Treatment of fluorine-containing pharmaceutical wastewater by VUV/UV process

Environmental Science and Pollution Research - As an advanced oxidation process, vacuum ultraviolet/ultraviolet (VUV/UV) has been intensively studied for drinking water treatment, but assessment of...     

VUV/UV/Cl2工艺去除饮用水中的乐果

乐果是常规饮用水处理技术难以去除的一种典型有机磷农药。为了能够控制并去除饮用水中的农药残留,达到进一步净化水质的目的,建立了降解动力学模型,采用模拟降解饮用水中乐果的方法,对比了乐果在紫外(UV)、氯(Cl2)、紫外/氯(UV/Cl2)、真空紫外/紫外(VUV/UV)和真空紫外/紫外/氯(VUV/UV/Cl2)5种工艺下的去除效果,并考察了乐果初始浓度、Cl2投加量、溶液p H、水中共存天然有机物(NOM)和无机阴离子(N O_3~-、Cl-、HCO_3~-、SO_4~(2-))对VUV/UV/Cl2工艺降解乐果的影响。结果表明:VUV/UV/Cl2对乐果的降解效率最高,乐果的去除率随其初始浓度的增加而减小;适当增加Cl2投加量,可提高乐果的降解效率;提高p H有利于乐果的降解;NOM对乐果的降解有一定的抑制作用;水中共存无机阴离子NO_3~-、Cl-和HCO_3~-可以捕获反应体系中的强氧化性羟基自由基(HO·),对乐果的降解起到抑制作用,而SO_4~(2-)因其捕获HO·的速率很低,无抑制作用。     

UV/ozone degradation of gaseous hexamethyldisilazane (HMDS)

As a carcinogen, hexamethyldisilazane (HMDS) is extensively adopted in life science microscopy, materials science and nanotechnology. However, no appropriate technology has been devised for treating HMDS in gas streams. This investigation evaluated the feasibility and effectiveness of the UV (185+254nm) and UV (254nm)/O(3) processes for degradation of gaseous HMDS. Tests were performed in two batch reactors with initial HMDS concentrations of 32-41mgm(-3) under various initial ozone dosages (O(3) (mg)/HMDS (mg)=1-5), atmospheres (N(2), O(2), and air), temperatures (28, 46, 65 and 80 degrees C), relative humilities (20%, 50%, 65%, 99%) and volumetric UV power inputs (0.87, 1.74, 4.07 and 8.16Wl(-1)) to assess their effects on the HMDS degradation rate. Results indicate that for all conditions, the decomposition rates for the UV (185+254nm) irradiation exceeded those for the UV (254nm)/O(3) process. UV (185+254nm) decompositions of HMDS displayed an apparent first-order kinetics. A process with irradiation of UV (185+254nm) to HMDS in air saturated with water at temperatures of 46-80 degrees C favors the HMDS degradation. With the condition as above and a P/V of around 8Wl(-1), k was approximately 0.20s(-1) and a reaction time of just 12s was required to degrade over 90% of the initial HMDS. The main mechanisms for the HMDS in wet air streams irradiated with UV (185+254nm) were found to be caused by OH free-radical oxidation produced from photolysis of water or O((1)D) produced from photolysis of oxygen. The economic evaluation factors of UV (185+254nm) and UV (254nm)/O(3) processes at different UV power inputs were also estimated.     

