Recent advances in H2O2-based advanced oxidation processes for removal of antibiotics from wastewater

Roles of Oxygen-Containing Functional Groups in Carbon for Electrocatalytic Two-Electron Oxygen Reduction Reaction

Recent years have witnessed great research interests in developing high-performance electrocatalysts for the two-electron (2e-) oxygen reduction reaction (ORR) that enables the sustainable and flexible synthesis of H2O2. Carbon-based electrocatalysts exhibit attractive catalytic performance for the 2e- ORR, where oxygen-containing functional groups (OFGs) play a decisive role. However, current understanding is far from adequate, and the contribution of OFGs to the catalytic performance remains controversial. Therefore, a critical overview on OFGs in carbon-based electrocatalysts toward the 2e- ORR is highly desirable. Herein, we go over the methods for constructing OFGs in carbon including chemical oxidation, electrochemical oxidation, and precursor inheritance. Then we review the roles of OFGs in activating carbon toward the 2e- ORR, focusing on the intrinsic activity of different OFGs and the interplay between OFGs and metal species or defects. At last, we discuss the reasons for inconsistencies among different studies, and personal perspectives on the future development in this field are provided. The results provide insights into the origin of high catalytic activity and selectivity of carbon-based electrocatalysts toward the 2e- ORR and would provide theoretical foundations for the future development in this field.

A review on the alternatives to antibiotics and the treatment of antibiotic pollution: Current development and future prospects

Antibiotics, widely used in the fields of medicine, animal husbandry, aquaculture, and agriculture, pose a serious threat to the ecological environment and human health. To prevent antibiotic pollution, efforts have been made in recent years to explore alternative options for antibiotics in animal feed, but the effectiveness of these alternatives in replacing antibiotics is not thoroughly understood due to the variation from case to case. Furthermore, a systematic summary of the specific applications and limitations of antibiotic removal techniques in the environment is crucial for developing effective strategies to address antibiotic contamination. This comprehensive review summarized the current development and potential issues on different types of antibiotic substitutes, such as enzyme preparations, probiotics, and plant extracts. Meanwhile, the existing technologies for antibiotic residue removal were discussed under the scope of application and limitation. The present work aims to highlight the strategy of controlling antibiotics from the source and provide valuable insights for green and efficient antibiotic treatment.

Degradation mechanism and decomposition of sulfamethoxazole aqueous solution with persulfate activated by dielectric barrier discharge

The present study focused on the degradation of sulfamethoxazole (SMX) aqueous solution and the toxicity of processing aqueous by the dielectric barrier discharge (DBD) activated persulfate (PS). The effects of input voltage, input frequency, duty cycle, and PS dosage ratio on the SMX degradation efficiency were measured. Based on the results of the Response Surface Methodology (RSM), SMX degradation efficiency reached 83.21% which is 10.54% higher than that without PS, and the kinetic constant was 0.067 min-1 in 30 min when the input voltage at 204 V (input power at 110.6 W), the input frequency at 186 Hz, the duty cycle at 63%, and the PS dosage ratio at 5.1:1. The addition of PS can produce more active particles reached 1.756 mg/L (O3), 0.118 mg/L (H2O2), 0.154 mmol/L (·OH) in 30 min. Furthermore, the DBD plasma system effectively activated an optimal amount of PS, leading to improved removal efficiency of COD, and TOC to 30.21% and 47.21%, respectively. Subsequently, eight primary by-products were pinpointed, alongside the observation of three distinct pathways of transformation. Predictions from the ECOSAR software indicated that most of the degradation intermediates were less toxic than SMX. The biological toxicity experiments elucidated that the treatment with the DBD/PS system effectively reduced the mortality of zebrafish larvae caused by SMX from 100% to 20.13% and improved the hatching rate from 55.69% to 80.86%. In particular, it is important to note that the degradation intermediates exhibit teratogenic effects on zebrafish larvae.

