Homogenous VUV advanced oxidation process for enhanced degradation and mineralization of antibiotics in contaminated water

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.

Nanohybrid Composites Based on TiO2 and Single-Walled Carbon Nanohorns as Promising Catalysts for Photodegradation of Amoxicillin

In this work, applications of nanohybrid composites based on titanium dioxide (TiO2) with anatase crystallin phase and single-walled carbon nanohorns (SWCNHs) as promising catalysts for the photodegradation of amoxicillin (AMOX) are reported. In this order, TiO2/SWCNH composites were prepared by the solid-state interaction of the two chemical compounds. The increase in the SWCNH concentration in the TiO2/SWCNH composite mass, from 1 wt.% to 5 wt.% and 10 wt.% induces (i) a change in the relative intensity ratio of the Raman lines located at 145 and 1595 cm-1, which are attributed to the Eg(1) vibrational mode of TiO2 and the graphitic structure of SWCNHs; and (ii) a gradual increase in the IR band absorbance at 1735 cm-1 because of the formation of new carboxylic groups on the SWCNHs' surface. The best photocatalytic properties were obtained for the TiO2/SWCNH composite with a SWCNH concentration of 5 wt.%, when approx. 92.4% of AMOX removal was achieved after 90 min of UV irradiation. The TiO2/SWCNH composite is a more efficient catalyst in AMOX photodegradation than TiO2 as a consequence of the SWCNHs' presence, which acts as a capture agent for the photogenerated electrons of TiO2 hindering the electron-hole recombination. The high stability of the TiO2/SWCNH composite with a SWCNH concentration of 5 wt.% is proved by the reusing of the catalyst in six photodegradation cycles of the 98.5 μM AMOX solution, when the efficiency decreases from 92.4% up to 78%.

Accelerated radical generation from visible light driven peroxymonosulfate activation by Bi2MoO6/doped gCN S-scheme heterojunction towards Amoxicillin mineralization: Elucidation of the degradation mechanism

A novel S-scheme photocatalyst Bi₂MoO₆ @doped gCN (BMO@CN) was prepared through a facile microwave (MW) assisted hydrothermal process and further employed to degrade Amoxicillin (AMOX), by peroxymonosulfate (PMS) activation with visible light (Vis) irradiation. The reduction in electronic work functions of the primary components and strong PMS dissociation generate abundant electron/hole (e^-/h⁺) pairs and SO₄^*-,*OH,O₂^*-reactive species, inducing remarkable degeneration capacity. Optimized doping of Bi₂MoO₆ on doped gCN (upto 10 wt%) generates excellent heterojunction interface with facile charge delocalization and e^-/h⁺ separation, as a combined effect of induced polarization, layered hierarchical structure oriented visible light harvesting and formation of S-scheme configuration. The synergistic action of 0.25 g/L BMO(10)@CN and 1.75 g/L PMS dosage can degrade 99.9% of AMOX in less than 30 min of Vis irradiation, with a rate constant (k_obs) of 0.176 min^-1. The mechanism of charge transfer, heterojunction formation and the AMOX degradation pathway was thoroughly demonstrated. The catalyst/PMS pair showed a remarkable capacity to remediate AMOX-contaminated real-water matrix. The catalyst removed 90.1% of AMOX after five regeneration cycles. Overall, the focus of this study is on the synthesis, illustration and applicability of n-n type S-scheme heterojunction photocatalyst to the photodegradation and mineralization of typical emerging pollutants in the water matrix.

Comparing the efficacy of various methods for sulfate radical generation for antibiotics degradation in synthetic wastewater: degradation mechanism, kinetics study, and toxicity assessment

