Total Organic Carbon Mineralization Research Articles

Construction of g-C3N4@Bi-MOF@BiOCl double Z-type heterojunctions for photodegradation of antibiotics under visible light irradiation: Mechanism, pathway, and toxicity assessment

In this study, flower-like microspheres dispersed double Z-type heterojunction g-C3N4@Bi-MOF@BiOCl photocatalysts were prepared using Bi-MOF as the structural template. The photocatalyst showed good degradation ability for both tetracycline antibiotics under simulated sunlight irradiation, as well as stable recyclability and total organic carbon mineralization (TOC). This excellent photocatalytic activity was mainly attributed to the formation of double Z-type heterojunctions that accelerated charge separation and transfer and drove stronger redox capacity. In addition, the effects of conditions such as catalyst dosage, initial concentration of tetracycline hydrochloride (TC) and initial pH (3–11) value of the solution on the photocatalytic reaction were investigated. The results of free radical trapping experiments and ESR analyses indicated that O2−, h+ and OH were the active free radicals that could not be neglected for the degradation of tetracycline hydrochloride (TC), and a possible degradation mechanism was further proposed. Finally, the possible pathways for degradation of the intermediates were rationally deduced by gas chromatography (GC–MS) and evaluated by ecotoxicity analysis based on the utilization rate (T.E.S.T.) of the intermediates produced. This study provides an effective idea for the rational design and synthesis of highly efficient dual Z-type photocatalysts for antibiotic contamination in water-polluted environments.

The impact of organic carbon mineralization on pollution and toxicity of toxic metal in sediments: Yellow Sea and East China Sea study

Organic carbon mineralization is the main driving force of metal migration and transformation in sediments, greatly influencing the distribution, pollution degree, and toxicity of toxic metals. However, relevant research on this subject is still limited. In this study, the concentration of toxic metals (Cr, Cd, Cu, Pb, Zn, Co, Fe, Mn, Ni, As) in the solid and liquid phase (porewater) of sediments were measured, toxic metal pollution degree and toxicity of the Yellow Sea (YS) and the East China Sea (ECS) were assessed. Combined with the rate of organic carbon mineralization, the impact of organic carbon mineralization was analyzed. The results showed that Ni was slightly enriched and posed a certain ecological risk, and As was moderately enriched in the studied area, Pb was at a moderate pollution level in the studied area. Zn, Co, Mn, and Fe were at a moderate pollution level in the mud area of SYS and the west coastal area of ECS. Additionally, the total organic carbon mineralization rate (TCMR) in the ECS (5.12–18.04 mmol C m−2 d−1) was slightly higher than that in the YS (3.29–14.46 mmol C m−2 d−1) during spring. Moreover, organic carbon mineralization promotes metal enrichment, and the TCMR was significantly correlated with the pollution load index. Thus, TCMR can be used as an indicator to predict the degree of metal pollution. Furthermore, organic carbon mineralization promotes the mobilization of Cu from the solid phase to the liquid phase, while facilitating the transfer of Cr, Pb, Co, Ni, and Fe from the liquid phase to the solid phase. This process increases the potential risks of Cu and reduces the toxicity of Cr, Pb, Co, Ni, and Fe. Therefore, the impact of organic carbon mineralization should be considered in future assessments and predictions of toxic metal pollution and toxicity.

Constructing Direct Z-Scheme Y2TmSbO7/GdYBiNbO7 Heterojunction Photocatalyst with Enhanced Photocatalytic Degradation of Acetochlor under Visible Light Irradiation.

