Filtration of Radioactive Aerosols By Glass Fibers

Abstract

An ozone (O₃) exposure assessment study was conducted in Toronto, Ontario, Canada during the winter and summer of 1992. A new passive O₃ sampler developed by Harvard was used to measure indoor, outdoor, and personal O₃ concentrations. Measurements were taken weekly and daily during the winter and summer, respectively. Indoor samples were collected at a total of 50 homes and workplaces of study participants. Outdoor O₃ concentrations were measured both at home sites using the passive sampler and at 20 ambient monitoring sites with continuous monitors. Personal O₃ measurements were collected from 123 participants, who also completed detailed time-activity diaries. A total of 2,274 O₃ samples were collected. In addition, weekly air exchange rates of homes were measured.

This study demonstrates the performance of our O₃ sampler for exposure assessment. The data obtained are further used to examine the relationships between personal, indoor (home and workplace), and outdoor O₃ concentrations, and to investigate outdoor and indoor spatial variations in O₃ concentrations. Based on home outdoor and indoor, workplace, and ambient O₃ concentrations measured at the Ontario Ministry of the Environment (MOE) sites, the traditional microenvironmental model predicts 72% of the variability in measured personal exposures. An alternative personal O₃ exposure model based on outdoor measurements and time-activity information is able to predict the mean personal exposures in a large population, with the highest R² value of 0.41.     

Characterization of Activated Carbon Fiber Filters for Pressure Drop,Submicrometer Particulate Collection,and Mercury Capture

ABSTRACT

The use of activated carbon fiber (ACF) filters for the capture of particulate matter and elemental Hg is demonstrated. The pressure drop and particle collection efficiency characteristics of the ACF filters were established at two different face velocities and for two different aerosols: spherical NaCl and combustion-generated silica particles. The clean ACF filter specific resistance was 153 kg m^-2 sec^-1. The experimental specific resistance for cake filtration was 1.6 × 10⁶ sec^-1 and 2.4 × 10⁵ sec^-1 for 0.5- and 1.5-μm mass median diameter particles, respectively. The resistance factor R was approximately 2, similar to that for the high-efficiency particulate air filters. There was a discrepancy in the measured particle collection efficiencies and those predicted by theory. The use of the ACF filter for elemental Hg capture was illustrated, and the breakthrough characteristic was established. The capacity of the ACF filter for Hg capture was similar to other powdered activated carbons.     

Fine Particle Collection Efficiency Related to Pressure Drop,Scrubbant and Particle Properties,and Contact Mechanism

Collection efficiencies are shown for control of fine particles in venturi scrubbers (1) as a function of pressure drop, and (2) as a function of throat area and liquid to gas ratio. A relationship of pressure drop to throat area, gas density, throat velocity, and liquid to gas ratio is given and is used to provide a method for estimating efficiency knowing only these scrubber design parameters. The effect of charged particles and of surface active agents on collection efficiency are discussed briefly.     

Effect of Ammonia Injection on Fabric Filter Pressure Drop

Experiments have been carried out to assess the effect of ammonia injection upstream of a small-scale fabric filter which collects ash from the burning of coal in Australia. The ammonia injection resulted in an increase in the pressure drop across the filter. This was apparently due to an increase in the cohesivity of the ash, which made dislodgement during cleaning more difficult. There were some indications that the ammonia-conditioned ash formed a more porous dust cake during the filtration cycle.     

The Recovery of Selenious Acid Aerosols on Glass Fiber Filters

Previous workers have shown that selenium is only partially trapped on a filter during air sampling. In some cases, these losses have been attributed to volatilization of selenium dioxide. Our results demonstrate that selenium dioxide, In the presence of moist air, is completely recovered (apparently as selenious acid aerosols) and that the previous shortfalls must be due to other selenium species as yet unidentified. Selenious acid aerosols In our study were formed by volatilizing selenium dioxide (≈3 mg) Into a stream of moist ambient air (relative humidity, >50%), and trapped on glass fiber filters using a high-volume air sampler. Selenium(IV) was ultrasonlcally extracted from the filter with water and analyzed by atomic absorption spectrometry. Selenious acid aerosols were trapped on the filters with high efficiency (105 ± 5 percent) using a 50 minute sampling period. With an extended sampling period (24 hours) the recovery was 103 ± 6 percent.     

Fiber Glass Fabric Filters for High Temperature Dust and Fume Control

Foliar markings on vegetation have proven a highly sensitive criterion for the presence of many air pollutants; proper evaluation of such effects can serve as a valuable and inexpensive tool for delineating an air pollution condition. Injury symptoms from fluoridt, sulfur dioxide, photochemical oxidants and other pollutants have been described and can be recognized by experienced observers. Field studies provide a valuable technique for appraising an air pollution problem when diagnosis is not confused by other factors. Careful inspection can avert difficulties arising in diagnosis where similar symptoms are produced by agents other than air pollutants. Several factors must be considered in appraising injury. These include a knowledge of the relative sensitivity of plant species to various pollutants, the syndrome of injury on a number of plants and species, and distribution and geographic relation of affected plants to the suspected source. Background information on cultural, environmental, disease and insect conditions which might be responsible for, or modify, foliar markings or chronic effects in question must also be understood. For some pollutants a chemical analysis of foliage and air may prove helpful. When these factors are studied, the presence, distribution and magnitude of an air pollution situation can be evaluated, thus providing a sensitive criterion of air quality.     