In the present study the aim was to investigate and compare various activation processes for amoxicillin degradation. UV radiation, ultrasound, heat, and hydrogen peroxide were selected as the persulfate activation methods. The effects of various parameters such as pH, persulfate concentration, reaction time, AMX concentration, radical scavengers, and anions were thoroughly investigated. The results showed that AMX degradation was following the pseudo-first order kinetic model. The reaction rate of 0.114 min-1 was calculated for the UV/PS process, which was higher than that of the other investigated processes. The AMX degradation mechanism and pathway investigations revealed that sulfate and hydroxyl radicals were responsible for the degradation of AMX by two degradation pathways of hydroxylation and the opening of the β-lactam ring. Competition kinetic analysis showed that the second-order rate constant of AMX with sulfate radicals was 8.56 × 109 L mol-1 s-1 in the UV/PS process. Cost analysis was conducted for the four investigated processes and it was found that 1.9 $m-3 per order is required in the UV/PS process for the complete destruction of AMX. Finally, cytotoxic assessment of the treated effluent on human embryonic kidney cells showed a considerable reduction in AMX-induced cell cytotoxicity, proving that the investigated process is sufficiently capable of completely destroying AMX molecules to nontoxic compounds. Therefore, it can be concluded that UV radiation is much more effective than other methods for persulfate activation and can be considered as a reliable technique for antibiotic removal.

A review on self-modification of zirconium dioxide nanocatalysts with enhanced visible-light-driven photodegradation of organic pollutants

Over the past few years, photocatalysis is one of the most promising approaches for removing organic pollutants. Zirconium dioxide (ZrO₂) has been shown to be effective in the photodegradation of organic pollutants. However, low photoresponse and fast electron-hole recombination of ZrO₂ affected the efficiency of catalytic performance. Modifying the photocatalyst itself (self-modification) is a prominent way to enhance the photoactivity of ZrO₂. Moreover, as ZrO₂-like photocatalysts have a large bandgap, improving the spectral response via self-modification could extend the visible light region and reduce the chance of recombination. Here, we review the self-modification of ZrO₂ for enhanced the degradation of organic pollutants. The approaches of the ZrO₂ self-modification, including the type of synthetic route and synthesis parameter variation, are discussed in the review. This will be followed by a brief section on the effect of ZrO₂ self-modification in terms of morphology, crystal structure, and surface defects for enhanced photodegradation efficiency. It also covers the discussion on the photocatalytic mechanism of ZrO₂ self-modification. Finally, some challenges with ZrO₂ catalysts are also discussed to promote new ideas to improve photocatalytic performance.

Comprehensive investigation of SARS-CoV-2 fate in wastewater and finding the virus transfer and destruction route through conventional activated sludge and sequencing batch reactor

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA transmission route was thoroughly investigated in the hospital wastewater, sewage collection network, and wastewater treatment plants. Samples were taken on four occasions from December 2020 to April 2021. The performance of two different wastewater treatment processes of sequencing batch reactor (SBR) and conventional activated sludge (CAS) was studied for virus destruction. For this purpose, liquid phase, solid phase and bioaerosol samples were taken from different units of the investigated wastewater treatment plants (WWTPs). The results revealed that all untreated hospital wastewater samples were positive for SARS-CoV-2 RNA. The virus detection frequency increased when the number of hospitalized cases increased. Detection of viral RNA in the wastewater collection system exhibited higher load of virus in the generated wastewater in areas with poor socioeconomic conditions. Virus detection in the emitted bioaerosols in WWTPs showed that bioaerosols released from CAS with surface aeration contains SARS-CoV-2 RNA posing a potential threat to the working staff of the WWTPs. However, no viral RNA was detected in the bioaerosols of the SBR with diffused aeration system. Investigation of SARS-CoV-2 RNA in WWTPs showed high affinity of the virus to be accumulated in biosolids rather than transporting via liquid phase. Following the fate of virus in sludge revealed that it is completely destructed in anaerobic sludge treatment process. Therefore, based on the results of the present study, it can be concluded that receiving water resources could not be contaminated with virus, if the wastewater treatment processes work properly.