This study presents a pioneering synthesis of a direct Z-scheme Y2TmSbO7/GdYBiNbO7 heterojunction photocatalyst (YGHP) using an ultrasound-assisted hydrothermal synthesis technique. Additionally, novel photocatalytic nanomaterials, namely Y2TmSbO7 and GdYBiNbO7, were fabricated via the hydrothermal fabrication technique. A comprehensive range of characterization techniques, including X-ray diffractometry, Fourier-transform infrared spectroscopy, Raman spectroscopy, UV-visible spectrophotometry, X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray energy-dispersive spectroscopy, fluorescence spectroscopy, photocurrent testing, electrochemical impedance spectroscopy, ultraviolet photoelectron spectroscopy, and electron paramagnetic resonance, was employed to thoroughly investigate the morphological features, composition, chemical, optical, and photoelectric properties of the fabricated samples. The photocatalytic performance of YGHP was assessed in the degradation of the pesticide acetochlor (AC) and the mineralization of total organic carbon (TOC) under visible light exposure, demonstrating eximious removal efficiencies. Specifically, AC and TOC exhibited removal rates of 99.75% and 97.90%, respectively. Comparative analysis revealed that YGHP showcased significantly higher removal efficiencies for AC compared to the Y2TmSbO7, GdYBiNbO7, or N-doped TiO2 photocatalyst, with removal rates being 1.12 times, 1.21 times, or 3.07 times higher, respectively. Similarly, YGHP demonstrated substantially higher removal efficiencies for TOC than the aforementioned photocatalysts, with removal rates 1.15 times, 1.28 times, or 3.51 times higher, respectively. These improvements could be attributed to the Z-scheme charge transfer configuration, which preserved the preferable redox capacities of Y2TmSbO7 and GdYBiNbO7. Furthermore, the stability and durability of YGHP were confirmed, affirming its potential for practical applications. Trapping experiments and electron spin resonance analyses identified active species generated by YGHP, namely •OH, •O2-, and h+, allowing for comprehensive analysis of the degradation mechanisms and pathways of AC. Overall, this investigation advances the development of efficient Z-scheme heterostructural materials and provides valuable insights into formulating sustainable remediation strategies for combatting AC contamination.

The Fabrication and Property Characterization of a Ho2YSbO7/Bi2MoO6 Heterojunction Photocatalyst and the Application of the Photodegradation of Diuron under Visible Light Irradiation.

A novel photocatalytic nanomaterial, Ho2YSbO7, was successfully synthesized for the first time using the solvothermal synthesis technique. In addition, a Ho2YSbO7/Bi2MoO6 heterojunction photocatalyst (HBHP) was prepared via the hydrothermal fabrication technique. Extensive characterizations of the synthesized samples were conducted using various instruments, such as an X-ray diffractometer, a Fourier transform infrared spectrometer, a Raman spectrometer, a UV-visible spectrophotometer, an X-ray photoelectron spectrometer, and a transmission electron microscope, as well as X-ray energy dispersive spectroscopy, photoluminescence spectroscopy, a photocurrent test, electrochemical impedance spectroscopy, ultraviolet photoelectron spectroscopy, and electron paramagnetic resonance. The photocatalytic activity of the HBHP was evaluated for the degradation of diuron (DRN) and the mineralization of total organic carbon (TOC) under visible light exposure for 152 min. Remarkable removal efficiencies were achieved, with 99.78% for DRN and 97.19% for TOC. Comparative analysis demonstrated that the HBHP exhibited markedly higher removal efficiencies for DRN compared to Ho2YSbO7, Bi2MoO6, or N-doped TiO2 photocatalyst, with removal efficiencies 1.13 times, 1.21 times, or 2.95 times higher, respectively. Similarly, the HBHP demonstrated significantly higher removal efficiencies for TOC compared to Ho2YSbO7, Bi2MoO6, or N-doped TiO2 photocatalyst, with removal efficiencies 1.17 times, 1.25 times, or 3.39 times higher, respectively. Furthermore, the HBHP demonstrated excellent stability and reusability. The mechanisms which could enhance the photocatalytic activity remarkably and the involvement of the major active species were comprehensively discussed, with superoxide radicals identified as the primary active species, followed by hydroxyl radicals and holes. The results of this study contribute to the advancement of efficient heterostructural materials and offer valuable insights into the development of sustainable remediation strategies for addressing DRN contamination.

Characterization of the benthic biogeochemical dynamics after flood events in the Rhône River prodelta: a data–model approach

