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Wet air oxidation (WAO) has an obvious advantage in treating wastewater with high concentration of organics, but harsh reaction conditions are required and the treatment efficiency has not reached a satisfactory level. Herein, we developed a low dosage of persulfate promoted WAO process (PWAO) to remove a model heterocyclic pollutant benzothiazole (BTH). The addition of persulfate remarkably enhanced the elimination of benzothiazole (BTH) and COD from water via degradation and polymerization. Under optimized operation condition (with 11.1 mM K2S2O8 addition into WAO), about 65.0% of BTH converted into microsphere polymers and more than 94.6% COD was eliminated from water after polymers separation. Electron paramagnetic resonance (EPR) analysis and quenching experiments revealed that OH was effectively generated in a wide range of reaction temperature and it played the key role in BTH degradation and polymerization, while SO4 − was detected at low temperature for its fast decomposition at high temperature. Quantum chemical calculation together with ultra-performance liquid chromatography with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS) analysis confirmed that the degradation and polymerization of BTH mainly started from the heterocyclic ring, followed by further oxidation or polymerization. Comparing with normal WAO process, the PWAO technology had an advantage in lower operating cost in removing per unit COD and carbon resource recycle, which indicates a promising prospect in treating wastewater with high concentration of heterocyclic compounds.

Manganese dioxides (MnO2) govern the polymerization of phenolic and anilinic pollutants in nature water body. The studies on the chemistry of different phases of MnO2 was relatively limited. Here we compared two MnO2, layer δ-MnO2 and tunnel γ-MnO2, on their reaction kinetics and removal pathways with acetaminophen (APAP) as model compound. We found the kinetics of acetaminophen transformation by MnO2 were largely influenced by pH values and MnO2 structures. In neutral systems, APAP removal by δ-MnO2 was faster than by γ-MnO2. This was attributed to the higher catalytic potential of δ-MnO2. In acidic systems, APAP removal by γ-MnO2 was faster than by δ-MnO2. This was attributed to the larger surface area and weaker electrostatic repulsion of γ-MnO2 to APAP in acidic conditions. Furthermore, the pathways of acetaminophen transformation were influenced by pH values. Dimerization and hydrolysis-oxidation were the two major APAP transformation pathways by both MnO2 in neutral and acidic systems. Low pH values induced the nucleophilic addition between quinoneimine (the product of hydrolysis-oxidation) and anilines (e.g., APAP and its dimers). Low pH values also promoted the dimerization degrees of APAP. The hydrophilicity of APAP transformation products by MnO2 were significantly reduced by low pH values. This work reconsidered the significances of acidity in the pollutants transformation by MnO2, and provided new perspectives to study the pollutants transformation by different phases of MnO2.

N-doped graphene has demonstrated exceptional activities in versatile metal-free catalytic processes. In this study, reduced graphene oxide (rGO) and N-doped rGO were synthesized by a facile approach via microwave reduction with a low energy input and short reaction time. The activities of the derived carbocatalysts were evaluated by catalytic ozonation of 4-nitrophenol (4-NP). Compared with thermally annealed rGOs in argon atmosphere, microwave treated rGO demonstrated a better performance in catalytic oxidation, and N-doping would further improve the catalytic activity. It is discovered that microwave irradiation not only gave rise to more edging sites and dangling bonds in rGO, making higher catalytic potentials for ozone decomposition than that from thermal annealing, but also resulted in a higher concentration of N dopants. XPS studies revealed that more graphitic N species were incorporated into the carbon basal plane during the microwave reduction processes. The reactive oxygen species (ROS) in 4-NP oxidation were evaluated and identified by liquid-phase electron spin resonance (ESR) and radical scavenging tests, which indicated the generation of O2 −, OH and 1O2 for 4-NP degradation. This study provides a facile protocol for fabricating advanced nanocarbon materials for green oxidation and enables new insights in catalytic ozonation with state-of-the-art carbocatalysis.

The detailed evolution mechanism of O3 into reactive oxygen species (ROS) is of paramount importance but remains elusive in catalytic ozonation. Herein, we report a density functional theory study to comprehensively reveal the specific evolution processes of O3 into ROS on the B-, N-, P-, and Si-doped graphene, including the adsorption, decomposition and ROS generation. In contrast to some previous reports that O3 would directly decompose into effective ROS on catalysts, our results indicate that after O3 adsorption, the decomposition products are ground state O2 and the adsorbed oxygen species (Oads). The Oads is more likely to act as a crucial intermediate for generating other ROS instead of directly attacking the organics. The type of the ROS and generation efficiency vary with the doped heteroatoms, and the heteroatoms of B, P and Si, or the neighboring C of N, would serve as active sites for O3 adsorption and decomposition. The N- and P-doped graphene are predicted to have the superior performance in ROS generation and catalytic stability. Finally, twenty representative descriptors were adopted to build the quantitative structure-activity relationship (QSAR) with the activation energy barrier of O3 decomposition. The result indicates that condensed dual descriptor (CDD) could be useful for preliminarily selecting the modified graphene catalysts, since it shows a very good linear relation with the activation energy barrier. This contribution provides an alternative way to gain fundamental insights into the mechanism of catalytic ozonation at the molecular level, and could be helpful for designing more-efficient catalysts in environmental remediation.