Further Evaluation of Glass Fiber Filters for Sampling Hydrogen Fluoride

Tests were conducted to determine the limitations of glass fiber filters in sampling atmospheric hydrogen fluoride. Filters without latex binder were more efficient collectors than those with the binder. Up to 75 μg F/in.² of filter area was collected by a single filter before the loss reached 5 percent. Two filters, one behind the other, collected over 250 μg F/in.² of filter area before loss through them reached five percent. By controlling the sampling rate and time to avoid exceeding the saturation limit, it is possible to use glass fiber filters for sampling over a wide range of fluoride concentrations.     

The Role of Pressure Drop and Flow Redistribution on Modeling Mercury Control Using Sorbent Injection in Baghouse Filters

Abstract

A mathematical model based on simple cake filtration theory was coupled to a reviously developed two-stage mathematical model for mercury (Hg) removal using powdered activated carbon injection upstream of a bag-house filter. Values of the average permeability of the filter cake and the filter resistance extracted from the model were 4.4× 10^?13 m² and 2.5 ×10^?4 m^?1, respectively. The flow is redistributed during partial cleaning of the filter, with flows higher across the newly cleaned filter section. The calculated average Hg removal efficiency from the baghouse is lower because of the high mass flux of Hg exiting the filter in the newly cleaned section. The model shows that calculated average Hg removal is affected by permeability, filter resistance, fraction of the baghouse cleaned, and cleaning interval.     

Filtration of Airborne Particulates by Gravel Filters: I. Initial Collection Efficiency of a Gravel Layer

An equation derived for initial collection of efficiency E₀ of a gravel bed filter predicts that — ln(1 — E₀) is proportional to the thickness of the gravel layer, to the — 5/3 power of the diameter of uniform gravels, and to the — 2/3 power of the Darcy airflow velocity. The experimental data obtained from NH₄CI fume removal from dry air at room temperature by sieved gravel fractions generally supported the equation, except that the effect of mean gravel size was represented by the —1.43 power of the average diameter.     

Predicting Cutoff Aerodynamic Diameter and Sharpness of Single Round-Nozzle Impactors with a Finite Impaction Plate Diameter

Abstract

This investigation numerically examined the cutoff aerodynamic diameter (da₅₀) and the sharpness (GSD) of the particle collection efficiency curve of impactors with a finite impaction plate diameter. Results revealed that the inertial impactors have a limited cutoff aerodynamic diameter at different air velocities. The extreme value of the cutoff aerodynamic diameter increases with the nozzle diameter (W)/the plate diameter (D_c). The computed da₅₀/D_c values of the impactors increase with W/D_c at various Reynolds numbers (Re) and with the nozzle-toplate distance (S)/D_c when Re is 100. The value of GSD slightly increases with W/D_c for Re of 10 and 100, although the effect of S/D_c on GSD is not evident at various Res. The particle collection efficiency curve of the impactor with a lower Re is less sharp than that with a high Re at various W/D_c and S/D_c values. Statistical equations closely fitted the obtained numerical results for Res of 10–3000. The equations are useful for directly calculating the cutoff aerodynamic diameter and the sharpness of the particle collection efficiency curve for single round-nozzle impactors with a finite impaction D_c.     

Influence of Suspended Clay Minerals and Humic Matter on the Solid Phase Extraction Efficiency of Selected Pesticides from Water

The purpose of this investigation was to determine the influence of humic acids (HA) and Ca-montmorillonite (CaM) on the solid-phase extraction (SPE) efficiency of atrazine, alachlor and α-cypermethrin from water samples at various pH-values. The nature and intensity of binding of the studied pesticides to CaM were determined by X-ray diffraction analysis and termogravimetric analysis (TGA) test. The studied pesticides eluted from discs were analysed by thin-layer chromatography (TLC). The effects of CaM and humic acid were generally pH-dependent and acted independently in extraction efficiency influence. Lower recovery of pesticides was observed at higher pH values when CaM was ≥0.1 g and was attributed to greater dispersion of clay, increased surface area and subsequent adsorption. Concentrations of dissolved organic carbon (DOC) in humic acid had less effect on the extraction efficiency when water was at pH 8 compared to water at pH 2, which was probably due to greater nonpolar interactions of the pesticides to the charge-neutralized humic acid molecule.     