Ferrate(VI)/percarbonate for the oxidation of micropollutants: Interactive activation and release of low-concentration hydrogen peroxide for efficient electron utilization

A novel "ferrate/percarbonate (Fe(VI)/SPC) co-oxidation process" was used to treat ciprofloxacin (CIP) and various micropollutants (MPs), which owned better performance than mixture of Fe(VI), Na2CO3 and H2O2. The mechanism investigation found that the low-concentration H2O2 (1-2 µM) released by SPC can promote the high-valent iron intermediates (Fe(IV)/Fe(V)) of Fe(VI) to the MP oxidation, and Fe(VI) products can also activate SPC to produce hydroxyl radical (·OH). The interactive activation of Fe(VI) and SPC was realized, which retained the high selectivity of Fe(VI) to electron-rich pollutants, and also made up the oxidation of electron-deficient pollutants through •OH, improving the degradation effect of various MPs by 20-30%, and the rate constant was increased by 1 to 3 times. Moreover, non-purgeable organic carbon (NPOC) determination confirmed that •OH participation reduced the NPOC value of CIP from 5.43 mg/L to 4.37 mg/L. The transformation pathway of CIP showed that Fe(VI)/SPC resulted in more hydroxylation intermediates of CIP than Fe(VI) alone. Acute toxicity assays found that the photoinhibition rate of CIP treated with Fe(VI) alone was 14.5%, while the sample treated with Fe(VI)/SPC showed no significant photoinhibition effect, which proved that the new process had good detoxification properties for CIP.

How Should We Activate Ferrate(VI)? Fe(IV) and Fe(V) Tell Different Stories about Fluoroquinolone Transformation and Toxicity Changes

Many studies have investigated activation of ferrate (Fe(VI)) to produce reactive high-valent iron intermediates to enhance the oxidation of micropollutants. However, the differences in the risk of pollutant transformation caused by Fe(IV) and Fe(V) have not been taken seriously. In this study, Fe(VI)-alone, Fe3+/Fe(VI), and NaHCO3/Fe(VI) processes were used to oxidize fluoroquinolone antibiotics to explore the different effects of Fe(IV) and Fe(V) on product accumulation and toxicity changes. The contribution of Fe(IV) to levofloxacin degradation was 99.9% in the Fe3+/Fe(VI) process, and that of Fe(V) was 89.4% in the NaHCO3/Fe(VI) process. The cytotoxicity equivalents of levofloxacin decreased by 1.9 mg phenol/L in the Fe(IV)-dominant process while they significantly (p < 0.05) increased by 4.7 mg phenol/L in the Fe(V)-dominant process. The acute toxicity toward luminescent bacteria and the results for other fluoroquinolone antibiotics also showed that Fe(IV) reduced the toxicity and Fe(V) increased the toxicity. Density functional theory calculations showed that Fe(V) induced quinolone ring opening, which would increase the toxicity. Fe(IV) tended to oxidize the piperazine group, which reduced the toxicity. These results show the different-pollutant transformation caused by Fe(IV) and Fe(V). In future, the different risk outcomes during Fe(VI) activation should be taken seriously.

Advanced oxidation/reduction processes (AO/RPs) for wastewater treatment, current challenges, and future perspectives: a review

Advanced oxidation/reduction processes (AO/RPs) are considered as effective water treatment technologies and thus could be used to solve the problem of water pollution. These technologies of wastewater treatment involve the production of highly reactive species such as •OH, H•, e-aq, SO4•-, and SO3•-. These radicals can attack the targeted contaminants present in aqueous media and result in their destruction. The efficiency of AO/RPs is highly affected by various operational parameters such as initial concentration of contaminant, solution pH, catalyst amount, intensity of light source, nature of oxidant and reductant used, and the presence of various ionic species in aquatic media. Among AO/RPs, the solar light-based AO/RPs are most widely used nowadays for contaminant removal from aqueous media because of their high environmental friendliness and cost effectiveness. By using these techniques, almost all types of pollutants can be easily removed from aquatic media within short intervals of time, and hence, the problem of water pollution can be solved effectively. This review focuses on various AO/RPs used for wastewater treatment. The effects of different operational parameters that affect the efficiency of these processes toward contaminant removal have been discussed. Besides, challenges and future recommendations are also briefly provided for the researchers in order to improve the efficiency of these processes.

