Use of residence time distribution for evaluation of gaseous pollutant volatilization from stored swine manure

Abstract

A quantification analysis for evaluation of gaseous pollutant volatilization as a result of mass transfer from stored swine manure is presented from the viewpoint of residence time distribution. The method is based on evaluating the moments of concentration vs. time curves of both air and gaseous pollutants. The concept of moments of concentration histories is applicable to characterize the dispersal of the supplied air or gaseous pollutant in a ventilated system. The mean age or residence time of airflow can be calculated from an inverse system state matrix [B]‐1 of a linear dynamic equation describing the dynamics of gaseous pollutant in a ventilated airspace. The sum elements in an arbitrary row i in matrix [B]‐1 is equal to the mean age of airflow in airspace i. The mean age of gaseous pollutant in airspace i can be obtained from the area under the concentration profile divided by the equilibrium concentration reading in that space caused by gaseous pollutant sources. Matrix [B]‐1 can also be represented in terms of the inverse local airflow rate matrix ([W]‐1), transition probability matrix ([P]), and air volume matrix ([V]) as, [B]‐1 =[W]‐1[P][V]. Finally the mean age of airflow in a ventilated airspace can be interpreted by the physical characteristics of matrices [W] and [P]. The practical use of the concepts is also applied in a typical pig unit.     

城市水环境控制单元污染物入河量估算方法

在资料不全且无法进行试验的地区,为了估算污染物进入目标水体的负荷,需要充分利用易获得的数据.使用污染源普查数据和土地利用数据,同时考虑距离对污染物入河过程的影响,来估算水环境控制单元内的污染物入河量.大辽河水环境控制单元营口段是以城区污染为主的城市水环境控制单元,以大辽河水环境控制单元营口段为例估算控制单元内污染物入河量,并进行分析.结果表明使用污染源普查数据和土地利用数据,在根据距离考虑入河系数的情况下能够较准确的估算出污染物入河量,可以为后期进行水环境容量核定工作提供基础数据,同时为城市规划管理者提供制定减排政策的依据.     

土壤对污染物的缓冲性研究进展

本文阐述了土壤对污染物的缓冲特性的概念，研究土壤对污染物缓冲性的目的和意义、历史、现状和前景，为土壤污染与防治提供了一定的理论依据。     

滇池水污染物浓度预测的人工神经网络模型

本文针对滇池日益严重的水污染现状,根据云南昆明西苑隧道断面2004年-2010年的监测资料,建立了基于BP神经网络的主要污染指标预测模型,并对其进行训练检验,研究结果表明：独立样本中pH、溶解氧、氨氮、高锰酸盐浓度的预测值与监测值的线性相关系数分别为0．952、0．967、0．945、0．936。结果证明该模型预测精度满足要求,通过准确地预测湖泊水污染物可以为治理湖泊营养化和综合利用水资源、规划管理、决策提供重要的科学依据。     

横向风作用下喷口间距对射流扩散火焰特征的影响研究*

为研究横向风作用下喷口间距对射流扩散火焰特征的影响,以双喷口火焰为研究对象,利用CCD摄像机拍摄火焰几何形态,研究横向风条件下喷口间距对火焰形态演化、火焰长度和火焰吹熄极限的影响。研究结果表明:喷口间距较小时,2束火焰因空气夹带竞争和压差作用,彼此相互倾斜融合,火焰融合概率随喷口间距增加而逐渐降低,火焰临界融合间距随横向风的增加先增大后减小;由于火焰的空气夹带和热反馈处于较高水平,2束火焰被少量拉伸,火焰长度先增加后减小;喷口间距较小时,火焰吹熄极限显著增加。     

基准氧含量在大气固定源污染物排放标准中的应用与启示

基准氧含量是大气固定源污染物排放标准中的一项重要指标,直接影响着对污染物排放浓度的达标判断。收集整理了近年来国家和地方制修订的主要大气固定源污染物排放标准,深入分析了基准氧含量指标在标准中的优化调整情况、实际应用效果及制修订背景和作用。针对基准氧含量在标准应用中仍存在着行业符合性划分不细致、适用条件不明确等问题,提出了以生产工艺和生产设施为基础,科学合理规定基准氧含量的建议。     