背景水质对过流式VUV/UV反应器降解水中阿特拉津的影响

为探究连续流进水模式下水中复杂的背景物质对真空紫外/紫外 (VUV/UV) 高级氧化工艺效率的影响,采用过流式VUV/UV反应器,考察了水中不同浓度的氯离子 (Cl^–) 、碱度 (HCO₃^–) 、硝酸盐 (NO₃^–) 和溶解性有机物 (DOM) 对微量污染物阿特拉津 (ATZ) 降解的影响。结果表明,上述背景组分对ATZ的VUV/UV降解均表现出一定的抑制作用,辐照时间为30 s时,ATZ去除率从空白组中的57%分别最多下降至33%、29%、40%和35%,且过流式条件下的抑制程度与文献中序批式反应器中的略有不同。污染物去除率下降的原因在于,一方面,三种无机阴离子都对VUV辐射有一定的蔽光效应,NO₃^–强于Cl^–强于HCO₃^–;另一方面,VUV辐照下Cl^–产生的Cl·和Cl₂^•–、NO₃^–产生的NO₂·和HO·都能补充水中氧化性自由基浓度,使得VUV贡献的ATZ降解速率常数的抑制程度低于VUV光子被阴离子竞争吸收的比例,但HCO₃^–对HO·较强的清除作用则导致了ATZ的降解速率常数的快速下降。低浓度DOM在VUV/UV辐照下可能产生的活性物种抵消了其对VUV/UV辐射的蔽光效应,但高浓度DOM对HO·的清除作用仍使其对ATZ降解产生了显著的抑制。在所有考察的水质条件下,ATZ降解所需的单位能耗E_EO介于0.61~1.56 kWh·m^-3。     

Photocatalytic mineralization of glyphosate in a small-scale plug flow simulation reactor by UV/TiO2

The present work involves the photocatalytic mineralization of glyphosate on a plug flow reactor by UV/TiO(2). The effect of catalyst loading shows an optimal value (0.4 g L(-1)) which is necessary to mineralize glyphosate. The kinetic rate of glyphosate mineralization decreases with the increasing initial concentration of glyphosate, and the data can be described using the first-order model. An alkaline environment is conducive to glyphosate mineralization. The mineralization efficiency increases with elevated flow rate to 114 mL min(-1), which is followed by a decrease with a further increase in flow rate due to the reduction of the residence time. The presence of external oxidants (K(2)S(2)O(8), H(2)O(2) and KBrO(3)) and photosencitizer (humic acid) can significantly enhance glyphosate mineralization. Photocatalysis oxidation ability of the three studied oxidants decrease in the order of: S(2)O(8)(2-) > BrO(3)(-) > H(2)O(2). Finally, the Langmuir-Hinshelwood (L-H) model was used to rationalize the mechanisms of reactions occurring on TiO(2) surfaces and L-H model constants were also determined.     

Photocatalytic mineralization of glyphosate in a small-scale plug flow simulation reactor by UV/TiO2

The present work involves the photocatalytic mineralization of glyphosate on a plug flow reactor by UV/TiO₂. The effect of catalyst loading shows an optimal value (0.4 g L^?1) which is necessary to mineralize glyphosate. The kinetic rate of glyphosate mineralization decreases with the increasing initial concentration of glyphosate, and the data can be described using the first-order model. An alkaline environment is conducive to glyphosate mineralization. The mineralization efficiency increases with elevated flow rate to 114 mL min^?1, which is followed by a decrease with a further increase in flow rate due to the reduction of the residence time. The presence of external oxidants (K₂S₂O₈, H₂O₂ and KBrO₃) and photosencitizer (humic acid) can significantly enhance glyphosate mineralization. Photocatalysis oxidation ability of the three studied oxidants decrease in the order of: S₂O₈ ^2? > BrO₃ ^? > H₂O₂. Finally, the Langmuir–Hinshelwood (L-H) model was used to rationalize the mechanisms of reactions occurring on TiO₂ surfaces and L-H model constants were also determined.     

真空紫外灯动态降解空气中低浓度甲醛的研究

以集中空调中处理室内可挥发性有机物(VOCs)为应用背景,搭建了试验台.实验研究了真空紫外灯(主波长254 nm,185 nm)降解甲醛的影响因素以及产生O3的情况.研究表明,在产生的O3浓度低于室内空气质量标准(0.16mg/m3)的情况下,真空紫外灯也能够高效地降解空气中低浓度甲醛(＜1 mg/m3);甲醛降解率与反应器空气流速及甲醛初始浓度成反比;降解速率与甲醛初始浓度成正比,与反应器空气的流速成反比;绝对湿度对真空紫外灯降解甲醛有一定的影响;反应器空间大小对甲醛降解影响比较显著.应用于集中空调系统净化室内空气中VOCs,取得了很好的效果.     

