Degradation of sulfadiazine in drinking water by a cathodic electrochemical membrane filtration process

Electrochemical filtration for drinking water purification: A review on membrane materials, mechanisms and roles

Electrochemical filtration can not only enrich low concentrations of pollutants but also produce reactive oxygen species to interact with toxic pollutants with the assistance of a power supply, making it an effective strategy for drinking water purification. In addition, the application of electrochemical filtration facilitates the reduction of pretreatment procedures and the use of chemicals, which has outstanding potential for maximizing process simplicity and reducing operating costs, enabling the production of safe drinking water in smaller installations. In recent years, the research on electrochemical filtration has gradually increased, but there has been a lack of attention on its application in the removal of low concentrations of pollutants from low conductivity water. In this review, membrane substrates and electrocatalysts used to improve the performance of electrochemical membranes are briefly summarized. Meanwhile, the application prospects of emerging single-atom catalysts in electrochemical filtration are also presented. Thereafter, several electrochemical advanced oxidation processes coupled with membrane filtration are described, and the related working mechanisms and their advantages and shortcomings used in drinking water purification are illustrated. Finally, the roles of electrochemical filtration in drinking water purification are presented, and the main problems and future perspectives of electrochemical filtration in the removal of low concentration pollutants are discussed.

Easily scale 3D conductive gradient fiber membrane for contaminants removal and fouling mitigation under electrochemical assistance

An electrochemical membrane filtration system provides an innovative approach to enhance contaminant removal and mitigate membrane fouling. There is an urgent need to develop portable, versatile, and efficient electrochemical membranes for affordable wastewater treatment. Here, a 3D conductive gradient fiber membrane (CC/PVDF) with a gradient porous structure was prepared using a two-step phase inversion method. Methyl orange (MO) was utilized as model organic substance to investigate the electrochemical performance of the CC/PVDF membrane. At applied potentials of +2 V, +3 V, -2 V and -3 V, the removal efficiency of MO was 5.1, 5.3, 4.8, and 5.1 times higher than at 0 V. A dramatic flux loss of 35.02% occurred on the membrane without electrochemistry, interestingly, whereas the flux losses were only 23.59%-10.24% in the applied potential after 30 min of filtration, which were approximately 1.18, 1.28, 1.29 and 1.38 times as high as that without electrochemistry, respectively. The enhanced removal and anti-fouling performances of the membranes were attributed to the functions of electrochemical degradation, electrostatic repulsion, and electrically enhanced wettability. Electrochemical generation of Hydrogen peroxide, along with HO• radicals, was detected and direct electron transfer and HO• were proved to be the dominant oxidants responsible for MO degradation. The intermediate oxidation products were identified by mass spectrometry, and an electrochemical degradation pathway of MO was proposed based on bond-breaking oxidation, ring-opening reactions, and complete oxidation. All the findings emphasize that the ECMF system possesses superior efficiency and creative potential for water purification applications.

Competitive adsorption analysis of antibiotics removal from multi-component systems using chemically activated spent tea waste: effect of operational parameters, kinetics, and equilibrium study

In this study, spent tea powder waste was chemically treated for the synthesis of adsorbent using two activating agents, i.e., sulfuric acid and phosphoric acid, to obtain sulfuric acid activated carbon (SAC) and phosphoric acid activated carbon (PAC). The performance of PAC and SAC for the sorption of tetracycline (TCY) and sulfadiazine (SDZ) antibiotics from mono-component (SDZ/TCY) and multi-component (SDZ + TCY) adsorption systems was investigated. Synergistic and antagonistic effects were studied in removing target pollutants in SDZ + TCY systems. Kinetic and equilibrium studies were modeled by different kinetic and isotherm models. The adsorption capacity was assessed using Langmuir's competitive model in a [Formula: see text]. Pseudo-first-order kinetic and Langmuir isotherm models best fit the experimental kinetic and equilibrium data to remove antibiotics. The Langmuir's maximum adsorption capacity (q_m) of PAC for the removal of SDZ and TCY in a [Formula: see text] was found to be 16.75 and 10.87 mg/g, and q_m of SAC for the removal of SDZ and TCY was found to be 24.69 and 23.20 mg/g, respectively. In SDZ + TCY multi-component system, adsorption of TCY was synergistic in nature for both PAC and SAC. Sorption of SDZ displayed an antagonistic effect in the SDZ + TCY system for both SAC and PAC. In conclusion, the activated carbons synthesized from spent tea waste could be effectively adopted for the simultaneous adsorption of SDZ and TCY from multi-component systems.

