• Strong metal-support interaction exists on Pt/Fe3O4 catalysts.• Pt metal particles facilitate the formation of oxygen vacancies on Fe3O4.• Fe3O4 supports enhance the strength of CO adsorption on Pt metal particles. The self-inhibition behavior due to CO poisoning on Pt metal particles strongly impairs the performance of CO oxidation. It is an effective method to use reducible metal oxides for supporting Pt metal particles to avoid self-inhibition and to improve catalytic performance. In this work, we used in situ reductions of chloroplatinic acid on commercial Fe3O4 powder to prepare heterogeneous-structured Pt/Fe3O4 catalysts in the solution of ethylene glycol. The heterogeneous Pt/Fe3O4 catalysts achieved a better catalytic performance of CO oxidation compared with the Fe3O4 powder. The temperatures of 50% and 90% CO conversion were achieved above 260°C and 290°C at Pt/Fe3O4, respectively. However, they are accomplished on Fe3O4 at temperatures higher than 310°C. XRD, XPS, and H2-TPR results confirmed that the metallic Pt atoms have a strong synergistic interaction with the Fe3O4 supports. TGA results and transient DRIFTS results proved that the Pt metal particles facilitate the release of lattice oxygen and the formation of oxygen vacancies on Fe3O4. The combined results of O2-TPD and DRIFTS indicated that the activation step of oxygen molecules at surface oxygen vacancies could potentially be the rate-determining step of the catalytic CO oxidation at Pt/Fe3O4 catalysts. The reaction pathway involves a Pt-assisted Mars-van Krevelen (MvK) mechanism. 相似文献
• UV/O3 process had higher TAIC mineralization rate than O3 process.• Four possible degradation pathways were proposed during TAIC degradation.• pH impacted oxidation processes with pH of 9 achieving maximum efficiency.• CO32– negatively impacted TAIC degradation while HCO3– not.• Cl– can be radicals scavenger only at high concentration (over 500 mg/L Cl–). Triallyl isocyanurate (TAIC, C12H15N3O3) has featured in wastewater treatment as a refractory organic compound due to the significant production capability and negative environmental impact. TAIC degradation was enhanced when an ozone(O3)/ultraviolet(UV) process was applied compared with the application of an independent O3 process. Although 99% of TAIC could be degraded in 5 min during both processes, the O3/UV process had a 70%mineralization rate that was much higher than that of the independent O3 process (9%) in 30 min. Four possible degradation pathways were proposed based on the organic compounds of intermediate products identified during TAIC degradation through the application of independent O3 and O3/UV processes. pH impacted both the direct and indirect oxidation processes. Acidic and alkaline conditions preferred direct and indirect reactions respectively, with a pH of 9 achieving maximum Total Organic Carbon (TOC) removal. Both CO32– and HCO3– decreased TOC removal, however only CO32– negatively impacted TAIC degradation. Effects of Cl– as a radical scavenger became more marked only at high concentrations (over 500 mg/L Cl–). Particulate and suspended matter could hinder the transmission of ultraviolet light and reduce the production of HO· accordingly. 相似文献
• The SRAO phenomena tended to occur only under certain conditions.• High amount of biomass and non-anaerobic condition is requirement for SRAO.• Anammox bacteria cannot oxidize ammonium with sulfate as electron acceptor.• AOB and AnAOB are mainly responsible for ammonium conversion.• Heterotrophic sulfate reduction mainly contributed to sulfate conversion. For over two decades, sulfate reduction with ammonium oxidation (SRAO) had been reported from laboratory experiments. SRAO was considered an autotrophic process mediated by anammox bacteria, in which ammonium as electron donor was oxidized by the electron acceptor sulfate. This process had been attributed to observed transformations of nitrogenous and sulfurous compounds in natural environments. Results obtained differed largely for the conversion mole ratios (ammonium/sulfate), and even the intermediate and final products of sulfate reduction. Thus, the