Jurnal Mahasiswa Prodi Teknik Mesin
Universitas Kristen Petra, Surabaya
The Design of an Environmentally Friendly Mask Waste Sterilizier as
an Alternative to Mask Waste Treatment during the COVID-19
Pandemic
Adriel, Evan1), Handoyo, Ekadewi Anggraini2)
Petra Christian University Mechanical Engineering Department1,2)
Jl. Siwalankerto 121-131, Surabaya 60236. Indonesia1,2)
Phone: 0062-31-8439040, Fax: 0062-31-84176581,2)
Email: evan21adriel@gmail.com1), ekadewi@petra.ac.id2)
Abstract. From late 2019 until now, the world has been shocked by the spread of
the Coronavirus, which causes the COVID-19 disease. Coronavirus is a highly
contagious virus, so people should wear a mask to prevent infection. The COVID-19
pandemic led to an increase in mask waste. Before being dumped into the final
disposal site, mask waste must be sterilized with the intention of stopping the spread
of the coronavirus. The objective of this design is to provide an alternative to mask
waste treatment in Indonesia, which still relies on incinerators that are less
environmentally friendly. According to the instructions of the Health Institute of the
People's Republic of China, mask waste will be immersed in hot water at > 56 C for
30 minutes. The water heating process will be carried out by a parabolic trough
solar collector. The solar collector will be 2 m long with a parabolic focal point of
375 mm. The results of this design obtained hot water with a temperature of 70 °C,
which can be used to sterilize used masks for 30 minutes. The final result of this
design is sterile masks that are safe to be disposed of.
Keywords: coronavirus; mask waste sterilizer; solar collector; heat transfer;
environmentally friendly.
1 Introduction
During the COVID-19 pandemic, there was an increase in the use of masks all over the world.
This has an impact on the rapid increase in the number of used masks as well. As a result, many
countries around the world, including Indonesia, face challenges in dealing with mask waste
because of the limited number of medical waste treatment facilities. During the pandemic,
Indonesia generated ±384 tons of medical waste per day, according to the World Health
Organization. At the same time, Indonesia has medical waste treatment facilities that can only treat
±314 tons of medical waste. It is known that the coronavirus is infectious, so to prevent further
spread of the virus, it would be best if the medical waste were sterilized first before going to the
final disposal sites. Every piece of medical waste has been contaminated by the coronavirus during
this pandemic. Without the sterilization process, the virus would have a chance to survive.
Furthermore, polypropylene plastics are now widely used for mask materials, which are difficult to
degrade, so they will provide a perfect place for the coronavirus to survive (Andrady, 2011).
The Ministry of Environment and Forestry of the Republic of Indonesia also urged the
importance of processing mask waste during this pandemic through an official circular, namely,
SE.02/MENLHK/PSLB3/PLB.3/2020. Two methods of medical waste treatment are suggested in
this official circular. The first method is incineration, in which medical waste are burned inside an
incinerator. This method always generates pros and cons because, on one hand, it is effective. A
large amount of medical waste can be processed in a relatively short time. But on the other hand,
this method is not environmentally friendly because it uses fossil fuel and generates emissions.
The second method is thermal disinfection. Thermal disinfection is defined as a medical waste
treatment that uses heat exposure to kill microorganisms. The proteins in the microorganisms will
be damaged, so the microorganisms will become inactive or die (Kampf, Voss, & Scheithauer,
2020). It will not require a high temperature to kill microorganisms because they are categorized
as organisms that are easy to kill. So, there are many potential heat sources for thermal
disinfection, one of which is solar thermal. Based on the reference journals, the coronavirus that
lived on used masks can be killed with thermal disinfection at a temperature of 56˚C for 30
minutes (Wang et al., 2020). The Health Institute of the People's Republic of China has already
approved the temperature and time requirements used by this journal. Therefore, this paper will
Jurnal Mahasiswa Prodi Teknik Mesin
Universitas Kristen Petra, Surabaya
describe an environmentally friendly mask sterilizer device design process that uses the thermal
disinfection method. The device will be equipped with a solar thermal collector to collect heat
energy from the sun using water as a heat transfer fluid so that the hot water produced then will be
used to sterilize used masks.
The purpose of this mask sterilizer design process is to provide an alternative for health
facilities in Indonesia that still don't have medical waste treatment devices. As a result, the
sterilizer device makes the used mask clean and free from viruses so that it is safe to dispose of it
at the final disposal sites. Moreover, in an emergency such as running out of masks, the sterile
mask could be used again. Also, there are other benefits to this mask sterilizer device. Certainly,
this device could help to stop the transmission of the coronavirus. Inventing a device to sterilize
used masks will eliminate the possibility of coronavirus infection that could happen because of the
large amounts of highly contagious medical waste. In addition, this design will support the use of
renewable energy to save our earth.
