Concentrations Of HO Research Articles

Synergistic mechanisms between chlorine-mediated electrochemical advanced oxidation and ultraviolet light for ammonia removal

The combination of chlorine-mediated electrochemical advanced oxidation (Cl-EAO) and ultraviolet (UV) radiation (UV-E/Cl) can efficiently remove ammonia from wastewater. However, the synergistic mechanisms between Cl-EAO and UV need to be explored in more detail. Thus, in this study, the ammonia oxidation performance of Cl-EAO and UV-E/Cl systems were compared, while the synergistic mechanisms were identified by the performance of UV/chlorine oxidation (UV–ClO) system and the results of electron paramagnetic resonance (EPR) analysis, free radical inhibition assays, and determination of steady-state concentration of free radicals. It was found that, compared with the Cl-EAO system, UV increased the ammonia removal rate by 42.85% and reduced the active chlorine concentration (56.64%) and nitrate yield (53.61%). In the Cl-EAO, and UV-E/Cl systems, Cl• were detected, and the free radical inhibition assays and determination of steady-state concentration of free radicals suggested that UV increased the concentration of Cl• by 51.47%, resulting in Cl• becoming the major contributor to ammonia oxidation in the UV-E/Cl system. Besides, UV also increase the concentrations of HO• and Cl2•-, which further promoted the organic matter removal in the real domestic wastewater. This study also discussed the ammonia oxidation performance of the UV-E/Cl system in real domestic wastewater, even with the presence of significant levels of organic and inorganic anions in the wastewater, UV increased the ammonia oxidation by 21.95%. The results of this study thus clarify the mechanisms and potential applications of UV-E/Cl technology.

Making waves: Opportunities and challenges of applying far-UVC radiation in controlling micropollutants in water.

Concerns over human health risks associated with chemical contaminants (micropollutants) in drinking waters are rising due to the increased use of reclaimed water or water supplies impacted by upstream wastewater discharges. Ultraviolet (UV)-driven advanced oxidation processes (UV-AOPs) using radiation sources that emit at 254nm have been developed as advanced treatments to degrade contaminants, while those UV-AOPs can be improved towards higher radical yields and lower byproduct formation. Several previous studies have suggested that Far-UVC radiation (200-230nm) is a promising radiance source to drive UV-AOPs because the direct photolysis of micropollutants and production of reactive species from oxidant precursors can both be improved. In this study, we summarize from the literature the photodecay rate constants of five micropollutants by direct UV photolysis, which are higher at 222 than 254nm. We experimentally determine the molar absorption coefficients at 222 and 254nm of eight oxidants commonly used in water treatment and present the quantum yields of the oxidant photodecay. Our experimental results also show that the concentrations of HO·, Cl·, and ClO· generated in the UV/chlorine AOP can be increased by 5.15-, 15.76-, and 2.86-fold, respectively, by switching the UV wavelength from 254 to 222nm. We also point out the challenges of applying Far-UVC for micropollutant abatement in water treatment, including the strong light screening effect of matrix components (e.g., carbonate, nitrate, bromide, and dissolved organic matter), the formation of byproducts via new reaction pathways, and the needs to improve the energy efficiency of the Far-UVC radiation sources.

Characterization of lignite deposits of Barmer Basin, Rajasthan: insights from mineralogical and elemental analysis.

The geochemistry of fly ash produced from the combustion of coal at thermal power plants presents a significant challenge for disposal and environmental impact due to its complex mineralogical and elemental composition. The objective of this study was to investigate the mineralogical and elemental distribution of thirty lignite samples from the Barmer Basin using advanced techniques such as X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). XRD analysis revealed the presence of minerals such as haematite (Fe2O3), nepheline, anhydrite, magnesite, andalusite, spinel and anatase. Other minor minerals included albite, siderite, periclase, calcite, mayenite, hauyne, pyrite, cristobalite, quartz, nosean and kaolinite. XRF analysis demonstrated that the most abundant elements in the Barmer Basin lignite ash were iron oxide (Fe2O3), sulphur oxide (SO3), calcium oxide (CaO), and quartz (SiO2) followed by minor traces of toxic oxides (SrO, V2O5, NiO, Cr2O3, Co2O3, CuO) that are known to have adverse effects on human health and the environment. The rare earth element (REE) composition showed higher concentrations of Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Sc at the Giral and lower concentrations at Sonari mine. The Barmer lignites recorded higher concentration of trace elements such as V, Cr, Co, Ni, Cu and Sr while lower concentration of Rb, Cs, Ba, Pb, As, Th and U were observed within optimal range. The study findings revealed the predominant mineral concentration, elemental makeup, trace elements and rare earth elements associated with lignite reserves in the Barmer Basin.

