Advanced remediation in the presence of ferrous iron and carbonate-containing water by oxygen-induced oxidation of organic contaminants.

Mechanistic investigations of an environmentally friendly and easy-to-implement oxidation method in the remediation of contaminated anoxic waters, i.e. groundwater, through the sole use of oxygen for the oxygen-induced oxidation of pollutants were the focus of this work. This was achieved by the addition of O2 under anoxic conditions in the presence of ferrous iron which initiated the ferrous oxidation and the simultaneous formation of reactive •OH radicals. The involvement of inorganic ligands such as carbonates in the activation of oxygen as part of the oxidation of Fe2+ in water was investigated, too. The formation of •OH radicals, was confirmed in two different, indirect approaches by a fluorescence-based method involving coumarin as •OH scavenger and by the determination of the oxidation products of different aromatic VOCs. In the latter case, the oxidation products of several typical aromatic groundwater contaminants such as BTEX (benzene, toluene, ethylbenzene, xylenes), indane and ibuprofen, were determined. The influence of other ligands in the absence of bicarbonate and the effect of pH were also addressed. The possibility of activation of O2 in carbonate-rich water i.e. groundwater, may also potentially contribute to oxidation of groundwater contaminants and support other primary remediation techniques.

Fe(II)/LXQ-10 bifunctional resin materials for boosting synergistic adsorption/oxidation of benzene in industrial waste gas.

A series of adsorption/oxidation bifunctional material with different Fe(II) loading amounts was prepared by using ultrahigh crosslinking adsorption resin (LXQ-10) as a carrier and FeCl2 as an impregnating solution. The bifunctional material was characterized by BET, SEM, XRD, XPS, and EPR. The effects of Fe loading, reaction temperature, and space velocity on benzene adsorption efficiency were investigated using self-made experimental equipment to explore the optimal reaction condition. The adsorption results were fitted and analyzed by using four typical models: the quasi-first-order kinetic model, the quasi-second-order kinetic model, Elovich's kinetic model, and the Weber and Morris kinetic model. The quasi-first-order kinetic model had the highest R2 value (0.998) and the best applicability. The fitting effect of the Freundlich equation (R2 = 0.997) was better than that of the Langmuir equation (R2 = 0.919). Furthermore, the effects of Fe loading, H2O2 concentration, benzene inlet concentration, and temperature on the catalytic oxidation efficiency of benzene were studied. The catalytic oxidation efficiency of 3-Fe(II)/LXQ-10 was maintained at about 95% at a temperature of 303 K and an H2O2 concentration of 150 mmol/L. Compared with the adsorption efficiency, the catalytic oxidation efficiency of bifunctional resin materials in a heterogeneous Fenton system was remarkably improved and had excellent stability. A possible migration and transformation path during benzene removal was proposed according to the results of the analysis of GC-MS intermediates. This study provided a novel process for the adsorption and oxidative degradation of VOCs.

Review of component designs for post-COVID-19 HVAC systems: possibilities and challenges.

The globally occurring recurrent waves of the COVID-19 pandemic, primarily caused by the transmission of aerosolized droplets from an infected person to a healthy person in the indoor environment, has led to the urgency of designing new modes of indoor ventilation. To prevent cross-contaminations due to airborne viruses, bacteria, and other pollutants in indoor environments, heating ventilation and air-conditioning (HVAC) systems need to be redesigned with anti-pandemic components. The three vital anti-pandemic components for the post-COVID-19 HVAC systems, as identified by the authors, are: a biological contaminant inactivation unit, a volatile organic compound decomposition unit, and an advanced air filtration unit. The purpose of the current article is to provide an overview of the latest research outcomes toward designing these anti-pandemic components and pointing out the future promises and challenges. In addition, the role of personalized ventilation in minimizing the risk of indoor cross-contamination by employing various air terminal devices is discussed. The authors believe that this article will encourage HVAC designers to develop effective anti-pandemic components to minimize the indoor airborne transmission.

