A case study of air pollution emissions from a print shop in
Chiang Kham, Phayao, Thailand

Objective

To determine whether a print shop in
Chiang Kham, Phayao, Thailand poses a threat to human health in the surrounding
community due to air polluting emissions.

Introduction

Air pollution refers to the presence
of toxic chemicals or compounds in the air at levels that may cause detrimental
changes to the quality of life. Air pollution is a serious environmental
problem that confronts today’s civilization. The major contributors to air
pollution are human activities such as improper industrial waste management, mining,
agriculture and construction but also natural processes such as volcanic
eruptions also release toxic gases into the atmosphere. Different types of air
pollution include radiation and chemicals. The chemical compounds that lower
air quality may exist in two forms;

·        
Gaseous form and

·        
Solid form (particulate matter suspended in air)

The chemical pollutants can be
reactive or non-reactive with surrounding air. An example of non-reactive
chemical pollutant includes volatile organic compounds (VOCs).

Volatile Organic
Compounds (VOCs) are organic compounds which have boiling points in the range
of 240 to 260 degrees centigrade (WHO). In recent years, Thailand is faced with
environmental problems due to the VOCs, therefore, taking appropriate measures
are crucial. The two characteristic toxic qualities of the VOCs include being
the precursor to particulate and oxidants derived from photochemical reactions
and the harmful nature of their inhalation. Therefore, scientific data gathered
by monitoring the emissions is necessary for the development of measures
against VOCs as well as establishing environmental emission standards. This case
study focuses on the specific volatile organic compound, glycerol, and a
constituent of printing ink.

Figure
1: Glycerol
structure

Gaussian emission model is used to
measure the maximum ground level emission concentration of air pollutant. A
point source is considered from where the air pollutant is emitted. The
concentration of air pollutant estimated by the model should be compared with
the international standard and immediate mitigation measures taken to eliminate
or reduce the concentration of air pollutants if the set limit is exceeded. In
addition, the model can be used as an environmental analysis technique. VOCs
have detrimental effects on human health at high concentrations.

The concentration at a given point
is;

C (x,y,z) = (Q/u?d y d z
) e{(-y2/2dy2)}e{(-z2/2dz2)}……………………………(1)

C (xyz) – concentration of emission
at point (xyz) in u g /m 3

Q- Emission rate in micrograms per
seconds

dy – horizontal
dispersion of emission in meters

dz – vertical dispersion
of emission in meters

u – Average wind speed at stack
height in meters per seconds

H – Effective stack height in meters

H = ?h + h

?h – plume rise in meters

h – Physical stack height in meters

d – H/?2 for neutral atmosphere
conditions

Therefore, the concentration of
emission is equal to emission rate divide by the wind speed multiplied by
exponential functions.

Emission rate   (lb/hr) = Emission factor × Maximum capacity
(units/hr)

Calculations

A print shop in Chiang Kham, Phayao,
Thailand is used as a case study to determine whether it poses a threat to
human health in the surrounding community due to air pollution emissions. A
Gaussian emission model can be used to estimate emissions, conduct dispersion
modeling, and recommend pollution control technologies.

Part
one; Emission estimates

The shop prints advertising
material, mainly vinyl sheet. Estimate the emissions of glycerol in µg/sec. 2-6
gallons per month is used for each of 4 colors of ink. As a worst case, assume
that 6 gallons per month of each color is used and that the percent glycerol is
the maximum listed in the MSDS sheet for each color. The shop opens from 8:30 –
18:00, six days a week.

Emission rate = (Emission factor
(EF) × activity (A) × (1-control)) / Total emissions (TE)

Emission estimates = mass of
glycerol / Total time of emission

On the MSDS sheets, the percent for
the components of the inks are by weight. To determine the volume of glycerol
used, you’ll need to determine its percent by VOLUME (and then multiply by the
6 gallons per month for total volume used for each color).

 Convert the weight percent to volume percent
as follows:

Assuming that 100 g of the ink
solution is available and using the weight percent given on the MSDS datasheet,
the weight (g) of each of the four ink components (dye, glycerol,
DL-hexane-1,2-diol, and water) can be determined as follows; 

The weight of each component is
divided by its density to determine volume. Densities of the ink components;

 DL-hexane-1, 2-diol: 0.951 g/mL 

Glycerol: 1.26 g/mL

Dye: 1.31 g/mL (value for a blue
disperse dye. The value applies to all dyes)

Water 1 g/mL

Density = mass (%weight)/volume

Hence, volume = mass
(%weight)/density

The volume percent of each component
is determined by dividing its volume by the sum of the volumes of the four
components.