A High-Radical-Yield Advanced Oxidation Process Coupling Far-UVC Radiation with Chlorinated Cyanurates for Micropollutant Degradation in Water.

Increasing the radical yield and reducing energy consumption would enhance the sustainability and competitiveness of advanced oxidation processes (AOPs) for micropollutant degradation in water. We herein report a novel AOP coupling far-UVC radiation at 222 nm with chlorinated cyanurates (termed the UV222/Cl-cyanurates AOP) for radical generation and micropollutant abatement in water. We experimentally determined the concentrations of HO•, Cl•, and ClO• in the UV222/Cl-cyanurates AOP in deionized water and swimming pool water. The radical concentrations are 10-27 times and 4-13 times, respectively, higher than those in the UV254/Cl-cyanurates AOP and the well-documented UV254/chlorine AOP under comparable conditions (e.g., same UV fluence and oxidant dosing). We determined the molar absorption coefficients and innate quantum yields of two chlorine species and two Cl-cyanurates at 222 nm and incorporated these parameters into a kinetic model. The model enables accurate prediction of oxidant photodecay rates as well as the pH impact on radical generation in the UV222/Cl-cyanurates AOP. We predicted the pseudo-first-order degradation rate constants of 25 micropollutants in the UV222/Cl-cyanurates AOP and demonstrated that many micropollutants can be degraded by >80% with a low UV fluence of 25 mJ cm-2. This work advances the fundamental photochemistry of chlorine and Cl-cyanurates at 222 nm and offers a highly effective engineering tool in combating micropollutants in water where Cl-cyanurates are suitable to use.

Insight into micropollutant abatement during ultraviolet light-emitting diode combined electrochemical process: Reaction mechanism, contributions of reactive species and degradation routes

Electrochemical process coupling with ultraviolet light-emitting diode for micropollutant abatement was evaluated in the treatment of wastewater containing Cl−. Four representative micropollutants, atrazine, primidone, ibuprofen and carbamazepine, were selected as target compounds. The impacts of operating conditions and water matrix on micropollutant degradation were investigated. Fluorescence excitation-emission matrix spectroscopy spectra and high performance size exclusion chromatography were employed to characterize the transformation of effluent organic matter in treatment. The degradation efficiencies of atrazine, primidone, ibuprofen and carbamazepine are 83.6 %, 80.6 %, 68.7 % and 99.8 % after 15 min treatment, respectively. The increment of current, Cl− concentration and ultraviolet irradiance promote the micropollutant degradation. However, the presence of bicarbonate and humic acid inhibit micropollutant degradation. The mechanism of micropollutant abatement was elaborated based on reactive species contributions, density functional theory calculation and degradation routes. Free radicals (HO•, Cl•, ClO• and Cl2•-) could be generated by chlorine photolysis and subsequent propagation reactions. The concentrations of HO• and Cl• are 1.14 × 10−13 M and 2.0 × 10−14 M in optimal condition, respectively, and the total contributions of HO• and Cl• for the degradation of atrazine, primidone, ibuprofen and carbamazepine are 24 %, 48 %, 70 % and 43 %, respectively. The degradation routes of four micropollutants are elucidated based on intermediate identification, Fukui function and frontier orbital theory. Micropollutants can be effectively degraded in actual wastewater effluent, and the small molecule compound proportion increases during effluent organic matter evolution. Compared with photolysis and electrolysis, the coupling of the two processes has potential for energy saving in micropollutant degradation, which shed light on the prospects of ultraviolet light-emitting diode coupling with electrochemical process for effluent treatment.

Mapping of trace elements in topsoil of arid areas and assessment of ecological and human health risks in Qatar

