Comparative Testing and Evaluation of Nine Different Air Samplers: End-to-End Sampling Efficiencies as Specific Performance Measurements for Bioaerosol Applications

Accurate exposure assessments are needed to evaluate health hazards caused by airborne microorganisms and require air samplers that efficiently capture representative samples. This highlights the need for samplers with well-defined performance characteristics. While generic aerosol performance measurements are fundamental to evaluate/compare samplers, the added complexity caused by the diversity of microorganisms, especially in combination with cultivation-based analysis methods, may render such measurements inadequate to assess suitability for bioaerosols. Specific performance measurements that take into account the end-to-end sampling process, targeted bioaerosol and analysis method could help guide selection of air samplers.

Nine different samplers (impactors/impingers/cyclones/ electrostatic precipitators/filtration samplers) were subjected to comparative performance testing in this work. Their end-to-end cultivation-based biological sampling efficiencies (BSEs) and PCR-/microscopy-based physical sampling efficiencies (PSEs) relative to a reference sampler (BioSampler) were determined for gram-negative and gram-positive vegetative bacteria, bacterial spores, and viruses.

Significant differences were revealed among the samplers and shown to depend on the bioaerosol's stress–sensitivity and particle size. Samplers employing dry collection had lower BSEs for stress-sensitive bioaerosols than wet collection methods, while nonfilter-based samplers showed reduced PSEs for 1 μm compared to 4 μm bioaerosols. Several samplers were shown to underestimate bioaerosol concentration levels relative to the BioSampler due to having lower sampling efficiencies, although they generally obtained samples that were more concentrated due to having higher concentration factors.

Our work may help increase user awareness about important performance criteria for bioaerosol sampling, which could contribute to methodological harmonization/standardization and result in more reliable exposure assessments for airborne pathogens and other bioaerosols of interest.

Copyright 2014 American Association for Aerosol Research     

What is New in Performance Plastics?

The field of performance plastics is showing remarkable vitality and growth, even though the participants find the price to be high in terms of technical and sales support required, together with high capital investment for plants.

There has been a high degree of proliferation of new products in the form of new polymers, new grades of existing polymers, as well as filled, reinforced, alloyed versions. While this does introduce new degrees of freedom in material selection, it is a source of significant confusion for the design engineers who have to cope with selecting the preferred material from among the many that are available. The choices and data bases are becoming confusing.

Various forms of relatively exotic, aromatic-monomer chemistry are being applied, but the emphasis appears to be on new amorphous polymers.

High-performance requirements exist in virtually all segments of the plastics field; the major end uses are in aerospace, automotive, business machines, electrical/electronics, food packaging, and medical applications.

Foreign presence has strongly increased as European companies have increased imports or have purchased established product lines or business units.

There will be continued pressure on the performance plastics from the lower priced materials which are countering with upgraded, modified, alloyed versions of their own. There is also increased competition between thermoplastics and thermosets as the result of material developments and process refinements.     

Recent Advances in Flame Retardancy of Polymeric Materials (Materials,Applications, Industry Developments,Markets)

The Fifth Annual Conference on Flame Retardancy was held May 24–26, 1994, at the Ramada Plaza Hotel, Stamford, Connecticut, USA. The conference was organized by Business Communications Company, Inc., Norwalk, Connecticut (Company President, Mr. Louis Naturman; Conference Coordinator, Mrs. Sharon D. Faust). New materials (polymers, blends, composites), their applications, industry developments, and markets were considered. Specifically, the most important topics were:

Introduction of new technological achievements and development in the field of flame retardancy (FR)

Review of the current state of science and technology in FR

Review of applications and markets for FR products

Presentation of recent developments in local and global standardization and in testing technology

Discussion of toxicity and environmental issues

Provision of a unique opportunity for newcomers to FR research technology and marketing to become acquainted with the FR field in all its aspects

Discussion of halogen-based and non-halogen-based flame retardant chemicals, syngergism, intumescence, FR mechanisms, modeling, flame parameters, inherently FR polymers, and polymer blends     

Controlling Blown Polyethylene Film Optical Properties

The conventional blown process imparts an inherent haze to the product. The percentage of haze varies with certain process variables:

1. Surface irregularities caused by melt flow phenomena

2. Crystallization behavior

3. Melt drawing phenomena in certain types of polyethylene     

Modeling of nonstationary processes during separation of multicomponent isotope mixtures

