The role of organic ligands in ferrous-induced photochemical degradation of 2,4-dichlorophenoxyacetic acid

Recent studies have shown that hydrogen peroxide is generated in a ferrioxalate-induced photoreductive reaction, but information about the effect of organic ligands on the photochemical behaviour of ferrous species is limited. The degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by a ferrous-catalyzed oxidation in the presence of various ligands such as formate, citrate, malelate, oxalate, and ethylenediaminetetra-acetic acid (EDTA) was studied. The experiments were conducted under either dark or irradiated (350n m) conditions. Forty-two percent and 34% of 2,4-D were removed by the Fe(2+)/oxalate/UV and Fe(2+)/citrate/UV processes, respectively, after 30 min of reaction and oxidative intermediates were obtained in both cases. The presence of hydroxylated intermediates suggests that 2,4-D may be attacked by hydroxyl radicals, which are the products of the photo-Fenton-like reaction. As such, hydrogen peroxide was produced by the photolysis of ferrous oxalate or ferrous citrate, referred to hereafter as photogenerated H(2)O(2). As expected, the total removal percentage of 2,4-D jumped to 97% when 1mM of hydrogen peroxide (so-called spiked H(2)O(2)) was externally added to the reaction vessel to initiate the Fe(2+)/oxalate/UV process. Therefore, the treatment of 2,4-D by the Fe(2+)/oxalate/H(2)O(2)/UV system can be operated in two steps: the photolysis of ferrous oxalate first, followed by adding the spiked H(2)O(2) sometime after the commencement of the reaction. A two-phase model has been developed to describe this tandem ferrous-catalyzed photooxidation, which would help to achieve the mineralization of 2,4-D.     

Using a hybrid approach to optimize experimental network design for aquifer parameter identification

The main objective of this study is to evaluate the land-use change and its relationship with its driving factors in the loess hilly region. In this study, a case study was carried out in Pengyang County. We set two land-use demand scenarios (a baseline scenario (scenario 1) and a real land-use requirement scenario (scenario 2)) during year 2001–2005 via assuming the effect of driving factors on land-use change keeps stable from 1993 to 2005. Two simulated land-use patterns of 2005 are therefore achieved accordingly by use of the conversion of land use and its effects model at small regional extent. Kappa analyses are conducted to compare each simulated land-use pattern with the reality. Results show that (1) the associated kappa values were decreased from 0.83 in 1993–2000 to 0.27 (in scenario 1) and 0.23 (in scenario 2) in 2001–2005 and (2) forest and grassland were the land-use types with highest commission errors, which implies that conversion of both the land-use types mentioned above is the main determinant of change of kappa values. Our study indicates the land-use change was driven by the synthetic multiply factors including natural and social–economic factors (e.g., slope, aspect, elevation, distance to road, soil types, and population dense) in 1993–2000 until “Grain for Green Project” was implemented and has become the dominant factor in 2001–2005.     

Atmospheric Aerosol over a Southeastern Region of Texas: Chemical Composition and Possible Sources

Speciated samples of PM_2.5 were collected at a site in Jefferson County, Texas by US EPA (Environmental Protection Agency) from July of 2003 to August of 2005. A total of 269 samples with 52 species were measured; however, 22 species were excluded in this study because of too many below-detection-limit data. The data set was analyzed by positive matrix factorization (PMF) to infer the sources of PM observed at the site. The analysis identified ten sources: sulfate-rich secondary aerosol I (35.9%), sulfate-rich secondary aerosol II (21.0%), cement/carbon-rich (11.7%), wood smoke (8.8%), metal processing (6.3%), motor vehicle/road dust (5.7%), nitrate-rich secondary aerosol (3.3%), soil (3.2%), sea salt (2.6%), and chloride depleted marine aerosol (1.6%). Sulfate and nitrate mainly exist as salts. The two sulfate-rich secondary aerosols account for almost 57% of the PM_2.5 mass concentration. The factor containing highest concentrations of Cl and Na was attributed to sea salt due to the proximity of the monitoring site to the Gulf of Mexico. The chloride depleted marine aerosol was related to the sea salt aerosol. Cement/carbon-rich, wood smoke, metal processing, and motor vehicle/road dust factor were likely to be the local sources.     