Soil is the incubator of human activities. Mapping of soil contaminants needs to be constantly updated. It is fragile in arid regions, especially if it accompanies dramatic and successive industrial and urban activities in addition to the climate change. Contaminants affecting soil are changing due to natural and anthropogenic influences. Sources, transport and impacts of trace elements including toxic heavy metals need continuous investigations. We sampled soil in accessible sites in the State of Qatar. An inductively coupled plasma-optical emission spectrometry (ICP-OES) and an inductively coupled plasma-mass spectrometry (ICP-MS) were used to determine the concentrations of Ag, Al, As, Ba, C, Ca, Ce, Cd, Co, Cr, Cu, Dy, Er, Eu, Fe, Gd, Ho, K, La, Lu, Mg, Mn, Mo, Na, Nd, Ni, Pb, Pr, S, Se, Sm, Sr, Tb, Tm, U, V, Yb and Zn. The study also presents new maps for the spatial distribution of these elements using the World Geodetic System 1984 (projected on UTM Zone 39N) which is based on socio-economic development and land use planning. The study assessed the ecological risks and human health risks of these elements in soil. The calculations showed no ecological risks associated with the tested elements in soil. However, the contamination factor (CF) for Sr (CF > 6) in two sampling locations calls for further investigations. More important, human health risks were not detected for population living in Qatar and the results were within the acceptable range of the international standards (hazard quotient HQ < 1 and Cancer risk between 10−5 and 10−6). Soil remains a critical component with water and food nexus. In Qatar and arid regions, fresh water is absent and soil is very poor. Our findings enhance the establishment of scientific strategies for investigating soil pollution and potential risks to achieve food security.

Microstructures, mechanical properties, corrosion, and biocompatibility of extruded Mg-Zr-Sr-Ho alloys for biodegradable implant applications

In this study, the microstructures, mechanical properties, corrosion behaviors, and biocompatibility of extruded magnesium-zirconium-strontium-holmium (Mg–Zr–Sr–Ho) alloys were comprehensively investigated. The effect of different concentrations of Ho on the microstructural characteristics, tensile and compressive properties, corrosion resistance, and biocompatibility were investigated. The microstructures of the extruded Mg-1Zr-0.5Sr-xHo (x = 0.5, 1.5, and 4 wt.%) alloys consisted of α-Mg matrix, fine α‒Zr particles, and intermetallic phase particles of Mg17Sr2 and Ho2Mg mainly distributed at the grain boundaries. Extensive {101¯2} tensile twins were observed in the partially recrystallized samples of Mg-1Zr-0.5Sr-0.5Ho and Mg-1Zr-0.5Sr-1.5Ho. Further addition of Ho to 4 wt.% resulted in a complete recrystallization due to activation of the particle stimulated nucleation around the Mg17Sr2 particles. The evolution of a rare earth (RE) texture was observed with the Ho addition, which resulted in the weakened basal and prismatic textures. Furthermore, a drastic increase of 200% in tensile elongation and 89% in compressive strain was observed with Ho addition increased from 0.5 to 4 wt%, respectively. The tension–compression yield asymmetry was significantly decreased from 0.62 for Mg-1Zr-0.5Sr-0.5Ho to 0.98 for Mg-1Zr-0.5Sr-4Ho due to the weakening of textures. Corrosion analysis of the extruded Mg–Zr–Sr–Ho alloys revealed the presence of pitting corrosion. A minimum corrosion rate of 4.98 mm y−1 was observed in Mg-1Zr-0.5Sr-0.5Ho alloy. The enhanced corrosion resistance is observed due to the presence of Ho2O3 in the surface film which reduced galvanic effect. The formation of a stabilized surface film due to the Ho2O3 was confirmed through the electrical impedance spectroscopy and XPS analysis. An in vitro cytotoxicity assessment revealed good biocompatibility and cell adhesion in relation to SaOS2 cells.

Effects of bromide ion on the formation and toxicity alteration of halonitromethanes from nitrate containing humic acid water during UV/chlor(am)ine disinfection