2 Methods
In this design process, a sterilizer device prototype will be built. The goal is to test the
capability of this device to collect heat energy from the sun, transfer it to the water, and sterilize
the used mask. Hence, to build the prototype, it will need to do some tests such as heat transfer
fluid (water) heating tests, used mask sterilizing tests, etc.
2.1. Type of Masks to be Sterilized
The masks that will be used in the experiment are as follows: regular medical face mask,
KF94 mask, and KN95 mask. Generally, these three types of masks use polypropylene plastic as
their main material, with the function of filtering viruses. A temperature range of 60 °C to 70 °C is
safe for polypropylene plastic-based masks, according to 3M, one of several mask manufacturers.
So, after the thermal disinfection sterilization process, sterile masks can still be used without any
degradation in their filtration ability.
Table 1. Materials specification of the KN95 Protective Mask
Table 2. Materials specification of the Supersoft Surgical Mask
Table 3. Materials specification of the KF94 Disposable Mask
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2.2. Waste Mask Sterilization Method
According to the official circular letter SE.2/MENLHK/PSLB3/PLB.3/3/2020 concerning the
management of infectious waste and household waste from COVID-19, there are several steps
before and after sterilizing used masks, ask the following below;
1. Used masks must be separated so that they are not mixed with domestic waste.
2. Before starting the sterilization process, used masks are prepared by unfolding them to
make sure all the mask parts are getting in contact with the hot water.
3. Used masks that are already unfolded will be placed inside the sterilization chamber and
soaked in hot water.
4. After the sterilization process is completed, the hot water is removed, and the sterile
masks can be drained.
5. Sterile masks are in a wet condition, so they will need to be dried using a drier.
6. The dried sterile masks are then chopped by a shredder before being packed and sent to
the final disposal sites.
During the sterilization process, every part of the used mask should be in contact with the
hot water to ensure viruses that contaminated the mask are killed. Besides that, stirring the hot
water during the sterilization process should be avoided and keep the mask from coming into
contact with the sterilization chamber. The purpose of these actions is to keep the shape of the
mask.
2.3. Indicator of Mask Sterilization Process Success
To be able to determine the success of the mask sterilization process, it is necessary to carry
out a virus titration that results in a reduction in the level of virus infectivity. After passing through
the sterilization process, used masks are declared to be safe if the coronavirus on the mask has
been reduced by >3log10 (U.S. Food and Drug Administration, April, 2020). It has been proved
that sterilizing used mask using >56˚C hot water for 30 minutes can reduce coronavirus infectivity
level by >5.01log10 (Rabenau et al., 2004). Because of the limitedness of tools and materials, this
paper uses the hot water temperature and sterilization time to be the indicators of mask
sterilization process success.
2.4. Device Design and Components
There will be three major components in this mask sterilization device: a fluid reservoir, a
solar thermal collector, and a sterilization chamber. A solar thermal collector will be used to
generate heat and transfer it to the water. The parabolic trough solar collector has been chosen as
the reference design for this solar thermal collector. So, the solar thermal collector is going to
consist of a concentrator, a receiver, and a layer of thermal insulation. High efficiency (60% –
80%), a simple design, and the ability to obtain a high temperature (300˚C – 400˚C) are reasons
why the parabolic trough was chosen as the reference design.
Figure 1. Mask Waste Sterilizer Design and its Components
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This sterilizer design has its own workflow. To understand it, each function of a component
should be known first. As seen from the figure above, there are eight components total. The
following is an explanation of each component function;
• Concentrator:
The concentrator is going to reflect sunlight towards the receiver. Some
calculations are needed to ensure that the concentrator precisely reflects the sunlight onto
the receiver surface. These calculations require a couple of the concentrator dimensions,
such as the width of the concentrator, the concentrator rim radius, etc. As a result, a
precise position of the receiver is obtained, called the focal point.
• Thermal Insulation:
The purpose of thermal insulation is to limit the transfer of energy. In this
design, the layer of thermal insulation is needed to prevent convection heat loss from the
receiver to the surroundings. To apply this action, the space between the inner diameter of
the insluation and the outer diameter of the receiver should be vacuumed. Vacuuming
creates gas pressure in this space below the ambient pressure. In other words, in this
space, there will be no free air at all. As a result, without any gas, the convection heat
transfer will be negligible.
• Receiver Pipe:
The receiver has the assignment to absorb and store heat from the sun. It gets
warmer by receiving the reflected sunlight from the concentrator. For this design, the
receiver will be made of a metal pipe. Water is going to flow inside the receiver pipe for
the purpose of convection heat transfer. Heat absorbed by the receiver pipe is transferred
to the water as it flows inside the pipe.