Abstract. At the land–sea interface, the benthic carbon cycle is strongly influenced by the export of terrigenous particulate material across the river–ocean continuum. Episodic flood events delivering massive sedimentary materials can occur, but their short-term impact on carbon cycling is poorly understood. In this paper, we use a coupled data–model approach to estimate the temporal variations in sediment–water fluxes, biogeochemical pathways and their reaction rates during these abrupt phenomena. We studied one episodic depositional event in the vicinity of the Rhône River mouth (NW Mediterranean Sea) during the fall–winter of 2021/22. The distributions of dissolved inorganic carbon (DIC), sulfate (SO42-) and methane (CH4) were measured in sediment porewaters collected every 2 weeks before and after the deposition of a 25 cm sediment layer during the main winter flood event. Significant changes in the distribution of DIC, SO42- and CH4 concentrations were observed in the sediment porewaters. The use of an early diagenetic model (FESDIA) to calculate biogeochemical reaction rates and fluxes revealed that this type of flood event can increase the total organic carbon mineralization rate in the sediment by 75 % a few days after deposition. In this period, sulfate reduction is the main process contributing to the increase in total mineralization relative to non-flood deposition. The model predicts a short-term decrease in the DIC flux out of the sediment from 100 to 55 mmolm-2d-1 after the deposition of the new sediment layer with a longer-term increase by 4 %, therefore implying an initial internal storage of DIC in the newly deposited layer and a slow release over relaxation of the system. Furthermore, examination of the stoichiometric ratios of DIC and SO42- as well as model output over this 5-month window shows a decoupling between the two modes of sulfate reduction following the deposition – organoclastic sulfate reduction (OSR) intensified in the newly deposited layer below the sediment surface, whereas anaerobic oxidation of methane (AOM) intensified at depth below the former buried surface. The bifurcation depth of sulfate reduction pathways, i.e., the sulfate–methane transition zone (SMTZ), is shifted deeper by 25 cm in the sediment column following the flood deposition. Our findings highlight the significance of short-term transient biogeochemical processes at the seafloor and provide new insights into the benthic carbon cycle in the coastal ocean.

Fenton-Like Oxidation Systems for Destruction of Azo Dyes in Aqueous Solutions

The kinetic regularities of degradation of the azo dye methyl orange (MO) in photoinitiated oxidizing systems have been studied using a xenon lamp (UV–Vis) as a source of quasi-solar radiation. According to the efficiency and rate of dye destruction, the considered oxidizing systems can be arranged in the following series: {UV–Vis} {UV–Vis/S2O2-8} {S2O2-8/Fe0} {UV–Vis/S2O2-8/Fe0} {UV–Vis/S2O2-8/Fe2+}. It has been established that in photoinitiated Fenton-like oxidizing systems there is not only complete conversion of MO but also its deep mineralization in aqueous solution; a decrease in the content of total organic carbon reaches 60%. In this case, the specific catalytic activity of iron ions in the combined system {UV–Vis/S2O2-8/Fe0} is much higher than in {UV–Vis/S2O2-8/Fe2+}. Using inhibitors of radical reactions, it has been proved that in the combined system {UV–Vis/S2O2-8/Fe0} both hydroxyl and sulfate anion radicals take part in oxidative degradation. An inhibitory influence of anions (bicarbonates, chlorides, nitrates, and sulfates) and natural dissolved organic matter (Suwanee River 2R101N) on the process of mineralization of total organic carbon during oxidative destruction of MO in the combined system {UV–Vis/S2O/Fe0} has been found.

High-efficient degradation of ibuprofen as typical PPCP through a novel electrochemical approach of traditional peroxone method

An electrogenerated peroxone process was innovatively structured to effectively degrade the antiphlogistic ibuprofen (IBU) representing typical refractory pharmaceutical. The process involved electrogenerated O3 from H2O oxidation using a Ti mesh/SnO2-F anode in membrane electrode assembly (MEA) and electrogenerated H2O2 from O2 reduction using a carbon-polytetrafluoroethylene (C/PTFE) cathode. The synergetic system of H2O2 and O3 formed in situ could generate hydroxyl radical (OH) to achieve IBU degradation and total organic carbon (TOC) removal. The effects of current density, aqueous initial pH, and coexisting anions on IBU removal efficiencies were investigated and then optimized as 30 mA/cm2 and neutral condition. As a result, IBU decomposition and TOC mineralization could be finished after 10 min and 120 min electrolysis, respectively. The stability of the synergetic system combining MEA with C/PTFE-O2 was also evaluated and confirmed through multiple cycles of electrogenerated peroxone based on TOC removal efficiency. In addition, IBU degradation pathways were proposed according to the identification of intermediates (e.g. hydroxylated IBU, phenolics, and carboxylic acids) by HPLC-MS/MS. These results manifested that this synergetic system is a promising technology to remove aqueous recalcitrant pharmaceuticals.

