Cu2O-promoted degradation of sulfamethoxazole by α-Fe2O3-catalyzed peroxymonosulfate under circumneutral conditions: synergistic effect, Cu/Fe ratios, and mechanisms

Application of artificial intelligence for the optimization of advanced oxidation processes to improve the water quality polluted with pharmaceutical compounds

Sulfamethoxazole and metronidazole are emerging pollutants commonly found in surface water and wastewater. These compounds have a significant environmental impact, being necessary in the design of technologies for their removal. Recently, the advanced oxidation process has been proven successful in the elimination of this kind of compounds. In this sense, the present work discusses the application of UV/H2O2 and ozonation for the degradation of both molecules in single and binary systems. Experimental kinetic data from O3 and UV/H2O2 process were adequately described by a first and second kinetic model, respectively. From the ANOVA analysis, it was determined that the most statistically significant variables were the initial concentration of the drugs (0.03 mmol L-1) and the pH = 8 for UV/H2O2 system, and only the pH (optimal value of 6) was significant for degradation with O3. Results showed that both molecules were eliminated with high degradation efficiencies (88-94% for UV/H2O2 and 79-98% for O3) in short reaction times (around 30-90 min). The modeling was performed using a quadratic regression model through response surface methodology representing adequately 90 % of the experimental data. On the other hand, an artificial neural network was used to evaluate a non-linear multi-variable system, a 98% of fit between the model and experimental data was obtained. The identification of degradation byproducts was performed by high-performance liquid chromatography coupled to a time mass detector. After each process, at least four to five stable byproducts were found in the treated water, reducing the mineralization percentage to 20% for both molecules.

Silica enhanced activation and stability of Fe/Mn decorated sludge biochar composite for tetracycline degradation

In this study, SiO₂-composited biochar decorated with Fe/Mn was prepared by co-pyrolysis method. The degradation performance of the catalyst was evaluated by activating persulfate (PS) to degrade tetracycline (TC). The effects of pH, initial TC concentration, PS concentration, catalyst dosage and coexisting anions on degradation efficiency and kinetics of TC were investigated. Under optimal conditions (TC = 40 mg L^-1, pH = 6.2, PS = 3.0 mM, catalyst = 0.1 g L^-1), the kinetic reaction rate constant could reach 0.0264 min^-1 in Fe₂Mn₁@BC-0.3SiO₂/PS system, which was 12 times higher than that in the BC/PS system (0.00201 min^-1). The electrochemical, X-ray diffractometer (XRD), Fourier transform infrared spectrum (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis showed that both metal oxides and oxygen-containing functional groups provide more active sites to activate PS. The redox cycle between Fe(II)/Fe(III) and Mn(II)/Mn(III)/Mn(IV) accelerated the electron transfer and sustained the catalytic activation of PS. Radical quenching experiments and electron spin resonance (ESR) measurements confirmed that surface sulfate radical (SO₄^•-) play a key role in TC degradation. Three possible degradation pathways of TC were proposed based on high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS) analysis, the toxicity of TC and its intermediates was analyzed by bioluminescence inhibition test. In addition to the enhanced catalytic performance, the presence of silica also improved the stability of the catalyst, as confirmed by cyclic experiment and metal ion leaching analysis. The Fe₂Mn₁@BC-0.3SiO₂ catalyst, derived from low-cost metals and bio-waste materials, offer an environmentally friendly option to design and implement heterogenous catalyst system for pollutant removal in water.

