Decomposition of 1,4-dioxane by vacuum ultraviolet irradiation: Study of economic feasibility and by-product formation

We report the first use of vacuum ultraviolet (VUV) treatment to decompose 1,4-dioxane, a persistent organic contaminant that is difficult to remove by conventional drinking water treatment processes. The efficiency of VUV treatment was compared to that of VUV- and UV-based advanced oxidation processes (AOPs) (VUV/TiO₂, VUV/H₂O₂, UV/TiO₂, and UV/H₂O₂), and by-product formation was investigated. VUV treatment decomposed 1,4-dioxane more rapidly than did UV and UV/TiO₂ treatments. The decomposition rate was enhanced when VUV irradiation was combined with TiO₂ or H₂O₂. VUV/H₂O₂ decomposed 1,4-dioxane more rapidly than UV/H₂O₂ at a low H₂O₂ dose (1 mg/L), but the rate difference became small at a high H₂O₂ dose (5 mg/L). Electrical energy per order analysis revealed that VUV treatment, and the VUV- and UV-based AOPs, were economically feasible for 1,4-dioxane decomposition. Using raw water samples, we investigated by-product formation during VUV treatment and the effect of VUV irradiation on chlorinated disinfection by-product formation potential. Although the samples contained high concentrations of bromide, no bromate was produced by VUV treatment. VUV treatment slightly decreased trihalomethane formation potential (THMFP), whereas haloacetic acid formation potential (HAAFP) was unchanged, and total aldehyde concentration increased. The trend in HAAFP agreed with that had been reported for the VUV irradiation with much higher dose (Buchanan et al., 2006), whereas the trend in THMFP was different from that with much higher dose. THMFP, HAAFP, and aldehyde concentration were reduced by subsequent treatment with granular activated carbon (GAC) or biological activated carbon (BAC). Nitrite was produced by VUV treatment but disappeared after subsequent BAC treatment. These results suggest that VUV treatment should be combined with GAC or BAC treatment to suppress by-product formation.     

亚甲基蓝褪色催化动力学光度法测定痕量Cu~(2+)

研究了在聚乙二醇-200(PEG-200)活化下,Cu2+催化H2O2氧化亚甲基蓝的褪色反应,建立了亚甲基蓝褪色催化动力学光度法测定痕量Cu2+的方法。在25mL容量瓶中,加入1.00mL pH为11.68的氨水溶液、2.00mL H2O2溶液(质量分数15%)、1.00mL亚甲基蓝溶液(质量浓度0.20mg/mL)、3.00mL PEG-200溶液,76℃恒温反应5min后冷却,测定吸光度,根据加Cu2+溶液和不加Cu2+溶液的吸光度差值与Cu2+质量浓度绘制了工作曲线,并由试样的吸光度差值确定痕量Cu2+含量。该法的测定波长为664nm,检出限为5.4×10-6g/L,最大相对标准偏差为2.58%,回收率为97.5%~104.5%。     

Biological elimination of H2S and NH3 from wastegases by biofilter packed with immobilized heterotrophic bacteria

Biotreatment of various ratios of H₂S and NH₃ gas mixtures was studied using the biofilters, packed with co-immobilized cells (Arthrobacter oxydans CH8 for NH₃ and Pseudomonas putida CH11 for H₂S). Extensive tests to determine removal characteristics, removal efficiency, removal kinetics, and pressure drops of the biofilters were performed. To estimate the largest allowable inlet concentration, a prediction model was also employed. Greater than 95% and 90% removal efficiencies were observed for NH₃ and H₂S, respectively, irrespective of the ratios of H₂S and NH₃ gas mixtures. The results showed that H₂S removal of the biofilter was significantly affected by high inlet concentrations of H₂S and NH₃. As high H₂S concentration was an inhibitory substrate for the growth of heterotrophic sulfur-oxidizing bacteria, the activity of H₂S oxidation was thus inhibited. In the case of high NH₃ concentration, the poor H₂S removal efficiency might be attributed to the acidification of the biofilter. The phenomenon was caused by acidic metabolite accumulation of NH₃. Through kinetic analysis, the presence of NH₃ did not hinder the NH₃ removal, but a high H₂S concentration would result in low removal efficiency. Conversely, H₂S of adequate concentrations would favor the removal of incoming NH₃. The results also indicated that maximum inlet concentrations (model-estimated) agreed well with the experimental values for space velocities of 50–150 h⁻¹. Hence, the results would be used as the guideline for the design and operation of biofilters.     

活性炭吸附硫化氢及微波辐照解吸研究

研究了两种活性炭对硫化氢的平衡吸附性能力,并对活性炭床层的穿透性进行了考察;吸附饱和和活性炭在微波辐射的作用下进行解吸。实验表明,解吸效率与微波作用时间及温度有关,在本实验条件下H2S解吸效率达90．1％。     

面粉增白剂生产过程中发生爆炸的主要原因及防范措施

分析了面粉增白剂主要成份过氧化苯甲酰（ＢＰＯ）在生产过程中发生爆炸的主要原因，对生产、检修、储存等诸环节中可能发生爆炸的危害程度进行了比较，从设施、设备、工艺流程、工具、仪表、制度、人员素质等方面提出了防止爆炸的可行措施     