The article presents a mathematical model for calculation of nonstationary hydraulic and separation processes in a gas centrifuge (GC) cascade for separation of multicomponent isotope mixtures. The model has been applied to calculate the parameters of nonstationary processes in a GC cascade for separation of krypton, germanium and tungsten isotopes. As a result, the specifics of the excess holdup distribution along the cascade stages has been identified, and variations of the isotope concentrations in a nonstationary process have been revealed. The data obtained show that the proposed mathematical model is able to adequately describe nonstationary hydraulic processes in GC cascades for separation of multicomponent isotope mixtures.

Highlights:

Mathematical model of cascade for separation of multicomponent isotope mixture has been developed.

The model verification has been done.

The isotope transient regularities into cascade during nonstationary processes has been identified.     

Anisokinetic Shrouded Nozzle System for Constant Low-Flow Rate Aerosol Sampling from Turbulent Duct Flow

An anisokinetic shrouded nozzle system was designed for sampling particles at a constant low flow rate from a ventilation duct to an aerodynamic particle sizer (APS). Shrouded anisokinetic nozzles are a means for sampling from a moving airstream with higher particle transmission than with unshrouded isokinetic nozzles. This shrouded nozzle sampling system was evaluated in an experimental ventilation duct system. Aspiration and transport efficiency measurements were made for five particle sizes in the range 1–13 μm at each of three duct air speeds in the range 2.2–8.8 m/s. Under these conditions, the shrouded nozzle system showed improved performance compared to buttonhook isokinetic nozzles, especially for larger particles and higher air speeds. Measured transmission efficiencies through the shrouded nozzle sampling system were generally higher and more reliably predictable than those through buttonhook isokinetic nozzles. Model predictions of transport and aspiration efficiencies of the shrouded nozzle system showed good agreement with measurements over the entire range of experimental conditions. The shrouded nozzle sampling system could be used to measure concentrations in ventilation ducts with an APS for particles in the diameter range 1–13 μm.

Copyright 2014 American Association for Aerosol Research     

Characteristics of traffic-induced fugitive dust from unpaved roads

The characteristics of fugitive dust emitted from vehicles traveling on unpaved dirt roads were measured using a suite of instruments including a real-time fugitive dust sampler. The fugitive dust sampler is formed from a combination of a large particle inlet and an optical particle spectrometer that reports particle sizes from 6 to 75 µm. The large particle inlet permits the sampling of particles up to 75 µm with only a moderate dependence of sampling efficiency on wind-speed. Measurements made with the sampler showed that particles as large as ～50 µm were suspended from vehicular movement on the dirt roads, with the mode of the fugitive dust particle number size distribution ～2 µm, while the mass distribution mode was ～7 µm. A comparison of the fugitive dust sampler measurements with those made using standard PM instruments showed that the conventional instruments have a wind-direction bias that can result in under-sampling of large particles. The current measurements suggest that particles suspended from dirt roadways are of importance for local air quality within the near-road environment.

Copyright © 2017 American Association for Aerosol Research     

Numerical Study of the RespiCon Sampler Performance in the Calm Air

Results of a numerical study of the RespiCon sampler performance in the calm air are presented. The air flow is described by the Navier–Stokes equations of axisymmetric stationary viscous flow of incompressible fluid that are numerically integrated by the computational fluid dynamics (CFD) software FLUENT. The collection efficiencies of RespiCon impactor stages agree quite well with experimental data and curves of the European standards for the thoracic and respirable dust fractions. The aspiration efficiencies derived from the numerical model overestimate the experimental data in the range of particle sizes of 10 μm < d_p < 40 μm; however, they correctly predict the value of maximal size of aspirated particles. A new design of the RespiCon sampler with a higher volume flow rate was developed.

Copyright 2014 American Association for Aerosol Research     

RADIAL FLOW HOLLOW FIBERREVERSE OSMOSIS: EXPERIMENTS AND THEORY

The performance of a hollow fiber reverse osmosis system is studied both theoretically and experimentally. Experiments were carried out for applied pressure ranging from 200 to 400 psig, feed rates varying from 75 to 380 cc/sec and for feed concentrations up to 34,000 ppm of sodium chloride.