A review of hydrogen chloride removal from calcium- and sodium-based sorbents

With the steady progress of ultra-low emissions in various industries, the management of unconventional pollutants is gradually attracting attention. A such unconventional pollutant that negatively affects many different processes and pieces of equipment is hydrogen chloride (HCl). Although it has strong advantages and potential in the treatment of industrial waste gas and synthesis gas, the process technology of removing HCl by calcium- and sodium-based alkaline powder has not yet been thoroughly studied. The impact of reaction factors on the dechlorination of calcium- and sodium-based sorbents is reviewed, including temperature, particle size, and water form. The most recent developments in sodium- and calcium-based sorbents for capturing hydrogen chloride were presented, and the dechlorination capabilities of various sorbents were contrasted. In the low-temperature range, sodium-based sorbents had a stronger dechlorination impact than calcium-based sorbents. Surface chemical reactions and product layer diffusion between solid sorbents and gases are crucial mechanisms. Meanwhile, the effect of the competitive behavior of SO₂ and CO₂ with HCl on the dechlorination performance has been taken into account. The mechanism and necessity of selective hydrogen chloride removal are also provided and discussed, and future research directions are pointed out to provide the theoretical basis and technical reference for future industrial practical applications.

Activation of Na2S2O8 by α-Fe2O3/CuS composite oxides for the degradation of Orange II under visible light irradiation

Layered α-Fe2O3/CuS nanoflowers with abundant active sites were synthesized by a hydrothermal method.

Enhanced peroxymonosulfate activation by hierarchical porous Fe3O4/Co3S4 nanosheets for efficient elimination of rhodamine B: Mechanisms, degradation pathways and toxicological analysis

Fenton-like catalysts have usually superior catalytic activities, however, some drawbacks of ion leaching and difficult-to-recovery limit their applications. In this work, a hierarchical porous Fe₃O₄/Co₃S₄ catalyst was fabricated via a simple phase change reaction to overcome these shortcomings. The introduced iron cooperates with cobalt achieving high-efficiency activation of peroxymonosulfate (PMS) to eliminate Rhodamine B (RhB). The results showed that 0.05 g/L Fe₃O₄/Co₃S₄ and 1 mM PMS could quickly remove 100% of 200 mg/L RhB within 20 min, and the removal rate of RhB remained above 82% after 5 cycles. Moreover, the as-prepared Fe₃O₄/Co₃S₄ possessed a great magnetic separation capacity and good stability of low metal leaching dose. Radical quenching experiments and electron paramagnetic resonance (EPR) techniques proved that sulfate radicals (SO₄^•-) were the dominant reactive oxygen species responding for RhB degradation. X-ray photoelectron spectroscopy (XPS) pointed out that the synergism of sulfur promoted the cycling of Co³⁺/Co²⁺ and Fe³⁺/Fe²⁺, boosting the electron transfer between Fe₃O₄/Co₃S₄ and PMS. Moreover, the degradation pathways of RhB were deduced by combining liquid chromatography-mass spectrometry (LC-MS) analysis and density functional theory (DFT) calculations. The toxicities of RhB and its intermediates were evaluated as well, which provided significant assistance in the exploration of their ecological risks.

Bacterial diversity in phosphorus immobilization of the South China Sea

Marine bacteria play indispensable roles in the phosphorus (P) cycle, primarily responsible for P assimilation and remineralization. The aim of this study was to determine diversity of marine aerobic bacteria from the South China Sea capable of P immobilization. Highly efficient P immobilized genera reached 87.72% of all genera, which were mainly distributed in epipelagic seawater zone and semi-deep sediment zone. Accumulated P in extracellular polymeric substances (EPS) accounted for about 70% of immobilized P of representative bacteria. The sum of bioavailable P (non-apatite inorganic phosphorus, organic phosphorus) amounted to more than 90% of total P in representative bacteria, and orthophosphate monoester was identified as the only extracellular P species. Marine bacteria which participated in P cycle were general, not specific genus. EPS of marine bacteria played an important role in P immobilization, and accumulated P species were bioavailable. Our results may provide a better insight for understanding roles of marine bacteria in P cycle.