3D simulation of hydrogen ignition in a rapid compression machine

Low-temperature (at T < 900–950 K) ignition delays of hydrogen–air mixtures are mainly measured in rapid compression machines (RCM). This communication is aimed at numerical simulation of ignition delays of hydrogen–air mixtures in the RCM by means of a coupled three-dimensional (3D) Unsteady Reynolds-Averaged Navier–Stokes (URANS) – Particle Method (PM) simulation of RCM operation capable of catching turbulence–chemistry interaction. The study indicates that the time history of piston motion in an RCM affects the final state of a test mixture at the end of compression stroke and therefore influences the phenomena relevant to test mixture ignition. More specifically, the calculations show that different laws of piston motion at a fixed average piston velocity (i.e., fixed piston displacement and fixed compression time) and fixed compression ratio result in different evolution of mean pressure, temperature and velocity fields in the RCM test section leading to different ignition behavior. The reasons for the arising differences lie in the fact that the local instantaneous piston velocity determines the roll-up vortex structure, strength and turbulence dissipation in it, heat transfer in test-section walls, and mass leakage through piston rings.     

Exhaust Emissions from a Gas-fuelled S.I. Engine

Attempts to improve engine performance are often accompanied by increased emissions. An effective approach to reduce emissions without necessarily a significant penalty in fuel economy is through operating S.I. engines on a range of gaseous fuels, and either leaning the operating mixture or diluting it with some exhaust gases.

The emission characteristics of an engine operated in turn on CH₄, H₂, CO and some of their mixtures are examined experimentally. The role of changes in some key factors affecting the production of the pollutants CO, NOx and unburned hydrocarbons were investigated. Guidelines for reducing the undesirable emissions are outlined.     

Toward better understanding vacuum ultraviolet–iodide induced photolysis via hydrogen peroxide formation,iodine species change,and difluoroacetic acid degradation

• UV/VUV/I^– induces substantial H₂O₂ and IO₃^– formation, but UV/I^– does not. • Increasing DO level in water enhances H₂O₂ and iodate productions. • Increasing pH decreases H₂O₂ and iodate formation and also photo-oxidation. • The redox potentials of UV/VUV/I^– and UV/VUV changes with pH changes. • The treatability of the UV/VUV/I^– process was stronger than UV/VUV at pH 11.0. Recently, a photochemical process induced by ultraviolet (UV), vacuum UV (VUV), and iodide (I^–) has gained attention for its robust potential for contaminant degradation. However, the mechanisms behind this process remain unclear because both oxidizing and reducing reactants are likely generated. To better understand this process, this study examined the evolutions of hydrogen peroxide (H₂O₂) and iodine species (i.e., iodide, iodate, and triiodide) during the UV/VUV/I^– process under varying pH and dissolved oxygen (DO) conditions. Results show that increasing DO in water enhanced H₂O₂ and iodate production, suggesting that high DO favors the formation of oxidizing species. In contrast, increasing pH (from 6.0 to 11.0) resulted in lower H₂O₂ and iodate formation, indicating that there was a decrease of oxidative capacity for the UV/VUV/I^– process. In addition, difluoroacetic acid (DFAA) was used as an exemplar contaminant to verify above observations. Although its degradation kinetics did not follow a constant trend as pH increases, the relative importance of mineralization appeared declining, suggesting that there was a redox transition from an oxidizing environment to a reducing environment as pH rises. The treatability of the UV/VUV/I^– process was stronger than UV/VUV under pH of 11.0, while UV/VUV process presented a better performance at pH lower than 11.0.     

Catalytic decomposition of hydrogen peroxide in the presence of alkylpyridines: Runaway scenarios studies

A number of runaway scenarios of the excess of hydrogen peroxide used during the N-oxidation of alkylpyridines, under closed and open conditions, were examined. It was found that, in most cases, if the volume of the liquid hydrogen peroxide solution occupies more than 10% of the total volume of a closed system (e.g. reactor and vent line between reactor and blockage), the production of gases raises the pressure so quickly that evaporation is completely suppressed. Higher than 70% filling levels result in complete expansion of the liquid. The MTSR(t) of the system falls rapidly if the normal process temperature is high, but if a runaway occurs exactly at the end of dosing, MTST will be very high and secondary decompositions will rapidly develop. The results of this study are currently being used to critically assess the current approaches and further the study of inherently safer designs.     

纳米零价铁催化过氧化氢强化修复4-氯硝基苯污染地下水的研究

化学氧化还原技术是快速修复受污染地下水的重要手段,为探明某污染场地地下水化学修复的可行性和有效性,通过FeSO4与NaBH4液相还原反应制备了纳米零价铁(nZVI)颗粒,对其进行了扫描电子显微镜(SEM)和X射线衍射(XRD)形貌观测与分析表征.采用制备的nZVI,在常温常压下催化H2O2修复4-氯硝基苯(4-ClNB)污染地下水.考察了不同工艺反应条件对修复效果的影响,分析探讨了工艺对特征污染物的降解机制.结果表明,在温度30℃、初始pH值3.0、nZVI质量浓度268.8mg·L-1、H2O2浓度4.90 mmol·L-1时,nZVI催化H2O2工艺能在30 min内完全转化降解污染地下水中4-ClNB.通过GC/MS、LC/MS和IC鉴定得到4-ClNB降解的主要中间产物,包括4-氯亚硝基苯、4-氯羟基苯胺、4-氯氧化偶氮苯、4-氯偶氮苯、4-氯苯胺、对苯醌、甲酸、乙酸、草酸和氯离子等,并在此基础上给出了4-ClNB可能的降解途径.