealed the ion-selective nature of BDD anode system. A five-level central composite rotatable design (CCRD) was then employed to describe the C2R conversion as a function of applied current density, NaCl concentration and temperature. The results obtained confirmed the strong capability of DSD to separate and identify the significant variables in BDD technology. Moreover, the strategy (DSD plus CCRD) employed here enabled a significant reduction in the number of experiments (from over 500 to only 38) compared to traditional screening methods. The possible degradation mechanism of C2R in BDD anode cells was also proposed.

Scale-up of electrochemical oxidation system for treatment of produced water generated by Brazilian petrochemical industry

Scale-up of anodic oxidation system is critical to the practical application of electrochemical treatment in bio-refractory organic wastewater treatment. In this study, the scale-up of electrochemical flow system was investigated by treating petrochemical wastewater using platinized titanium (Ti/Pt) and boron-doped diamond (BDD) anodes. It was demonstrated that flow cell was successfully scaled-up because when it was compared with batch mode (Rocha et al. 2012b), higher performances on organic matter removal were achieved. Under the suitable operating conditions and better anode material, the chemical oxygen demand (COD) of petrochemical wastewater was reduced from 2,746 to 200 mg L(-1) within 5 h with an energy consumption of only 56.2 kWh m(-3) in the scaled-up BDD anode system. These results demonstrate that anode flow system is very promising in practical bio-refractory organic wastewater treatment.

Energy consumption of electrooxidation systems with boron-doped diamond electrodes in the pulse current mode

A pulse current technique was conducted in a boron-doped diamond (BDD) anode system for electrochemical wastewater treatment. Due to the strong generation and weak absorption of hydroxyl radicals on the diamond surface, the BDD electrode possesses a powerful capability of electrochemical oxidation of organic compounds, especially in the pulse current mode. The influences of pulse current parameters such as current density, pulse duty cycle, and frequency were investigated in terms of chemical oxygen demand (COD) removal, average current efficiency, and specific energy consumption. The results demonstrated that the relatively high COD removal and low specific energy consumption were obtained simultaneously only if the current density or pulse duty cycle was adjusted to a reasonable value. Increasing the frequency slightly enhanced the COD removal and average current efficiency. A pulse-BDD anode system showed a stronger energy saving ability than a constant-BDD anode system when the electrochemical oxidation of phenol of the two systems was compared. The results prove that the pulse current technique is more cost-effective and more suitable for a BDD anode system for real wastewater treatment. A kinetic analysis was presented to explain the above results.

Scale-up of B-doped diamond anode system for electrochemical oxidation of phenol simulated wastewater in batch mode

Scale-up of boron-doped diamond (BDD) anode system is critical to the practical application of electrochemical oxidation in bio-refractory organic wastewater treatment. In this study, the scale-up of BDD anode system was investigated on batch-mode electrochemical oxidation of phenol simulated wastewater. It was demonstrated that BDD anode system was successfully scaled up by 121 times without performance deterioration based on the COD and specific energy consumption ( E sp) models in bath mode. The COD removal rate and E sp for the scaled-up BDD anode system through enlarging the total anode area while keeping similar configuration, remained at the similar level as those before being scaled up, under the same area/volume value, current density, retention time and wastewater characteristics. The COD and E sp models used to describe the smaller BDD anode system satisfactorily predicted the performance of the scaled-up BDD anode system. Under the suitable operating conditions, the COD of phenol simulated wastewater was reduced from 540 mg l −1 to 130 mg l −1 within 3 h with an E sp of only 34.76 kWh m −3 in the scaled-up BDD anode system. These results demonstrate that BDD anode system is very promising in practical bio-refractory organic wastewater treatment.

The improvement of boron-doped diamond anode system in electrochemical degradation of p-nitrophenol by zero-valent iron

Boron-doped diamond (BDD) electrodes are promising anode materials in electrochemical treatment of wastewaters containing bio-refractory organic compounds due to their strong oxidation capability and remarkable corrosion stability. In order to further improve the performance of BDD anode system, electrochemical degradation of p-nitrophenol were initially investigated at the BDD anode in the presence of zero-valent iron (ZVI). The results showed that under acidic condition, the performance of BDD anode system containing zero-valent iron (BDD-ZVI system) could be improved with the joint actions of electrochemical oxidation at the BDD anode (39.1%), Fenton's reaction (28.5%), oxidation–reduction at zero-valent iron (17.8%) and coagulation of iron hydroxides (14.6%). Moreover, it was found that under alkaline condition the performance of BDD-ZVI system was significantly enhanced, mainly due to the accelerated release of Fe(II) ions from ZVI and the enhanced oxidation of Fe(II) ions. The dissolved oxygen concentration was significantly reduced by reduction at the cathode, and consequently zero-valent iron corroded to Fe(II) ions in anaerobic highly alkaline environments. Furthermore, the oxidation of released Fe(II) ions to Fe(III) ions and high-valent iron species (e.g., FeO 2+, FeO 4 2−) was enhanced by direct electrochemical oxidation at BDD anode.