The imperial (UK) gallons is equal
to 4.54609 liters

If 1000ml = 1 litre

Therefore, 1 UK gallon = 4546.09 ml

Converting 6gallons of each of the
color components to milliliters (ml);

6 gallons = (6 × 4546.09) ml

                 = 27276.54ml

Using the density equation;

Mass of color component = density ×
volume

Density of dye (each color) =
1.31g/ml and density of glycerol = 1.26g/ml

Therefore, mass = 1.31g/ml ×
27276.54ml

                               = 35732.26g of
each dye per month

Amount of glycerol in each color
component is calculated below. The MSDS data sheet provided provides the
percent of glycerol in each color component of the ink. Glycerol is a volatile
liquid and hence is emitted into the air causing pollution. Glycerol is an
example of non- reactive air pollutant.

Table
1: Percent weight of
color components in printing ink

Ink
color component

Composition
(% weight)

Black

20-25

Cyan

25-33

Magenta

25-33

Yellow

28-35

 

Percent of glycerol in black ink =
25%

Therefore, amount in black ink =
0.25 × 35732.26 g at

                                                         
= 8933.06g wt glycerol

Percent of glycerol in cyan ink =
33%

Therefore, amount of glycerol in
cyan ink = 0.33 × 35732.26 g at

                                                                    
       = 11791.64g at glycerol

Percent of glycerol in magenta ink =
33%

Therefore, amount of glycerol in
magenta = 0.33 × 35732.26 g at

                                                                            
= 11791.64g wt glycerol

Percent of glycerol in yellow ink =
35%

Therefore, amount of glycerol =
0.35 × 35732.26 g wt

                                                      
= 12506.29g wt glycerol

The total emission of glycerol can
be found from the summation of emissions from individual colors present in ink.

Total emissions = (8933.06 +
11791.64 + 11791.64 + 12506.29) g wt glycerol per month

Therefore, total emissions =
45022.63 g wt glycerol per month

Time of emissions = 9.5 × 3600 × 6
× = 820800 seconds

Glycerol emissions estimates = mass
of glycerol in the four colors /total time

Emission estimates = (45022.63 ×10 6)/820800
ug/s

                                    = 5.4 × 10 4
ug/s

Part
two: Dispersion modeling

A spreadsheet is used to determine
glycerol concentration downwind from the print shop using the provided
information below;

The printing room dimensions; 7m, 5m
and 2.7m height. The printing emissions escape passively through the windows
around the room. There is no plume rise due to buoyancy that is there is no
combustion source to elevate temperatures in the room or momentum (that is no
fan).Glycerol from the printing ink is volatile and escapes filling the
printing room before escaping passively through the windows. Therefore volume
to be considered is equal to the volume of the room which is to be occupied by
volatile glycerol.

Volume in consideration = (7 × 5 ×
2.7m 3

 Therefore, volume = 94.5 m 3

The concentration of
glycerol can be determined from the rate of emission from the source (Q), the
prevailing wind speed (U) and direction (x) and the height of the center-line
of the plume above ground (H), at any point (x,y,z).

Equation (1) is applied;

Cmax = (Q/U?d y
d z) exp ((-1/2) × (H 2 /d z 2  ))

U – Wind speed (m/s)

The wind speed is given as 1m/s

Emission rate = 5.4 × 10 4 ug/s
and ? = 3.142

Correct calculation of glycerol
emission depends on the calculation of d y and d y   and d z values. When the
point source is elevated, an approximate value can be determined from below
formulas;

d y = (I y ×
x) and also d z = (I y × x)

Where I y and I z are
wind speed fluctuations in the x and y directions respectively. Under neutral
conditions, I y and I z approximate values is obtained;

I y = (0.88/ (ln (Hs
/Z) – 1)) and

I z = (0.50/ (ln (Hs/Z –
1))

Hs= 1.8m (breathing height)

Where; Hs is
the release height, and z is the aerodynamic roughness representing different
topographic ground conditions.

Glycerol vapors fills the room then
starts to escape through the windows acting as a point source. The volume of
glycerol is 94.5m 3 (that is the volume of glycerol is equal to the
volume of the room).