UV/chlor(am)ine are efficient for achieving multiple-barrier disinfection and maintaining residuals, while bromide (Br−) has notable impacts on the formation and toxicity of halonitromethanes (HNMs) during UV/chlor(am)ine disinfection. This study investigated the effects of Br− on HNMs formation and toxicity alteration during UV/chlor(am)ine disinfection of nitrate containing humic acid (HA) water. Results reveal that the maximum concentration of HNMs during UV/chlorine disinfection was 12.03 μg L−1 with 0.2 mg L−1 Br−, which was 22.5% higher than that without Br−, and the predominant species of HNMs were converted from trichloronitromethane (TCNM) to dibromonitromethane (DBNM) and tribromonitromethane (TBNM). However, the maximum concentration of HNMs during UV/chloramine disinfection was 3.69 μg L−1 with 0.2 mg L−1 Br−, which was increased by 26.0% than that without Br−, and the predominant species of HNMs were converted from dichloronitromethane (DCNM) to bromochloronitromethane (BCNM) and DBNM. Notably, the HNMs species and yields during UV/chloramine disinfection were less than those during UV/chlorine disinfection, primarily due to the higher concentrations of HO· and reactive chlorine/bromine species in UV/chlorine. Also, in the ranges of the Br−:Cl2 molar ratio from 0 to 0.32 and pH from 6.0 to 8.0, the Br−:Cl2 molar ratio of 0.16 and acidic pH contributed to the HNMs formation during UV/chlorine disinfection, and a high Br−:Cl2 molar ratio and neutral pH contributed to the HNMs formation during UV/chloramine disinfection. Note that the incorporation of Br− significantly improved the calculated cytotoxicity (CTI) and genotoxicity (GTI) of HNMs formed, and the calculated CTI and GTI of HNMs formed during UV/chloramine disinfection were 28.19 and 48.90% of those during UV/chlorine disinfection. Based on the diversity of nitrogen sources, the possible formation pathways of HNMs from nitrate containing HA water were proposed during UV/chlor(am)ine disinfection in the presence of Br−. Results of this study indicated that UV/chloramine can reduce the formation and toxicity of HNMs efficiently.

Molecular level insights into HO• and Cl2•−-Mediated transformation of dissolved organic matter in landfill leachate concentrates during the Fenton process

Cl2•− can be the dominant radical species when high salinity wastewater is treated by advanced oxidation processes (AOPs). In this study, the steady-state concentrations of HO•, Cl• and Cl2•− were determined during the Fenton treatment of two landfill leachate concentrates with significantly different Cl− concentrations (XPNF: 1406 mg/L; SNNF: 8036 mg/L). Based on the steady-state concentrations of the radical species and measured second-order rate constants with dissolved organic matters (DOM), HO• accounted for 76.2% of DOM transformation in XPNF, while Cl2•− accounted for 96.5% in SNNF. The DOM transformation dominated by HO• or Cl2•− was then thoroughly compared to investigate the reactivities of HO• and Cl2•− with DOM at molecular level using high-resolution mass spectrometry. The results showed that formulas with low oxidation degree (O/C < 0.5) were preferentially removed by HO• and HO• was more reactive towards compounds with high saturation degree (H/C > 1.5) compared with Cl2•−. In contrast, Cl2•− was more reactive to the compounds with lower saturation level (H/C < 1.5) and the reaction of Cl2•− with DOM was less dependent on DOM oxidation degree. In addition, HO• preferentially reacted with the CHON compounds with low N content, while Cl2•− was more reactive to CHON compounds with higher N content compared with HO•. To our knowledge, this is the first study to distinguish the difference in the reactivity of HO• and Cl2•− towards DOM at molecular level.

Dosing low-level ferrous iron in coagulation enhances the removal of micropollutants, chlorite and chlorate during advanced water treatment

Drinking water utilities are interested in upgrading their treatment facilities to enhance micropollutant removal and byproduct control. Pre-oxidation by chlorine dioxide (ClO2) followed by coagulation-flocculation-sedimentation and advanced oxidation processes (AOPs) is one of the promising solutions. However, the chlorite (ClO2–) formed from the ClO2 pre-oxidation stage cannot be removed by the conventional coagulation process using aluminum sulfate. ClO2– negatively affects the post-UV/chlorine process due to its strong radical scavenging effect, and it also enhances the formation of chlorate (ClO3–). In this study, dosing micromolar-level ferrous iron (Fe(II)) into aluminum-based coagulants was proposed to eliminate the ClO2– generated from ClO2 pre-oxidation and benefit the post-UV/chlorine process in radical production and ClO3– reduction. Results showed that the addition of 52.1-µmol/L FeSO4 effectively eliminated the ClO2– generated from the pre-oxidation using 1.0 mg/L (14.8 µmol/L) of ClO2. Reduction of ClO2– increased the degradation rate constant of a model micropollutant (carbamazepine) by 55.0% in the post-UV/chlorine process. The enhanced degradation was verified to be attributed to the increased steady-state concentrations of HO· and ClO· by Fe(II) addition. Moreover, Fe(II) addition also decreased the ClO3– formation by 53.8% in the UV/chlorine process and its impact on the formation of chloro-organic byproducts was rather minor. The findings demonstrated a promising strategy to improve the drinking water quality and safety by adding low-level Fe(II) in coagulation in an advanced drinking water treatment train.

