filtration of bioaerosols using fibrous air filter media.

by:Booguan     2020-09-01
Effects of Air microorganisms on indoor air qualityIAQ)
And people\'s health.
In the early twenties
In the first century, hundreds of people died of SARS.
Severe acute respiratory syndrome
Around the world, H5N1 bird flu has brought disasters to both humans and humans.
Flu may break tomorrow.
Therefore, it is necessary to take certain precautions to protect people from the epidemic.
Filtration is one of the main means to control indoor air quality, it can prevent the invasion and spread of microorganisms in indoor environment.
Filtration of particles has been widely studied, but there are still very few filtration of microorganisms
Understanding phenomena (Washam 1966).
With a further understanding of the unique properties of microorganisms in the submicroscale range, they have received increasing attention.
Test plan proposed in ASHRAE RP
Final report 909 (
Karin and Hanley 1996)
An integrated system for the evaluation of air filters for antimicrobial agents is described and a test scheme supported by strict quality assurance practices is proposed, but there is no model for the penetration of standard testrig and biological aerosol
Experimental devices and test schemes were developed to measure the efficiency of surgical masks and respirator using microbial aerosol challenge (Brosseau et al. 1993). M.
Chelonae biological aerosol, phthalate (DOP)
, And polystyrene latex (PSL)
It is used in the above system and the results are compared.
The filtration collection of Dop is linearly related to the filtration collection of mycobacteria and PSL spherical aerosol ([r. sup. 2]= 0. 99)
It is proved that inert aerosol can predict the collection of biological aerosol (Chen et al. 1994).
Also created a certification system for the filtration efficiency of the unloaded N95 respirator (an N-
Series filters with at least 95% efficiency).
Reporting efficiency of respirator compared to dust/fog (DM)
Dust/smoke/fog (DFM)
Fight against bacteria similar in size and shape to M. Tuberculosis.
The results show that the filtration efficiency is 99 in all cases. 5% or higher (Qian et al. 1998).
Some analyses have shown that existing filtration models can be used to predict the filtration efficiency of bacteria and spores at the logarithmic mean diameter, rather than at the arithmetic mean diameter (Kowalskiet al. 1999).
By solving the key aspects of filter size and predicting the performance of the filter on air microorganisms, the filtration performance of air microorganisms was studied (
Kowalski, Bahnfleth 2002).
However, the current theoretical research on biological aerosol filtration is not enough, and most models cannot accurately predict the filtration performance of filter media.
On the other hand, although scientists have made great efforts in the study of biological aerosol filtration, there is no general test of the biological product efficiency test that rigis is available or proposed for filter media.
The air filtration media investigated in previous studies did not span the range of air filters from low to high efficiency particles (HEPA)media.
The filter media selected in this survey cover all the media of fiberglass commonly used in central air conditioning
Condition system.
Even if the intended application involves biological air filtration, such as the food industry, pharmaceutical and hospital, commercial filters can only be marked by their non-biological efficiency.
There is no international standard for efficiency testing of fiber filtration media for biological aerosol and other challenge particles.
To fill this gap, a test system was designed and the efficiency of several biological aerosol filter media samples was determined.
The biological aerosol filtration efficiency of specific fiber media depends on the aerosol properties of microorganisms.
The newly discovered microbial viscosity of charleira (S. marcescens)
It\'s a near-pole-
Shaped bacteria whose colonies are bright red at below a certain temperature, so it is easy to distinguish as microbial markers from other markers.
System design of experimental test bench (Figure 1)
Designed to provide a stable and repeatable biological aerosol with a constant concentration during the sampling period.
The drilling rig controls the sampling flow and adapts to various sampling methods.
The system consists of three parts: the Bioaerosol generation part, the test filter part including the sample installation, and the sampling part.
Collison nebulizers are used for the generation of non-biological aerosol and biological aerosol particles, while optical particle counters (OPC)
The andhuaxin sampler is the detector used in the sampling area.