A comprehensive review on reactive oxygen species (ROS) in advanced oxidation processes (AOPs)

In this account, the reactive oxygen species (ROS) were comprehensively reviewed, which were based on electro-Fenton and photo-Fenton processes and correlative membrane filtration technology. Specifically, this review focuses on the fundamental principles and applications of advanced oxidation processes (AOPs) based on a series of nanomaterials, and we compare the pros and cons of each method and point out the perspective. Further, the emerging reviews regarding AOPs rarely emphasize the involved ROS and consider the convenience of radical classification and transformation mechanism, such a review is of paramount importance to be needed. Owing to the strong oxidation ability of radical (e.g., •OH, O₂^•-, and SO₄^•-) and non-radical (e.g., ¹O₂ and H₂O₂), these ROS would attack the organic contaminants of emerging concern, thus achieving the goal of environmental remediation. Hopefully, this review can offer detailed theoretical guidance for the researchers, and we believe it able to offer the frontier knowledge of AOPs for wastewater treatment plants (WWTPs).

Molecular-level characterization of natural organic matter in the reactive electrochemical ceramic membrane system for drinking water treatment using FT-ICR MS

Applications of electrochemical advanced oxidation processes are rising in drinking water treatment for effective mitigation of refractory organic compounds. This study explored the fate of natural organic matter (NOM) (lake water and standard NOM (SRNOM solution)) at molecular-level in the reactive electrochemical membrane (REM) system utilizing Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Fluorescence spectroscopy showed above 90 % removal of the humic-like component in both lake water and SRNOM solution in 10 min of REM operation compared to 70-80 % removal of the fulvic-like component after 30 min. REM-based treatment effectively eliminated (>70 %) the disinfection byproduct precursors. The lake water, sharing ~70 % of similar compounds with SRNOM, displayed a different propensity toward electrochemical oxidation, and its finished water was characterized with relatively lower double-bond equivalent (DBE), nominal oxidation state of carbon (NOSC), and aromaticity compared to that of SRNOM. The chloride ions in the water matrix of lake water impacted the electrochemical oxidation and generated significantly different transformation products than SRNOM solution. The heteroatoms (N and S) containing compounds (CHON and CHOS) were preferentially degraded in lake water; however, CHOS compounds were removed fewer in SRNOM. The electrosorption and electrochemical oxidation on the REM surface were the significant contributors for NOM removal. The newly formed compounds were mostly retained on the REM surface and fewer were released in finished water. This study is believed to help understand the fate of NOM in real source drinking water during electrochemical treatment.

Piezo-promoted persulfate activation by SrBi2B2O7 for efficient sulfadiazine degradation from water

Combining piezoelectric effect and persulfate (PS) activation is a newly developed strategy for refractory emerging contaminants removal. In this work, borate SrBi₂B₂O₇ (SBBO) is firstly developed as a piezoelectric material to piezo-assisted activation of PS for the removal of sulfadiazine (SDZ) under ultrasonic irradiation (US). SDZ could be efficiently degraded by 85.61 % in the system of PS/SBBO/US with a pseudo-first-order rate constant of 0.0520 min^-1, which is faster than that in the systems of PS/SBBO (0.0210 min^-1), SBBO/US (0.0041 min^-1), PS/US (0.0074 min^-1), and PS/BaTiO₃/US (0.0120 min^-1). The excellent degradation performance of the PS/SBBO/US system is mainly attributed to the piezoelectric effect of the SBBO which plays an important role in PS activation and accelerating reaction. Two oxidation processes, radical process (•O₂^- and •SO₄^-) and non-radical process (¹O₂ and electron transfer), exist during the SDZ degradation. The system of PS/SBBO/US also attains excellent removal efficiency in different SDZ contained water bodies. The possible degradation pathways mainly include cleavage of bonds, ring-opening, and hydroxylation process, and the toxicity of intermediates was predicted by T.E.S.T. software. This study provides new insight into piezoelectric catalysis associated with PS activation for SDZ removal.