Effectiveness of In-Room Air Filtration and Dilution Ventilation for Tuberculosis Infection Control

Abstract

Tuberculosis (TB) is a public health problem that may pose substantial risks to health care workers and others. TB infection occurs by inhalation of airborne bacteria emitted by persons with active disease. We experimentally evaluated the effectiveness of in-room air filtration systems, specifically portable air filters (PAFs) and ceiling-mounted air filters (CMAFs), in conjunction with dilution ventilation, for controlling TB exposure in high-risk settings. For each experiment, a test aerosol was continuously generated and released into a full-sized room. With the in-room air filter and room ventilation system operating, time-averaged airborne particle concentrations were measured at several points. The effectiveness of in-room air filtration plus ventilation was determined by comparing particle concentrations with and without device operation. The four PAFs and three CMAFs we evaluated reduced room-average particle concentrations, typically by 30% to 90%, relative to a baseline scenario with two air-changes per hour of ventilation (outside air) only. Increasing the rate of air flow recirculating through the filter and/or air flow from the ventilation did not always increase effectiveness. Concentrations were generally higher near the emission source than elsewhere in the room. Both the air flow configuration of the filter and its placement within the room were important, influencing room air flow patterns and the spatial distribution of concentrations. Air filters containing efficient, but non-high efficiency particulate air (HEPA) filter media were as effective as air filters containing HEPA filter media.     

膜生物反应器中新型无纺布膜过滤特性及膜污染特征

通过无纺布和聚偏氟乙烯平板膜组件在相同操作条件下的对比实验,研究无纺布膜的过滤特性。结果表明,2种膜的膜生物反应器COD、氨氮平均去除率均＞90%。过膜压力变化表明在长期运行条件下,无纺布可适于作为膜生物反应器的过滤介质,其过滤机理为膜表面滤饼层形成动态膜,从而增强了膜截留能力。膜污染研究表明,无纺布膜阻力主要来自滤饼层（占总阻力的83.6%）,经清洗后膜通量可恢复至94%。扫描电镜显示膜表面滤饼层较厚,结合膜阻力分析结果认为,该滤饼层对膜污染和可逆性影响较大。对膜表面和膜孔中胞外聚合物（EPS）的红外分析证实,其中含有蛋白质和多糖物质,而且组分分析表明蛋白质是膜污染物EPS中的主要组分,在膜孔中的含量比滤饼层中还高。     

Fibers,Electrostatics, and Filtration: A Review of New Technology

This symposium sponsored by the Fiber Society and the Filtration Society has provided a clear indication that the “black-art” era of filtration has passed or is on its way out. The R & D efforts reviewed here by investigators from diverse disciplines provide evidence that these high efficiency particulate control devices can be made to function not only more consistently at high levels but now with even better control of the fine, health damaging particles. The outstanding improvement in every filtration parameter, reliably attainable by aerosol charging and/or by imposing an electric field on the filter, indicates clearly that fabric filtration has now reached an even higher plateau in particulate control technology.     

Further Effects of Temperature and Pressure on Photochemical Oxidant Production

A procedure is described for producing a sulfur dioxide (SO₂) contaminated atmosphere within a body plethysmograph, exposing man to this atmosphere while maintaining the SO₂ concentration at a given level, and measuring the concentration with less than a oneminute lag time. A syringe is used to introduce incremental volumes of SO₂ limiting the maximum SO₂ concentration in the chamber and assuring safety of the subject. A Titrilog SO₂ analyzer with its rapid response characteristics provides quick measurement of the SO₂ concentration. The body plethysmograph used in this manner serves simultaneously as a pulmonary function measuring device and as an exposure chamber.     

高效堆肥菌种的筛选及在城市污泥堆肥上的应用

分离筛选出了4株猪粪堆肥菌种,初步的分类鉴定表明它们均属于芽孢杆菌属.利用这些菌种制成混合菌剂,并进行城市污泥堆肥对比试验,结果显示,接菌处理在各项堆肥指标上明显优于未接菌的空白处理,自制菌与酵素菌在堆肥过程中具有非常相似的发酵能力,均能加快堆肥的升温速度,提高堆肥的最高温度,加快物料含水率的下降.说明自制菌不但可以应用于猪粪的堆肥发酵,在城市污泥高温堆肥方面也有很好的应用潜力.     

Efficiency of deposition of pesticide droplets on flat cards and spheres

Abstract

The mass flux of a cloud of droplets heading towards a collector can be decomposed into its horizontal and vertical components. While only the vertical mass flux contributes to droplet deposition on a flat card by the mechanism of sedimentation, both flux components contribute to deposition on a sphere by both mechanisms of inertial impaction and sedimentation. Calculated collection efficiencies decrease as wind speed increases for cards but as wind speed increases for spheres, a minimum collection efficiency is reached at a certain wind speed. The average collection efficiencies, as measured in the field trial portion of this study, are highly linearly correlated with wind speed for cards. For spheres, however, no correlation was found between the average collection efficiency and wind speed.