Nutrient ratios and the complex structure of phytoplankton communities in a highly turbid estuary of Southeast Asia

Phytoplankton diversity and abundance in estuarine systems are controlled by many factors. Salinity, turbidity, and inorganic nutrient concentrations and their respective ratios have all been proposed as principal factors that structure phytoplankton diversity and influence the emergence of potentially toxic species. Although much work has been conducted on temperate estuaries, less is known about how phytoplankton diversity is controlled in tropical, monsoonal systems that are subject to large, seasonal shifts in hydrology and to rapidly changing land use. Here, we present the results of an investigation into the factors controlling phytoplankton species composition and distribution in a tropical, monsoonal estuary (Bach Dang estuary, North Vietnam). A total of 245 taxa, 89 genera from six algal divisions were observed. Bacillariophyceae were the most diverse group contributing to 51.4 % of the microalgal assemblage, followed by Dinophyceae (29.8 %), Chlorophyceae (10.2 %), Cyanophyceae (3.7 %), Euglenophyceae (3.7 %) and Dictyochophyceae (1.2 %). The phytoplankton community was structured by inorganic nutrient ratios (DSi:DIP and DIN:DIP) as well as by salinity and turbidity. Evidence of a decrease in phytoplankton diversity concomitant with an increase in abundance and dominance of certain species (e.g., Skeletonema costatum) and the appearance of some potentially toxic species over the last two decades was also found. These changes in phytoplankton diversity are probably due to a combination of land use change resulting in changes in nutrient ratios and concentrations and global change as both rainfall and temperature have increased over the last two decades. It is therefore probable in the future that phytoplankton diversity will continue to change, potentially favoring the emergence of toxic species in this system.     

Degradation of sulfonamides during anaerobic composting of swine manure

Residual antibiotics in manure pose a potential threat to public and ecological health as a result of the application of manure from animals treated with antibiotics to land. The environmental fate of sulfonamides (SAs) in swine manure after composting and field application remains largely unknown. We studied the degradation of the antibiotics sulfadiazine (SD), sulfathiazole (ST), and sulfamethazine (SM2) during anaerobic composting. We tested the effects of temperature and antibiotic concentration on degradation rates. We also evaluated the changes in pH, moisture, and biological degradation material in manure spiked with SAs and in a control. Results showed that the 3 SAs decreased by between 52.31% and 90.30% in all 9 treatments following 14 days of anaerobic composting, and the highest removal efficiencies were observed at a temperature of 35°C and initial concentrations of 6.03, 6.48, and 6.32?µg/g of SD, ST, and SM2, respectively, which were degraded by 90.30%, 85.78%, and 75.18%. Removal efficiencies for all SAs correlated well with moisture and biological degradation material of the manure. These results indicate that composting may be a practical and effective way to reduce concentrations of these three SAs in swine manure prior to its land application.     

Biological monitoring of chlorpyrifos exposure to rice farmers in Vietnam

Chlorpyrifos is the most common organophosphate insecticide registered for use in Vietnam and is widely used in agriculture, particularly rice farming. However, chlorpyrifos exposure to and adverse effects on farmers has not been evaluated. In this study, biological monitoring of chlorpyrifos exposure in a group of rice farmers was conducted after a typical application event using back-pack spraying.Urine samples (24 h) were collected from the rice farmers before and post insecticide application. Samples were analysed for 3,5,6-trichloropyridinol (TCP), the major urinary metabolite of chlorpyrifos, using an enzymatic pre-treatment before extraction followed by HPLC-MS/MS. Absorbed Daily Dose (ADD) of chlorpyrifos for farmers were then estimated from urinary TCP levels, expressed as μg g⁻¹ creatinine. The analytical method for urinary TCP had a low detection limit (0.6 μg L⁻¹), acceptable recovery values (80-114%), and low relative percentage differences in duplicate and repeated samples.Post-application chlorpyrifos ADD of farmers varied from 0.4 to 94.2 μg kg⁻¹ (body weight) d⁻¹ with a mean of 19.4 μg kg⁻¹ d⁻¹ which was approximately 80-fold higher than the mean baseline exposure level (0.24 μg kg⁻¹ d⁻¹). Hazard Quotients (ratio of the mean ADD for rice farmers to acute oral reference dose) calculated using acute oral reference doses recommended by United States and Australian agencies varied from 2.1 (Australian NRA), 4.2 (US EPA) to 6.9 (ATSDR).Biological monitoring using HPLC-MS/MS analysis of urinary TCP (24 h) was found to be an effective method for measuring chlorpyrifos exposure among farmers. This case study found that Vietnamese rice farmers had relatively high exposures to chlorpyrifos after application, which were likely to have adverse health effects.     