A catalytic ozonation process using MgO/persulfate for degradation of cyanide in industrial wastewater: mechanistic interpretation, kinetics and by-products

Cyanide-laden wastewaters generated from mining and electroplating industries are extremely toxic and it is of vital importance to treat them prior to discharge to receiving water resources. The present study aims to oxidize cyanide using an ozonation process catalyzed by MgO and persulfate (PS). A MgO nanocatalyst was synthesized using the sol–gel method and characterized. The results show that the synthesized catalyst had a BET surface area of 198.3 m² g⁻¹ with a nanocrystalline particle size of 7.42 nm. In the present study, the effects of different operational parameters were investigated, and it was found that the MgO/O₃/PS process is able to oxidize 100 mg L⁻¹ of cyanide after 30 min under optimum operational conditions. Cyanide degradation mechanisms in the MgO/O₃/PS process were completely investigated and the main radical species were identified using scavenging experiments. It was found that sulfate and hydroxyl radicals both contributed to the cyanide degradation in the MgO/O₃/PS process. Cyanide degradation by-products were also tracked and it was found that cyanate and ammonium species are primarily generated during the oxidation, but increase of reaction time allowed their conversion to much less toxic compounds such as nitrate and bicarbonate. Cyanide degradation was also conducted in real industrial wastewater containing 173 mg L⁻¹ of cyanide. Although there was a reduction in cyanide removal rate, the MgO/O₃/PS process was able to completely oxidize cyanide within 70 min. Finally, it can be concluded that the ozonation process catalyzed by MgO and persulfate is an efficient and reliable advanced oxidation process for removal of cyanide from industrial wastewater.

Cyanide-laden wastewaters are extremely toxic and it is of vital importance to treat them prior to discharge to receiving water resources.

Effective electro-Fenton-like process for phenol degradation on cerium oxide hollow spheres encapsulated in porous carbon cathode derived from skimmed cotton

The uniform size cerium dioxide hollow spheres which were prepared by the SiO₂ hard template method were loaded on microporous porous carbon obtained by carbonization derived from skimmed cotton (CSC) for electro-Fenton-like degradation of phenol. The microstructures of CSC/CeO₂ composite materials were characterized utilizing XRD, BET, XPS, SEM, and TEM. The electrochemical performance of the CSC/CeO₂ cathodes was studied through cyclic voltammetry and electrochemical impedance spectroscopy. The prepared CSC has a hollow tubular structure, and cerium dioxide is evenly loaded on the surface of the CSC in the form of uniform-sized hollow spheres. The CSC/CeO₂ materials have a great specific surface area (287.73 m² g^-1) and a uniform poresize. The electrochemical performance analysis demonstrated that the redox ability of the material greatly was improved by loading CeO₂ on the porous carbon surface of the skimmed cotton. The load ratio of cerium dioxide hollow spheres affects the structure and properties of CSC/CeO₂ materials. Ce³⁺ and Ce⁴⁺ were co-existed in CSC/CeO₂, which promoted the generation of H₂O₂ and ^.OH, and improved the catalytic activity of composite materials. The degradation efficiency of phenol reached 97.6% in 120 min, and the CSC/CeO₂ cathode manifested excellent stability after being experimented 20 times. CSC/CeO₂ composite material has great practical value in the treatment of phenolic wastewater and has promise for further application.

Characterization and genome functional analysis of an efficient nitrile-degrading bacterium, Rhodococcus rhodochrous BX2, to lay the foundation for potential bioaugmentation for remediation of nitrile-contaminated environments

Nitriles are a class of extremely toxic chemicals with extensive applications, and these compounds pose potential risks to humans and ecosystems. The activated sludge isolate Rhodococcus rhodochrous BX2 efficiently metabolizes aliphatic nitriles. However, the molecular underpinnings of the degradation mechanism of aliphatic nitriles by BX2 remain unknown, and the metabolic fate of aliphatic nitriles also has not been elucidated. Here, strain BX2 was capable of completely mineralizing three aliphatic nitriles. Bioinformatic analysis yielded a deeper insight into the genetic basis of BX2 for efficient degradation of aliphatic nitriles and adaptation to harsh environments. Transcriptional, enzyme activity and metabolite analyses confirmed that the intracellular inducible nitrile hydratase/amidase pathway is the preferred metabolic pathway. Our findings provide an in-depth understanding of the environmental fate of aliphatic nitriles and, most importantly, offer a new perspective on the potential applications of the genus Rhodococcus in bioremediation and the development of degradation enzyme resources.