Inactivation behavior and intracellular changes in Escherichia coli during electro-oxidation process using Ti/Sb-SnO2/PbO2 anode: Elucidation of the disinfection mechanism.

This study investigates the behavior and intracellular changes in Escherichia coli (model organism) during electro-oxidation with Ti/Sb-SnO2/PbO2 anode in a chlorine free electrochemical system. Preliminary studies were conducted to understand the effect of initial E. coli concentration and applied current density on disinfection. At an applied current density 30 mA cm-2, 7 log reduction of E. coli was achieved in 75 min. The role of reactive oxygen species' (ROS) in E.coli disinfection was evaluated, which confirmed hydroxyl (•OH) radical as the predominant ROS in electro-oxidation. Observations were carried out at cell and molecular level to understand E.coli inactivation mechanism. Scanning electron microscopy images confirmed oxidative damage of the cell wall and irreversible cell death. Intracellular and extracellular protein quantification and genetic material release further confirmed cell component leakage due to cell wall rupture and degradation due to •OH radical interaction. Change in cell membrane potential suggests the colloidal nature of E. coli cells under applied current density. Plasmid deoxyribonucleic acid degradation study confirmed fragmentation and degradation of released genetic material. Overall, effective disinfection could be achieved by electro-oxidation, which ensures effective inactivation and prevents regrowth of E. coli. Disinfection of real wastewater was achieved in 12 min at an applied current density 30 mA cm-2. Real wastewater study further confirmed that effective disinfection is possible with a low cost electrode material such as Ti/Sb-SnO2/PbO2. Energy consumed during disinfection was determined to be 4.978 kWh m-3 for real wastewater disinfection at applied current density 30 mA cm-2. Cost of operation was estimated and stability of the electrode was studied to evaluate the feasibility of large scale operation. Relatively low energy and less disinfection time makes this technology suitable for field scale applications.

Theoretical insights into the gas/heterogeneous phase reactions of hydroxyl radicals with chlorophenols: Mechanism, kinetic and toxicity assessment.

Emission of 2-chlorophenols (2-CPs) can cause serious air pollution and health problems. Here, the reaction kinetics and products of key radicals in 2-CPs photo-oxidation are explored in both gaseous and heterogeneous reactions. Quantum chemical calculations show that •OH-addition pathways are more preferable than H-abstraction pathways in gas phase, while that is opposite in heterogeneous phase. At 298 K, the overall rate coefficients of the title reactions in gas and heterogeneous phases are 3.48 × 10-13 and 2.37 × 10-13 cm3 molecule-1 s-1 with half-lives of 55.3 h and 81.2 h, respectively. The strong H-bonds between linear Si3O2(OH)8 and 2-CPs change the energy barriers of initial •OH-addition and H-abstraction reactions, resulting in the competition between heterogeneous reactions and gas phase reactions. The products in heterogeneous reactions are chloroquinone and HONO, which can cause atmospheric acid deposition and eco-toxicity. In gas phase, self-cyclization of alkoxy radical (RO•) leads to formation of •HO2 and highly­oxygenated molecules, which cause formation of secondary organic aerosol. It is emphasized that oxidation of 2-CPs by •OH leads to formation of more toxic products for aquatic organisms. Therefore, more attention should be focused on the products originated from •OH-initiated reactions of (2-)CPs in gaseous and heterogeneous reactions.

Electrochemical degradation of atrazine by BDD anode: Evidence from compound-specific stable isotope analysis and DFT simulations.