• Body Frame:
The body frame is a structure for the mask waste sterilization device. The
material for this component is made of metal, which was chosen because of its properties
that are strong and tough, so it is suitable as a structure.
• Sterilization Chamber:
The sterilization chamber is one of the crucial components as it provides the
place for the sterilization process. This component should be able to maintain a water
temperature above 56˚C for 30 minutes, so it needs good material and insulation to keep
heat in the water.
• Fluid Reservoir:
The fluid reservoir is a place to store clean water before it circulates into the
device’s piping system.
• Fluid Pump:
The purpose of this component is to circulate clean water from the fluid
reservoir through the receiver pipe and then end up in the sterilization chamber.
The following are the steps of the mask waste sterilizer device workflow. There will be six
steps. It will be explained from the beginning, before the water heating process, until the used
mask sterilization process.
1. First, components should be prepared. The heat transfer fluid (clean water) is filled into
the fluid reservoir. At the same time, the device can be placed in the sun to pre-heat the
receiver pipe. The sterilization chamber must be prepared and filled with 15–20 pieces of
used masks. Using a vacuum pump, vacuum the space between the inner diameter of the
thermal insulation layer and the outer diameter of the receiver pipe.
2. As a result of the reflection of sunlight from the concentrator, the temperature of the
receiver pipe will increase.
3. Once the receiver has begun to warm up, turn on the fluid pump to circulate water into
the receiver pipe.
4. The water that circulates will receive heat that is transferred from the hot receiver pipe.
After finishing circulating through the receiver pipe, the water will come out in hot
conditions and end up in the sterilization chamber.
5. Inside the chamber, the hot water will come into contact with the used masks so that the
sterilization process can immediately begin.
6. The sterilization process is carried out for 30 minutes, and then the sterile mask can be
drained.
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Temperature monitoring should be carried out while the mask waste sterilizer device is
working. There are a couple of data temperatures that must be noted, specifically the surface
temperature of the receiver pipe, the temperature inside the chamber, etc. The data is important for
the device's output analysis and improvement design. A couple of thermocouples will be needed to
do this activity. In addition, the surrounding conditions, such as the ambient temperature, wind
speed, and solar beam radiation, must also be monitored. The wind speed is monitored using an
anemometer and the solar beam radiation using a pyranometer.
Figure 2. Mask Waste Sterilizer Device Workflow Illustrations
2.5. Calculations dan Device Prototype Making Process
For implementing the mask waste sterilizer design, some calculations are needed as the basis
of the prototype making process. There are two types of calculation analysis: optical analysis and
thermal analysis. The results of this analysis are the technical specifications of the sterilizer device.
A couple of things that should be calculated are shown in the following figure below;
Figure 3. Calculation steps in the Optical and Thermal Analysis of Solar Thermal Collectors
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In the thermal analysis process, it is necessary to calculate all possible heat loss processes that
may occur during the device's working. To help the process of calculating the heat transfer, it will
be easier to analyze it with the help of a thermal resistance diagram, as seen below.
Figure 4. Thermal Resistance Diagram inside the Receiver Pipe and the Thermal Insulation
Based on the calculations from the previous step, the optical and thermal analysis of the solar
thermal collector results in a technical specification. This specification includes the dimensions
and materials of the components. It is important to understand that the selection of component
materials is based on the function of the component itself.
• Concentrator:
It needs a high-reflectivity material to reflect the sunlight onto the receiver well. A
mirror sticker made of aluminium is chosen because of its high-reflectivity properties that
could reflect 88% to 98% of the light.
• Thermal Insulation:
An acrylic tube is selected as the thermal insulation layer of the design. Considering
that this component is intended to serve as a thermal insulation, it will require a material
with low thermal conductivity. Acrylic has a low thermal conductivity of 0.2 W/m K and
a transparent color. Thus, it will be suitable for this component and won't interfere with
the process of sunlight reflecting from the concentrator onto the surface of the receiver
pipe.
• Receiver Pipe:
The receiver needs a high thermal conductivity material because of its function to
absorb heat. In terms of thermal conductivity, copper has a value of 380 W/m K. Thus,
copper will be an excellent choice. In addition, black paint will be applied to the copper
to improve its ability to absorb heat.
• Body Frame:
As a structure, the body frame will use hollow iron for its material. Iron has solid
properties and provides weight for the balance of the device.
• Sterilization Chamber:
The sterilization chamber should be made from metal and insulated with a layer of
thermal insulation. During the sterilization process, the chamber must maintain a constant
temperature inside for 30 minutes. So, a metal pan is chosen.
• Fluid Reservoir:
For this component, anything that can carry water can be used. In this paper, a gallon
is used.