Effect of operating conditions and water matrix on the performance of UV combined electrochemical process for treating Chloride-containing solution and its reaction mechanism

The performance of ultraviolet combined electrochemical (EC) process for treating chloride-containing (UV/EC/Cl-) solution was evaluated based on the N, N-Diethyl-m-toluamide (DEET) degradation. The influences of operating conditions and water matrix on the DEET degradation were investigated, and the reaction mechanism of UV/EC/Cl- process was discussed based on the analysis of DEET degradation pathway, the detection of the steady-state concentrations of active free radicals and the analysis of free radicals scavenging. The observed reaction rate constant of DEET degradation in UV/EC/Cl- process (0.093 min−1) is significantly higher than that of UV/Cl2 process (0.036 min−1), and the synergistic effect on the DEET degradation is remarkable in UV/EC/Cl- process. The current and chloride concentration have remarkable impact on the DEET degradation, while the initial pH, reaction temperature, and initial DEET concentration have slight influence on the DEET degradation. The impact of alkalinity on DEET degradation is more significant than that of ammonia, while sulfate and phosphate have slight effect on the DEET degradation. The active points attacked by free radicals on DEET molecule were predicted basing on density functional theory. During the DEET degradation, small molecular products are produced through a series of reactions such as hydrogen abstraction, substitution, dealkylation, and ring-opening. The steady-state concentrations of HO• and Cl• in UV/EC/Cl- process (1.57 × 10-13 M and 2.37 × 10-14 M, respectively) are higher than those of UV/Cl2 process (1.23 × 10-13 M and 1.07 × 10-14 M, respectively), and HO• and Cl• play key roles in the DEET degradation during the UV/EC/Cl- process.

Atmospheric oxidation capacity and its contribution tosecondary pollutants formation

<p indent="0mm">Atmospheric oxidation capacity (AOC) is defined as the oxidation reaction rates of primary pollutants in the atmospheric chemical process, which is characterized by the oxidants concentration or the reaction rates. Atmospheric oxidation plays an important role in the formation of secondary pollutants, and works as an important indicator for the study of secondary pollution. Since 2013, the Chinese Government implemented unprecedented strident regulations to improve air quality. Although the overall levels of fine particulate matter (PM_2.5) have dropped considerably throughout China, it remains unclear how secondary pollutants have responded to the emission reductions in view of complex gas-precursor relationship and gas-particle interactions. Previous studies also reported the positive correlation between the AOC level and secondary pollutant concentrations. The updated Community Multi-scale Air Quality (CMAQ) model with the SAPRC 11 photo-chemical mechanism as well as the observation data was applied in this study to investigate the relationship of the secondary pollutants (ozone and secondary aerosols) and their precursors with the major oxidants (HO₂, OH and NO₃ radicals) in years 2013 and 2020 in China. And the process analysis tool was implemented in the CMAQ model to determine the key oxidants budget, which could better understand the primary sources and sinks of these oxidants. This analysis was able to calculate the chemical reaction rates at each integration time step. Radical source reactions were generally photolysis reactions, and the sink reactions removed radicals through the formation of stable products. The anthropogenic emissions were from Multiresolution Emission Inventory for China (MEIC) database, and the biogenic emissions were calculated from the Model of Emissions of Gas and Aerosols from Nature (MEGAN). The meteorology inputs were generated from the Weather Research and Forecasting (WRF) model. The CMAQ model predictions agree well with the observations, with most of the model performance within the criteria. The results show that the AOC level keeps identical from 2013 to 2020 throughout China. In the North China Plain (NCP) and the Pearl River Delta (PRD), the slightly increasing trends of AOC are even reported, which may aggravate the secondary pollution. The enhanced AOC level in the NCP is mainly from the reduced PM_2.5 concentration, which is regarded as the important sink of AOC. In addition, the concentration of major oxidants also represents different regional characteristics. The highest concentrations of HO_{<italic>x</italic>} and NO₃ radical are reported in the Sichuan Basin (SCB) and NCP, respectively. The ozone photolysis and the formation of HNO₃ (OH+NO₂) are reported as the most important AOC primary sources and sinks, respectively. In the NCP, the HONO photolysis is found as an important AOC source, which is consistent with previous studies. The AOC level increases significantly during the high ozone episode (increasing rate up to 475%). Also, the high level of AOC is corresponding to the significant increase of the secondary organic aerosols, indicating its important role in the formation of secondary pollutants. In summer, the reduction of NO_{<italic>x</italic>} emissions can reduce the AOC level. Meanwhile, a more complex response between the NO_{<italic>x</italic>} emissions and AOC level is found in winter. More rational emission reduction ratio of NO_{<italic>x</italic>} and volatile organic compounds (VOCs) should be applied to better control the AOC in China. In the future, more effective AOC control strategies should be established to reduce the PM_2.5 and O₃ coordinately in the 14th Five-Year Plan of China.

