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.     

能量代谢动力学模型对污水处理参数优化

从本质上说,微生物的降解的过程就是微生物能量代谢的过程,从能量守恒原理出发,通过简化,导出了能量代谢动力学模型,从而从微观领域建立了能量参数与系统参数之间的联系,同时通过模型实验求解出其中的参数,找出微生物比增殖速率和基于ATP的能量比利用速率之间的关系,进而可以根据实际进水水质对系统参数进行计算,优化处理过程,用以确定和校正一些凭经验设计的关键参数。因此,能量代谢方程在理论上和实践上都具有重要的意义。     

基于三波长透射率的水体色度检测标准

为了推动有关分光光度法测量水体色度的国家标准的建立,对美国和台湾地区的水体色度标准检测方法进行了研究,提出了新的基于三波长透射率测量水体色度的方法。根据现行国家标准中的色度学相关数据,选择在595、555和445 nm 3个波长处的光谱透射率计算水样的三刺激值,依照国标推荐的色差公式建立了测量水样色度的标准检量线。利用所提出的新的水体色度测量方法对5个水样的色度值进行了实际测量,结果表明,新的测量方法所得到的水体色度值与铂钴比色法一致。     

活性炭纤维吸附含溴甲烷气体的性能

采用动态吸附法在25℃下,测定了3种活性炭纤维(ACF-1、ACF-2和ACF-3)对含溴甲烷气体的吸附性能和回收效果,并对活性炭纤维的孔结构进行表征.探讨了孔结构、溴甲烷浓度、气体流量、循环使用次数等因素对活性炭纤维吸附溴甲烷性能的影响.结果表明,活性炭纤维比表面积大小及0.4～0.8 nm左右的微孔数量决定了其对溴甲烷吸附性能的优劣;气体中溴甲烷的浓度的提高使活性炭纤维对溴甲烷的穿透和饱和吸附量增加,而气体流量的增加则使活性炭纤维对溴甲烷的穿透和饱和吸附量降低,但两者均使穿透和饱和吸附时间缩短;活性炭纤维多次循环使用后,对溴甲烷的吸附容量明显地降低,循环12次后达到稳定吸附,其稳定吸附值为133.5 mg/g.     

Computational fluid dynamics modeling of laboratory flames and an industrial flare

A computational fluid dynamics (CFD) methodology for simulating the combustion process has been validated with experimental results. Three different types of experimental setups were used to validate the CFD model. These setups include an industrial-scale flare setups and two lab-scale flames. The CFD study also involved three different fuels: C₃H₆/CH₄/Air/N₂, C₂H₄/O₂/Ar, and CH₄/Air. In the first setup, flare efficiency data from the Texas Commission on Environmental Quality (TCEQ) 2010 field tests were used to validate the CFD model. In the second setup, a McKenna burner with flat flames was simulated. Temperature and mass fractions of important species were compared with the experimental data. Finally, results of an experimental study done at Sandia National Laboratories to generate a lifted jet flame were used for the purpose of validation. The reduced 50 species mechanism, LU 1.1, the realizable k-? turbulence model, and the EDC turbulence–chemistry interaction model were used for this work. Flare efficiency, axial profiles of temperature, and mass fractions of various intermediate species obtained in the simulation were compared with experimental data and a good agreement between the profiles was clearly observed. In particular, the simulation match with the TCEQ 2010 flare tests has been significantly improved (within 5% of the data) compared to the results reported by Singh et al. in 2012. Validation of the speciated flat flame data supports the view that flares can be a primary source of formaldehyde emission.

ImplicationsValidated computational fluid dynamics (CFD) models can be a useful tool to predict destruction and removal efficiency (DRE) and combustion efficiency (CE) under steam/air assist conditions in the face of many other flare operating variables such as fuel composition, exit jet velocity, and crosswind. Augmented with rigorous combustion chemistry, CFD is also a powerful tool to predict flare emissions such as formaldehyde. In fact, this study implicates flares emissions as a primary source of formaldehyde emissions. The rigorous CFD simulations, together with available controlled flare test data, can be fitted into simple response surface models for quick engineering use.     

