Electrochemical Filtration System Research Articles

Copper Nanowire Networks: An Effective Electrochemical Peroxymonosulfate Activator toward Nitrogenous Pollutant Abatement.

Herein, we developed an electrochemical filtration system for effective and selective abatement of nitrogenous organic pollutants via peroxymonosulfate (PMS) activation. Highly conductive and porous copper nanowire (CuNW) networks were constructed to serve simultaneously as catalyst, electrode, and filtration media. In one demonstration of the CuNW network's capability, a single pass through a CuNW filter (τ < 2 s) degraded 94.8% of sulfamethoxazole (SMX) at an applied potential of -0.4 V vs SHE. The exposed {111} crystal plane of CuNW triggered atomic hydrogen (H*) generation on sites, which contributed to effective PMS reduction. Meanwhile, with the involvement of SMX, a Cu-N bond was formed by the interactions between the -NH2 group of SMX and the Cu sites of CuNW, accompanied by the redox cycling of Cu2+/Cu+, which was facilitated by the applied potential. The different charges of the active Cu sites made it easier to withdraw electrons and promote PMS oxidation. Theoretical calculations and experimental results were combined to suggest a mechanism for pollution abatement with CuNW networks. The results showed that system efficacy for the degradation of a wide array of nitrogenous pollutants was robust across a broad range of solution pH and complex aqueous matrices. The flow-through operation of the CuNW filter outperformed conventional batch electrochemistry due to convection-enhanced mass transport. This study provides a new strategy for environmental remediation by integrating state-of-the-art material science, advanced oxidation processes, and microfiltration technology.

Biofouling suppresses effluent toxicity in an electrochemical filtration system for remediation of sulfanilic acid-contaminated water

Electrochemical filtration system (EFS) has received broad interest due to its high efficiency for organic contaminants removal. However, the porous nature of electrodes and flow-through operation mode make it susceptible to potential fouling. In this work, we systematically investigated the impacts of biofouling on sulfanilic acid (SA) removal and effluent toxicity in an EFS. Results showed that the degradation efficiency of SA slightly deteriorated from 92.3% to 81.1% at 4.0 V due to the electrode fouling. Surprisingly, after the occurrence of fouling, the toxicity (in terms of luminescent bacteria inhibition) of the EFS effluent decreased from 72.3% to 40.2%, and cytotoxicity assay exhibited similar tendency. Scanning electron microscopy and confocal laser scanning microscopy analyses revealed that biofouling occurred on the porous cathode, and live microorganisms were the dominant contributors, which are expected to play an important role in toxicity suppression. The relative abundance of Flavobacterium genus, related to the degradation of p-nitrophenol (an aromatic intermediate product of SA), increased on the membrane cathode after fouling. The analysis of degradation pathway confirmed the synergetic effects of electrochemical oxidation and biodegradation in removal of SA and its intermediate products in a bio-fouled EFS, accounting for the decrease of the effluent toxicity. Results of our study, for the first time, highlight the critical role of biofouling in detoxication using EFS for the treatment of contaminated water.

A novel electrocatalytic filtration system with carbon nanotube supported nanoscale zerovalent copper toward ultrafast oxidation of organic pollutants

In this study, we designed an integrated electrochemical filtration system for catalytic activation of peroxymonosulfate (PMS) and degradation of aqueous microcontaminants. Composites of carbon nanotube (CNT) and nanoscale zero valence copper (nZVC) were developed to serve as high-performance catalysts, electrode and filtration media simultaneously. We observed both radical and nonradical reaction pathways, which collectively contributed to the degradation of model pollutants. Congo red was completely removed via a single-pass through the nZVCCNT filter (τ <2 s) at neutral pH. The rapid kinetics of Congo red degradation were maintained across a wide pH range (from 3.0–7.0), in complicated matrixes (e.g., tap water and lake water), and for the degradation of a wide array of persistent organic contaminants. The superior activity of nZVCCNT stems from the boosted redox cycles of Cu2+/Cu+ in the presence of an external electric field. The flow-through design remarkably outperformed the conventional batch system due to the convection-enhanced mass transport. Mechanism studies suggested that the carbonyl group and electrophilic oxygen of CNT served as electron donor and electron acceptor, respectively, to activate PMS to generate •OH and 1O2via one-electron transport. The electron-deficient Cu atoms are prone to react with PMS via surface hydroxyl group to produce reactive intermediates (Cu2+-O-O-SO3−), and then 1O2 will be generated by breaking the coordination bond of the metastable intermediate. The study will provide a green strategy for the remediation of organic pollution by a highly efficient and integrated system based on catalytic oxidation, electrochemistry, and nano-filtration techniques.