Biological Aerosol is passed in 6-
Jet Collision nebulizer with pressure 0. 05 MPa (7. 25 psi).
Record the airflow rate and pressure through the rotor flowmeter and pressure gauge. The high-
Concentrated biological aerosol in Collison nebulizer is mixed with dry filtered air in the mixing chamber, resulting in diluted and stable biological aerosol.
The concentration of [remains stable]+ or -]
10%, does not change with the change of air flow.
Pumps used to produce aerosol and dilute air maintain experimental devices under positive pressure to prevent microorganisms from entering the system in the ambient background. [
Figure 1 slightly]
Test filter media installation Assembly designed according to en1822-
3 Keep the filter medium and the internal system closed (CEN 1998).
It is driven by compressed air from the laboratory (
No description in figure 1.
In this setting, the effective filtering area exposed is [10. sup. 4][mm. sup. 2](15. 5 [in. sup. 2])
The speed of the filter media surface is 0. 053 m/s (0. 17 ft/s)
When the system air volume is 32 L/min (1. 13 cfm).
Sampling bacteria and non-biological particles with Andersen sampler and OPC from upstream and downstream sampling locations, respectively.
OPC for particle counting is the MetOne A2400 particle counter with 6 particle size channels (0. 3, 0. 5, 0. 7, 1. 0, 2. 0, 5. 0 [micro]m)
The sample flow rate is 28. 3 L/min (1 cfm).
During the sampling of the HEPA filter media, the dilution (
No description in figure 1)
Used to test particles upstream.
Measure the pressure drop of filter media with pressure gauge. A six-
Stage Andersen samples were used for biological aerosol sampling.
It operates under rated airflow 28. 3 L/min (1 cfm).
Under these experimental conditions, the flow of the sampling section is turbulent.
Suction theory predicts diffusion and deposition loss of particles with aerodynamic diameter up to about 1 [micro]
M has no significant effect on sampling efficiency (Andersen 1958).
In contrast, inertial collisions can be important and need attention in the design of the sampling line.
The sampling line with a large radius of curvature will minimize this loss.
Therefore, a sharp bend is avoided in the system (
Cheng and Wang 1981).
After sampling, the Microorganisms cultured on the nutrient medium were incubated at the appropriate temperature for 24 hours and then positive-hole method.
In order to form the efficiency of the filter medium, the Bioaerosol concentration upstream and downstream is calculated using Equation 1: C (cfu/[m. sup. 3])= [[N(cfu)x1000]/[t(min)x 28. 3(L/min)]](1)
C = the concentration of biological aerosol N = therefore, S.
The Marcescens colonies are bright red and are easily distinguished from the detected bacterial colonies. Although S.
Sticky bacteria have been found to have a pathogenic effect on some people, so it is no longer recommended to track bacterial movements in schools, and as mentioned above, it is used for these experiments because appropriate safeguards have been implemented, isolate the interior of the system from the laboratory air. [
Figure 2:
The indicated bacteria used in the experiment were cultured for at least five generations to maintain vitality.
According to ASTMStandard F2101-01 (ASTM 2001), a high-
The concentration mixture incubated in the orbital shaker for 48 hours should be diluted to about 5 x [10. sup. 5]cfu/mL (8. 20 x [10. sup. 6]cfu/[in. sup. 3]).
It is made with sterilized protein powder water to provide trace nutrients that maintain the vitality of bacteria in the solution. Amodified six-
Spray collision nebulizers atomize bacterial suspended matter into a multi-dispersed aerosol.
The working pressure of the nebulizer is about 0. 05 MPa (7. 25 psi)
The corresponding traffic is about 6. 67 L/min (0. 236 cfm)
The aerosol production rate is 0. 1 mL/min(3. 53 x [10. sup. -6]cfm).
Since about 95% of the drops contain only one bacteria and the drops quickly evaporate in a glass container, the size of the particles is close to the size of a single bacteria.