Enhanced Radical Generation in an Ultraviolet/Chlorine System through the Addition of TiO2.

Ultraviolet (UV)/chlorine draws increasing attention for the abatement of recalcitrant organic pollutants. Herein, it was found that TiO2 would significantly promote the degradation of dimethyl phthalate (DMP) in the UV/chlorine system (from 19 to 84%). Hydroxyl radicals (HO•) and chlorine radicals (Cl•) were the dominant reactive species for DMP degradation in the UV/chlorine/TiO2 system. Chlorine decayed much faster in UV/chlorine/TiO2 compared with UV/chlorine, which is possibly because photogenerated electrons (ecb-) and superoxide radicals (O2•-) have high reactivity with chlorine. As a result, the recombination of photogenerated holes (hvb+) and ecb- was inhibited and the accumulation of HO• and Cl• was facilitated. A kinetic model was established to simulate the reaction process, and it was found that the concentrations of HO• and Cl• were several times to dozens of times higher in UV/chlorine/TiO2 than that in UV/chlorine. The contributions of HO• and Cl• to DMP degradation were 70.3 and 29.7% by model simulation, respectively, and were close to the probe experiment result. In the UV/chlorine/TiO2 system, the degradation of DMP did not follow pseudo-first-order kinetics but the degradation of benzoate fitted well with pseudo-first-order kinetics. This phenomenon was elucidated by the structure of the pollutant and TiO2 and further tested by calculating the adsorption energy (Eads)/binding energy (Eb) with density functional theory. Due to faster decay of chlorine, lower amounts of disinfection byproducts formed in UV/chlorine/TiO2 compared with UV/chlorine. Adding TiO2 into the UV/chlorine system can promote the degradation of recalcitrant organic pollutants in an aqueous environment.

Formation and mechanisms of hydroxyl radicals during the oxygenation of sediments in Lake Poyang, China

Seasonal flooding-drought transformation process of lake sediments lead to changes of dissolved oxygen and redox conditions and the resultant generation of hydroxyl radical (HO•). To date, information on HO• formation and its regulators in seasonal lake sediments is largely unexplored. In this study, a total of nineteen sediments were collected from Lake Poyang, China, with the formation and mechanisms of HO• during the oxygenation process exploring via the incubation experiments, Fe K-edge X-ray adsorption spectroscopy, ultrafiltration, and fluorescent spectroscopy. Results showed that the concentrations of HO• generated ranged from 3.75 ± 1.13 to 271.8 ± 22.81 μmol kg−1, demonstrating high formation potential and obvious spatial heterogeneity. The yield of HO• formed was positively correlated with the contents of Fe(II), sedimentary organic carbon, and dissolved organic carbon, showing a general contribution of these reduced substances to HO• formation. Furthermore, application of Fe K-edge X-ray adsorption spectroscopy revealed the key species of sedimentary Fe-smectite for HO• formation due to its high peroxidase-like activity. Besides inorganic Fe(II), the sedimentary dissolved organic matters (DOMs) represented an important regulator for HO• formation, which contributed about 2–11% of the total HO• generation. Moreover, the DOM-induced formation potential was found to be highly related to the molecular weight distribution that the low molecular weight- (LMW, <1 kDa) fraction exhibited higher HO• formation potential than the bulk and high molecular weight- (HMW, 1 kDa-0.45 μm) counterparts. In addition, the omnipresent mineral Fe(II)-DOM interaction in sediment matrix exhibited another 2–6% of contribution to the total HO• production. This study highlighted the importance of contents and species of Fe(II) and DOM in manipulating the HO• yield, providing new insight into understanding the formation mechanisms of HO• in the seasonal lake sediment.