Destination of organic pollutants during electrochemical oxidation of biologically-pretreated dye wastewater using boron-doped diamond anode

Electrochemical oxidation of biologically-pretreated dye wastewater was performed in a boron-doped diamond (BDD) anode system. After electrolysis of 12 h, the COD was decreased from 532 to 99 mg L −1 (<100 mg L −1, the National Discharge Standard of China). More importantly, the destination of organic pollutants during electrochemical oxidation process was carefully investigated by molecular weight distribution measurement, resin fractionation, ultraviolet-visible spectroscopy, HPLC and GC–MS analysis, and toxicity test. As results, most organic pollutants were completely removed by electrochemical oxidation and the rest was primarily degraded to simpler compounds (e.g., carboxylic acids and short-chain alkanes) with less toxicity, which demonstrated that electrochemical oxidation of biologically-pretreated dye wastewater with BDD anode was very effective and safe. Especially, the performance of BDD anode system in degradation of large molecular organics such as humic substances makes it very promising in practical applications as an advanced treatment of biologically-pretreated wastewaters.

Synergies between electrochemical oxidation and activated carbon adsorption in three-dimensional boron-doped diamond anode system

In order to enhance the performance of boron-doped diamond (BDD) anode system, activated carbon is added into BDD anode system to construct a three-dimensional electrode system. The degradation rates of p-nitrophenol and COD were significantly improved by 2–7 times compared to two-dimensional BDD anode system. More importantly, the synergy between electrochemical oxidation and activated carbon adsorption was observed. Investigations revealed that the synergy was not only resulted from direct electrochemical oxidation at activated carbon, but also from electro-catalysis of activated carbon to indirect electrochemical oxidation mediated by hydroxyl radicals. Although oxygen was reduced to hydrogen peroxide at the activated carbon surface, but the oxidation of hydrogen peroxide was not the main reason for the improvement of three-dimensional electrode system due to its relative weak oxidation capacity. Instead, the decomposition of hydrogen peroxide to hydroxyl radicals at catalysis of activated carbon played an important role on the enhancement of three-dimensional electrode system.

Scale-up of BDD anode system for electrochemical oxidation of phenol simulated wastewater in continuous mode

Scale-up of boron-doped diamond (BDD) anode system is significant to the practical application of electrochemical oxidation in bio-refractory wastewater treatment. In this study, the performance of a smaller BDD anode (24cm2) system in continuous mode electrochemical oxidation of phenol simulated wastewater was first investigated and well described by the response surface methodology (RSM). Furthermore, the RSM was extended to examine the scale-up feasibility of BDD anode systems with similar configurations. It was demonstrated that both COD degradation efficiency and specific energy consumption could be expected at the same level even as the system was enlarged over 100 times, which implied that BDD anode system could be successfully scaled up through controlling the same retention time, current density, initial COD, and conductivity conditions. Based on this study, a larger BDD anode (2904cm2) system was constructed and systematic measurements were made on its performance in electrochemical oxidation of phenol simulated wastewater. Very good agreement was found between measured and predicted results by RSM. At the optimized conditions, the larger BDD anode system could easily reduce the COD of phenol simulated wastewater from 633mgL−1 to 145mgL−1 (<150mgL−1, National Discharge Standard of China) during 80min with specific energy consumption only 31kWhkgCOD−1.

Advanced treatment of biologically pretreated coking wastewater by electrochemical oxidation using boron-doped diamond electrodes

Electrochemical oxidation is a promising technology to treatment of bio-refractory wastewater. Coking wastewater contains high concentration of refractory and toxic compounds and the water quality usually cannot meet the discharge standards after conventional biological treatment processes. This paper initially investigated the electrochemical oxidation using boron-doped diamond (BDD) anode for advanced treatment of coking wastewater. Under the experimental conditions (current density 20–60 mA cm −2, pH 3–11, and temperature 20–60 °C) using BDD anode, complete mineralization of organic pollutants was almost achieved, and surplus ammonia–nitrogen (NH 3–N) was further removed thoroughly when pH was not adjusted or at alkaline value. Moreover, the TOC and NH 3–N removal rates in BDD anode cell were much greater than those in other common anode systems such as SnO 2 and PbO 2 anodes cells. Given the same target to meet the National Discharge Standard of China, the energy consumption of 64 kWh kgCOD −1 observed in BDD anode system was only about 60% as much as those observed in SnO 2 and PbO 2 anode systems. Further investigation revealed that, in BDD anode cell, organic pollutants were mainly degraded by reaction with free hydroxyl radicals and electrogenerated oxidants (S 2O 8 2−, H 2O 2, and other oxidants) played a less important role, while direct electrochemical oxidation and indirect electrochemical oxidation mediated by active chlorine can be negligible. These results showed great potential of BDD anode system in engineering application as a final treatment of coking wastewater.