Bacterial particles are mainly in 4-6 (0. 65-3. 3 [micro]m)
Only a small fraction of the particles hit and stayed in the first three stages.
Aerodynamic diameter of Ecoli and S.
The viscosity is about a month. 87[micro]m (
Chen, Li 2005and 1. 14 [micro]m (Kowalski et al. 1999)
, Respectively, consistent with the cutting size of the above sample feeder.
For each measurement, the system is allowed to stabilize for at least five minutes before each sampling run.
Usually, the sampling time is from 20-
30 seconds upstream sampling, 5-
Sample downstream for 10 minutes.
During these duration, the plates were not overloaded with sampled bacteria.
Four kinds of fiber air filtration media (A, B, C, and D)
Made in China was used in the experiment.
Detailed specifications are listed in Table 1.
The classification of filter media is based on EN779 and EN1882 (CEN 2002; CEN 1998).
Type A and Type B are medium-effective filter media for the removal of more than 1 grain [micro]
M, while Type C and D are HEPA media that remove small particles greater than 0. 3 [micro]m.
The classification of HEPA filters is based on the filtration efficiency at the most penetrating particle size (MPPS).
Figure 3 shows their SEM images.
Since these four fiberglass filter media are usually used in the air
Air conditioning system, hope that the experimental results are useful for ordinary air conditioning system
Treatment application. [
Figure 3 slightly]
Results and Discussion Four filter media were tested at system airflow rates of 32 L/min at 10, 15, 20 and 25 (0. 35, 0. 53, 0. 71, and 0. 88 for 1. 13cfm)
Artificial bacterial aerosol and inert aerosol (e. g. , DOP).
For analysis, the efficiency of granularity ratio is compared.
In the experiment, the upstream and downstream sampling time of biological aerosol filtration was 30 seconds and 5 minutes respectively, while the sampling time of DOP filtration was 1 minute and the sampling flow rate was 2. 83 L/min (0. 1 cfm)
Including upstream and downstream.
At the media surface velocity 0, the average particle count efficiency of the filter medium with a doping aerosol. 053 m/s (0. 174 ft/s)(
Air Volume 32 L/min [1. 13 cfm])
As shown in Table 2.
The filtration speed of HEPA filters in typical commercial devices for biological aerosol filtration efficiency is about 0. 53 m/s (1. 74 ft/s)(CEN 1998; IEST 2005).
In order to minimize the error of test speed, four filter media were tested with the same media speed 0. 53 m/s (1. 74 ft/s)(
[Air flow speed 32 L/min]1. 13 cfm])with E. coli and S.
Marcescensbioaerosols.
Efficiency is shown in Tables 3 and 4.
Each efficiency noted is an average of three measurements under the same conditions.
Although more replication is preferred, due to time instability ([+ or -]10%)
In the bio-air concentration, the measurement needs to be completed within 30 minutes.
From the above test results, the two test Bio-aerosol provide a similar filtration efficiency trend for each filter medium tested.
The efficiency of samples A and B for biological aerosol is relatively high.
This means that the medium effect air filter is the right device to remove biological particles from the airProcessing Unit (AHUs).
Both C and d are efficient in removing biological products from the air, close to 100%.
All efficiency measured with E
E. Coli is more than S.
Especially for HEPA media C and D.
In the measurement, bacteria from the ambient air of the background, their colonies are similar to E.
E. Coli can easily collect and count asE.
Causing an error.
This is more serious than the impact of upstream sampling on downstream sampling, so the measurement efficiency is lower, especially for more efficient samples.
For S, the experimental removal efficiency of media C and D is 100%.
The error with less test results is S for both viscosity and day.
Marcescens is a good microbial marker for environmental background bacteria.
Biological Aerosol removal efficiency at 32 L/min (1. 13cfm)
For both c and D are 100%, they are considered higher at lower flow rates.