Membrane bioreactor and advanced oxidation processes for combined treatment of synthetic wastewater containing naproxen, bisphenol A, and sulfamethoxazole

Environmental and health issues caused by the abundance of emerging pollutants in the aquatic environment motivate the research into wastewater treatment methods. In the present study, a membrane bioreactor (MBR) and advanced oxidation processes (AOPs) were combined for the efficient treatment of a synthetic wastewater containing naproxen (NPX), bisphenol A (BPA), and sulfamethoxazole (SMX). The MBR setup consisted of a sequencing batch reactor (SBR) linked to an external filtration system. Track-etch membranes (TEM) with pore size of 10 nm, 50 nm, and 100 nm and a phase inversion membrane (PIM) were used. The total organic carbon (TOC) removal for the SBR was in the range of 78–86 %, while the degradation of NPX, BPA, and SMX observed was 11 %, 45 %, and 6 %, respectively. All of the four membranes tested showed insignificant TOC removal efficiencies ranging from 1 % to 6 %. In the case of emerging pollutants, the highest removal values were observed for the 10 nm TEM: 11 %, 93 %, and 14 % for NPX, BPA, and SMX, respectively. The removal of BPA using membranes was possibly linked to sorption and size exclusion. Finally, the effluents from SBR and MBR were treated using UV-driven AOPs. Persulfate (PS) was used as an oxidant, and UV light, zero-valent iron (ZVI), goethite, and iron (II) sulfate heptahydrate were used as activators. Complete mineralization of TOC and removal of emerging pollutants were achieved after 30 min for MBR effluents using UV/PS 10 mM /ZVI 25 mg/L, which shows the high potential of using MBR and AOPs in combination.

Oxygen vacancies enhanced natural manganese sand activation by PMS for CBZ degradation: Intermediate toxicity and DFT calculations

The preparation of sulfate-based advanced oxidation catalysts is usually both complex and expensive. In this study, natural manganese sand enriched with oxygen vacancies was prepared by NaBH4 reduction of natural manganese sand for activating peroxymonosulfate (PMS) to remove carbamazepine (CBZ). 70% of carbamazepine was degraded at 120 min when natural manganese sand enriched with oxygen vacancies and PMS were dosed at 0.4 g/L and 0.3 g/L respectively, and the reaction rate constant of the natural manganese sand system with rich oxygen vacancies was 7 times that of the common system. The mineralization of total organic carbon (TOC) reached 41.9%. Combined EPR and radical quenching assays revealed that degradation of pollutants relied on the involvement of free radicals and non-free radicals, in which singlet oxygen was dominant. The XPS results showed that the redox cycles of Fe3+/Fe2+ and Mn4+/Mn3+/Mn2+ promoted the generation of free radicals. Density functional theory results also showed that the energy required for PMS to adsorb on natural manganese sand with many oxygen vacancies was decreased, and the OO bond was elongated, which was beneficial to the catalytic reaction. According to LC-MS and Fukui function, the degradation route of CBZ was predicted, and the toxicity of the breakdown products was calculated. The research provides a reference for introducing oxygen vacancies in natural catalysts to improve degradation performance for “green (source) to green (application)”.

Evaluation of Leachate Recirculation as a Stabilisation Strategy for Landfills in Developing Countries

This study evaluated leachate recirculation (LR) as a stabilisation strategy for landfills using bioreactor experiments with excavated waste from a tropical landfill in Colombia. The experimental evaluation was performed in two 115 L bioreactors, one simulating the operation of a landfill with LR, Br2, where the leachate produced was recirculated at a rate of 0.8 L d−1, and a control system without LR, Br1. Both systems reached stabilisation indicator values on a dry matter (DM) basis for volatile solids VS (<25% DM) and a biochemical methane potential BMP (≤10 mL CH4 g−1 DM). Likewise, towards the end of the experiment, the leachate generated in Br2 reached stabilisation indicator values for BOD5 (<100 mg L−1) and the BOD (biological oxygen demand)/COD (chemical oxygen demand) ratio (<0.1). Although the stabilisation criterion for COD was not met in any bioreactor (<200 mg L−1), LR helped to release 19% more oxidisable organic matter in Br2 than in Br1, indicating a reduction in the contaminating potential of the waste in the case of uncontrolled discharges of leachate to the environment. Regarding biogas production, the generation of CH4 in Br2 was more intense and its cumulative production was 34.5% higher than Br1; thus, Br2 achieved CH4 emission rates, indicating waste stabilisation (<1.0 L CH4 m−2 h−1) sooner than Br1, showing an accelerating effect of LR on waste degradation. A carbon mass balance indicated that waste degradation, in terms of the initial total organic carbon mineralisation and the C gas discharge via CH4, was greater in Br2. These results demonstrate the LR potential to accelerate the stabilisation of a landfill but also to reduce greenhouse gas emissions in final disposal sites where biogas is also captured and utilised for energy production; a key aspect when improving the sustainability of landfill operations in developing countries.