Shape-controllable synthesis of MnO2 nanostructures from manganese-contained wastewater for phenol degradation by activating peroxymonosulphate: performance and mechanism

Nanostructured manganese oxide materials were prepared from manganese-contained wastewater (MW) using a facile hydrothermal method and adopted as a catalyst to degrade phenol via activation of peroxymonosulphate (PMS). In the WM environment, δ-MnO₂ (flower-like Mn-2 with nanosheets) was transformed to α-MnO₂ (needle-like Mn-4 with nanowires). Catalytic evaluation experiments demonstrated that the needle-like MnO₂ was highly efficient for phenol removal, with a degradation efficiency of 100% within 15 min at the optimal conditions of catalyst dosage 0.2 g/L, PMS dosage 1.5 g/L, initial phenol concentration 0.025 g/L, initial pH 3 and temperature 25°C. Moreover, the needle-like MnO₂ catalyst could be recycled and the regenerated material after calcination remained excellent catalytic activity. On the surface of catalysts, PMS was activated by Mn^IV to generate [Formula: see text] which was the major reactive species attacking phenol. Overall, the needle-like MnO₂ prepared from MW was an efficient catalyst with low cost for organic wastewater treatment, realizing both Mn resource recycle and organic wastewater treatment.

Improved membrane sequencing batch reactor: effect of carbon and nitrogen volumetric loading rate on dephosphatation

A lab-scale anaerobic-anoxic-aerobic membrane bioreactor (A₂NO-MBR) fed with synthetic wastewater was operated to investigate the impact of influent carbon and nitrogen volumetric loading rate (VLR) on dephosphatation, and the corresponding influent concentration was 100-300 mg L^-1 (COD), 24-50 mg L^-1 (NH₄⁺-N) and 4.8-6.0 mg L^-1 (TP), respectively. The results demonstrated that carbon VLR had a negligible effect on the COD removal with effluent below 50 mg L^-1, and high and stable removal capacity for phosphorus were also obtained, regardless of carbon VLR change. Whereas TN removal efficiency was positively correlated with carbon VLR reduction, and lower carbon VLR produced a negative effect on TN removal. In addition, since nitrate served as an electron acceptor for denitrifying phosphorus removal (DPR), a significant effect on nitrogen and phosphorus removal was observed with different nitrogen VLR. The TN and TP removal efficiency was 68.30 ± 1.36%, 70.70 ± 1.23%, 45.19 ± 1.72% and 41.63 ± 3.09%, 98.14 ± 0.53%, 53.34 ± 2.68% with influent nitrogen VLR of 0.024 ± 0.001, 0.034 ± 0.001 and 0.045 ± 0.001 kg-N/(m³ d), respectively. Moreover, bacterial community structure of sludge samples in Run I and V from anaerobic-anoxic-aerobic-SBR (named A₂OSBR_1 and A₂OSBR_2) and membrane bioreactor (named N-MBR_1 and N-MBR_2) revealed that Candidatus_Accumulibacter was the most dominant genus in A₂OSBR_1 (21.50%) and A₂OSBR_2 (18.98%). The relative lower carbon VLR favoured the enrichment of Saprospiraceae, which was related with DPR, with the proportion of 9.31% and 14.61% in A₂OSBR_1 and A₂OSBR_2. Besides, Nitrospira and Nitrosomonas with proportions of 11.14%, 5.38% in N-MBR_1 and 10.72%, 6.77% in N-MBR_2 were observed, which were likely responsible for the nearly complete nitrification.

Response of an aerobic denitrifier to titanium dioxide nanoparticles exposure

The cytotoxicity of titanium dioxide nanoparticles (TiO₂ NPs) to microorganisms has attracted great attention over the past few decades. As an important participator in the nitrogen cycle, aerobic denitrifiers have been proven to be negatively affected by TiO₂ NPs, but the mechanism of this effect remains unclear. In this study, the bacteria-nanoparticle interaction was investigated by exposing an aerobic denitrifier, Pseudomonas stutzeri PCN-1 to different concentrations of TiO₂ NPs at the dark condition, in order to investigate the cytotoxicity mechanism. The results illustrated that aerobic denitrification was inhibited at different TiO₂ NPs concentrations from 1 to 128 mg/L, accompanied by the postponement of nitrate reduction and the accumulations of nitrite and nitrous oxide. But this inhibitory effect was mitigated with increasing TiO₂ NPs concentrations. Further studies revealed that expressions of aerobic denitrification genes were also inhibited with the presence of TiO₂ NPs, and the inhibition effect on napA and nirS genes was more significant than that on nosZ and cnorB, which might directly bring about the delayed nitrate reduction and hindered nitrite transfer. Moreover, the decreased toxicities at higher TiO₂ NPs concentrations could be attributed to the formation of larger aggregates (>1000 nm), which greatly reduced the chance for direct interactions between NPs and bacterial membranes, as well as the interruption of denitrifying genes expressions. These findings were meaningful for the formation of deep insights into the mechanism of TiO₂ NPs cytotoxicity as well as the development of strategies to control the negative effect of nanoparticles in the environment.Aerobic denitrification characteristics of strain PCN-1 under different carbon sources.