A mathematical model is proposed to predict productivity, ?, and product concentration, θ_p. The model involves solving membrane transport equations simultaneously with the hydrodynamic equations. The solubility-diffusion-imperfection, or pore diffusion model, is used to describe solute and solvent transport across the membrane. The axial gradients of shell side concentration, neglected in previous investigations, are taken into account. The differential equations are solved numerically by the 4th Order Runge-Kutta method.

Predicted values of ? and θ_p agree within 8% and 17% respectively, with experimental data over the entire range of operating conditions. However, membrane transport coefficients were found to be concentration dependent.

An approximate analysis shows that the concentration polarization is negligible in present day hollow fiber systems.     

The Photochemical Generation of Ozone : Present State–of–the–Art

This paper reflects an investigation of the feasibility of photochemical generation of ozone by irradiating gases containing oxygen with Hg lamps of the highest performance emitting the 185 nm line. Besides the expected photostationary equilibrium, determining factors for practical yields in ozone generation by the 185 nm wavelength are : the reactor and gas temperature, the reactor geometry, and the gas composition, as well as the pressure.

Further developments are expected in the field of lamp construction and also improvement of reactor geometry. A better knowledge of the aging of the lamps is required, as well as of the photochemical reactions of oxygen in the technologies applied.

Systems presently available are most promising for application on small scale or in areas of public water distribution which have no developed structure.

     

First Year Operation Report of the Corona Discharge Ozone Swimming Pool Water Treatment Systems at the Peck Aquatic Facility,Milwaukee, Wisconsin

The two corona discharge ozone swimming pool water treatment systems installed in the Peck Aquatic Center in Milwaukee, WI now have been in continuous operation since September, 1987. The two pools are part of the Karl Jewish Campus Facility of the Harold and Judy Sampson Campus of the Milwaukee Jewish Community Center.

The operation of these water treatment systems has shown that safe and high quality pool water is obtained reliably and economically. One pool (Main Pool) is of Olympic size, the other (Learner pool) is designed especially for use by children. Both pools utilize a full corona discharge ozone water treatment system. They were the first ozone systems in the U.S. to be built for public pools using the process of ozonation, flocculation, filtration, ozone removal and residual chlorination.

An extensive testing program was initiated in cooperation with the Wisconsin Department of Health. The bacteriological water quality from these swimming pools was in compliance with Wisconsin State Health Regulations and the German DIN Standard 19,643.

The first year of operation of the Peck Aquatic Center has shown that the corona discharge ozone pool water treatment process can:

1) Operate reliably in a public swimming pool environment without the need for highly or special operator qualifications.

2) Produce continuously bacteria- and virus-free pool water without the harmful and unpleasant effects of chlorine.

3) Creates a user constituency group praising and promoting the use of “minimal chlorine swimming” in the community.     

Biological Filtration for Ozone and Chlorine DBP Removal

This paper presents results from a water treatment pilot testing program in Winnipeg, Canada (pop. 650,000) which evaluated a DAF/ozone/deep bed filtration process. As part of the testing program, biological filtration using GAC and anthracite media was assessed for the removal of ozone DBPs and background chlorine DBPs (due to upstream chlorination of the source water). The results were used to evaluate the effectiveness of biological filtration for DBP removal.

High filtration rates were tested in this study. The 2.1m deep filters were run at a hydraulic loading rate (HLR) of 35 m/h with an empty bed contact time (EBCT) of only 3.6 minutes.

The important findings of this work are

?The high-rate biologically active carbon (BAC) filters met the objective of controlling ozone DBPs. These results confirm that high rate, low EBCT filters can provide significant biodegradation. Anthracite biofilters provided significantly less removal of ozone DBPs.

?The high rate BAC filters showed significant reduction of background HAAs. BAC reduced the background HAAs to below the long-term target of 30 μg/L. Anthracite biofilters did not exhibit HAA removal.

?Biological filtration with either media was ineffective for background THM removal. The long-term target of 40 μg/L could not be achieved without GAC adsorption.     