Efficient electrochemical removal of 5-fluorouracil pharmaceutical from wastewater by mixed metal oxides via anodic oxidation process

Nowadays, the entry of organic compounds into water resources is one of the leading global concerns due to the lack of water resources and rapid population growth. In this research, anodic oxidation (AO) method was used to remove 5-fluorouracil (5-FU) from aqueous solutions via Ni/RuO2 and Ti/IrO2–TiO2–RuO2 electrodes as cathode and anode, respectively. For this purpose, the characterization analysis of the electrodes, including X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, and atomic force microscopy were performed. The electrochemical performance of the anode was investigated via cyclic voltammetry analysis. Then, the effect of operational variables, including applied current (mA), initial pH of the solution, initial 5-FU concentration (mg/L), and process time (min) on the 5-FU removal efficiency under the AO process was evaluated via artificial neural network (ANN) modeling. The results revealed that the maximum 5-FU removal efficiency was 96.96%. The applied current intensity, pH, initial 5-FU concentration, and process time were 300 mA, 5, 20 mg/L, and 140 min, respectively. Moreover, the investigation of 5-FU removal by-products and mineralization efficiency of the AO process was carried out via gas chromatography-mass spectrometry and total organic carbon analysis, respectively. The total organic carbon mineralization efficiency was 84.80% after 6 h of reaction time. The reusability and stability of the Ti/IrO2–TiO2–RuO2 anode on 5-FU removal efficiency were measured and showed an approximately 5% decay in 5-FU removal efficiency after eight consecutive runs. The overall results and analysis confirmed this method is capable of removing 5-FU through Ti/IrO2–TiO2–RuO2 anode and Ni/RuO2 cathode from aqueous medium.

Photo-Fenton-Like Treatment of Municipal Wastewater

In this work, the photochemical treatment of a real municipal wastewater using a persulfate-driven photo-Fenton-like process was studied. The wastewater treatment efficiency was evaluated in terms of total carbon (TC), total organic carbon (TOC) and total nitrogen (TN) removal. Response surface methodology (RSM) in conjunction Box-Behnken design (BBD) and multilayer artificial neural network (ANN) have been utilized for the optimization of the treatment process. The effects of four independent factors such as reaction time, pH, K2S2O8 concentration and K2S2O8/Fe2+ molar ratio on the TC, TOC and TN removal have been investigated. The process significant factors have been determined implementing Analysis of Variance (ANOVA). Both RSM and ANN accurately found the optimum conditions for the maximum removal of TOC (100% and 98.7%, theoretically), which resulted in complete mineralization of TOC at the reaction time of 106.06 min, pH of 7.7, persulfate concentration of 30 mM and K2S2O8/Fe2+ molar ratio of 7.5 for RSM and at the reaction time of 104.93 min, pH of 7.7, persulfate concentration of 30 mM and K2S2O8/Fe2+ molar ratio of 9.57 for ANN. On the contrary, the attempts to find the optimal conditions for the maximum TC and TN removal using statistical, and neural network models were not successful.

Integration of olive stones in the production of Fe/AC-catalysts for the CWPO treatment of synthetic and real olive mill wastewater