An efficient CuO-γFe2O3 composite activates persulfate for organic pollutants removal: Performance, advantages and mechanism

CuO-γFe₂O₃ was fabricated as a novel and effective persulfate (PS) catalyst to remove bio-refractory organic pollutants. Characterization results showed that CuO-γFe₂O₃ possessed a relatively large surface area among transition metal oxides which provided favorable adsorption and activation sites for PS to degrade pollutants. There was an obvious synergy between CuO and γFe₂O₃ in the composite, which played 84.7% role in Acid orange 7 (AO7) removal. Under the optimal conditions (CuO-γFe₂O₃ dosage = 0.6 g L^-1, PS dosage = 0.8 g L^-1, unadjusted solution pH), almost complete AO7 was rapidly eliminated in 5 min. Moreover, the wide workable pH range (2-13), good stability (0.82 mg L^-1 Cu leached, almost no Fe leached) and reusability (4 times) were the significant virtues of CuO-γFe₂O₃ for wastewater treatment. Besides, the reaction mechanism mainly based on the interaction among Cu(II/III) and Fe(II/III) species for sulfate radical (SO₄^-) generation was emphatically elucidated by the analyses of radicals, PS utilization, TOC removal and metal chemical states. Finally, CuO-γFe₂O₃+PS system displayed desirable removal of multiple organic pollutants with different molecular structures. In light of the prominent advantages of CuO-γFe₂O₃+PS, this work extended activated PS process in treating refractory organic wastewater.

In situ preparation of a nanocomposite comprising graphene and α-Fe2O3 nanospindles for the photo-degradation of antibiotics under visible light

Preparation of α-Fe₂O₃ nanospindle (NS) decorated graphene sheets for antibiotic degradation.

The enhanced effect of oxalic acid on the electroreduction of Cr(VI) via formation of intermediate Cr(VI)-oxalate complex

In this study, the enhanced effect of oxalic acid (Ox) on Cr(VI) electroreduction was evaluated. It was found that for Cr(VI)-contaminated solution ([Cr(VI)]₀ = 1.0 mM, pH = 3.0), addition of 5.0 mM Ox can significantly increase Cr(VI) reduction from 0.36 to 1.0 mM within 90 min electrolysis reaction, accompanying with the increase of current efficiency from 19% to 53%. Increasing initial Ox concentration (0-10 mM) and electric current (10-40 mA) facilitated Cr(VI) reduction, whereas it was inhibited with decreasing solution pH value (2.0-3.5) and elevating Cr(VI) concentration (0.1-2.0 mM), respectively. Results show that reactive electron was the primary reductant for the heterogeneous reduction of Cr(VI) on the cathode. In addition, Ox can also serve as an electron donor for the homogeneous reduction of Cr(VI). During this process, the formation of Cr(VI)-oxalate complex is indispensable for the enhanced Cr(VI) reduction. The coordination of Ox with Cr(VI) did not only make the structure of Cr(VI) more distorted but also improved the reactivity of Cr(VI) in Cr(VI)-oxalate complex toward reduction reaction. In general, this study provides an energy-efficient and environmentally benign strategy for the treatment of Ox and Cr(VI) co-contaminated wastewater.