Extremely efficient electro-Fenton-like Sb(III) detoxification using nanoscale Ti-Ce binary oxide: An effective design to boost catalytic activity via non-radical pathway

Environmental risks posed by discharge of the emerging contaminant antimony (Sb) into water bodies have raised global concerns recently. The toxicity of Sb has been shown to be species-dependent, with Sb(III) demonstrating much greater toxicity than Sb(V). Here, we proposed an electrochemical filtration system to achieve rapid detoxification of Sb(III) via a non-radical pathway. The key to this technology was an electroactive carbon nanotube filter functionalized with nanoscale Ti-Ce binary oxide. Under an electric field, in situ generated H2O2 could react with the Ti-Ce binary oxide to produce hydroperoxide complexes, which enabled an efficient transformation of Sb(III) to the less toxic Sb(V) (τ < 2 s) at neutral pH. The impact of important operational parameters was assessed and optimized, and system efficacy could be maintained over a wide pH range and long-term operation. An optimum detoxification efficiency of> 90% was achieved using lake water spiked with Sb(III) at 500 μg/L. The results showed that Ti/Ce-hydroperoxo surface complexes were the dominant species responsible for the non-radical oxidation of Sb(III) based on extensive experimental evidences and advanced characterizations. This study provides a robust and effective strategy for the detoxification of water containing Sb(III) and other similar heavy metal ions by integrating state-of-the-art advanced oxidation processes, electrochemistry and nano-filtration technology.

Reactive electrically conducting membranes for phosphorus recovery from livestock wastewater effluents

We present a novel ‘proof-of-concept’ electrochemically based membrane filtration process for the recovery of nitrogen and phosphorus from livestock wastewater following an anaerobic digestion step. Reactive electrically conducting membranes are shown to precipitate and separate struvite, an eco-friendly fertilizer from synthetic livestock wastewater, resulting in the production of a solid fertilizer and a high-quality water stream, fit for irrigation. The recovery process is based on electrochemical hydrolysis and control of local pH in proximity to the surface of the membrane, and therefore, does not require chemical additives for pH adjustment. The system was assessed at varying concentrations of nitrogen and phosphorus corresponding to diluted and concentrated livestock wastewater (up to 1000 mg/L of N and P). Experimental results show up to 65% removal of phosphorus and nitrogen in the first 30 min of electrochemical filtration, and the precipitates were analytically confirmed to be struvite. In addition, the recovery process was shown efficient as it resulted in limited membrane fouling and flux reduction. Fouling and precipitation results were explained by a mathematical model describing the concentration of N, P, Mg ions in the presence of an external electric field. Accordingly, precipitation takes place in proximity to the membrane's surface but not directly on it, thus, limiting surface fouling. The electrochemical filtration system does not require chemical additives for pH adjustment, and the cost associated with electrochemical membrane-based struvite recovery was calculated to be $158 per ton of dry struvite, which is about 1.4 times lower in comparison to conventional recovery approaches. Overall, the electrochemical filtration system may be a promising alternative for nutrient recovery from livestock wastewater in terms of operational costs, recovery efficiency, and fouling mitigation.

Sea urchin-like FeOOH functionalized electrochemical CNT filter for one-step arsenite decontamination

Advanced nanotechnologies for efficient arsenic decontamination remain largely underdeveloped. The most abundant inorganic arsenic species are neutrally-charged arsenate, As(III), and negatively-charged arsenite, As(V). Compared with As(V), As(III) is 60 times more toxic and more difficult to remove due to high mobility. Herein, an electrochemical filtration system was rationally designed for one-step As(III) decontamination. The key to this technology is a functional electroactive carbon nanotube (CNT) filter functionalized with sea urchin-like FeOOH. With the assistance of electric field, CNT-FeOOH anodic filter can in situ transform As(III) to less toxic As(V) while passing through. Then, as-produced As(V) could be effectively sequestrated by FeOOH. The sufficient exposed sorption sites, flow-through design, and filter’s electrochemical reactivity synergistically guaranteed a rapid arsenic removal kinetic. The underlying working mechanism was unveiled based on systematic experimental investigations and theoretical calculations. The system efficacy can be adapted across a wide pH range and environmental matrixes. Exhausted CNT-FeOOH filters could be effectively regenerated by chemical washing with diluted NaOH solution. Outcomes of the present study are dedicated to provide a straightforward and effective strategy by integrating electrochemistry, nanotechnology, and membrane separation for the removal of arsenic and other similar heavy metals from water bodies.