A critical review on classifications, characteristics, and applications of electrically conductive membranes for toxic pollutant removal from water: Comparison between composite and inorganic electrically conductive membranes

Research efforts have recently been directed at developing electrically conductive membranes (EMs) for pressure-driven membrane separation processes to remove effectively the highly toxic pollutants from water. EMs serve as both the filter and the electrode during filtration. With the assistance of a power supply, EMs can considerably improve the toxic pollutant removal efficiency and even realize chemical degradation to reduce their toxicity. Organic-inorganic composite EMs and inorganic EMs show remarkable differences in characteristics, removal mechanisms, and application situations. Understanding their differences is highly important to guide the future design of EMs for specific pollutant removal from water. However, reviews concerning the differences between composite and inorganic EMs are still lacking. In this review, we summarize the classifications, fabrication techniques, and characteristics of composite and inorganic EMs. We also elaborate on the removal mechanisms and performances of EMs toward recalcitrant organic pollutants and toxic inorganic ions in water. The comparison between composite and inorganic EMs is emphasized particularly in terms of the membrane characteristics (pore size, permeability, and electrical conductivity), application situations, and underlying removal mechanisms. Finally, the energy consumption and durability of EMs are evaluated, and future perspectives are presented.

Efficient removal of micropollutants from low-conductance surface water using an electrochemical Janus ceramic membrane filtration system

Electrochemical membrane filtration (EMF) technology is effective to remove the micropollutant in the wastewater but its efficacy is drastically compromised in treating the surface water having a typically low conductivity. In this work, a Janus Fe-Pt electrochemical ceramic membrane (ECM) was fabricated by depositing a thin Fe layer on the side of a ceramic membrane facing feed (cathode) and Pt layer on the other side facing permeate (anode). The low Fe-Pt electrode distance (∼1 mm) ensured a decent conductance of the EMF system even in the low-salinity surface water and thereby maintained the removal efficiency of the micropollutant. It was identified that hydroxyl radicals (•OH) generated via anodic water oxidation and cathodic heterogenous Fenton process on bilateral sides of ECM were the dominant reactive oxygen species. The EMF system not only achieved 74% removal of atrazine (ATZ) from the low-conductance synthetic surface water with a low energy consumption (3.6 Wh per gATZ or 7.2 Wh m ^- 3), but also realized a stable removal of ATZ from real surface water over a continuous filtration experiment of 168 h. The theoretical computations and experimental analysis identified the degradation pathway, i.e., the dechlorination and dealkylation of ATZ in the EMF system. This study highlights the great potential of the Janus ECM in removing micropollutants from low-conductance surface water and wastewater.

Recent advances in electrocatalytic membrane for the removal of micropollutants from water and wastewater

The increasing occurrence of micropollutants in water and wastewater threatens human health and ecological security. Electrocatalytic membrane (EM), a new hybrid water treatment platform that integrates membrane separation with electrochemical technologies, has attracted extensive attention in the removal of micropollutants from water and wastewater in the past decade. Here, we systematically review the recent advances of EM for micropollutant removal from water and wastewater. The mechanisms of the EM for micropollutant removal are first introduced. Afterwards, the related membrane materials and operating conditions of the EM are summarized and analyzed. Lastly, the challenges and future prospects of the EM in research and applications are also discussed, aiming at a more efficient removal of micropollutants from water and wastewater.

Pilot-scale and mechanistic study of the degradation of typical odors and organic compounds in drinking water by a combined UV/H2O2-BAC process