Effective recycling of spent graphite from lithium-ion batteries (LIBs) has a strong application potential. In this research, anode scrap of spent LIBs is efficiently recovered and reused as high-performance cathode in electro-Fenton system. Role of different recovery processes in the reuse of anode scrap powder in electro-Fenton system is focused, including Anode raw powder (RP), acid leaching (AL), acid and alkali leaching (AAL) residual powder. The results indicate functional groups of anode powder are changed by different leaching processes, which can significantly affect the subsequent reuse in electro-Fenton system. According to evaluation by electrochemical characterization, the AAL has a higher hydrogen peroxide (H2O2) selectivity and yield than RP and AL due to highly active two-electron reduction of oxygen (O2). Interestingly, when anode powder is reused in electro-Fenton system, the AL electrode achieves 100% bisphenol A (BPA) removal in 70 min and 87.4% COD removal in 240 min, showing the best degradation efficiency. The reason can be attributed to higher carboxylic group content (35.83%) of AL powder than that of AAL (7%). Thus, part of iron ion in solution can be adsorbed on the surface of AL cathode, forming a partial heterogeneous iron oxidation-reduction. Furthermore, the reusability of AL electrode is evaluated. Compared with other carbon cathode, the AL cathode with a low current density still maintains 100% BPA removal after 10 reuse cycles. Since it is inherent with high reusability and environmental friendliness comparing with traditional cathode materials, this research demonstrates a potentially new approach to cooperatively treat pollutants from solid waste and waste water.

The recent thrust in utilizing microbial electrolysis cell (MEC) has led to accelerated attention in environmental decontamination. One key factor that governs this process is electron transfer efficiency. In this study, neutral red (NR) is involved as electron transfer mediator to investigate whether it could contribute to MEC performance. Afterwards, influence of electrode material selection on NR addition system was also studied. The results indicate MEC with NR shows better electrochemistry activity, which means sulfate-reducing bacteria (SRB) can response to electron transfer mediator NR. Further study reveals graphite felt triggers a better synergy with NR to facilitate electron utilization efficiency of the system subsequently maintains bacteria metabolic activity for a longer time. Sulfate removal in this reactor reaches 79.0% with electron utilization efficiency of 54.2%. To explore the mechanism, electrode bioelectrochemical property, microorganism activity and community were investigated. Electrode morphology analysis confirms graphite felt affords abundant space for the growth of electroactive microorganisms especially SRB and promotes electron exchange through cooperating with NR, which fits in with electrochemical impedance spectroscopy (EIS) analysis. High-throughput sequencing analysis confirms improved reactor can fortify the population dominant of SRB in the community which greatly raises electron utilization efficiency of SRB.

The effective V(V) and Cr(VI) separation is very difficult due to their similarity in physiochemical properties. In this research, almost completely separation of V(V) and Cr(VI) with primary amine N1923 was firstly demonstrated by employing multistage countercurrent extraction (MCE) with annular centrifugal contactors (ACCs). The optimum operation conditions of single-stage extraction with ACC were determined by systematic experiments, and best conditions of the rotor speed, the flow rate and the flow ratio of organic phase to aqueous phase were obtained. The loaded-organic phase can be reused for extraction process after stripping with ammonia/sodium hydroxide. Vanadium, in the leaching/aqueous solution with the initial pH of 6.1, was reached to extraction equilibrium by three-stage countercurrent extraction with ACCs. V(V) and Cr(VI) were separated through 21 stages of countercurrent extraction with ACCs. 95.1% of vanadium and almost none of chromium were extracted, with the separation factor approaching infinity. Through the mechanism of hydrogen bond association and different species of two metals in the leaching/aqueous solution, an in-depth analysis to correlate the results obtained and the chemical reactions with ACCs has been made in order to establish a firm conclusion with aim of the guidance in industrial application.

Microbial electrolysis cell (MEC) coupled with sulfate-reducing bacteria (SRB) was used to degrade sulfate-rich wastewater which was deficient in electron donors. Results confirmed that SRB could trigger vigorous synergy with an applied current. An applied electrical field of 1.5 mA (R1) resulted in the highest sulfate removal, which was 14.9% higher than that of the control reactor (R0). In addition, organic-substance consumption decreased with the increase of applied current. The concentration of lactic dehydrogenase (LDH), an indicator of cell rupture, increased by 3.59 times at 2.5 mA; that of ATP, an indicator of cell metabolism, sharply decreased under 2.5 and 3.5 mA. This finding indicated that high current led to plasmatorrhexis, low growth rate, and metabolic activity, subsequently reduced sulfate-reduction efficiency. Conversely, a proper current resulted in the enhancement of extracellular secretion, which was conducive to biofilm formation as further confirmed by detection through SEM. Electrochemical impedance spectroscopy (EIS) illustrated the SRB in the biofilm could accelerate the rate of direct electron transfer to cathode. Genus-level results further revealed that the dominant bacterium Desulfovibrio , an SRB, was richer in the cathode biofilm and R1, compared with R0.