喀斯特坡耕地浅层地下孔(裂)隙发育过程中径流产污特征

降雨径流产生的非点源污染是地下水污染的重要来源,喀斯特坡耕地浅层地下孔(裂)隙养分流失是造成该地区地下水污染的关键因素.通过模拟喀斯特坡耕地地下孔(裂)隙特征,采用人工模拟降雨和室内分析相结合的方法,研究浅层地下孔(裂)隙发育过程中降雨径流产污特征.结果表明:喀斯特坡耕地地下径流产污是一个极其复杂的过程,微度(1%)孔(裂)隙发育的坡耕地径流全氮、全磷和全钾流失量随雨强变化不明显,全氮和全磷流失量均在70 mm·h-1雨强达到最大值;轻度(3%)孔(裂)隙发育的坡耕地全氮、全磷流失量在雨强50 mm·h-1时达到最大值;中度(5%)孔(裂)隙发育的坡耕地全氮、全磷、全钾流失量则在雨强为90 mm·h-1时达到最大值;各孔(裂)隙发育条件下的全氮、全磷、全钾养分流失量对坡度的响应不明显,轻度发育下的全氮和全磷流失量最大,在中度发育条件下,坡耕地土壤中全钾流失总量最大;不同雨强、坡度条件下的地下径流全氮、全磷和全钾次产污模数随地下孔(裂)隙度变化亦不明显,其中全氮次产污模数在4.38~58.72 mg·h-1·m-2,全磷在0.16~3.15 mg·h-1·m-2,全钾在0.16~3.03 mg·h-1·m-2范围变化.     

人工湿地水处理技术研究进展存在问题与改进

论述了人工湿地技术的除污机理和影响因素,并介绍了目前该技术所存在的问题,同时针对问题提出了相应的解决方法。     

Apparent diffusion coefficients and chemical species of neptunium (V) in compacted Na-montmorillonite

Diffusion of neptunium (V) in compacted Na-montmorillonite was studied through the non-steady state diffusion method. In this study, two experimental attempts were carried out to understand the diffusion mechanism of neptunium. One was to establish the diffusion activation energy, which was then used to determine the diffusion process in the montmorillonite. The other was the measurement of the distribution of neptunium in the montmorillonite by a sequential batch extraction. The apparent diffusion coefficients of neptunium in the montmorillonite at a dry density of 1.0 Mg m-3 were from 3.7 x 10(-12) m2 s-1 at 288 K to 9.2 x 10(-12) m2 s-1 at 323 K. At a dry density of 1.6 Mg m-3, the apparent diffusion coefficients ranged between 1.5 x 10(-13) m2 s-1 at 288 K and 8.7 x 10(-13) m2 s-1 at 323 K. The activation energy for the diffusion of neptunium at a dry density of 1.0 Mg m-3 was 17.5 +/- 1.9 kJ mol-1. This value is similar to those reported for diffusion of other ions in free water, e.g., 18.4 and 17.4 kJ mol-1 for Na+ and Cl-, respectively. At a dry density of 1.6 Mg.m-3, the activation energy was 39.8 +/- 1.9 kJ mol-1. The change in the activation energy suggests that the diffusion process changes depending on the dry density of the compacted montmorillonite. A characteristic distribution profile was obtained by the sequential extraction procedure for neptunium diffused in compacted montmorillonite. The estimated fraction of neptunium in the pore water was between 3% and 11% at a dry density of 1.6 Mg m-3 and at a temperature of 313 K. The major fraction of the neptunium in the montmorillonite was identified as neptunyl ions sorbed on the outer surface of the montmorillonite. These findings suggested that the activation energy for diffusion and the distribution profile of the involved nuclides could become powerful parameters in understanding the diffusion mechanism.     

The effect of a biofilm on solute diffusion in fractured porous media

At sites in fractured rock where contamination has been exposed to the rock matrix for extended periods of time, the amount of contaminant mass residing in the matrix can be considerable. Even though it may be possible to diminish concentrations by the advection of clean water through the fracture features, back diffusion from mass held in the matrix will lead to a continuing source of contamination. In such an event, the development of a biofilm (a thin film of microbial mass) on the wall of the fractures may act to limit or prevent the back diffusion process. The objective of this preliminary study is to explore the influence imparted by the presence of a biofilm on the process of matrix diffusion. The investigation was conducted using radial diffusion cells constructed from rock core in which biofilm growth was stimulated in a central reservoir. Once biofilms were developed, forward diffusion experiments were conducted in which a conservative solute migrated from the central reservoir into the intact rock sample. Diffusion experiments were performed in a total of 11 diffusion cell pairs where biofilm growth was stimulated in one member of the pair and inhibited in the other. The effect of the presence of a biofilm on tracer diffusion was determined by comparison of the diffusion curves produced by each cell pair. A semi-analytical model that accounts for the presence of a biofilm was used to investigate the effect of the biofilm on mass transfer due to changes in the effective porosity, effective diffusion coefficient, and the depth of penetration of the biofilm into the intact rock. The results show that the biofilm acted to plug the rock matrix, rather than forming a discrete layer on the reservoir surface. The reduction in effective porosity due to the biofilm ranged from 6% to 52% with the majority of the samples in the 30% to 50% range. Based on the present results, with more efficient biofilm stimulation, it is reasonable to assume that a more complete plugging of the microcrack porosity might be possible, leaving a much thicker and efficient barrier than could be achieved via a surface biofilm.