Odor problems are challenging issues in water treatment. Advanced oxidation has a significant degradation effect on these odors; however, some issues, such as oxidant residues and disinfection byproducts, exist in the use of advanced oxidation in actual water treatment. Because of the above issues, a combined advanced oxidation process has emerged-the UV/H₂O₂ -biological activated carbon (BAC) process can play a strong oxidizing role in advanced oxidation and uses the physical adsorption and biological effects of activated carbon. However, there have been few studies on the odor degradation mechanism and characteristics of activated carbon biofilms in actual water treatment. This paper systematically studied the organic and odor substances removal effects and mechanism of a pilot combined UV/H₂O₂-BAC process. The results showed that UV/H₂O₂-BAC technology had a good removal effect on odor substances under long-term stable operation. The concentrations of geosmin (GSM) and 2-methylisoborneol (2-MIB) after systemic treatment were below 5 ng/L. The removal rates of DOC, UV₂₅₄ and H₂O₂ by the combined process were 53.60%, 73.08% and 60.20%, respectively. The results of full-scan determination of GSM and 2-MIB degradation by gas chromatography-mass spectrometry (GC-MS) were consistent with those of front-track analysis. The diversity, richness and evenness of microorganisms in the lower activated carbon layer were higher than those in the middle and upper activated carbon layers. The greater the difference in the carbon layer height was, the greater the difference in the biological community structure.

Electrochemical advanced oxidation processes coupled with membrane filtration for degrading antibiotic residues: A review on its potential applications, advances, and challenges

Antibiotic pollution is mainly caused by aquaculture wastewater and pharmaceuticals, which are frequently used by humans. Due to limited treatment efficiency or improper selection of treatment methods, these antibiotic residues may be very harmful in human drinking water and aquatic environments. The EAOPs coupling membrane technology (EAOPs-membrane) can play their own advantages, which can significantly improve the degradation efficiency and alleviate membrane pollution (electrochemical manners). In this context, this review mainly collecting researches and information on EAOPs-membrane treatment of antibiotic pollution published between 2012 and 2020. Discussed the different combinations of these two technologies, the mechanism of them in the system to improve the processing efficiency, prolong the working time, and stabilize the system structure. Mainly due to the synergistic effect of electrochemical behavior such as electric repulsion and in-situ oxidation, the membrane fouling in the system is alleviated. In this review it was summarized that the selection of different membrane electrode materials and their modifications. The paper also elaborates the existing challenges facing the EAOPs-membrane methods for antibiotic pollution treatment, and their prospects.

An electrochemical membrane biofilm reactor for removing sulfonamides from wastewater and suppressing antibiotic resistance development: Performance and mechanisms

Sulfonamides, such as sulfadiazine (SDZ), are frequently detected in water and wastewater with their toxic and persistent nature arousing much concern. In this work, a novel electrochemical membrane biofilm reactor (EMBfR) was constructed for the removal of SDZ whilst suppressing the development of antibiotic resistance genes (ARGs). Results showed that the EMBfR achieved 94.9% removal of SDZ, significantly higher than that of a control membrane biofilm reactor (MBfR) without electric field applied (44.3%) or an electrolytic reactor without biofilm (77.3%). Moreover, the relative abundance of ARGs in the EMBfR was only 32.0% of that in MBfR, suggesting that the production of ARGs was significantly suppressed in the EMBfR. The underlying mechanisms relate to (i) the change of the microbial community structure in the presence of the electric field, leading to the enrichment of potential aromatic-degrading microorganisms (e.g., Rhodococcus accounting for 51.0% of the total in the EMBfR compared to 10.0% in the MBfR) and (ii) the unique degradation pathway of SDZ in the EMBfR attributed to the synergistic effect between the electrochemical and biological processes. Our study highlights the benefits of EMBfR in removing pharmaceuticals from contaminated waters and suppressing the development (and transfer) of ARGs in the environment.

Membrane Separation Coupled with Electrochemical Advanced Oxidation Processes for Organic Wastewater Treatment: A Short Review

Research on the coupling of membrane separation (MS) and electrochemical advanced oxidation processes (EAOPs) has been a hot area in water pollution control for decades. This coupling aims to greatly improve water quality and focuses on the challenges in practical application to provide a promising solution to water shortage problems. This article provides a summary of the coupling configurations of MS and EAOPs, including two-stage and one-pot processes. The two-stage process is a combination of MS and EAOPs where one process acts as a pretreatment for the other. Membrane fouling is reduced when setting EAOPs before MS, while mass transfer is promoted when placing EAOPs after MS. A one-pot process is a kind of integration of two technologies. The anode or cathode of the EAOPs is fabricated from porous materials to function as a membrane electrode; thus, pollutants are concurrently separated and degraded. The advantages of enhanced mass transfer and the enlarged electroactive area suggest that this process has excellent performance at a low current input, leading to much lower energy consumption. The reported conclusions illustrate that the coupling of MS and EAOPs is highly applicable and may be widely employed in wastewater treatment in the future.