hypothesis of biological conversion pathways of ammonium and sulfate in anammox consortia is implausible. In this study, continuous reactor experiments (with working volume of 3.8L) and batch tests were conducted under normal anaerobic (0.2≤DO<0.5 mg/L) / strict anaerobic (DO<0.2 mg/L) conditions with different biomass proportions to verify the SRAO phenomena and identify possible pathways behind substrate conversion. Key findings were that SRAO occurred only in cases of high amounts of inoculant biomass under normal anaerobic condition, while absent under strict anaerobic conditions for same anammox consortia. Mass balance and stoichiometry were checked based on experimental results and the thermodynamics proposed by previous studies were critically discussed. Thus anammox bacteria do not possess the ability to oxidize ammonium with sulfate as electron acceptor and the assumed SRAO could, in fact, be a combination of aerobic ammonium oxidation, anammox and heterotrophic sulfate reduction processes. 相似文献
• Highly efficient debromination of BDE-47 was achieved in the ZVZ/AA system.• BDE-47 debromination by the ZVZ/AA can be applied to a wide range of pH.• AA inhibits the formation of (hydr)oxide and accelerates the corrosion of ZVZ.• Reduction mechanism of BDE-47 debromination by the ZVZ/AA system was proposed. A new technique of zero-valent zinc coupled with ascorbic acid (ZVZ/AA) was developed and applied to debrominate the 2,2′,4,4′-Tetrabromodiphenyl ether (BDE-47), which achieved high conversion and rapid debromination of BDE-47 to less- or non-toxic forms. The reaction conditions were optimized by the addition of 100 mg/L ZVZ particles and 3 mmol/L AA at original solution pH= 4.00 using the solvent of methanol/H2O (v:v= 4:6), which could convert approximately 94% of 5 mg/L BDE-47 into lower-brominated diphenyl ethers within a 90 min at the ZVZ/AA system. The high debromination of BDE-47 was mainly attributed to the effect of AA that inhibits the formation of Zn(II)(hydr)oxide passivation layers and promotes the corrosion of ZVZ, which leads to increase the reactivity of ZVZ. Additionally, ion chromatography and gas chromatography mass spectrometry analyses revealed that bromine ion and lower-debromination diphenyl ethers formed during the reduction of BDE-47. Furthermore, based on the generation of the intermediates products, and its concentration changes over time, it was proposed that the dominant pathway for conversion of BDE-47 was sequential debromination and the final products were diphenyl ethers. These results suggested that the ZVZ/AA system has the potential for highly efficient debromination of BDE-47 from wastewater. 相似文献
• Effects of metabolic uncoupler TCS on the performances of GDMBR were evaluated.• Sludge EPS reduced and transformed into dissolved SMP when TCS was added.• Appropriate TCS increased the permeability and reduced cake layer fouling.• High dosage aggravated fouling due to compact cake layer with low bio-activity. The gravity-driven membrane bioreactor (MBR)system is promising for decentralized sewage treatment because of its low energy consumption and maintenance requirements. However, the growing sludge not only increases membrane fouling, but also augments operational complexities (sludge discharge). We added the metabolic uncoupler 3,3′,4′,5-tetrachlorosalicylanilide (TCS) to the system to deal with the mentioned issues. Based on the results, TCS addition effectively decreased sludge ATP and sludge yield (reduced by 50%). Extracellular polymeric substances (EPS; proteins and polysaccharides) decreased with the addition of TCS and were transformed into dissolved soluble microbial products (SMPs) in the bulk solution, leading to the break of sludge flocs into small fragments. Permeability was increased by more than two times, reaching 60–70 L/m2/h bar when 10–30 mg/L TCS were added, because of the reduced suspended sludge and the formation of a thin cake layer with low EPS levels. Resistance analyses confirmed that appropriate dosages of TCS primarily decreased the cake layer and hydraulically reversible resistances. Permeability decreased at high dosage (50 mg/L) due to the release of excess sludge fragments and SMP into the supernatant, with a thin but more compact fouling layer with low bioactivity developing on the membrane surface, causing higher cake layer and pore blocking resistances. Our study provides a fundamental understanding of how a metabolic uncoupler affects the sludge and bio-fouling layers at different dosages, with practical relevance for in situ sludge reduction and membrane fouling alleviation in MBR systems. 相似文献