A pilot scale of electrochemical integrated treatment technology and equipment driven by solar energy for decentralized domestic sewage treatment

Based on the natural air diffusion electrode (NADE) cathode, a solar-driven electrochemical integrated sewage treatment technology and equipment in a pilot scale was developed to treat dispersed rural wastewater. The non-aeration NADE had efficient and stable H2O2 production performance, maintaining the H2O2 output between 1474 and 1535 mg h-1 within 50 h with the current efficiency of 77.4%-80.6%. This electrochemical integrated wastewater treatment system was coupled with technologies such as dual-cathode electro-Fenton, peroxi-coagulation and photoelectro-Fenton, which effectively improved the conversion and utilization efficiency of H2O2. It integrated Fenton-like oxidation, electro-oxidation and UV/H2O2, as well as Fe(OH)3-dominated flocculation, which could effectively remove various pollutants in wastewater. The integrated sewage treatment equipment (500 L d-1) realized the effective treatment of a rural decentralized domestic sewage, achieving simultaneous removal of chemical oxygen demand (COD), NH3-N, total phosphorus (TP) and bacteria. Driven by solar energy, its application feasibility, superiority and stability have been proved, providing theoretical and technical support for the efficient and low-consumption treatment of dispersed organic wastewater.

Construction of Liquid Crystal-Based Sensors Using Enzyme-Linked Dual-Functional Nucleic Acid on Magnetic Beads

The development of liquid crystal (LC)-based sensors with superior performances such as high portability, excellent stability, great convenience, and remarkable sensitivity is highly demanded. This work proposes a new strategy for constructing the LC-based sensor using enzyme-linked dual-functional nucleic acid (d-FNA) on magnetic beads (MBs). The detection of kanamycin (KA) is demonstrated as a model. Acetylcholinesterase (AChE) is assembled onto the KA aptamer-modified MBs with a d-FNA strand that consists of an AChE aptamer and the complementary sequence of a KA aptamer. As the specific recognition of KA by its aptamer triggers the release of AChE from the MBs, the myristoylcholine (Myr) solution after incubation with the MBs causes the black image of the LCs due to the formation of the Myr monolayer at the aqueous/LC interface. Otherwise, in the absence of KA, AChE is still decorated on the MBs and causes the hydrolysis of Myr. Therefore, a bright image of LCs is obtained. The detection of KA is successfully achieved with a lower detection limit of 48.1 pg/mL. In addition, a thin polydimethylsiloxane (PDMS) layer-coated glass and a portable optical device are used to improve the stability and portability of the LC-based sensor to advance potential commercial applications. Furthermore, the detection of KA in milk with a portable device is demonstrated, showing the potential of the proposed enzyme-linked LC-based sensor.

Optimization of process parameters for trimethoprim and sulfamethoxazole removal by magnetite-chitosan nanoparticles using Box-Behnken design

The contamination of the aquatic environment with antibiotics is among the major and developing problems worldwide. The present study investigates the potential of adsorbent magnetite-chitosan nanoparticles (Fe3O4/CS NPs) for removing trimethoprim (TMP) and sulfamethoxazole (SMX). For this purpose, Fe3O4/CS NPs were synthesized by the co-precipitation method, and the adsorbent characteristics were investigated using XRD, SEM, TEM, pHzpc, FTIR, and VSM. The effect of independent variables (pH, sonication time, adsorbent amount, and analyte concentration) on removal performance was modeled and evaluated by Box-Behnken design (BBD). The SEM image of the Fe3O4/CS adsorbent showed that the adsorbent had a rough and irregular surface. The size of Fe3O4/CS crystals was about 70 nm. XRD analysis confirmed the purity and absence of impurities in the adsorbent. TEM image analysis showed that the adsorbent had a porous structure, and the particle size was in the range of nanometers. In VSM, the saturation magnetization of Fe3O4/CS adsorbent was 25 emu g-1 and the magnet could easily separate the adsorbent from the solution. The results revealed that the optimum condition was achieved at a concentration of 22 mg L-1, a sonication time of 15 min, an adsorbent amount of 0.13 g/100 mL, and a pH of 6. Among different solvents (i.e., ethanol, acetone, nitric acid, and acetonitrile), significant desorption of TMP and SMX was achieved using ethanol. Also, results confirmed that Fe3O4/CS NPs can be used for up to six adsorption/desorption cycles. In addition, applying the Fe3O4/CS NPs on real water samples revealed that Fe3O4/CS NPs could remove TMP and SMX in the 91.23-95.95% range with RSD (n = 3) < 4. Overall, the Fe3O4/CS NPs exhibit great potential for removing TMP and SMX antibiotics from real water samples.