So measured at 10, 15, 20 and 25 liters/min (0. 35, 0. 53, 0. 71, and 0. 88cfm)
Made for samples A and B only.
Average removal results.
As shown in Table 5.
Table 5 shows that the efficiency of the two filter media is 80%-85% and 97. 5%-99.
5% respectively;
However, there is no significant variation between efficiency and airflow rate.
Small changes are due to two reasons.
First, the aerodynamic diameter of the two microorganisms is 0. 87 [micro]m and 1. 14 [micro]m.
Diffusion is not the main filtering mechanism for these sizes.
Therefore, the settling time of particles has little effect on the removal of particles with the change of wind speed.
Secondly, although the main filtering mechanism of particles in this range is inertia collision, the speed is low ([
Less than or equal to]0. 0533 m/s [[
Less than or equal to]0. 175 ft/s])
As pointed out in this study, the rebound of particles is not large (Phillips et al. 1996)
So the momentum of the bacterial particles is not very obvious.
Due to these reasons and the presence of errors, there is little change in filter efficiency.
Comparison of biological aerosol and DOP filter bacterial particles is mainly collected in 4-stage6(0. 65-3. 3[micro]m)
The aerodynamic diameter of the Anderson sampler because of two E. coli and S.
Adhesion is about nuclear power sources in space 【micro]m.
With the addition of DOP and OPC, the particle count is from 0. 5-2. 0[micro]
M is used to compare with the concentration of biological aerosol because their geometric uniform diameter is 1 [micro]m.
Using a theoretical model (
Dahani Yala and Liu, 1980b)
Predict filter efficiency. [eta]= 1. 6[([1-c]/[Ku]). sup. [1/3]]P[e. sup. [-2/3]][C. sub. D]+0. 6([1-c]/[Ku])([R. sup. 2]/[1 + R])[C. sub. R](2)[C. sub. D]= 1 + 0. 388Kn[([1-c]/[Ku]Pe). sup. [1/3]](3)[C. sub. R]= 1 + [[1. 966Kn]/R](4)
Therefore, other methods, such as sterilization, may be required in addition to filtration.
Conclusion a test platform was developed for testing filtration media with biological and non-biological aerosol challenges.
The test system includes a generator and a sampling device.
The biological air removal efficiency of different types of filter media can be marked by a test system.
Two microbial markers were used in the test to clarify the effects of ambient background microorganisms and to distinguish the factors affecting filtration efficiency.
The efficiency trend of the two microbial aerosol is similar, which indicates that the test data are reliable.
However, the filtering efficiency of E.
The biological aerosol of E. Coli is lower than that of ofS. marcescens.
The reason for this may be an error in calculating E.
When background environment microorganisms from the air have the same colony appearance, E. Coli colonies. Therefore, S.
It is recommended in filtration tests for the use of sticky bacteria because it has a great advantage in distinguishing target colonies from background microorganisms.
The results show that the efficiency of biological aerosol is higher than that of DOP and theoretical efficiency.
The results also show that the medium-effect air filter is suitable for filtration of biological particles AHUs.
The F8 mid-effect air filter is the best option to remove most biological aerosol.
The monotonous relationship between the high efficiency of DOP and the high efficiency of biological aerosol indicates the filtration efficiency measured with 1 [DOP particles]micro]
M may help to predict the removal efficiency of biological aerosol for filtration media.
We would like to express our thanks for the funding of China\'s National Key Technology R & D program.
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Dr. Liu Junjie, Dr. Han Jianqi of Ruiying complete Peng Li Guiyuan, won the doctor in February 22, 2008;
Liu Junjie, who was admitted in May 27, 2009, is an associate professor in architectural environmental engineering at the School of Environmental Science and Technology of Tianjin University. Ruiyingqi, Li quanpeng, Han Guiyuan, andJiancheng Qi is a researcher and deputy director of the National Conservation Engineering Center in Tianjin, China.
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