Antibiotic resistance in wastewater treatment plants: understanding the problem and future perspectives

Antibiotics residues (AR), antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARG) are a new class of water contaminants, due to their adverse effects on aquatic ecosystems and human health. Contamination of water bodies occurs mainly by the excretion of antibiotics incompletely metabolized by humans and animals and is considered the main source of contamination of antibiotics in the environment. Given the imminent threat, the World Health Organization (WHO) has categorized the spread of antibiotics as one of the top three threats to public health in the twenty-first century. The Urban Wastewater Treatment Plants (UWWTP) bring together AR, ARB, ARG, making the understanding of this peculiar environment fundamental for the investigation of technologies aimed at combating the spread of bacterial resistance. Several methodologies have been employed focusing on reducing the ARB and ARG loads of the effluents, however the reactivation of these microorganisms after the treatment is widely reported. This work aims to elucidate the role of UWWTPs in the spread of bacterial resistance, as well as to report the efforts that have been made so far and future perspectives to combat this important global problem.

Can Cu2ZnSnS4 nanoparticles be used as heterogeneous catalysts for sulfadiazine degradation?

As a quaternary copper-based semiconductor, Cu₂ZnSnS₄ (CZTS) is drawing growing attention and is anticipated as a promising photocatalyst, thanks to its large absorption coefficient, exceptional photostability, and theoretical power conversion efficiency. However, CZTS has never been used as an activator of H₂O₂ for the degradation of refractory organic pollutants. In this study, the synthesis of CZTS nanoparticles obtained with diverse morphologies and crystallinities using solvents of deionized water (CZTS-W) and ethylene glycol (CZTS-EG) was examined in the activation of H₂O₂ to degrade sulfadiazine (SDZ). The results revealed that CZTS coupled with H₂O₂ could be an effective system for the degradation of SDZ. Compared to CZTS-EG, CZTS-W presented higher reusability in consecutive cycles with negligible leaching of copper. Reactive oxygen species quenching tests and electron paramagnetic resonance analyses illustrated that •O₂^-, •OH, and ¹O₂ contributed to the degradation of SDZ, and ¹O₂ prevailed over •O₂^- and •OH. The mechanistic investigation showed that efficient degradation could be associated to the effective recycling of Cu(II)/Cu(I) and low-valent/high-valent sulfur. Also, the degradation pathways of SDZ have been proposed through the detection of intermediate products. This study manifests that CZTS synthesized using deionized water is encouraging for the elimination of organic pollutants.

Porous visible light-responsive Fe3+-doped carbon nitride for efficient degradation of sulfadiazine

The development of efficient solar driven catalyst for the degradation of antibiotics has become increasingly important in environmental protection. However, the reported efficient photocatalysts for antibiotic degradation are limited. In this work, porous Fe³⁺-doped graphitic carbon nitride (g-C₃N₄) with outstanding photocatalytic ability is synthesized and then used as the photocatalyst for the efficient degradation of sulfadiazine (SDZ) under visible light. A series of characterization results indicate that Fe³⁺ is successfully doped into the interlayer of g-C₃N₄ and is stabilized in g-C₃N₄ by Fe-N coordination bond. The SEM, DRS and ESI and transient photocurrent results demonstrated that Fe³⁺-doped g-C₃N₄ has a porous structure, a low band gap, improved separation efficiency of photogenerated electron and holes as well as a wider light absorption range. Such improved physical and chemical properties greatly enhanced the photocatalytic ability. Using Fe³⁺-doped g-C₃N₄ for photocatalytic degradation of SDZ under white light, almost complete degradation of SDZ was achieved with a degradation efficiency as high as 99.8% (whereas only 52.1% for bulk g-C₃N₄) within 90 min. The degradation was mainly ascribe to ¹O₂ during the irradiation, and also a small amount of •O₂^-, OH• and h⁺ are involved in the degradation process. The Fe³⁺-doped g-C₃N₄ was applicable for the degradation of a wide range of antibiotic pollutants.