The ground level concentration of
glycerol is required and therefore, z=0. Equation (1) reduces to;

C (x, y, 0) = {Q/u?dydz}
e{(y^2/2dy^2)}e{(-H2/2dy^2)}

Maximum concentration occurs when

dz = H/?2

Assuming that there is maximum
concentration and H = 2.7m, dz can be calculated.

dz = (2.7/?2)

dz = 1.9

The value of dz can be substituted
in the equation dz = Iz × 8. Rearranging the equation, Iz = dz ÷8 = 1.9 ÷ 8

                  Iz = 0.23

The zo value can be obtained by
substituting Iz value in the equation;

Iz = {(0.5/ (ln Hs/Z) – 1}

Z = 0.07

dy can be calculated from zo value

Iy = (0.88/(ln 1.8/0.07) – 1)

Iy = 0.39 and dz = 3.12

C (x, y, 0) = {5.4 × 10 4 /1
× 3.142 ×3.12 × 1.9} e (-5/2 × 3.12 2) (-2.7 2 /2 ×
1.9^2)

 Maximum concentration of glycerol = 8.6 × 10 -1
ug

Part
three; Recommended technologies

From the worksheet, the emission
concentration of glycerol (ECG) is. The emitted glycerol exceeds the
recommended emission concentration (REC), and hence there is for emission
reduction using the appropriate available technology.

% emission = (ECR/REC)
×100…………………………………………. (4)

Percent emission reduction = %E –
%SD

Where, %SD – standard emission

A decision-making matrix can be used
to help in choosing the appropriate technology (for example incinerator,
adsorbed or bio-filter in this case). Parameters to be considered in
decision-making for the above technologies include;

·        
removal efficiency,

·        
appropriateness for the pollutants to be controlled,

·        
capital and operating costs (including pressure drop and
other operating expenses),

·        
suitability for the gas stream temperature and relative
humidity (25°C, 20% RH),

·        
Space required, and any other appropriate factors.

Table
2: Decision-making matrix

Parameter

Incinerator

Adsorber

Bio-filter

Efficiency
%

80-90

95-99

60-75

Suitability

Suitable

Suitable

Suitable

Initial
capital

High

High

Low

Costs
$cfm

10-35

15-90
for recuperative and 20-150 for regenerative

15-75

Space
required

Large

Medium

Variable

Relative
humidity

Low

Medium

High

Gas
stream appropriateness

appropriate

Appropriate

Appropriate

 

According to decision-making matrix
above, bio-filter is the best emission reduction technique. This technique
eliminates gaseous emissions and low concentration volatile organic compounds
(VOCs). The process is known as biofiltration. Bio-filters constitute a box
whose size can be as small as one cubic yard. In bio-filters, microorganisms
are brought into contact with pollutants contained in the air stream. Filters
on the inside acts as the breeding ground for the microorganisms that live in a
thin layer of moisture known as a biofilm. Biofilm surrounds the particles
which make up the filter media.