The first demonstration of a novel isolated fungus Eutypella sp. BJ associated with the biodegradation of polyvinyl alcohol

The aim of this work is to study the potential degradation of polyvinyl alcohol (PVA) by a novel fungus Eutypella sp. BJ isolated from soil compost. When it was cultured on a semi-synthetic medium containing PVA at 30 °C and 160 rpm for 8 days, the removal rates of PVA 1788, 1799 and 2488 reached 87.40%, 86.31% and 44.80%, respectively. Gel permeation chromatography (GPC) analysis revealed significant reductions of the number average molecular weight and the weight average molecular weight of PVA 1788 from 47 358 to 13 345 and from 71 387 to 24 238, respectively, after 8 days. Fourier transform infrared spectroscopy (FTIR) indicated that some substances containing carbonyl groups (likely aldehydes or ketones) might have been produced during the biodegradation process. These results indicate that the isolate has potential for degrading PVA. This study provides the first demonstration that Eutypella has the ability to assimilate PVA.

An isolated fungus Eutypella sp. BJ is firstly demonstrated to have the ability to degrade polyvinyl alcohol.

Implementation of martite nanoparticles prepared through planetary ball milling as a heterogeneous activator of oxone for degradation of tetracycline antibiotic: Ultrasound and peroxy-enhancement

The aim of the present study was to employ martite nanoparticles synthesized through planetary ball milling instead of conventional sources of iron for the activation of Oxone in order to decompose tetracycline (TC) antibiotic in the aquatic phase. Accordingly, martite nanoparticles-activated Oxone exhibited a remarkable improvement in degrading TC molecules up to 87%. The results indicated an increased decomposition rate of TC with increasing Oxone concentration, martite nanoparticles dosage, and initial pH. In the absence of ultrasound, the decomposition rate of TC was 0.0481 min^-1 within 30 min, while the implementation of ultrasound at 320 W and addition of hydrogen peroxide at 40 mM led to increase in the decomposition rate up to 0.0770 and 0.0907 min^-1, respectively. The presence of carbonate and even persulfate ions suppressed the decomposition rate. Inversely, the addition of chloride and carbon tetrachloride enhanced the reactor performance in terms of TC degradation. Within four consecutive experimental runs, only 10.8% was dropped in the decomposition rate, indicating the appropriate reusability potential of martite nanoparticles. The results confirmed the appropriate ability of the treatment process in degrading and mineralizing the target pollutant but a longer exposure time is required for an efficient mineralization.

Sulfate radical oxidation combined with iron flocculation for upgrading biological effluent of coking wastewater

Because the components of the coking wastewater was biologically toxic and hence inhibit the actions of microorganisms in conventional biological treatment processes,the biological effluent of coking wastewater (BECW) still remains much recalcitrant pollutants. In the current work, we set out to explore the feasibility of using a proposed advanced oxidation method, involving the persulfate-activated zero-valent iron system (PS/ZVI), to realize a deep treatment of BECW. The efficiency levels at which sulfate radical oxidation combined with iron flocculation removed pollutants, specifically TOC, phenolic compounds (PCs), cyanide, and suspended solids (SSs), as well as removing colour were investigated in batch tests. Increasing the persulfate concentration generally resulted in improved pollutant removal, with maximum removal efficiency levels of 58.5%, 68.4%, 61% 99.9% and 91.04% for TOC, PCs, SS, cyanide and colour, respectively. Note that the coexisting inorganic ions CO₃²⁻ and HCO₃⁻ were strong competitors of the radical consumption of TOC, but this interference was eliminated by adjusting the pH to 4.5. Also, flocculation of the generated Fe³⁺ ions from the radical reaction significantly enhanced SS removal. GC-MS analysis showed that the compositional diversity of the BECW decreased after oxidation. Meanwhile its biodegradability increased, indicating less bio-toxicity reaching the natural water body. This study suggests that the PS/ZVI system may be an alternative safer and more efficient method than Fenton's method for carrying out an advanced treatment of coking wastewater.

Sulfate radical oxidation combined iron flocculation towards up-grading of biological effluent of coking wastewater.