真空紫外灯动态降解空气中低浓度甲醛的研究

以集中空调中处理室内可挥发性有机物（VOCs）为应用背景，搭建了试验台。实验研究了真空紫外灯（主波长254nm，185nm）降解甲醛的影响因素以及产生O3的情况。研究表明，在产生的O3浓度低于室内空气质量标准（0．16mg／m^3）的情况下，真空紫外灯也能够高效地降解空气中低浓度甲醛（〈1mg／m^3）；甲醛降解率与反应器空气流速及甲醛初始浓度成反比；降解速率与甲醛初始浓度成正比，与反应器空气的流速成反比；绝对湿度对真空紫外灯降解甲醛有一定的影响；反应器空间大小对甲醛降解影响比较显著。应用于集中空调系统净化室内空气中VOCs，取得了很好的效果。     

真空紫外光臭氧降解偏二甲肼的研究

研究比较了臭氧氧化（O₃）、紫外臭氧（O₃/UV）和真空紫外臭氧（O₃/VUV）对推进剂——偏二甲肼的处理效果,O₃/VUV最为有效,反应速率常数分别比O₃/UV和O₃高39.8%和65.6%,中间产物——甲醛去除得更迅速,反应50 min即无法检出。初始pH 9时,O₃/VUV降解偏二甲肼的速率最快,达到0.4461 min^-1;反应速率常数随臭氧投加量的增加而线性增大;随偏二甲肼初始浓度从100 mg/L增加到2 000 mg/L,反应动力学由一级转为零级。碳酸盐浓度在0～2 mmol/L范围内对O₃/VUV降解偏二甲肼没有明显的抑制作用。偏二甲肼的无机氮产物以氨离子为主,无机氮只占总氮的40%～60%,说明仍有相当比例的氮以有机氮形式存在。     

Analysis of gaseous diisocyanates in air using chemosorption sampling

A sampling procedure for 2,4- and 2,6-toluenediisocyanate (TDI) and 4,4′-diphenylmethane diisocyanate (MDI) in the range 0.007-0.7 mg/m³ in a 15 L air sample is described. The sampling is performed with 9-(N-methylaminomethyl)-anthracene (MAMA) adsorbed on a solid sorbent, Amberlite XAD-2. The recoveries are 80–100% in this chemosorption reaction. The urea derivatives are desorbed with N,N-dimethylformamide and analysed by high performance liquid chromatography (HPLC). Samples and prepared chemosorption tubes are stable for at least two weeks if stored in the dark. To complete the investigation, field measurements of TDI were performed in an industrial atmosphere.     

Photolysis of low concentration H2S under UV/VUV irradiation emitted from microwave discharge electrodeless lamps

The photolysis of simulating low concentration of hydrogen sulfide malodorous gas was studied under UV irradiation emitted by self-made microwave discharge electrodeless lamps (i.e. microwave UV electrodeless mercury lamp (185/253.7 nm) and iodine lamp (178.3/180.1/183/184.4/187.6/206.2 nm)). Experiments results showed that the removal efficiency (eta H2S) of hydrogen sulfide was decreased with increasing initial H2S concentration and increased slightly with gas residence time; H2S removal efficiency was decreased dramatically with enlarged pipe diameter. Under the experimental conditions with pipe diameter of 36 mm, gas flow rate of 0.42 standard l s(-1), eta H2S was 52% with initial H2S concentration of 19.5 mg m(-3) by microwave mercury lamp, the absolute removal amount (ARA) was 4.30 microg s(-1), and energy yield (EY) was 77.3 mg kW h(-1); eta H2S was 56% with initial H2S concentration of 18.9 mg m(-3) by microwave iodine lamp, the ARA was 4.48 microg s(-1), and the EY was 80.5mg kW h(-1). The main photolysis product was confirmed to be SO4(2-) with IC.     