A by-product of olive mill’s operation (olive stone, OS) was transformed into activated carbon (AC) and used as support to prepare Fe-based catalysts, which were employed on the catalytic wet peroxide oxidation (CWPO) of olive mill wastewater (OMW). Three Fe-impregnation routes were tested: incipient wetness impregnation (IWI), adsorption (Ads), and hydrothermal (HT), resulting in catalysts with distinct iron loadings, particle sizes and surface dispersion. OSAC-Fe catalysts were characterized by N2 and CO2 physisorption, XRD, XPS, FTIR, HRTEM, EDX, and HRSEM techniques. Catalysts’ activity and stability was first compared in the degradation of synthetic polyphenolic solutions. After one cycle (240 min), catalysts’ sorption capacity was considerably exhausted and OH radicals were found to be the main oxidative species responsible for total phenolic content (TPh) removal. OSAC-Fe-IWI and OSAC-Fe-Ads performed better than OSAC-Fe-HT after four consecutive cycles (53 and 48 vs. 38% TPh removals, respectively), also showing considerably lower cumulative Fe leaching values (2.2 and 2.8 vs. 10 wt%). The most promising materials were used for depuration of real OMW samples. Under smooth operational conditions ([OSAC-Fe-IWI] = 2.0 g/L, [H2O2] = 0.5 g/L, pH0 ~ 4.9, T0 = 25 °C), 55% TPh removal was attained after 240 min, resulting in a significant reduction of the effluent’s toxicity (from 100% Vibrio fischeri bioluminescence inhibition to 36%), 37% chemical oxygen demand degradation, and 21% total organic carbon mineralization. Promising catalytic performances were also achieved by OSAC-Fe-Ads, despite its considerably lower iron loading, highlighting the importance of Fe surface dispersion.

Organic Degradation Potential of Real Greywater Using TiO2-Based Advanced Oxidation Processes

In keeping with the circular economy approach, reclaiming greywater (GW) is considered a sustainable approach to local reuse of wastewater and a viable option to reduce household demand for freshwater. This study investigated the mineralization of total organic carbon (TOC) in GW using TiO2-based advanced oxidation processes (AOPs) in a custom-built stirred tank reactor. The combinations of H2O2, O3, and immobilized TiO2 under either dark or UVA irradiation conditions were systematically evaluated—namely TiO2/dark, O3/dark (ozonation), H2O2/dark (peroxidation), TiO2/UVA (photocatalysis), O3/UVA (Ozone photolysis), H2O2/UVA (photo-peroxidation), O3/TiO2/dark (catalytic ozonation), O3/TiO2/UVA (photocatalytic ozonation), H2O2/TiO2/dark, H2O2/TiO2/UVA, H2O2/O3/dark (peroxonation), H2O2/O3/UVA (photo-peroxonation), H2O2/O3/TiO2/dark (catalytic peroxonation), and H2O2/O3/TiO2/UVA (photocatalytic peroxonation). It was found that combining different treatment methods with UVA irradiation dramatically enhanced the organic mineralization efficiency. The optimum TiO2 loading in this study was observed to be 0.96 mg/cm2 with the highest TOC removal (54%) achieved using photocatalytic peroxonation under optimal conditions (0.96 mg TiO2/cm2, 25 mg O3/min, and 0.7 H2O2/O3 molar ratio). In peroxonation and photo-peroxonation, the optimal H2O2/O3 molar ratio was identified to be a critical efficiency parameter maximizing the production of reactive radical species. Increasing ozone flow rate or H2O2 dosage was observed to cause an efficiency inhibition effect. This lab-based study demonstrates the potential for combined TiO2-AOP treatments to significantly reduce the organic fraction of real GW, offering potential for the development of low-cost systems permitting safe GW reuse.

Assessment of solar-assisted electrooxidation of bisphenol AF and bisphenol A on boron-doped diamond electrodes

Bisphenol (BP) analogues in wastewater effluent and groundwater pose a potential threat to human health due to their ability to disrupt steroidogenesis. A new solar-assisted electrochemical process (SECP) was developed and evaluated for the degradation of BP analogues. The effects of quenchers, current density, initial pH, supporting electrolyte, and aqueous matrix on the removal kinetics of bisphenol AF (BPAF) and bisphenol A (BPA) were investigated. The kinetic constants of BPAF, BPA, and bisphenol S (BPS) in the SECP with irradiation intensity of 500 mW cm−2 were 0.017 ± 0.002 min−1, 0.022 ± 0.002 min−1, and 0.012 ± 0.001 min−1, respectively. The changes in the degradation rates of BPAF, BPA, and BPS in the presence of quenchers indicated the relative contribution of hydroxyl radical (●OH) oxidation, anodic electrolysis, and singlet (1O2) oxygenation in the degradation of BPs in the SECP. The enhanced rate of generation of ●OH and 1O2 was observed in the SECP compared with those in the conventional electrochemical system. The identification of the transformation products (TPs) of BPAF demonstrated that hydroxylation, ring cleavage, β-scission, and defluorination were the major processes during the oxidation in the SECP. The conversion to fluoride ions (76%) and mineralization of total organic carbon (72%) in the SECP indicated further degradation of TPs. The results from this study improved our understanding of the degradation of BP analogues in the electrooxidation irradiated by solar light and help to establish the application potential of the SECP for the effective degradation of emerging contaminants in wastewater.