Effect of Ho3+ ion concentration on structure and spectroscopic properties of LiPbB5O9:Ho3+ phosphor

• LiPbB 5 O 9 :Ho 3+ phosphor is prepared by solid state reaction method. • Energy transfer in LiPbB 5 O 9 :Ho 3+ is attributed to “nearest neighboring ions”. • Color coordinates of LiPbB 5 O 9 :Ho 3+ phosphors represent greenish-yellow region. • LiPbB 5 O 9 :0.08 Ho 3+ phosphor may find application in W-LEDs. Lithium lead borate (LiPbB 5 O 9 :Ho 3+ ) phosphors doped with distinct concentrations of Ho 3+ ions were prepared by solid state reaction technique. Structural characteristics were studied from X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and FT-Raman characterizations. Spectroscopic properties were studied from UV–Vis–NIR and photoluminescence (PL) spectra. From XRD investigations, crystallite sizes were calculated from Debye-Scherrer (D-S) and William-Hall (W-H) methods. Optical energy band gaps were calculated by using Tauc's relation for direct and indirect allowed transitions. The emission spectra of LiPbB 5 O 9 :Ho 3+ phosphors were recorded by monitoring the excitation wavelength at λ exc = 397 nm. Lifetime decay curves of 5 S 2 energy level of Ho 3+ ion were studied for distinct concentrations of Ho 3+ ions. Energy transfer mechanism was investigated for LiPbB 5 O 9 :Ho 3+ phosphor. Concentration quenching was observed at 0.08 mol% of Ho 3+ concentration among various concentrations. CIE color coordinates were computed and they showed the greenish-yellow region for various Ho 3+ concentrations. The present, LiPbB 5 O 9 :0.08Ho 3+ phosphor may be useful for the greenish-yellow emitting phosphor applications.

Generation mechanisms of active free radicals during ciprofloxacin degradation in the ultrasonic/K2S2O8 system.

Ciprofloxacin (CIP) removal efficiency in aqueous solutions in the ultrasonic (US), K2S2O8, and US/K2S2O8 systems was investigated. The free radical generation and action ratio were studied based on variations of K2S2O8 concentration, ultrasonic power, pH, and the addition of isopropanol (ISP) or tert-butyl alcohol (TBA) in the US/K2S2O8 system. The results showed that under conditions of 20 mg·L-1 CIP concentration, 20 mmol·L-1 K2S2O8 concentration, an ultrasonic power of 360 W and pH = 7, CIP removal efficiency in the US/K2S2O8 system was 92.20% after 180 min. The reaction in the US/K2S2O8 system was explicitly divided into two stages: free radical generation and pollutants degradation. The ultrasonic and chain reaction facilitated enhanced generation of SO4-• and HO•. The presence of K2S2O8 can promote HO• generation and K2S2O8 concentration also exerted a significant effect on SO4-• generation, however, high concentrations were not beneficial to the reaction. Quenching reactions occurred under high concentrations of HO• and SO4-•. During the initial stage of the reaction, HO• played a more prominent role than SO4-•, however, the role of SO4-• gradually increased as the reaction proceeded and eventually surpassed HO•.

Burst of hydroxyl radicals in sediments derived by flooding/drought transformation process in Lake Poyang, China

Oxygenation of the reduced species has been regarded as the major source for hydroxyl radical (HO) generation in aquatic environments. Yet, the O2-induced formation of HO in lake sediments during the flooding/drought transformation process remained largely unexplored. In this study, two types of sediments from Wucheng (WC) and Nanji (NJ) area in Lake Poyang, China, were collected, respectively, with the burst of HO derived by flooding/drought transformation process exploring via the incubation experiments. Results showed that no obvious HO can be detected for the two sediments during the flooding period, while the concentrations of HO increased rapidly for the flooding/drought transformation process due to the enhanced dissolved oxygen contents. The highest concentrations of HO in the surface sediment were 2.45 ± 0.19 μmol kg−1 for WC sediment and 0.69 ± 0.25 μmol kg−1 for NJ sediment, showing higher burst potential of HO for the former. The contents of Fe(II) in the surface sediments for WC area (589.3 ± 37.29 mg kg−1) were about two times higher than those for NJ area (308.4 ± 94.01 mg kg−1) during the flooding period. Oxygenation of the surface Fe(II) contributed significantly to the burst of HO in the flooding/drought transformation process. Moreover, the higher percentage of humic-like substances in WC sediment indicated that the dissolved humic fraction exhibited also important role in the HO formation due to electrons transfer under redox conditions. This study highlighted the importance of reactive reduced species in manipulating the burst of HO in lake sediment, which is essential for understanding the geochemical cycling of several major and trace elements as well as the behavior and fate of the contaminants in aquatic ecosystems.