Denitrification controls in urban riparian soils: implications for reducing urban nonpoint source nitrogen pollution

The purpose of this research was to thoroughly analyze the influences of environmental factors on denitrification processes in urban riparian soils. Besides, the study was also carried out to identify whether the denitrification processes in urban riparian soils could control nonpoint source nitrogen pollution in urban areas. The denitrification rates (DR) over 1 year were measured using an acetylene inhibition technique during the incubation of intact soil cores from six urban riparian sites, which could be divided into three types according to their vegetation. The soil samples were analyzed to determine the soil organic carbon (SOC), soil total nitrogen (STN), C/N ratio, extractable NO₃ ^?-N and NH₄ ⁺-N, pH value, soil water content (SWC), and the soil nitrification potential to evaluate which of these factors determined the final outcome of denitrification. A nitrate amendment experiment further indicated that the riparian DR was responsive to added nitrate. Although the DRs were very low (0.099?~?33.23 ng N₂O-N g^?1 h^?1) due to the small amount of nitrogen moving into the urban riparian zone, the spatial and temporal patterns of denitrification differed significantly. The extractable NO₃ ^?-N proved to be the dominant factor influencing the spatial distribution of denitrification, whereas the soil temperature was a determinant of the seasonal DR variation. The six riparian sites could also be divided into two types (a nitrate-abundant and a nitrate-stressed riparian system) according to the soil NO₃ ^?-N concentration. The DR in nitrate-abundant riparian systems was significantly higher than that in the nitrate-stressed riparian systems. The DR in riparian zones that were covered with bushes and had adjacent cropland was higher than in grass-covered riparian sites. Furthermore, the riparian DR decreased with soil depth, which was mainly attributed to the concentrated nitrate in surface soils. The DR was not associated with the SOC, STN, C/N ratio, and pH. Nitrate supply and temperature finally decided the spatiotemporal distribution patterns of urban riparian denitrification. Considering both the low DR of existing riparian soils and the significance of nonpoint source nitrogen pollution, the substantial denitrification potential of urban riparian soils should be utilized to reduce nitrogen pollution using proper engineering measures that would collect the polluted urban rainfall runoff and make it flow through the riparian zones.     

水质工程用紫外光消毒器的CFD数值模拟

紫外光消毒法是一种重要的污水深度处理方法,消毒器内部辐射强度的分布情况、微生物的停留时间及其运动轨迹对灭菌效果起着至关重要的作用。本文首次在国内系统介绍了采用计算流体动力学(CFD)手段对紫外光消毒器进行数值模拟研究的理论基础和技术路线,指出辐射强度的计算和停留时间的确定是其中的关键。以特定结构的紫外光消毒器为对象,对其内部流场进行了模拟计算,讨论了挡板位置不同所引起的消毒器内部速度场的变化情况;应用离散坐标辐射模型(DO)对紫外光辐射强度分布进行了模拟,同时加入离散粒子模型(DPM)来模拟消毒器内微生物的停留时长和运动轨迹,为最终计算微生物所受紫外光辐射剂量奠定了坚实的基础。     

光纤传导可见光降解亚甲基蓝

针对浓度大、色度高的印染废水难以处理的情况,选用加入光纤的光催化体系进行研究。采用溶胶凝胶法制备了Ag+/TiO2粉体光催化剂,用固体紫外可见光谱、X射线衍射对其进行表征。选用亚甲基蓝溶液作为目标降解物,评价了Ag+/TiO2在可见光下的光催化活性。分别考察了加入石英芯侧光光纤与塑料侧光光纤反应体系下,催化剂量、光纤数量、光照强度和pH值等因素对亚甲基蓝降解实验的影响。结果表明,选用20 mg/L的亚甲基蓝,采用催化剂量为11.67 g/L,500根侧光光纤,300 W的外部光源,pH值约为11时,光催化降解效果最佳,均能达到90%以上。     

微生物制剂与玄武岩纤维联用处理城市废水

为了探索一种新型的去除水体中有机物的工艺,以模拟城市废水为研究对象,研究不同工况条件下,复合微生物制剂、组合双环玄武岩纤维填料以及复合微生物制剂与组合双环玄武岩纤维填料结合对模拟城市废水中COD的去除情况。实验结果表明,复合微生物制剂与组合双环玄武岩纤维填料结合在曝气的情况下对COD的去除能力较高。在复合微生物制剂与组合双环玄武岩纤维填料结合的条件下,对COD浓度为500 mg/L左右的模拟城市废水的去除效率可达 97.22%;影响模拟城市废水中COD去除效果的各因素的主次顺序依次为反应时间>曝气时间>投加量=pH;得出最佳工况参数是:复合微生物制剂的投加量为0.05 g/L,曝气时间为72 h,反应时间为96 h,pH为7。