Efficient photocatalytic degradation of furosemide by a novel sonoprecipited ZnO over ion exchanged clinoptilolite nanorods

This work presents, a detailed investigation for photocatalytic degradation of the drug furosemide (FRS) using zinc oxide (ZnO) supported on ion-exchanged natural zeolite clinoptilolite (ICLT). The ZnO/ICLT nanophotocatalysts were effectively synthesized by sonoprecipitation method which enhanced the photocatalytic performance by increasing the surface area and decreasing the particle size, compared to conventional precipitated samples. Microstructure and optical properties of prepared catalysts were characterized using XRD, XRF, FESEM, surface particle size distribution, TEM, EDX, BET, BJH, DRS and UV-visible spectroscopy techniques. XRD data confirmed the formation of ZnO. FESEM images revealed small particle size of active metals and low numbers of agglomerations which is in accordance with EDX dot mapping results. The average particle size of ZnO in ZnO(15%)/ICLT whit sonication was 20.5 nm whereas it was 34.8 nm without sonication. Moreover, the literature review indicated that ultrasound irradiation during the precipitation of samples has not been studied yet which highlight the importance of evaluating this nanophotocatalyst for wastewater treatment applications. The maximum degradation rate was observed for 15 wt% ZnO among various contents of ZnO used in synthesized nanocomposites. The influence of key operational parameters such as catalyst dosage, initial FRS concentration and pH on the photocatalytic degradation was assessed. Total organic carbon mineralization rate of FRS solution and energy consumption were also assessed to compare the ability of different processes in FRS degradation. Results showed also excellent reusability of fabricated nanophotocatalyst. Finally a plausible degradation mechanism for photocatalytic degradation of FRS was proposed.

The responses of soil organic carbon mineralization and microbial communities to fresh and aged biochar soil amendments

AbstractWhile biochar soil amendment has been widely proposed as a soil organic carbon (SOC) sequestration strategy to mitigate detrimental climate changes in global agriculture, the SOC sequestration was still not clearly understood for the different effects of fresh and aged biochar on SOC mineralization. In the present study of a two‐factorial experiment, topsoil samples from a rice paddy were laboratory‐incubated with and without fresh or aged biochar pyrolyzed of wheat residue and with and without crop residue‐derived dissolved organic matter (CRM) for monitoring soil organic matter decomposition under controlled conditions. The six treatments included soil with no biochar, with fresh biochar and with aged biochar treated with CRM, respectively. For fresh biochar treatment, the topsoil of a same rice paddy was amended with wheat biochar directly from a pyrolysis wheat straw, the soil with aged biochar was collected from the same soil 6 years following a single amendment of same biochar. Total CO2 emission from the soil was monitored over a 64 day time span of laboratory incubation, while microbial biomass carbon and phospholipid fatty acid (PLFA) were determined at the end of incubation period. Without CRM, total organic carbon mineralization was significantly decreased by 38.8% with aged biochar but increased by 28.9% with fresh biochar, compared to no biochar. With CRM, however, the significantly highest net carbon mineralization occurred in the soil without biochar compared to the biochar‐amended soil. Compared to aged biochar, fresh biochar addition significantly increased the total PLFA concentration by 20.3%–33.8% and altered the microbial community structure by increasing 17:1ω8c (Gram‐negative bacteria) and i17:0 (Gram‐positive bacteria) mole percentages and by decreasing the ratio of fungi/bacteria. Furthermore, biochar amendment significantly lowered the metabolic quotient of SOC decomposition, thereby becoming greater with aged biochar than with fresh biochar. The finding here suggests that biochar amendment could improve carbon utilization efficiency by soil microbial community and SOC sequestration potential in paddy soil can be enhanced by the presence of biochar in soil over the long run.