The Galvano-Fenton process: Experimental insights and numerical mechanistic investigation applied to the degradation of acid orange 7

In the present study, the kinetics of degradation of acid orange 7 (AO7) by the Galvano-Fenton process is assessed experimentally and simulated numerically in order to figure out the mechanism of generation and consumption of free radicals with this novel advanced oxidation process. 10 mg/L of the azo dye are degraded during 20 min by combining a copper-iron Galvanic cell to Fenton mechanism at pH 3. The electrochemical and electrolytic reactions are approached following two scenarios, whose the more complex includes the cathodic and anodic reactions, the Fenton scheme and the formation of ferric and ferrous irons complexes and salt as well as the reactivity of sulfate ions. The numerical results demonstrated a high correlation coefficient of 93.5% with experimental results using this latter scenario, while the identified pathways of generation and consumption of HO• and SO4•−, considering their contribution to the initiation reactions of the chain mechanism of AO7 degradation, demonstrated a significant participation of SO4•−. The sensitivity of the process to the corrosion current was examined numerically over the range 0.3 to 1 mA, the results exhibited the achievement of a steady state for the molar concentrations of HO• and SO4•−. This observation was explained by the continuous release of Fe2+ catalyst in the Galvano-Fenton process, in contrast with the classic Fenton scheme. The comparison of both Galvano-Fenton and classic Fenton processes in one hand, and Galvano-Fenton and electro-Fenton processes in the other hand, was further investigated and discussed numerically.

The multiple roles of chlorite on the concentrations of radicals and ozone and formation of chlorate during UV photolysis of free chlorine

Chlorine dioxide (ClO2) has emerged as a promising alternative to free chlorine for water disinfection and/or pre-oxidation due to its reduced yields of chlorinated disinfection byproducts. ClO2 decomposes to form chlorite (ClO2−), which influences the following advanced oxidation processes (AOPs) for micropollutant abatement in drinking water. This study aims at investigating the effects of ClO2− on the concentrations of reactive species (e.g., radicals and ozone) and on the formation of chlorate in the UV/chlorine AOP. Results showed that the concentration of ClO· in the UV/chlorine process remarkably decreased by 98.20–100.00% in the presence of ClO2− at concentration of 0.1–1.0 mg·L−1 as NaClO2. The concentrations of HO· and ozone decreased by 42.71–65.42% and by 22.02–64.31%, respectively, while the concentration of Cl· was less affected (i.e., 31.00–36.21% reduction). The overall concentrations of the reactive species were differentially impacted by ClO2−’s multiple roles in the process. UV photolysis of ClO2− generated HO· but not Cl·, ClO· or ozone under the drinking water relevant conditions. ClO2− also competed with chlorine for UV photons but this effect was minor (< 1.0%). The radicals/ozone scavenging by ClO2− outcompeted the above two to lead to the overall decreasing concentrations of the reactive species, in consistency with the kinetic model predicted trends. ClO2− reacted with radicals and ozone to form chlorate (ClO3−) but not perchlorate (ClO4−). HO· played a dominant role in ClO3− formation. The findings improved the fundamental understanding on micropollutant abatement and inorganic byproduct formation by the UV/chlorine process and other AOPs in ClO2−-containing water.

Predictive models for the degradation of 4 pharmaceutically active compounds in municipal wastewater effluents by the UV/H2O2 process

Pharmaceutically active compounds (PhACs) have been frequently detected in aquatic environment and raised concerns because of their environmental persistence and potential ecological risk, especially carbamazepine (CBZ), erythromycin (ERY), atenolol (ATL) and clofibric acid (CA). The UV/H2O2 advanced oxidation process was considered as an effective process to remove pharmaceuticals in wastewater. Because of the diverse structure of pharmaceuticals and the various wastewater matrices, this study established two models to predict the degradation of 4 PhACs in wastewater by UV/H2O2. Besides, the degradation pathway and toxicity of 4 PhACs by UV/H2O2 were explored. The degradation of 4 PhACs by UV/H2O2 followed the pseudo first-order kinetics pattern. The degradation rate of pharmaceuticals decreased as CBZ > ATL > CA > ERY. A kinetic model combining the steady state concentrations of HO∙ successfully predicted the degradation process of pharmaceuticals in 14 secondary municipal wastewater effluents. Also, a water matrix prediction model by response surface methodology (RSM) was established to estimate the degradation of pharmaceuticals well. A detailed and systematic comparison of two models in the objectives of models, predicting target contaminants, types of wastewater and parameters of models was made. In addition, the tentative transformation pathways of 4 PhACs by UV/H2O2 were proposed. 4 PhACs after UV/H2O2 treatment enhanced the toxicity, and prolongation of treatment time can reduce the toxicity on the luminescence.