N-TiO2/rGO纳米材料可见光下催化降解微囊藻毒素-LR的效果

以尿素、钛酸丁酯、氧化石墨烯为原料,采用水热法制备了N-TiO2/rGO复合纳米光催化剂,通过SEM、BET、XRD、Raman、FT-IR、UV-vis DRS等分析方法对催化剂进行了表征和分析,研究了该复合材料在可见光下对水中Microcystin-LR的降解动力学及相关反应机理.结果表明,相较未负载的N-TiO2...     

Hydrochloric acid aerosol and gaseous hydrogen chloride partitioning in a cloud contaminated by solid rocket exhaust

Partitioning of hydrogen chloride between hydrochloric acid aerosol and gaseous HC1 in the lower atmosphere was experimentally investigated in a solid rocket exhaust cloud diluted with humid ambient air. Airborne measurements were obtained of gaseous HCl, total HCl, relative humidity and temperature to evaluate the conditions under which aerosol formation occurs in the troposphere in the presence of hygroscopic HCl vapor. Equilibrium predictions for HCl aerosol formation accurately predict the measured HCl partitioning over a range of total HCl concentrations from 0.6 to 16 ppm.     

Study on the photodegradation of amidosulfuron in aqueous solutions by LC-MS/MS

Sulfonylurea herbicides are extensively widespread for the protection of a variety of crops and vegetables because of their low application rates, high selectivity and low persistency in the environment; unfortunately, their low persistence does not always correspond to a lower toxicity, since new species potentially more toxic and stable than the precursor herbicides can form, owing to natural degradation processes. Here, the photodegradation of amidosulfuron in aqueous solutions was studied by high-performance liquid chromatography with diode array detection and tandem mass spectrometry to identify the degradation products in order to outline the environmental fate of the molecules generating from the simulation of one of the natural processes that can occur, i.e., photoinduced degradation. The photodegradation process results in a first order kinetic reaction with a t _1/2 value of 276 h (11.5 days) and a kinetic constant of 0.0027 h^?1, and three possible degradation products were identified. The results obtained are then compared to those obtained in previous works carried out in comparable experimental conditions about nicosulfuron and tribenuron-methyl, two sulfonylurea herbicides belonging to different classes, and to literature data: hypotheses on the existence of preferential degradation pathways are then drawn, in consequence of the molecular structure of the sulfonylurea pesticide. In particular, the use of organic solvents to obtain complete solubilization of the sample plays a fundamental role and deeply influences the degradation processes that, therefore, not always fully adhere to the actual natural photodegradation pathways. Moreover, considerations about toxicity were driven since the complete mineralisation of the sample is not reached: even when the parent pesticides are totally degraded, they are, however, transformed into other organic compounds showing, if subject to ecotoxicological tests, at least the same toxicity of the precursor herbicides. The evidence here presented suggests that, at least for the class of sulfonylurea pesticides, their professed low persistence actually does not produce any real advantage.     

Some insights into short-term variability of total gaseous mercury in urban air

The concentrations of total gaseous mercury (Hg) were determined at hourly intervals along with relevant environmental parameters that include both meteorological plus criteria pollutant data during two field campaigns (September 1997 and May/June 1998). The mean concentrations of Hg for the two study periods were computed as 3.94 and 3.43 ng m⁻³, respectively. By separating the data into daytime and nighttime periods, we further analyzed diurnal variation patterns for both seasons. Using our Hg data sets, we were able to recognize two contrasting diurnal variation patterns of Hg between two different seasons that can be characterized as: (1) the occurrences of peak Hg concentration during daytime (fall) and (2) slight reductions in daytime Hg concentration relative to nighttime (summer). To study the systematic differences in diurnal patterns between two different seasons, we analyzed Hg data in terms of different statistical approaches such as correlation (and linear regression) and factor analysis. Results of these analyses consistently indicated that different mechanisms were responsible for controlling the daytime distribution patterns of Hg. When the relationship between Hg and concurrently determined O₃ is considered, its reaction with ozone is unlikely to limit Hg levels as the dominant sink mechanism (within the ranges of ozone concentrations found during this study, regardless of season). It is on the other hand suspected that the variation of boundary layer conditions between day/night periods may have been important in introducing the relative reduction in daytime Hg levels during summer. To further provide a general account of short-term variations in Hg distribution data, it is desirable to describe other unknown sink mechanisms.     