Application of seasonal freeze-thaw to pretreat raw material for accelerating green waste composting

The recalcitrance of green waste, caused by its high lignocellulose content, is a technical challenge for accelerating green waste composting. However, because lignocellulose degradation in litter (similar to green waste) can be promoted during the freeze-thaw season, and the composting is difficult to implement in this period (due to the low temperature); seasonal freeze-thaw was intended to be used as a pretreatment strategy for the existing technical challenge in the winter of cold regions. In this process, green waste was pretreated with seasonal freeze-thaw to enhance its lignocellulose degradation for subsequent composting. To verify this assumption, two strategies for the pretreatment were used: the green waste was either drenched or immersed in water during the freeze-thaw season, and the effects on subsequent composting were evaluated. The results demonstrated that both strategies can significantly promote the mineralization of TOC (total organic carbon, by 2.73%–8.01% compared with the control, the following comparisons were all based on the control), TN (total nitrogen, by 0.21%–0.52%), and lignocellulose (lignin degradation was promoted by 3.52%–3.73%, cellulose degradation was promoted by 13.23%–14.26%) during composting and that the synthesis of humus was also enhanced (by 19.19%–21.43%). Furthermore, since the loss of NH4+N and NO3−N was significantly less in the drenched treatment than in the immersed treatment (by 9.15% for the loss of NH4+N and 7.66% for the loss of NO3−N), drenching the green waste during the freeze-thaw season might be a better strategy than immersing for nitrogen conservation. An additional advantage of drenching compared to immersing is water conservation.

Enhanced degradation of sulfathiazole by electro-Fenton process using a novel carbon nitride modified electrode

A novel carbon nitride graphite-based gas diffusion electrode (g-C3N4@GDE) was fabricated and then was used as a cathode in electro-Fenton (EF) to treat sulfathiazole (STZ, a target organic pollutant) at the very first time. The effects of g-C3N4 doping on electronic properties were explored by Liner scanning voltammetry (LSV), density functional theory (DFT) calculation and rotating disk electrode (RDE). LSV showed an improvement of the electroactive surface area, while DFT calculation showed that the active center increased after N-doping. RDE result indicated that g-C3N4@GDE cathode favored 2 electron reduction. Regarding H2O2 accumulation, g-C3N4@GDE reached 2.59 mg h−1 cm−2 and was comparable with the previous investigations. In addition, approximately 100% of STZ degradation coupled with 75.16% total organic carbon (TOC) mineralization could be achieved after 180 min electrolysis under the following conditions: applied current 50 mA, [STZ]0 = 500 mg L−1, [Fe2+] = 100 μM and pH = 3. Moreover, a plausible STZ degradation pathway during EF was proposed based on the detected aromatic intermediates, short-chain carboxylic acids and inorganic ions. Finally, 5 cycles experiments showed that the g-C3N4@GDE cathode had a good stability in terms of STZ degradation and TOC mineralization.

Effective mineralization of anti-epilepsy drug carbamazepine in aqueous solution by simultaneously electro-generated H2O2/O3 process

A novel electro-generated hydroxyl radical (OH) technique was constructed to effectively degrade the anti-epilepsy carbamazepine (CBZ) representing typical recalcitrant pharmaceutical only through electrochemical method as an alterative peroxone process. The technique involves simultaneously electro-generated H2O2 using a carbon-polytetrafluoroethylene (C/PTFE) cathode to reduce the injected O2 and electro-generated O3 using H2O oxidation with a Ti mesh/PbO2 anode in membrane electrode assembly (MEA). The significant OH formation through the synergetic system of in-situ produced H2O2 and O3 electrochemically could achieved carbamazepine decomposition and total organic carbon (TOC) removal as compared to electro-generated H2O2 or O3 alone. The main influential factors including current density and aqueous pH were investigated to reveal their effect on CBZ removal efficiencies. Under optimal parameters, CBZ decomposition and TOC mineralization could be completely accomplished after 10 min and 90 min electrolysis, respectively. According to intermediates distribution (e.g. hydroxylated CBZ, phenolics, and carboxylic acids) identified by HPLC-MS/MS, the degradation pathways were proposed for CBZ removal by the synergetic system of C/PTFE-O2 and MEA. The above results indicated that this electrochemically synergetic system is a potential technique to further purify the water contaminated by recalcitrant pharmaceuticals.