Dramatic enhancement effects of l-cysteine on the degradation of sulfadiazine in Fe3+/CaO2 system

Excessive sulfonamides accumulated in soil and groundwater seriously menace the ecological environment and human health. The performance of a Fenton-like system applying Fe³⁺ and calcium peroxide (CaO₂) in the presence of l-cysteine(l-cys) for sulfadiazine (SDZ) degradation was investigated. Compared with other chelating agents such as citric acid, butyric acid and Ethylenediaminetetraacetic acid, l-cys could effectively promote the SDZ removal in Fe³⁺/CaO₂ system. With the addition of 0.5 mM l-cys, the SDZ degradation increased from 2.14% to 66.53% in 60 min. High concentration of HCO₃^- inhibited the degradation of SDZ while slightly negative effects on SDZ degradation were observed in the presence of Cl^- or humic acid (HA) in l-cys/Fe³⁺/CaO₂ system. Electron paramagnetic resonance (EPR) analysis and radicals scavenge tests affirmed the generation of OH and O₂- in l-cys/Fe³⁺/CaO₂ system. Possible degradation pathway of SDZ was speculated and the toxicity of SDZ intermediates was further evaluated. l-cys could enhance the reduction of Fe³⁺ to Fe²⁺ and reduced the Fe³⁺ precipitation due to the l-cys could form stable complexes with Fe³⁺. l-cys/Fe³⁺/CaO₂ system exhibited high mineralization ability. Overall, these results indicated that l-cys is a promising chelating agent for sulfadiazine wastewater treatment.

Sulfadiazine biodegradation by Phanerochaete chrysosporium: Mechanism and degradation product identification

Antibiotic contaminants have become a severe environmental problem in recent years and finding effective ways to deal with this issue is of great importance. In this study, Phanerochaete chrysosporium was used to degrade sulfadiazine (SDZ), which is frequently detected in the culture medium of isolates from soil and surface water systems. The results demonstrate that 10 mg L^-1 SDZ can be completely degraded by P. chrysosporium under conditions of pH 5.7 and 30 °C within 6 days. The Q-Exactive-MS/MS analysis identified and confirmed several different SDZ degradation intermediates, and four proposed degradation pathways of SDZ were deduced. Moreover, enzyme activity tests revealed that manganese peroxidase and ligninolytic peroxidase played important roles in SDZ degradation. Moreover, a transcriptome analysis method was performed to explore the mechanism and pathways of SDZ degradation by P. chrysosporium in greater detail. The results of GO and KEGG analysis strongly suggest that the metabolism pathway is significantly activated and plays an important role in antibiotic degradation. Further, this is the first study to identify SDZ degradation intermediates and two main intermediates were found to be involved in possible SDZ degradation pathways. This study is also the first report results from RNA sequencing to evaluate genome-wide changes of P. chrysosporium to further explore SDZ degradation mechanism.

Development of a moving-bed electrochemical membrane bioreactor to enhance removal of low-concentration antibiotic from wastewater

Removal of low-concentration (ng/L ~ μg/L) antibiotics from water calls for the development of cost-effective treatment technologies. In this study, a novel moving-bed electrochemical membrane bioreactor (MEMBR) was developed for removing sulfamethoxazole (SMX). Results showed that the introduction of external electric field and carbon felt particles could efficiently eliminate SMX (removal efficiency of 88.9%). In contrast, the moving-bed membrane bioreactor (MMBR) took a long time to acclimate microorganism, reaching a removal efficiency of 43.9%. Transmembrane pressure increase rate was much lower in MEMBR (1.06 kPa/d) compared to MMBR (1.72 kPa/d). The presence of carriers increased the generation of reactive oxygen species, contributing to SMX removal. Microbial community analysis revealed that the introduction of electric field could increase microbial community richness/diversity and enrich the phyla of Actinobacteria and Gemmatimonadete, potentially capable of mineralizing SMX. These results clearly demonstrated the potential of this novel MEMBR to be used for enhanced micropollutants removal from water/wastewater.