Theoretical study on the reaction of anthracene with sulfate radical and hydroxyl radical in aqueous solution

Sulfate radical (SO₄^-) and hydroxyl radical (OH) generated from persulfate or peroxymonosulfate in AOPs have been widely used in contaminant degradation. Anthracene (ANT) can be decomposed by SO₄^- and OH. The processes of ANT decomposition were investigated using theoretical calculations in this paper. The initiation reactions of ANT, anthrone, anthraquinone (ATQ) and 1-hydroxylanthraquinone (1-hATQ) by two radicals are studied. The highest free energy barriers of initiation reactions are 22.30 kcal mol^-1 in ATQ + SO₄^- reaction and 6.84 kcal mol^-1 in ATQ + OH reaction. Comparing the rate constants of initiation reaction through the two radicals at 273-373 K, it can be concluded that SO₄^- and OH both play important roles on the initiation of ANT and anthrone at lower pH. For ATQ and 1-hATQ, OH is more important than SO₄^- in the initiation process, which indicates that the indirect influence of SO₄^- are more significant in the degradation processes of ATQ and 1-hATQ. This study provides theoretical confirmations for the mechanisms of reactions of ANT with SO₄^- and OH, and evaluates the importance of SO₄^- and OH according to the reaction rates. The work can give more insight into the degradation of PAHs by radicals.

Degradation of imipramine by vacuum ultraviolet (VUV) system: Influencing parameters, mechanisms, and variation of acute toxicity

Degradation of imipramine (IMI) in the VUV system (VUV₁₈₅ + UV₂₅₄) was firstly evaluated in this study. Both HO^• oxidation and UV₂₅₄ direct photolysis accounted for IMI degradation. The quantum yields of UV₂₅₄ direct photolysis of deprotonated and protonated IMI were 1.31×10^-2 and 3.31×10^-3, respectively, resulting in the higher degradation efficiency of IMI at basic condition. Increasing the initial IMI concentration lowered the degradation efficiency of IMI. While elevating reaction temperature significantly improved IMI degradation efficiency through the promotion of both the quantum yields of HO^• and the UV₂₅₄ direct photolysis rate. The apparent activation energy was calculated to be about 26.6 kJ mol^-1. Negative-linear relationships between the k_obs of IMI degradation and the concentrations of HCO₃^-/CO₃^2-, NOM and Cl^- were obtained. The degradation pathways were proposed that cleavage of side chain and hydroxylation of iminodibenzyl and methyl groups were considered as the initial steps for IMI degradation in the VUV system. Although some high toxic intermediate products would be produced, they can be further transformed to other lower toxic products. The good degradation efficiency of IMI under realistic water matrices further suggests that the VUV system would be a good method to degrade IMI in aquatic environment.

Degradation of Nystatin in aqueous medium by coupling UV-C irradiation, H2O2 photolysis, and photo-Fenton processes

Oxidative degradation and mineralization of the antifungal drug Nystatin (NYS) was investigated using photochemical advanced oxidation processes UV-C irradiation (280-100 nm), H₂O₂ photolysis (UV/H₂O₂), and photo-Fenton (UV/H₂O₂/Fe³⁺). The effect of operating parameters such as [H₂O₂], [Fe³⁺], and [NYS] initial concentrations on degradation efficiency and mineralization ability of different processes was comparatively examined in order to optimize the processes. Photo-Fenton was found to be the most efficient process attaining complete degradation of 0.02 mM (19.2 mg L^-1) NYS at 2 min and a quasi-complete mineralization (97%) of its solution at 5 h treatment while UV/H₂O₂ and UV-C systems require significantly more time for complete degradation and lower mineralization degrees. The degradation and mineralization kinetics were affected by H₂O₂ and Fe³⁺ initial concentration, the optimum dosages being 4 mM and 0.4 mM, respectively. Consumption of H₂O₂ during photo-Fenton treatment is very fast during the first 30 min leading to the appearance of two stages in the mineralization. The evolution of toxicity of treated solutions was assessed and confirmed the effectiveness of photo-Fenton process for the detoxification of NYS solution at the end of treatment. Application to real wastewater from pharmaceutical industry containing the target molecule NYS showed the effectiveness of photo-Fenton process since it achieved 92% TOC removal rate at 6-h treatment time.