• PAM degradation in thermophilic AD in comparison with mesophilic AD.• PAM degradation and its impact on thermophilic and mesophilic AD.• Enhanced methane yield in presence of PAM during thermophilic and mesophilic AD.• PAM degradation and microbial community analysis in thermophilic and mesophilic AD. Polyacrylamide (PAM) is generally employed in wastewater treatment processes such as sludge dewatering and therefore exists in the sludge. Furthermore, it degrades slowly and can deteriorate methane yield during anaerobic digestion (AD). The impact or fate of PAM in AD under thermophilic conditions is still unclear. This study mainly focuses on PAM degradation and enhanced methane production from PAM-added sludge during 15 days of thermophilic (55°C) AD compared to mesophilic (35°C) AD. Sludge and PAM dose from 10 to 50 g/kg TSS were used. The results showed that PAM degraded by 76% to 78% with acrylamide (AM) content of 0.2 to 3.3 mg/L in thermophilic AD. However, it degraded only 27% to 30% with AM content of 0.5 to 7.2 mg/L in mesophilic AD. The methane yield was almost 230 to 238.4 mL/g VSS on the 8th day in thermophilic AD but was 115.2 to 128.6 mL/g VSS in mesophilic AD. Mechanism investigation revealed that thermophilic AD with continuous stirring not only enhanced PAM degradation but also boosted the organics release from the sludge with added PAM and gave higher methane yield than mesophilic AD. 相似文献
Food crops such as cassava, cocoyam and other tuber crops grown in mining communities uptake toxic or hazardous chemicals
such as arsenic, and cadmium, from the soil. Cassava is a stable food for Ghanaians. This study evaluated human health risk
from eating cassava grown in some mining communities in Ghana such as Bogoso, Prestea, Tarkwa and Tamso, which are important
mining towns in the Western Region of Ghana. The study evaluated cancer and non-cancer health effects from eating cassava
grown in the study areas in accordance with US Environmental Protection Agency’s Risk Assessment guidelines. The results of
the study revealed the following: cancer health risk for Tamso, 0.098 (RME – Reasonable Maximum Exposure) and 0.082 (CTE –
Central Tendency Exposure). This means that approximately 10 and 8 out of 100 resident adults are likely to suffer from cancer
related cases by RME and CTE parameters respectively. For Prestea, we have 0.010 and 0.12, which also means that approximately
1 out of 100 and 10 resident adults out of 100 are also likely to suffer from cancer related diseases by RME and CTE parameters.
The results of the study obtained were found to be above the acceptable cancer risk range of 1× 10−6 to 1× 10−4, i.e., 1 case of cancer out of 1 million or 100,000 people respectively. 相似文献
Dissipation behaviour of endosulfan and dichlorvos in/on cauliflower, variety Snowball-16, was studied during rabi season
(Sep.–March) 2003–2004. Endosulfan and dichlorvos were sprayed @ 350 and 110g a.i. with 115 g a.i., respectively, 80 days
after transplanting. Samples were taken at the interval of 0 (1h after spray), 3, 5, 7, and 10 days after spray (DAS) in triplicate
and residues were estimated on GC-ECD system equipped with capillary column. The initial deposits of 3.452 and 0.295μgg−1 of endosulfan and dichlorvos dissipated to 0.084 (97.56%) and 0.009 (96.95%), respectively after 10 DAS. Residues of endosulfan
reached below maximum residue limit of 2μgg−1 one day after spray and of dichlorvos were below MRL value of 0.5μgg−1 even on 0 day. Dissipation pattern followed first order kinetics for both the insecticides with half life periods of 1.81
and 2.08 days for endosulfan and dichlorvos, respectively. 相似文献