The high-efficient extraction of vanadium using primary amine and its application in the utilization of the chromium-bearing vanadium slag (V–Cr slag) were studied in this work. The extraction mechanism and the possible difficulties in the application were both considered. From the results, the extraction percentage of vanadium using free primary amine with the hydrogen bond association mechanism is higher than that in the acidic environment by primary amine salts. The inorganic ions and other impurities existing in the system were all considered to research for the continuous operation of the extraction. Furthermore, the viscosities of the fresh organic phase and the recycled organic phase were determined using the extractant not only N1923 but also LK-N21, where the viscosity of the latter system increased slightly during the recycled process of the extractant. Based on the above results, the pilot and the commercial experiment were carried out. In the large-scale experiment, the vanadium was extracted and the product of 99.5 wt.% vanadium pentoxide was obtained, and the mass loss of the extractant was only 0.1%.

The degradation of a series of phenolic compounds in a novel dielectric barrier discharge (DBD) plasma reactor was studied in this paper. The effect of various parameters, such as applied voltage, water flowrate, initial concentrations of organics, solution conductivity and pH, was investigated to achieve a high removal efficiency for phenolic compounds. The complete degradation of p-CH3 could be achieved within 32 min, and the highest energy yield was about 3.5 g/kWh. Electron paramagnetic resonance analysis and radical quenching experiment indicated that OH played an important role in phenols degradation, along with ozone molecules. O2− and 1O2 also possibly contributed to phenols degradation. Substituted phenols were more easily degraded, especially nitrophenol with strong electron withdrawing groups, originating from OH and O2− attack. The intermediates of different phenolic compound generated in the degradation process were identified by Mass spectroscopy (MS) and the corresponding mechanism were proposed to strengthen the understanding of mechanism. A DBD plasma and activated carbon combined technique is further proposed to promote the conversion of oxygen into ROS (reactive oxygen species) and enhance the mineralization rate of substituted phenols.

Nitrogen-containing heterocyclic contaminants (NHCs) have aroused intense environmental issues in waterbody because of their high toxicity and strong recalcitrance against natural degradation. In this study, ozonation degradation on four typical NHCs - benzotriazole (BTA), benzimidazole (BMZ), indazole (IDZ), and indole (IDO) was carried out to investigate the effects of N atoms on degradation efficiency. Global softness of the NHCs was calculated by density functional theory (DFT) and correlated with ozonation efficiency. It was discovered that higher global softness of the NHCs resulted in the greater degradation efficiency. Mineralization results together with the quenching tests results suggested that NHCs with ortho-positioned N atoms in heterocyclic ring are easier to be mineralized, while the presence of para-positioned N atoms increased the recalcitrance for destruction. Apart from hydroxyl radicals, superoxide radicals and singlet oxygens were also identified by electron paramagnetic resonance (EPR) spectra. Condensed Fukui index was employed to probe the potential active sites for both direct ozone oxidation and radical-based attack. Single point energies were further calculated among these active sites to seek the initial-stage hydroxylation intermediates. Combined the calculation results with the identified intermediates from time-of-flight mass spectroscopy (TOF-MS), degradation routes of the NHCs were proposed. This study discovered structure-dependent behavior of NHCs on ozonation efficiency and envisaged a more accurate strategy for establishing the degradation pathway.

The objective of this work is to study the influence of the type and number of basic sites of activated carbon (AC) on the AC-enhanced ozonation of oxalate. A commercial activated carbon (AC) was thermally treated with N-2, H-2, and NH3 at different temperatures. The results of chemical and textural characterization of the original and modified ACs show that the specific surface area and number of basic sites generally increased with increasing treatment temperature, whereas the acidic oxygen-containing groups decreased. Nitrogen-containing groups formed after NH3 treatment. The oxalate removal rate increased in ozonation systems with modified ACs compared with that of systems with the original AC. Oxalate degradation increased when ACs with higher numbers of basic sites and larger specific surface areas were used, except for the AC treated under NH3 at 900 degrees C. Oxalate removal was attributed to surface oxidation and HO. oxidation in bulk solution. The former process was dominant in the ozonation system with 0.2 g/L AC at pH 7. The experimental results indicate pyrrole groups may enhance ozone decomposition to generate HO. in bulk solution, while pyridine groups possibly decreased the surface oxidation of oxalate. Other basic sites, such as basal planes and basic oxygen-containing groups, enhanced oxalate removal through surface oxidation, and indirectly weakened HO. oxidation of oxalate in bulk solution. (C) 2014 Elsevier B.V. All rights reserved.