Degradation of antibiotics by modified vacuum-UV based processes: Mechanistic consequences of H2O2 and K2S2O8 in the presence of halide ions

In this work, the degradation of cefalexin, norfloxacin, and ofloxacin was examined via various advanced oxidation processes (AOPs). Direct photolysis by ultraviolet (UV) and vacuum ultra violet (VUV) was less effective for the degradation of fluoroquinolone antibiotics such as norfloxacin and ofloxacin than that of cefalexin. Both hydrogen peroxide (H₂O₂) and potassium persulfate (K₂S₂O₈) assisted UV/VUV process remarkably enhanced fluoroquinolone degradation. The addition of K₂S₂O₈ was superior to H₂O₂ under VUV irradiation, with the best removal efficiency of norfloxacin and ofloxacin being almost 100% within 3 min in the presence of VUV/K₂S₂O₈. The ofloxacin degradation rate was accelerated as concentrations of H₂O₂ and K₂S₂O₈ was increased to 3 mM, but the degradation rate was slightly decreased with excess H₂O₂ (>3 mM). The performance of modified VUV processes (i.e., VUV/H₂O₂ and VUV/K₂S₂O₈) was inhibited at highly alkaline condition (pH 11). The co-existence of halides (Cl^- and Br^-) enhanced antibiotics degradation via the modified VUV processes, but the reaction was almost unaffected in the presence of single halides. This study demonstrated that modified VUV processes (especially VUV/K₂S₂O₈) are efficient for eliminating fluoroquinolone antibiotics from water, which can be considered as a clean and green method for the treatment of antibiotics-containing industrial wastewater.

Surface restructuring of red mud to produce FeO x (OH) y sites and mesopores for the efficient complexation/adsorption of β-lactam antibiotics

In this work, iron oxide in the red mud (RM) waste was restructured to produce mesopores with surface [FeO _x (OH) _y ] sites for the efficient complexation/adsorption of β-lactam antibiotics. Red mud composed mainly by hematite was restructured by an acid/base process followed by a thermal treatment at 150-450 °C (MRM150, MRM200, MRM300, and MRM450) and fully characterized by Mössbauer, XRD, FTIR, BET, SEM, CHN, and thermogravimetric analyses. The characterization data showed a highly dispersed Fe³⁺ oxyhydroxy phase, which was thermally dehydrated to a mesoporous α-Fe₂O₃ with surface areas in the range of 141-206 m² g^-1. These materials showed high efficiencies (21-29 mg g^-1) for the adsorption of β-lactam antibiotics, amoxicillin, cephalexin, and ceftriaxone, and the data was better fitted by the Langmuir model isotherm (R ² = 0.9993) with monolayer adsorption capacity of ca. 39 mg g^-1 for amoxicillin. Experiments such as competitive adsorption in the presence of phosphate and H₂O₂ decomposition suggested that the β-lactamic antibiotics might be interacting with surface [FeO _x (OH) _y ] species by a complexation process. Moreover, the OH/Fe ratio, BET surface area and porosity indicated that this complexation is occurring especially on [FeO _x (OH) _y ]_surf sites contained in the mesopore space.

Simultaneous nitrate reduction and acetaminophen oxidation using the continuous-flow chemical-less VUV process as an integrated advanced oxidation and reduction process

This work was aimed at investigating the performance of the continuous-flow VUV photoreactor as a novel chemical-less advanced process for simultaneously oxidizing acetaminophen (ACT) as a model of pharmaceuticals and reducing nitrate in a single reactor. Solution pH was an important parameter affecting the performance of VUV; the highest ACT oxidation and nitrate reduction attained at solution pH between 6 and 8. The ACT was oxidized mainly by HO while the aqueous electrons were the main working agents in the reduction of nitrate. The performance of VUV photoreactor improved with the increase of hydraulic retention time (HRT); the complete degradation of ACT and ∼99% reduction of nitrate with 100% N2 selectivity achieved at HRT of 80min. The VUV effluent concentrations of nitrite and ammonium at HRT of 80min were below the drinking water standards. The real water sample contaminated with the ACT and nitrate was efficiently treated in the VUV photoreactor. Therefore, the VUV photoreactor is a chemical-less advanced process in which both advanced oxidation and advanced reduction reactions are accomplished. This unique feature possesses VUV photoreactor as a promising method of treating water contaminated with both pharmaceutical and nitrate.