Direct charge transfer (DCT) and •OH attack played important roles in contaminant degradation by BDD electrochemical oxidation. Their separate contributions and potential bond-cleavage processes were required but lacking. Here, we carried out promising compound-specific isotope fractionation analysis (CSIA) to explore 13C and 2H isotope fractionation of atrazine (ATZ), followed by assessing the reaction pathway by BDD anode. The correlation of 2H and 13C fractionation allows to remarkably differentiate DCT process and •OH attack, with Λ values of 18.99 and 53.60, respectively. Radical quenching identified that •OH accounted for 79.0%-88.5% in the whole reaction. While CSIA methods provided biased results, which suggested that ATZ degradation exhibited two stages with •OH contributions of 24.6% and 84.3% respectively, confirming CSIA was more sensitive and provided more possibilities to estimate degradation processes. Combined with Fukui index and intermediate products identification, we deduced that dechlorination-hydroxylation mainly occurred in the first 30 min by DCT reaction. While lateral chain oxidation with C-N broken was the governing route once •OH was largely generated, with the production of DEA (m/z 188), DIA (m/z 174), DEIA (m/z 146) and DEIHA (m/z 128). Our results demonstrated that isotope fractionation can offer "isotopic footprints" for identifying the rate-limiting steps and bond breakage process, and opens new avenues for degradation pathways of contaminants.

Influence of processing conditions on the synergism between UV irradiation and chlorine toward the degradation of refractory organic pollutants in UV/chlorine advanced oxidation system.

The synergy of applying UV/chlorine advanced oxidation process (AOP) for the degradation of organic pollutants was usually reported. However, very limited information is available on the influence of processing conditions on the resulted synergism. In this work, C.I. reactive green 12 (RG12), a refractory textile dye, has been selected as a pollutant model to examine the synergism dependence of operational conditions in UV/chlorine AOP. Initial tests conducted with 500 µM of chlorine and 20 mg L-1 of RG12 have resulted in a high synergy index (SI) of 3. Operating conditions sensitively affect the value of SI. This latter increased with increasing initial chlorine and RG12 concentrations up to certain optimums at 500 µM of chlorine and 20 mg L-1 of RG12 and decreased afterward. The best SI value, i.e. 3, was obtained at pH 5, followed by pH 7 (SI = 2.2) and then pH 9-10.5 (SI ~ 2). On the other hand, the synergistic index decreased importantly from 3 at 25 °C to only 1.2 at 55 °C. Finally, by using different radical scavengers, it was found that among various suspected oxidants, only ●OH and Cl2●- play a key role in the synergistic effect between UV and chlorine toward RG12 degradation.

Insight into elemental mercury (Hg0) removal from flue gas using UV/H2O2 advanced oxidation processes.

Elemental mercury (Hg0) emitted from coal-fired power plants and municipal solid waste (MSW) incinerators has caused great harm to the environment and human beings. The strong oxidized •OH radicals produced by UV/H2O2 advanced oxidation processes were studied to investigate the performance of Hg0 removal from simulated flue gases. The results showed that when H2O2 concentration was 1.0 mol/L and the solution pH value was 4.1, the UV/H2O2 system had the highest Hg0 removal efficiency. The optimal reaction temperature was approximately 50 °C and Hg0 removal was inhibited when the temperature was higher or lower. The yield of •OH radicals during UV/H2O2 reaction was studied by electron paramagnetic resonance (EPR) analysis. UV radiation was the determining factor to remove Hg0 in UV/H2O2 system due to •OH generation during H2O2 decomposition. SO2 had little influence on Hg0 removal whereas NO had an inhibitory effect on Hg0 removal. The detailed findings for Hg0 removal reactions over UV/H2O2 make it an attractive method for mercury control from flue gases.

The fluorescence detection of glutathione by ∙OH radicals' elimination with catalyst of MoS2/rGO under full spectrum visible light irradiation.

In this study, a new method for the detection of glutathione (GSH) was designed based on the ∙OH radicals' elimination system due to the reducing ability of GSH for the first time. Fluorescence method with terephthalic acid (TA) as the probe was employed for the quantification of ∙OH radicals' production and elimination. Experimental conditions of ∙OH radicals' production were optimized in detail, and ∙OH radicals were found to be efficiently produced by the excellent catalysis performance of MoS2/rGO under full spectrum visible light irradiation. The introduction of GSH make fluorescent intensity decrease due to the elimination of ∙OH radicals. For the present fluorescence based GSH sensor, a wide detection range of 60.0-700.0 µM and excellent selectivity have been achieved. Furthermore, it has been successfully employed for the determination of GSH in commercial drug tablets and human serum.