Dependence of CPC cut-off diameter on particle morphology and other factors

In this investigation, we summarize performance parameters of 24 TSI CPCs model 3772 and 9 TSI CPCs model 3790 determined at the World Calibration Aerosol Centre Physics hosted by the Leibniz Institute for Tropospheric Research. Model 3790 CPCs are basically identical to model 3772 laminar continuous flow type butanol-based CPCs with a modified temperature difference between saturator and condenser. The average 50% detection efficiency for silver particles for 3772 and 3790 instruments was found to be 7.52 ± 0.04 nm and 24.34 ± 0.29 nm (average mobility diameter ± standard deviation), respectively. Small changes of the temperature difference between saturator and condenser cause larger shifts of the 50% detection efficiencies of 3790 CPCs compared to 3772 CPCs. In addition to the known calibration material dependence of the 50% detection efficiencies of 3790 CPCs, we found a dependence on the morphology of the particles used for calibration. In our experiments more spherical particles shifted the 50% detection efficiencies towards larger mobility diameters.

Copyright © 2016 American Association for Aerosol Research     

Diffusion Sampler for Measurement of Acidic Ultrafine Particles in the Atmosphere

The adverse health effect of acidic ultrafine particles (AUFPs) has been widely recognized in scientific societies. These particles mainly deposit on the surface by diffusion and so far there is no mature method for the measurement of airborne AUFPs. The purpose of this study was to develop a diffusion sampler (DS) with iron nanofilm detectors to effectively measure the number concentration and size distribution of airborne AUFPs in indoor and outdoor environments. The developed DS was made of stainless steel with a flat and rectangular channel with 1.0 mm height, 50 mm width, and 500 mm length. The iron nanofilm detectors were deployed on rectangular recesses inside the sampler at three different locations along the length of the channel to collect the ultrafine particles. The exposed detectors were then scanned using an atomic force microscope (AFM) to numerate and distinguish the AUFPs from the nonacidic UFPs. Prior to sampling, the semi-empirical equations for the diffusive deposition efficiency of particles at the different detector locations in the sampler were obtained on the basis of theoretical diffusive mechanism and modified by the experimental data using polystyrene latex (PSL) standard particles. After calibration, the DS + AFM method and a commercially available online measurement system, i.e., scanning mobility particle sizer (SMPS) incorporated with a condensation particle counter (CPC), were simultaneously used in a 4-week field measurement. Both methods showed very good agreement in terms of total particle number concentration and size distribution. The results indicate that the diffusion sampler is effective for the quantification of ambient acidic ultrafine particles.

Copyright 2014 American Association for Aerosol Research     

A RELATIONSHIP BETWEEN CHEMICAL STRUCTURE AND THE CRITICAL TEMPERATURE

Six distillation column models have been used in studies of the usefulness of the Inverse Nyquist Array (INA) method for design of dual composition control for distillation. Five of the column models are experimental, one describing an industrial column, the others four pilot plants. One column model is obtained by modeling from first principles.

The control strategies investigated and compared are multiloop SISO, 2-way decoupling and l-way decoupling. The control variables are the standard ones, i.e. reflux flow and boilup.

In most of the cases INA has been found to be a useful tool for design of the loops and for comparison of the different control approaches. INA has also been found to be useful for simultaneous tuning of the decouplers and the feedback controllers.

For 2-way decoupling the criterion to minimize interaction at the critical frequency for each primary feedback loop has been found useful in most, but not all, cases. The scheme can be designed by pure gains in the decouplers and there is no reason to introduce dynamics into the decouplers—the systems studied are already sufficiently rich in dynamics.

INA has been found to be a suitable vehicle for the choice between the two possible l-way decoupling schemes.

With the design approach taken, l-way decoupling has been found to provide considerably better control quality than 2-way decoupling in two of the six systems, the differences in control quality being small in the other cases.

The effect of model mismatching on the results, caused e.g. by process nonlinearities, is discussed and simple rules to decrease the parameter sensitivity for 2-way decoupling schemes are given. When model mismatching is considered, the advantage of l-way decoupling over 2-way decoupling seems to increase.

One deficiency of the INA design as used in this paper is that it does not single out the design which is to be preferred on the grounds of robustness.     

Removal of Aromatic Nitro Compounds from Water by Ozonation

Experimental studies were carried out on the removal of five species of aromatic nitro hydrocarbons by ozonation. Ultraviolet spectrograms with distinct absorption peaks were plotted for each of them. It has been found that the absorbances of aqueous solutions containing the single compounds mentioned above increase to different extents at the wave lengths ranging from 200 to 230 nanometers with increase of ozone dosages. This is ascribed to the nitrite ions splitting out of the benzene rings and being further oxidized to nitrate ions by ozonation.