Rapid decontamination of tetracycline hydrolysis product using electrochemical CNT filter: Mechanism, impacting factors and pathways.

In this study, electrooxidation of the tetracycline hydrolysis products was investigated using a carbon nanotube (CNT) electrochemical filter and 4-epianhydrochlortetracycline (EACTC) as a model compound. Electrochemical filtration of 10μmolL-1 EACTC at a voltage of 2.5V and a flow rate of 1.5mLmin-1 (hydraulic residence time <3s) provided an oxidation flux of 1251±28μmolh-1 m-2. Replacement of the Ti cathode with a CNT filter cathode increased the EACTC oxidative flux by 1.3 fold at a voltage of 2.5V. The electrochemical filtration process is effective for the degradation of EACTC and the reduction of the antimicrobial activity based on liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) analysis and luminescent bacteria test. The high oxidation flux within 300min (1212-1263μmolh-1 m-2) and affordable cost (0.25kWh m-3) at a voltage of 2.5V show the potential application of the electrochemical filtration system as a promising unit for EACTC degradation. These findings provided new insights into the rational design principles of novel continuous-flow filtration system aimed to efficiently remove hydrolysis products of the antibiotic tetracycline.

Design of Surface-Modified Electrodes for the Electrochemical Adsorption of Platinum-Based Anticancer Drugs

The design of a hemofiltration method that minimizes the side effects produced by the accumulation of Pt-based drugs such as cisplatin represents an important technology for cancer treatment. This work establishes the foundation for the development of an efficient platform for the electrochemical hemofiltration and simultaneous sensing of antitumor drugs, such as cisplatin and carboplatin, from physiological medium. The electrochemical filtration system is based on a gold surface-modified electrode using tris(carboxyethyl)phosphine ligands as scavengers of the Pt-based drug complexes. The platinum–phosphine interaction is shown to be more time efficient, as compared to the naturally occurring form of a glutathione–platinum adduct, and displayed a highly cooperative nature of binding. Altogether, we demonstrate that the presence of ligands capable of binding to Pt results in a differential spectroscopic and electrochemical response and the potential to adsorb and monitor the concentration of Pt salts in c...

Fabrication of a novel conductive ultrafiltration membrane and its application for electrochemical removal of hexavalent chromium

The presence of Cr(VI) in the water/wastewater has serious environmental hazards due to its high toxicity. Ultrafiltration membranes are widely used in water/wastewater treatment due to their low cost and simple operation. However, conventional ultrafiltration membrane has low rejection of ions which limits its application for Cr(VI) removal. In terms of this, the CNT/PVDF/stainless steel mesh conductive ultrafiltration membrane was developed via nonsolvent induced phase separation (NIPS) method in this study. The properties of the membranes were characterized and the mechanism for the removal of Cr(VI) under different operational conditions was investigated. The results showed that the new generate membrane has good electrical conductivity and high mechanical strength. The conductive ultrafiltration membrane can realise the efficient removal of Cr(VI) under the application of voltage. It was found that the electrostatic repulsion between CrO42−/HCrO4− and negatively charged membrane plays a main role in Cr(VI) removal in the absence of electrolyte while electrochemical reduction plays an important role in Cr(VI) removal in the presence of electrolyte. Moreover, the removal efficiency of Cr(VI) was positively correlated with the ionic strength and residence time. The acidic condition was favorable for the removal of Cr(VI) when lower cell potentials (1 V, 3 V) were applied to the membrane and the neutral condition was beneficial for the removal of Cr(VI) removal when the applied cell potential increased to 5 V. Increase of the residence time by adjusting membrane operational pressure can further enhance the Cr(VI) removal. The highest removal of Cr(VI) (95.2%) was achieved under the best operation conditions (5 V, pH 7, 100 mM Na2SO4, 3.4 s residence time). It was demonstrated that the conductive membrane offers a promising way of Cr(VI) removal in the electrochemical filtration system.