Eco-friendly oxidation of a reactive textile dye by CaO2: effects of specific independent parameters

Textile wastewater containing dyes poses significant risks to the environment. Advanced oxidation processes (AOPs) effectively eliminate dyes by converting them into harmless substances. However, AOPs have drawbacks such as sludge formation, metal toxicity, and high cost. As an alternative to AOPs, calcium peroxide (CaO2) offers an eco-friendly and potent oxidant for dye removal. Unlike certain AOPs that generate sludge, CaO2 can be directly employed without resulting in sludge formation. This study examines the use of CaO2 for oxidizing Reactive Black 5 (RB5) in textile wastewater without any activator. Various independent factors-pH, CaO2 dosage, temperature, and certain anions-were investigated for their influence on the oxidation process. The effects of these factors on dye oxidation were analyzed using the Multiple Linear Regression Method (MLR). CaO2 dosage was determined to be the most influential parameter for RB5 oxidation, while the optimal pH for oxidation with CaO2 was found to be 10. The study determined that 0.5 g of CaO2 achieved approximately 99% efficiency in oxidizing 100 mg/L of RB5. Additionally, the study revealed that the oxidation process is endothermic, with an activation energy (Ea) and standard enthalpy (ΔH°) for RB5 oxidation by CaO2 determined as 31.135 kJ mol-1 and 110.4 kJ mol-1, respectively. The presence of anions decreased RB5 oxidation, with decreasing effectiveness observed in the order of PO43-, SO42-, HCO3-, Cl-, CO32-, and NO3-. Overall, this research highlights CaO2 as an effective, easy-to-use, eco-friendly, and cost-efficient method for removing RB5 from textile wastewater.

Recent Advances of Electrocatalyst and Cell Design for Hydrogen Peroxide Production

Electrochemical synthesis of H2O2 via a selective two-electron oxygen reduction reaction has emerged as an attractive alternative to the current energy-consuming anthraquinone process. Herein, the progress on electrocatalysts for H2O2 generation, including noble metal, transition metal-based, and carbon-based materials, is summarized. At first, the design strategies employed to obtain electrocatalysts with high electroactivity and high selectivity are highlighted. Then, the critical roles of the geometry of the electrodes and the type of reactor in striking a balance to boost the H2O2 selectivity and reaction rate are systematically discussed. After that, a potential strategy to combine the complementary properties of the catalysts and the reactor for optimal selectivity and overall yield is illustrated. Finally, the remaining challenges and promising opportunities for high-efficient H2O2 electrochemical production are highlighted for future studies.

Peracetic acid activation via the synergic effect of Co and Fe in CoFe-LDH for efficient degradation of pharmaceuticals in hospital wastewater

As an oxidant, peracetic acid (PAA) is gradually applied in advanced oxidation processes (AOPs) for pollutants degradation due to its high oxidation and low toxicity. In this study, the prepared Co₂Fe₁-LDH showed excellent PAA activation ability for efficient degradation of various pharmaceuticals with a removal efficiency ranging from 82.3% to 100%. Taking sulfamethoxazole (SMX) as a model pharmaceutical, it's found that organic radical (R-O^•) with high concentration of 5.27 × 10^-13 M is the dominant ROS responsible for contaminants degradation. Further analysis demonstrated that bimetallic synergistic effect between Co and Fe can improve electron transfer ability of Co₂Fe₁-LDH, resulting in the accelerated conversion of Co from +3 to +2 valence state with a high reaction rate (4.3 × 10¹-1.483 × 10² M^-1 s^-1) in this system. Density functional theory (DFT) reveals that C1, C3, C5 and N11 with higher ƒ⁰ and ƒ^-values concentrated on aniline group of SMX are the main attack sites, which is consistent with the results of degradation products. Besides, Co₂Fe₁-LDH/PAA system can effectively reduce biological toxicity after reaction, due to lower biotoxicity of degradation products and the carbon sources provided by PAA. In application, Co₂Fe₁-LDH/PAA system was capable of resisting the influence of water matrix and effectively removing pollutants in actual hospital wastewater. Importantly, this study comprehensively evaluated the ability of Co₂Fe₁-LDH/PAA system to remove organics and improve the biodegradability of actual hospital wastewater, providing guidance for application of PAA activation system.