It has been indicated that the removal of the five species of aromatic nitro compounds by ozonation can well be expressed mathematically by first order reaction equations. Besides, the reaction constants and half-life periods for various species of the tested nitro compounds were calculated at different temperatures and pH.

An ozonation effect index (OI) was developed in the study to express the degree of degradation of substrates by ozonation, by means of which the five aromatic nitro hydrocarbons were compared with each other and finally ranked in the following order from greatest to smallest degrees of degradation:

p-nitroaniline > nitrobenzene > p-dinitrobenzene > p-nitrotoluene > m-dinitrobenzene

It has also found that the CODm/M ratio increases with ozone doses. This means that some easily degradable intermediates are produced, and increase in concentration with increase of ozone dose in the ozonation process.

The mechanisms of removing the five aromatic nitro hydrocarbons are discussed from the viewpoint of orienting effects of substituent groups on the aromatic rings.     

Large Particle Penetration During PM10 Sampling

The objective of the present study was to characterize the performance of a federal reference method (FRM) PM₁₀ size-selective inlet using analysis methods designed to minimize uncertainty in measured sampling efficiencies for large particles such as those most often emitted from agricultural operations. The performance of an FRM PM₁₀ inlet was characterized in a wind tunnel at a wind speed of 8 km/h. Data were also collected for 20 and 25 μm particles at wind speeds of 2 and 24 km/h. Results of the present sampler evaluation compared well with those of previous studies for a similar inlet near the cutpoint, and the sampler passed the criteria required for certification as a FRM sampler when tested at 8 km/h. Sampling effectiveness values for particles with nominal diameters of 20 and 25 μm exceeded 3% for 8 and 24 km/h wind speeds in the present study and were statistically higher than both the “ideal” PM₁₀ sampler (as defined in 40 CFR 53) and the ISO (1995) standard definition of thoracic particles (p < 0.05) for 25 μm particles leading to the potential for significant sampling bias relative to the “ideal” PM₁₀ sampler when measuring large aerosols.

Copyright 2014 American Association for Aerosol Research     

Hydroxyl Radical Oxidation Processes For The Removal Of Triazine From Natural Water

The purpose of this study was to point out processes that can provide triazine oxidation via hydroxyl radical production in a water treatment line. We focus our attention on:

- oxido-flocculation, using Fe²⁺, H₂O₂

- inter-oxidation, using O₃, H₂O₂ and eventually an heterogeneous catalyst.

- disinfection, using UV, O₃ and H₂O₂ combinations.

Results show that triazines can be removed by all these processes with different efficiencies. At full scale, the O₃/H₂O₂ process presents the best performances from an economical and technical point of view.     

STAGEWISE COUNTERCURRENT WASHING OF CHEMICAL PULP: A MULTICOMPONENT MASS TRANSFER ANALYSIS

The washing of chemical pulp in a countercurrent cascade of rotary vacuum filters is described in terms of a model of the multicomponent mass transfer process occurring in the wash zone of each stage. The classical Norden Efficiency Factor method is extended to the multicomponent case. Relationships among the system loss ratios, wash and recycle ratios, and the number of stages are developed.

In the paper industry, chemical pulps are washed to recover cooking chemicals and to obtain satisfactory quality for subsequent processing. With the present increased emphasis on pulp mill closure, the industry is attempting to reduce losses from brown stock washing systems. This leads to the need for improved engineering models of the washing operation for either design or control purposes.

Countercurrent washing, either stagewise or continuous, is generally used to obtain good recoveries at relatively low dilution ratios. In the stage-wise mode, rotary vacuum filters are commonly employed with reslurrying of the stock between stages.

The important chemical species in this separation process are sodium and lignin. In addition, other attributes, such as color and BOD₅, are of increasing importance with respect to the performance of pulp washing systems. Aggregate characteristics, such as total dissolved solids (TDS) are also of concern.

This paper considers stagewise countercurrent washing of pulp in a cascade of rotary vacuum filters. A model of the multicomponent mass transfer process occurring in the wash zone of each stage is developed and incorporated into the system material balances to produce results useful for either design or performance calculations.