响应面优化CCl4增强超声降解左旋氧氟沙星模拟废水

利用响应面优化实验设计方法对CCl₄增强超声降解左旋氧氟沙星模拟废水的影响因素进行探讨和分析,考察了溶液初始pH值、超声功率、左旋氧氟沙星初始浓度的影响。应用Box-Behnken中心组合设计得到一个二次多项式数学模型,确定了US/CCl₄降解左旋氧氟沙星的优化条件:初始pH值6.8,超声功率189 W,左旋氧氟沙星初始浓度为5 mg/L时,左旋氧氟沙星的去除率达到最大(82.99%)。经实验验证, 实际值与模型预测值吻合性良好,偏差仅为0.036%。     

多溴联苯醚降解和分析研究进展

介绍了多溴联苯醚(PBDEs)在环境中的分布情况,综述了近年来国内外对PBDEs测定方法以及化学催化降解、生物降解和热解等PBDEs降解技术的研究进展,并对PBDEs研究的未来发展方向进行了展望。     

循环式超声强化光催化降解双酚A

设计了一种循环式超声强化光催化反应器,以TiO2作为光催化剂,研究了超声功率、TiO2加入量、循环液流速和空气流量对双酚A(BPA)降解效果的影响。实验结果表明:超声与光催化过程在循环式超声强化光催化反应器中实现了较好的协同效应;在初始BPA质量浓度为20.0mg/L、超声功率为600W、TiO2加入量为7g/L、循环液流速为4.05×10-2m/s、空气流量为200mL/min的条件下,反应150min后,BPA降解率可达90.5%,溶液中剩余BPA质量浓度仅为1.8mg/L,反应240min后TOC去除率可达84.5%。     

Electrochemical oxidation of herbicide bifenox acid in aqueous medium using diamond thin film electrode

The electrochemical oxidation of bifenox acid was studied at a boron-doped diamond thin film by cyclic voltammetry and galvanostatic electrolysis. The course of the electrolysis was monitored by measurement of chemical oxygen demand (COD) and by gas chromatography/mass spectrometry (GC / MS) analysis. It was found that exhaustive electrolysis leads to degradation and, ultimately, to mineralization of the starting herbicide. The degradation intermediates were identified showing that the oxidation process begins with the fragmentation of the molecule followed by reactions involving the hydroxyl radical, which is generated by the discharge of water. The study of the effect of current density and concentration showed that the degradation efficiency increases with decreasing current densities and increasing concentrations. The whole results were interpreted in a mechanistic scheme involving two oxidation pathways, the first is a direct oxidation at the electrode and the second uses hydroxyl radical as mediator of the oxidation. Finally, a kinetic study based on spectrophotometric measurements showed that the degradation process is pseudo first order.     

Enhanced biodegradation of endosulfan and its major metabolite endosulfate by a biosurfactant producing bacterium

The present study was carried out to isolate bacteria capable of producing biosurfactant that solublize endosulfan (6,7,8,9,10,10-Hexachloro-1,5,5a,6,9,9a-hexahydro- 6,9-methano-2,4,3-benzodioxathiepine-3-oxide) and for enhanced degradation of endosulfan and its major metabolite endosulfate. The significance of the study is to enhance the bioavailability of soil-bound endosulfan residues as its degradation is limited due to its low solubility. A mixed bacterial culture capable of degrading endosulfan was enriched from pesticide-contaminated soil and was able to degrade about 80% of α-endosulfan and 75% of β-endosulfan in five days. Bacterial isolates were screened for biosurfactant production and endosulfan degradation. Among the isolates screened, four strains produced biosurfactant on endosulfan. ES-47 showed better emulsification of endosulfan and degraded 99% of endosulfan and 94% of endosulfate formed during endosulfan degradation. The strain reduced the surface tension up to 37 dynes/cm. The study reveals that the strain was capable of degrading endosulfan and endosulfate with simultaneous biosurfactant production.     

