In our hometown, Taiwan, the color of the sky often turns gray. The amount of PM2.5, which gradually gains attention, is not just a local problem but also a global issue. Those who are sensitive to air pollution usually feel uncomfortable and have to wear a mask all the time. To avoid that many people started to go indoors. However, indoor air quality was proved to be 10 times worse than outdoors but is still often ignored. In addition, people nowadays stay indoors more often. Thus, it’s crucial to solve these problems and 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 windows, 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 on the filtration of CO2 and toxic gases such as volatile organic compounds (VOCs), as air purifiers cannot remove all of them through filtration.

Investiations on CO2, VOCs, and their effects

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

We measured the CO2 concentrations in 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 doesn’t cause any effects to people
700~1000 ppm: people are more likely to get dissatisfied and brain stiffnesses
1000~2500 ppm: people can already sense that the air is turbid and feel drowsy
2500~5000 ppm: people can get headache, lethargy, sluggishness, heartbeat hasten, and mild nausea
above 5000 ppm: it may cause severe hypoxia or coma

CO2 concentration analysis in common areas of our daily lives (e.g., the classroom, auditorium, table-tennis room, school bus, gym and the vehicle) was presented on the Human Practices page.

As for VOCs such as benzene and chloroform, even a little of them will cause eye, nose and throat irritation, while if inhaled excess amount of them will cause damage to the 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 an increased heart rate, and prolonged exposure may cause death. Accordingly, the indoor concentrations of benzene are 3-4 times compared to outdoor concentrations. This is a crucial problem in our lives because people spend more time indoors nowadays.
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 have a limited regeneration time because of the corrosion by oxidative solvents.

Chemical absorption:

The chemical materials with CO2/ VOCs-binding or -holding capacities are used to capture 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 and 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 traditionl 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 engineered 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 perform poorer photosynthesis and CO2 fixation rate than microalgae. The plants also take up a lot of space.
We did some research about indoor plants to reduce CO2. But after some calculations, we obtained 2777 potted plants needed for the CO2 exhaled by one person at any time.
Micro-algae can remove CO2 with higher efficiency but still has a 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.
Thinking based on Synthetic Biology theories, we searched for enzymes to facilitate the microalgae purification system.
- Carbonic anhydrase (CA): CA is an enzyme that catalyzes the reaction of converting gaseous CO2 to dissolved bicarbonate, which can easily be 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 subtilis 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 because of its ability to lower the technical difficulty and reduce the cost of production.

Prospect

In the future, we will put more efforts on making more multifunctional enzymes to remove other indoor air pollutants to make indoor air 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