A chloride-radical-mediated electrochemical filtration system for rapid and effective transformation of ammonia to nitrogen

Water contamination from ammonia has recently became a global concern. Herein, a chloride-radical-mediated electrochemical filtration system has been developed towards effective and rapid conversion of ammonia to nitrogen (N2). This continuous-flow system consists of a nanoscale tin oxide modified carbon nanotube (SnO2-CNT) anode and a Pd−Cu co-modified Ni foam (Pd−Cu/NF) cathode. The SnO2-CNT anode enables the Cl− oxidation to a chloride radical (Cl) at a proper anode potential (e.g., 2.5 V vs. Ag/AgCl) without severe self-oxidation. The macro-porous Pd−Cu/NF cathode further reduces anodic by-products (e.g., NO3− and NO2−) to N2. EPR and scavenging tests indicate that Cl was the dominant radical specie responsible for ammonia conversion. Anode potentials, chloride concentration, flow rate and solution pH were identified as key parameters affecting the overall conversion performance. The proposed continuous-flow system showed enhanced conversion kinetics as compared to the conventional batch reactor due to the convectively enhanced mass transport. This study provides new insight for the rational design of advanced continuous-flow systems towards ammonia decontamination from water bodies.

Crossflow electrochemical filtration for elimination of ibuprofen and bisphenol a from pure and competing electrolytic solution conditions.

For the first time, a crossflow electrochemical filtration system containing multiwalled carbon nanotubes (MWNTs) blended with buckypaper as a flat sheet dual membrane electrode was investigated for the removal of two contaminants of emerging concern, Ibuprofen and Bisphenol A. Breakthrough experiments revealed that a crossflow configuration could be highly efficient in eliminating both contaminants at applied DC potentials of 2 and 3 V over an extended period, from pure salt electrolyte as well as from synthetic secondary wastewater effluent. The shear flow provided consistent surface coverage resulting in excellent sorption performance. The long residence time of the two contaminants within the membrane (18.3 s) was sufficient enough to allow for almost complete degradation of phenolic aromatic products and quinoid rings and the resulting formation of aliphatic carboxylic acids, which was more evident at a higher applied potential (3 V). The formation of the non-toxic aliphatic carboxylic acids is a clear indication of the superior electrochemical performance of the crossflow mode over the dead-end flow-through system. Moreover, this study provides an in-depth understanding of different factors such as filter surface area and residence time that can greatly affect the removal of the contaminants considered.

One-dimensional structured IrO2 nanorods modified membrane for electrochemical anti-fouling in filtration of oily wastewater

Abstract An electrochemical antifouling filtration apparatus was designed to mitigate the fouling effect, the most significant challenge to the membrane filtration process. The utilized membrane element was fabricated by a conductive 1D IrO2 nanorod (NR) layer, serving as both the electrode and the filtration media. The 1D IrO2 NRs coating was modified on Al2O3 ceramic membrane using a facile thermal decomposition method from the mixtures of chloride precursor solution with the addition of Sb. The distinct 1D morphology of coating showed rough surface and high porosity, possessing surface area of 149.2 m2/g. The sheet resistance of the fabricated layer could be further reduced through the addition of Ru in order to improve the electrical and electrochemical performance. When electrochemical reactions were used for fouling control at high solution conductivity, the extent of fouling was decreased by at least 20% at 0.15 A, with time-average permeate flux enhanced by almost 44% owing to the generated gas bubbles layer and reactive intermediates on the membrane surface. The membrane fouling can also be significantly minimized by electrophoretic effect, when no appreciable current is passed through the system at desired electric field strength. In contrast with uncoated Al2O3 membrane which showed rapid decline of permeate flux after only 40 min of operation, the 1D Sb and Ru doped IrO2 NRs membrane exhibited only 25.2% drop in permeate fluxes after 2.8 h of operation at the electric field strength of 13 V/cm. Therefore, the designed electrochemical filtration system with 1D Sb and Ru doped IrO2 NRs membrane provides a promising alternative for membrane fouling control with electrochemical reactions and/or electrophoresis as the main working effects.