Speciation and persistence of doxycycline in the aquatic environment: Characterization in terms of steady state kinetics

The aim of the present work was to establish the kinetics for the degradation of doxycycline in the aquatic environment with a view to arriving at a kinetic model that can be used to predict the persistence of antibiotic with confidence. The degradation of doxycycline in both water and sediment phases of aquatic microcosm experiments, as well as in distilled water control experiments, was studied over a period of 90 days. An initial 21% loss due to adsorption by the sediment was observed in the microcosm experiment soon after charging. Biphasic zero-order linear rates of degradation, attributed to microbial degradation of the free and sediment or colloidal particle-adsorbed antibiotic, were observed for both water phase (2.3 × 10^?2 and 4.5 × 10^?3 μgg^?1 day^?1) and sediment phase (7.9 × 10^?3 and 1.5 × 10^?3 μgg^?1 day^?1) of the microcosm experiment. The covered distilled water control experiment exhibited a monophasic zero-order linear rate (1.9 × 10^?3 μgg^?1 day^?1) attributed to hydrolysis, while the distilled water experiment exposed to natural light exhibited biphasic liner rates attributed to a combination of hydrolysis and photolysis (2.9 × 10^?3 μgg^?1 day^?1) and to microbial degradation (9.8 × 10^?3 μgg^?1 day^?1). A kinetic model that takes into account hydrolysis, photolysis, microbial degradation as well as sorption/desorption by colloidal and sediment particles is presented to account for the observed zero-order kinetics. The implications of the observed kinetics on the persistence of doxycycline in the aquatic environment are discussed.     

Disappearance of dimethoate,methamidophos and pirimicarb in lettuce

Abstract

Foliar sprays of dimethoate at 150 or 300 g a.i./ha, methamidophos at 450 or 900 g a.i./ha and pirimicarb at 140 or 280 g a.i./ha were applied for control of the green peach aphid, Myzus pericae (Sulzer), and the lettuce aphid, Nasonovia ribisnigri (Mosley), about 2 weeks before the lettuce started heading, and again about 1 week from harvest. In lettuce, dimethoate partially oxidized to its oxon and pirimicarb converted to its methylamino‐ and/or formyl methylamino‐analogues. Most residues were present in the outer leaves which were exposed directly to the sprays; only traces of residues were detected in samples of the inner head leaves. Total residues disappeared rapidly. Pirimicarb was the least persistent and only traces of residues (<0.01 ppm) were detected in marketable heads. Concentrations of dimethoate, including the oxon and of methamidophos were well below their respective tolerances of 2 and 1 ppra respectively.     

Persistence and biodegradation of carbaryl in soils

Abstract

The persistence of the methylcarbamate pesticide carbaryl was studied in four soils under flooded conditions. A substantial portion of the pesticide was recovered from all soils even after 15 days of its application, with the recovery ranging from 37% in an alluvial soil to 73% in an acid sulfate soil. The degradation of carbaryl was more rapid under flooded conditions than under nonflooded conditions. A bacterium, Pseudomonas cepacia, isolated from a flooded soil amended with a related methylcarbamate pesticide carbofuran, degraded carbaryl in a mineral medium supplemented with yeast extract.     

Persistence of diflubenzuron and bay sir 8514 in natural and sterile sandy loam and organic soils

Abstract

Disappearance rates of 10 ppm technical diflubenzuron (N(((4‐chloro‐phenyl)amino)carbonyl)‐2,6‐diflurobenzamide, Dimilin^®) and BAY SIR 8514 (2‐chloro‐N(((4‐trifluoromethoxyphenyl)amino)carbonyl)benzamide) applied on quartz sand to natural sandy loam and muck soils were significantly greater than for the corresponding sterilized soils, e.g. 47–51% vs. 68–87% BAY SIR 8514 and 2–12% vs. 80–87% diflubenzuron remaining at 12 wk, indicating that soil microorganisms play a major role in their degradation. Kinetic analysis of the data based on a first order dependence on the insecticide concentration showed that the rate constants for these disappearance reactions decreased with time.     

Electrochemical Monitoring of Methylparathion Degradation in an Acid Aqueous Medium in Presence of Cu(II)

Abstract

A study was undertaken to determine the effect of Cu(II) in degradation of methylparathion (o,o-dimethyl o, 4-nitrophenyl phosphoriotioate) in acid medium. Initial electrochemical characterization of Cu(II) and methylparathion was done in an aqueous medium at a pH range of 2–7. Cu(II) was studied in the presence of different anions and it was observed that its electroactivity depends on pH and is independent of the anion used. Methylparathion had two reduction signals at pH ≤ 6 and only one at pH > 6. The pesticide's transformation kinetic was then studied in the presence of Cu(II) in acid buffered aqueous medium at pH values of 2, 4, and 7. Paranitrophenol appeared as the only electroactive product at all three pH values. The reaction was first order and had k values of 5.2 × 10^?3 s^?1 at pH 2, 5.5 × 10^?3 s^?1 at pH 4 and 9.0 × 10^?3 s^?1 at pH 7. It is concluded that the principal degradation pathway of methylparathion in acid medium is a Cu(II) catalyzed hydrolysis reaction.