The contaminants are
adsorbed and metabolized by the microbes. The clean air escapes into the
atmosphere. Most biofilters today can filter odor as well as VOCs with
efficiencies higher than 90%. The biofilter can filter out the low
concentration of pollutants with concentrations of (<1000 ppm). Bio-filter design parameters Space A simple biofiltration unit can handle approximately 30ft3/min. Biofilter can be designed to occupy a small or large space depending on the volume of air to be treated. Maintenance The maintenance of this system would require weekly site visits during initial stages of operations. The frequency of site visits reduces with time hence minimizing on operation and maintenance costs. Residence Time The amount of time the microbes are in contact with the contaminated air stream is known as residence time defined by Void Volume/Volumetric Flow Rate. Higher efficiency is produced by long residence time. However, residence time should be minimized to accommodate larger flow rates. Humidity The humidity of gas stream maintains the moisture content of the biofilter media. Gas streams introduced to the biofiltration system are usually pumped through a humidifier before entering the biofilter. The gas stream relative humidity should be greater than 95%. Pressure Drop Should be minimized. An increase in pressure drop requires more blower power and can result in air channeling through the media. Pressure drop is directly related to the moisture content in the media and the media pore size. An Increase in moisture content and decreased pore size result in increased pressure drop. Pressure drop range between 1 and ten hPa. Incinerator Oxidation of the VOCs pollutants takes place. Oxidation is the most commonly used technique. Oxidation can be thermal or catalytically. An oxidation process with heat recovery is a good economical option. However, the process has disadvantages; ·         It destroys the valuable VOCs. ·         The oxidation process requires specific operating conditions and design of incinerator. This depends on the composition of the VOCs. ·         Toxic combustion products may be generated in the process, which needs further processing. Therefore, application of thermal oxidation is the limit because of the disadvantages which offset its advantages. Some of these limitations can are overcome by the use of a catalytic combustion.     Adsorber The process is known as adsorption. Adsorption is the next most favored technique. It has good removal (recovery) efficiency, though it requires higher capital investment and operating costs. Desorption of adsorbent and separation of VOCs from desorbed solution increase the complexity and cost of the process. Activated carbon, though a cheap adsorbent, has many limitations, e.g., the possibility of fire. The printing shop in question is a small industry with limited resources and will, therefore, choose a reduction technique that requires low initial capital investment and less space to achieve the emission standard set by the government of Thailand. The best choice will be biofiltration process because; ·         Bio-filters require lower capital costs, lower operating costs, low chemical usage, and no combustion source. ·         Biofiltration units can be designed to fit into any industrial setting physically. A biofiltration unit can be designed as any shape and size. ·         Biofiltration technology has an efficiency above 90% for low concentrations of contaminants (<1000 ppm). Determination of bed dimensions To calculate the surface area of the biofilter requires the following parameters: volumetric flow rate, the preferred media depth  and the Empty Bed Contact Time (EBCT). The determination is thus, follows:   Vm = Q × EBCT / 60 s/min  Where: Vm = Media volume (m3)                    Q = Airflow rate (m3/min)                    EBCT = Empty Bed Contact Time (s) The media depth can be used when the biofilter space area is not limiting as below: Am = Vm/Dm Where: Am = media area (m2), and                              Dm = Media depth (m) Load value (flow rate) = 90g/m3/hr If in one hour, flow rate = 90g/m3 Making an assumption that EBCT = 8hr Therefore, Vm = 90 × 8 =72 m3 Vm = 72m3 Am = Vm/Dm and assuming that the depth required is 5m to find the space needed. Therefore, Am = (72/5) m                             = 14.4m 2 Selection of bio-filter media Selection of a suitable media is crucial for best performance and increased efficiency. The biofilter media include; peat, heather, composted sewage sludge, granular carbon, etc. The media used should provide nutrients to microorganisms, minimize pressure drop, and the moisture content maintained between 30% and 60% to support the microbial population. Also, a controlled sprinkler system should be installed inside the biofilter to ensure a proper bed moisture. A suitable biofilter media is that of compost considering that it satisfies the above conditions. Executive summary VOCs are common air pollutants emitted by chemical and petrochemical industries. Control of the VOCs is a significant concern of the industries' commitment towards the environment. It is, therefore, necessary to limit and vapor emissions such as the VOCs because they affect climate change, growth and decay of plants, and the health of human beings and all animals. Different technologies have been developed in an effort towards the reduction of VOCs emissions; adsorption, biofiltration, incineration (oxidation), etc. Biofiltration is the most recent technology. Besides, regulation on controlling vapor emissions in the air have been issued worldwide. Incineration technique is the most common, though it destroys valuable VOCs. The technique requires specific conditions and design of incinerator, and hence its use is limited. Incineration (oxidation) is a good option when VOCs recovery is not important both regarding costs and efficiency. Adsorption is a recovery technique with high recovery efficiency, though high capital investment and costs are required. Also, activated carbon has many limitations though it is a cheap adsorbent. If VOCs recovery is essential, adsorption technique is a good alternative. Biofiltration is a cheap and effective alternative for VOCs elimination. However, commercial application is limited due to its selective destruction and sluggishness. Using the decision-making matrix with cost, initial capital investment and space as the factors to be considered to choose emission reduction technique, biofiltration is the best alternative in this case.         Reflection questions 1.      How will this assignment help address community needs in Thailand? Volatile organic compounds (VOCs) is a serious environmental concern due to their detrimental effects towards human health in high concentration. Therefore, development of technology that can best minimize or eliminate the emissions is necessary. This assignment discusses the standard emission set worldwide and VOCs emissions and the technique developed to reduce such compounds to levels or another compound which does not have health effects. Therefore, this assignment helps to create environmental awareness as far as VOCs emissions are concerned. In addition, application of the techniques discussed will serve as a step to Thailand towards meeting internationally set standards for VOCs emissions. 2.  What did you learn from this assignment? This assignment discusses air pollution via VOCs emissions and the technique suitable to eliminate or reduce such emissions. Hence the project helps me have a broad understanding of air pollution as a result of emission of volatile organic compounds, the set emission standards worldwide and the technologies that have developed to minimize or eliminate VOCs emission. 3.   How can you use what you learned in this assignment in the future? Application of the knowledge discussed at the industrial setting can help reduce the health effect caused by VOCs to the community that neighbor industry in question. Also, the concept can serve as a step towards developing better techniques that are more efficient and incur fewer costs.           Reference Faisal l. Khan, Alone Kr. Choshal (2000). Removal of VOCs from polluted air.

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Schmidt, Larry Jacobson, and Richard Nicolai. Biofilter design information. Web
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Selvi B. Anit, Robert J. Artuz. Biofiltration of
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