Effect of UV radiation and temperature on mineralization and volatilization of coumaphos in water

This study was undertaken to determine the dissipation and degradation of coumaphos [O-(3-chloro-4-methyl-2-oxo-2H-1-benzopyran-7-yl) O,O-diethyl phosphorothioate] under different sunlight conditions and at different temperatures. The effect of the ultra violet (UV) component of solar radiation was also studied using quartz tubes in addition to other radiation in the visible range using glass tubes and the results were compared with those obtained under the dark light conditions. Water suspensions of coumaphos were incubated at three temperatures viz. 22 degrees C, 37 degrees C and 53 degrees C in closed systems to study the effect of temperature. Volatilization, mineralization and degradation of coumaphos increased with an increase in temperature and exposure to solar radiation, particularly under the UV component of the solar radiation. Major loss of the pesticide occurred through volatilization. The optimum temperature for the degradation of coumaphos was found to be at 37 degrees C. The data obtained from the mineralization and degradation studies indicated that 53 degrees C crosses the biological range for suitable growth of microorganism. UV radiation exposure along with maintaining temperature at 37 degrees C may prove useful in the dissipation and/or degradation of coumaphos prior to its disposal as waste from cattle dipping vats.     

Measurements of diurnal concentration variations of gaseous HCl in air in the sub-nanogram range

A method of measuring gaseous HCl based on diffusion samplers has been developed. This sampling method allows a filterless dynamic gas-aerosol separation. After thermal desorption, HCl is converted into 2-chlorocyclohexanol by gas-phase reaction with 7-oxabicyclo(4.1.0)heptane. The derivatization product is analysed by GC-separation using an electrolytic conductivity detector (HECD). The minimum concentration detectable is: 40 pptv HCl. Several results of measurements of gaseous HCl in air are reported. Gaseous HCl is present in concentrations between about 0.1 and 1.4 ngℓ⁻¹ at STP in rural areas and 0.2 and 3.0 ng ℓ⁻¹ at STP in urban areas. Diurnal and spatial variations and the influence of climate were measured and are discussed.     

Effect of UV radiation and temperature on mineralization and volatilization of coumaphos in water

This study was undertaken to determine the dissipation and degradation of coumaphos [O-(3-chloro-4-methyl-2-oxo-2H-1-benzopyran-7-yl) O,O-diethyl phosphorothioate] under different sunlight conditions and at different temperatures. The effect of the ultra violet (UV) component of solar radiation was also studied using quartz tubes in addition to other radiation in the visible range using glass tubes and the results were compared with those obtained under the dark light conditions. Water suspensions of coumaphos were incubated at three temperatures viz. 22°C, 37°C and 53°C in closed systems to study the effect of temperature. Volatilization, mineralization and degradation of coumaphos increased with an increase in temperature and exposure to solar radiation, particularly under the UV component of the solar radiation. Major loss of the pesticide occurred through volatilization. The optimum temperature for the degradation of coumaphos was found to be at 37°C. The data obtained from the mineralization and degradation studies indicated that 53°C crosses the biological range for suitable growth of microorganism. UV radiation exposure along with maintaining temperature at 37°C may prove useful in the dissipation and/or degradation of coumaphos prior to its disposal as waste from cattle dipping vats.