Catalytic Destruction of Dichloromethane Using Perovskite-Type Oxide Catalysts

Abstract

Dichloromethane (DCM, also known as methylene chloride [CH₂Cl₂]) is often present in industrial waste gas and is a valuable chemical product in the chemical industry. This study addresses the oxidation of airstreams that contain CH₂Cl₂ by catalytic oxidation in a tubular fixed-bed reactor over perovskite-type oxide catalysts. This work also considers how the concentration of influent CH₂Cl₂ (C_o = 500-1000 ppm), the space velocity (GHSV = 5000-48,000 1/hr), the relative humidity (RH = 10-70%) and the concentration of oxygen (O₂ = 5-21%) influence the operational stability and capacity for the removal of CH₂Cl_2.

The surface area of lanthanum (La)-cobalt (Co) composite catalyst was the greatest of the five perovskite-type catalysts prepared in various composites of La, strontium, and Co metal oxides. Approximately 99.5% CH₂Cl₂ reduction was achieved by the catalytic oxidation over La-CoO₃-based perovskite catalyst at 600 °C. Furthermore, the effect of the initial concentration and reaction temperature on the removal of CH₂Cl₂ in the gaseous phase was also monitored. This study also provides information that a higher humidity corresponds to a lower conversion. Carbon dioxide and hydrogen chloride were the two main products of the oxidation process at a relative humidity of 70%.     

中小化工燃煤锅炉烟气脱硫技术路线的选择

在分析了燃煤烟气脱硫方式以及中小化工燃煤锅炉特点的基础上,对中小化工燃煤锅炉适宜的烟气脱硫技术路线进行了技术经济比较.认为选择脱硫路线时应考虑技术的成熟度及可靠性、脱硫剂和运行的成本、副产物的利用等因素.建议在烟气量小于8×105 m3/h时采用干法脱硫工艺;在烟气量大于8×105 m3/h时采用石灰石-石膏法脱硫工艺...     

Solubilization properties of polycyclic aromatic hydrocarbons by saponin, a plant-derived biosurfactant

The enhanced solubilization of polycyclic aromatic hydrocarbons (PAHs) by saponin, a plant-derived non-ionic biosurfactant, was investigated. The results indicated that the solubilization capabilities of saponin for PAHs were greater than some representative synthetic non-ionic surfactants and showed strong dependence on solution pH and ionic strength. The molar solubilization ratio (MSR) of saponin for phenanthrene was about 3-6 times of those of the synthetic non-ionic surfactants, and decreased by about 70% with the increase of solution pH from 4.0 to 8.0, but increased by approximately 1 times with NaCl concentration increased from 0.01 to 1.0 M. Heavy metal ions can enhance saponin solubilization for phenanthrene and the corresponding MSR values increased by about 25% with the presence of 0.01 M of Cd²⁺ or Zn²⁺. Saponin is more effective in enhancing PAHs solubilization than synthetic non-ionic surfactants and has potential application in removing organic pollutants from contaminated soils.     

亚硝基胍对泥鳅红细胞微核及核异常的诱发

研究了诱变剂对泥鳅红细胞微核和核异常的诱发作用,以寻求较为简便的检测水体中污染物对遗传物质的损害程度及毒理效应的方法。试验以亚硝基胍（MNNG）作为诱变剂,研究其不同浓度和染毒时间对泥鳅红细胞微核形成和核异常的影响。试验结果表明,在一定浓度范围内,微核细胞率与亚硝基胍浓度呈正相关;但当浓度过高时,微核细胞率反而降低。此外,研究还发现,随着亚硝基胍浓度的升高,微核细胞率出现高峰的时间也相应提前。从试验结果来看,微核测定法确是遗传毒理学试验中一个较为理想的监测手段。     

催化裂化钠碱脱硫液中钙镁离子的去除

研究了化学沉淀法和氨基膦酸型螯合树脂吸附法对催化裂化钠碱脱硫液中Ca~(2+)和Mg~(2+)的去除效果。实验结果表明:NaOH沉淀法可有效去除钠碱脱硫液中的Mg~(2+),当溶液pH为12、反应时间为15 min时,Mg~(2+)去除率达91.6%;NaOH-Na_2CO_3联合沉淀法无法去除钠碱脱硫液中的Ca~(2+);经过NaOH溶液有效除Mg~(2+)后的脱硫液再采用氨基膦酸型螯合树脂吸附柱去除其中的Ca~(2+)和Mg~(2+),可使出水硬度小于2 mg/L。提高进水pH、降低进水流量、降低进水硬度均可提高单位体积树脂的处理水量。