In our motherland, Taiwan, the color in the sky often turns gray from blue. The amount of PM2.5 which gradually catches people's attention is not just a local problem but also a global issue. Those who are sensitive to air pollution usually feel uncomfortable and wear a face mask all the time. However, indoor air quality was proved to be 10 times worse than outdoors and is often ignored by people. Modern people stay much more time inside the house or a closed area. Thus, it’s emergent to solve these problems. Moreover, we want to do human practices to raise the awareness of indoor air quality.

Indoor Air Quality

Poor air quality significantly affects our daily lives. Gases, chemicals, and other pollutants in the air can cause headaches, eye irritations, allergies, fatigue, etc. The direct way to improve indoor air quality is to simply open the window, but sometimes the air outdoors is even worse than the air indoors, and therefore we cannot open the window in these kinds of situations due to a plentiful amount of pollutants such as toxic gases and PM (particulate matter) particles outdoors.

Air Purifiers

The air purifiers can help a little by filtering some of these particles, but there are still issues filtering CO2 and toxic gases such as volatile organic compounds (VOCs), as air purifiers cannot remove all of them through filtering.

CO2 and VOCs investigation and their effects

CO2 and some kinds of VOCs that can hardly be dealt with through air purifiers can cause problems to our health. High CO2 concentration indoors has an adverse effect on human performance, while a small amount of VOCs can easily cause a negative impact on us.

We measured the CO2 concentrations of common places indoors and learned a lot about how people feel about indoor air quality through human practices research.

450~700 ppm: the air is fresh, and it doesn’t cause any effects to people
700~1000 ppm: people are more likely to get dissatisfaction and brain stiffness occur
1000~2500 ppm: people sense that the air is turbid and start feeling drowsy
2500~5000 ppm: people get headache, lethargy, sluggishness, heartbeat hasten, and mild nausea
above 5000 ppm: it may cause severe hypoxia or coma

More CO2 concentration analysis of our work in common areas of our daily lives (e.g., the classroom, auditorium, table-tennis room, school bus, gym and the vehicle) was presented in Human Practices page.
For VOCs as benzene and chloroform, a little of them will cause eye, nose and throat irritation, while inhaled excess amount of them will cause damage to liver, kidney and central nervous system. A brief exposure to 3000 ppm of benzene will lead to headache, 10000~20000 ppm will result in confusion and rapid heart rate, and long exposure may cause death. Accordingly, the indoor concentrations of benzene ranged up to 3.4 times the outdoor concentrations. This is a crucial problem in our lives because people spend more and more time indoors.
The problem of excessive CO2 and VOCs indoors is indeed existing in our daily life and may have severely influenced our health. So we must come up with a solution to solve this problem.

Our Goal

Current way to reduce CO2/VOCs concentration

We consulted experts in order for us to understand the current methods to reduce CO2/VOCs concentration. We went to meet the professors in National Chung Hsing University and Tunghai University to find out the physical and chemical methods, respectively. We also invited an expert in algae culture from biotech industry to have a discussion with us to discover the biological approach in dealing with this issue.

Physical absorption:

One of the current physical ways is utilizing organic solvents like propylene carbonate, and using solid absorbents such as carbon or Zeolite to absorb CO2 pr VOCs. The methods aren't feasible due to the demand of much energy and high temperature during the process of absorption and desorption. In addition, the materials has limited regeneration time because of the corrosion by oxidative solvents.

Chemical absorption:

The chemical materials with CO2 or VOCs-binding or -holding capacity are used as capturing solvents including monoethanolamine, potassium carbonate and chilled ammonia, etc. The complexity of the system makes it difficult to achieve a consistent and optimal performance.

Biological absorption:

The biological way is to take advantage of photosynthesis in plants or microalgae but with limited efficiency. Some kinds of indoor potted plants are found can remove VOCs but very slowly.
The table below shows the advantages and disadvantages of current methods and a comparison to our idea in this project.

Compared to other absorption approaches, our product can reduce CO2 and VOCs concentration efficiently, which is a function that common air purifiers don't have, and it only requires little space and power.

Our approach in Synthetic Biology - Microalgae Purification System with Bio-active Enzymes

We thought about applying synthetic biology to develop a photobioreactor system consisting of microalgae (or cyanobacteria) with a few kinds of enzymes produced by genetically engineering Bacillus subtilis. The system is more efficient in improving indoor air quality than traditional air purifiers which are unable to remove CO2 and VOCs.

Scientific Inquiry For Our Project

Plants has poorer photosynthesis and CO2 fixation than microalgae. And the plants also take lots of space.
We did some research about indoor plants to reduce CO2. But after calculation, we obtained 2777 potted plants needed for CO2 exhaled by one person at any time.
Microalgae can remove CO2 with higher efficiency but still with wide space demand.
In order to figure out the efficiency of CO2 removal with microalgae, we studied the related papers and got the number of 16 m²/day/person. It’s not feasible to build up such a volume for one person in a limited space.
Think based on Synthetic Biology, we search for enzymes to facilitate the microalgae purification system.
- Carbonic anhydrase (CA): CA is an enzyme to catalyze the reaction of gaseous CO2 converted to dissolved bicarbonate, which can easily taken up by microalgae in the culture media.
- Cytochrome P450 2E1 (CYP2E1): CYP2E1 can break down benzene and chloroform (i.e., VOCs) to small molecules such as phenol and CO2, respectively, which can be absorbed and metabolized by microalgae.
Make like an iGEMer. We plan to genetically engineer Bacillus subtilus 168, which is a GRAS (Generally Recognized as Safe (GRAS) strain. We design a BioBrick with genes of GFP, CA and CYP2E1 under Bacillus promoter of PliaI, which can be controlled and induced by bacitracin. We construct the expression cassette onto pSB1C3 as BioBrick parts and onto pBS0E as a replicative plasmid in Bacillus subtilis.
Furthermore, we will use the Bacillus total lysates as biocatalysts instead of the purified proteins due to lowering the technical difficulty and reducing the cost of production.

Prospect

In the future, we will make an effort on making more multifunctional enzymes to remove other indoor air pollutants and make indoor air always fresh.

Reference

Chen, P.H., Liu, H.L., Chen, Y.J., Cheng, H., Lin, W.L., Yeh, C.H., Chang, C.H., 2012. Enhancing CO2 bio-mitigation by genetic engineering of cyanobacteria. Energy and Environmental Science 5, 8318–8327.
Satish, Usha, et al. “Is CO2an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2Concentrations on Human Decision-Making Performance.” Environmental Health Perspectives, vol. 120, no. 12, 2012, pp. 1671–1677., doi:10.1289/ehp.1104789.
“Volatile Organic Compounds' Impact on Indoor Air Quality.” EPA, Environmental Protection Agency, 6 Nov. 2017, https://www.epa.gov/indoor-air-quality-iaq/volatile-organic-compounds-impact-indoor-air-quality.
“Agency for Toxic Substances and Disease Registry.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, https://www.atsdr.cdc.gov/.
a SELECTED POLLUTANTS - Euro.who.int. http://www.euro.who.int/__data/assets/pdf_file/0009/128169/e94535.pdf.
Carbon Dioxide Capture by Chemical Absorption: A Solvent Comparison Study
Ozturk, B., and D. Yilmaz. “Absorptive Removal of Volatile Organic Compounds from Flue Gas Streams.” Process Safety and Environmental Protection, vol. 84, no. 5, 2006, pp. 391–398., doi:10.1205/psep05003.
Study of the removal difference in indoor particulate matter and volatile organic compounds through the application of plants