Jurnal Mahasiswa Prodi Teknik Mesin
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•
Fluid Pump:
This design will need a water pump to circulate water into the device's system.
Because there is no need for pressure, a drinking water pump will be enough to use.
Table 4. The Mask Waste Sterilizer Device Technical Specifiation
From the optical analysis of the solar thermal collector, a parabolic chart of the concentrator
model was also obtained, as seen below;
Figure 5. Parabolic Chart of the Concentrator Model Designed
The mask waste sterilizer device prototype is built based on the technical specifications as
seen in table 4 above. Every result of the calculations in optical and thermal analysis is used as the
basis of all manufacturing processes needed.
Figure 6. Prototype of Mask Waste Sterilizer Device
Jurnal Mahasiswa Prodi Teknik Mesin
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Figure 7. Used Masks Inside the Sterilization Chamber and the Reflection of Sunlight on the Receiver Pipe
Figure 8. The Vacuum Pump and Pressure used in the test
3 Result and Discussion
The mask waste sterilizer device was tested several times by heating clean water used for the
sterilization process. Five variations of flow rate were carried out to determine the effect of
flowrate on the heat transfer process. The testing process started at 10.00 am and ended at 13.00 or
14.00 pm. The device was placed parallel to the direction of the North-South axis. The space
between the inner diameter of the thermal insulation tube and the outer diameter of the receiver
pipe will be vacuumed with a pressure of 400 mmHg to prevent convection heat loss. A 10-liter
pan was used as the sterilization chamber and was wrapped up by a couple pieces of fabric as the
insulation. The following is the result of the tests and is shown as charts;
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(a)
(b)
(c)
(d)
Figure 9. The Test Results using 1.5 liter/min Flow Rate (a) First Test, (b) Second Test, (c) Third Test, and
(d) Fourth Test
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Figure 10. The Test Results using 2 liter/min Flow Rate
Figure 11. The Test Results using 3 liter/min Flow Rate
Figure 12. The Test Results using 4 liter/min Flow Rate
Figure 13. The Test Results using 6 liter/min Flow Rate
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From several tests, the best results were obtained using a water flow rate of 1.5 liter/min. In
other words, the highest water outlet temperature was obtained when water with a 1.5 liter/min
flow rate flowed into the mask waste sterilizer device. Based on the other results, a conclusion can
be drawn that the lower water flow rate will result in a higher water outlet temperature. This
happens because a lower flow rate gives the water more time to absorb heat transfer from the
receiver pipe, which results in a more stable and higher water temperature. At the same time, a
higher water flow rate has no ability to do the same thing. In addition, water flow rate is not the
only one that affects the water outlet temperature. Other factors like the ambient temperature, solar
beam radiation, and water inlet temperature also affect the result of the test. More than other
factors, solar beam radiation has the most significant effect on the test results. Higher solar beam
radiation will make the surface of the receiver pipe absorb more heat from the sun, which, of
course, affects the receiver pipe and water temperature. During the tests, the highest value of solar
beam radiation was 716 W/m2.
At flow rate of 1.5 liter/min, the temperature of the water outlet reached ±80°C, which caused
the temperature inside the sterilization chamber to be stable at >56°C for the sterilization duration
required. Because of that, the water temperature is sufficient to sterilize the used masks. As a
result, this mask waste sterilization process using the designed device is already in accordance
with the procedure of the Health Institute of the People's Republic of China. The thermal
efficiency of the device results in 45% – 52% when the target water outlet temperature is reached.
4 Conclusion
From the design of this environmentally friendly mask sterilizer device and several testing
processes, the following conclusions can be drawn;
1. The temperature of the outlet water exceeds the target level, even beyond what was
planned. This occurs because the current value of solar beam radiation is greater than the
value used in thermal calculations. In addition, before the tests begin, the device is placed
in the sun for a short period of time to heat up the receiver pipe.
2. The concentrator is positioned parallel to the north-south axis and produces the best
sunlight reflection toward the receiver between 10.00 am and 13.00 pm.
3. The most optimal water heating process is carried out using a water flow rate of 1.5
liter/min and produces a thermal efficiency of 45% – 52%.
4. Heating 10 liters of water in the device's solar thermal collector cannot be done at once.
Instead, it must be divided into several batches so that the temperature of the receiver
pipe can return to its high temperature when new cold-water flows.
5. There is a decrease in the water temperature inside the sterilization chamber due to heat
loss from the chamber to the environment during the mask sterilization process. Adding
better insulation material might be the solution to this problem.
6. The device designed has succeeded in sterilizing used masks and is already in compliance
with the procedure of the Health Institute of the People's Republic of China.
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Universitas Kristen Petra, Surabaya
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