The starting point of our project was a look at the world as it is. We have marvelous technologies which make our lives better, things that were problems 100 years ago we can't think of anymore and all information can be shared faster than ever. However, there is also something terribly wrong with this world. Temperature is rising, animals go extinct and the price of our advancement is pulling fossil fuels out of the earth that have been there for millions of years.

We love all these advancements. We would lie if we say we didn't. But we do want to solve the downside of our development. Therefore we looked into a surprising polluter: plastic. Plastic is a wonderful product and these days it is impossible to live without it. Therefore we looked into the production of plastic. Can we make clean plastic, which does not pollute the earth? And what should we do with this plastic? On the Human Practices pages you'll found where our journey brought us; from schools to festivals; from start-ups to multinationals. We started off by calculating the Carbon Footprint of styrene.

Carbon footprint analysis

Producing styrene from organic waste

The aim

We are facing an huge increase in global population, from the current world population of f 7.6 billion to an expected 9.8 billion in 2050 [1]. This projected increase in global population leads to an increase in both food and energy consumption, which in turn in is associated with an increased emission of greenhouse gasses. Right now, we live in a plastic generation. The global production and consumption of plastics have been on the rise for over 50 years now, reaching a plastic consumption of 297.5 million tons by the end of 2015 [2]. Plastic products from the petrochemical industry have a high carbon footprint (Boonniteewanich, Pitivut, Tongjoy, & Lapnonkawow, 2014). The combination of global population increase and a mass consumed non-eco-friendly product, in the form of petroleum-based plastics, could be disastrous. This is one of the reasons that the Groningen iGEM team’s project attempts to produce (bio)styrene, a building block for many plastics, from cellulose as an alternative to substitute the petroleum-based styrene. In this section we have carried out a partial Life Cycle Assessment (LCA) to identify the environmental impact of both petroleum-based styrene and bio-based styrene. The main purpose is to provide an insight of the environmental burden that is caused by the worldwide styrene industry in terms of carbon dioxide equivalent emissions (CO2-eq) and to showcase our greener alternative.

For our LCA analysis we have used the Dutch GER-Values. These values are used for a ‘cradle to gate’ analysis and include all emissions that are needed to produce a certain product. These processemisions of the products do exclude any carbon fluxes from or to the atmosphere. In case of a bio-based feedstock this is a complete analysis because the carbon uptake is balanced with the emissions once the product is disposed. For fossil styrene a value of 3,1 KG needs to be added to this (Croezen & Lieshout, 2015) because these emission will lead to a net carbon emission. (see figure 1) (Croezen & Lieshout, 2015). A full LCA should also include other impact categories however it is decided not to include these. The reason for this that we discovered the LCA analysis in a late phase of the project which forced us to simplify the analysis.

Analysis

For our analysis, we compared the process of producing styrene from a bio-based feedstock to the process of producing styrene with petroleum as a feedstock. To define the cradle to gate emission of petroleum-based styrene we contacted two experts of the company CE Delft, the authors of a report stating the Gross Energy Requirements values (GER) of industrial feedstock (Croezen & Lieshout, 2015). With their expert help, we were able to define the cradle to gate emission of petroleum-based styrene for our analysis, the value being: 7.8 CO2-eq per kilogram styrene.

Now we need to compare the GER of petroleum-based styrene with the GER of our StyGreen. In order to do this we need to define the GER of StyGreen. The first step in defining the amount of CO2-eq per kilogram StyGreen is, defining the feedstock that is going to be used. We explored many different feedstock options. After comparing all possibilities, we decided to use recycled toilet paper. The main reason for this choice was the sustainability aspect. Toilet paper is product that is not used for anything at this moment. Therefore, it does not hold much monetary value at all, or it holds even negative monetary value. Which means that we can potentially add value to the life-cycle of toilet paper. Another reason for choosing toilet paper, is that we do not want to compete with the food industry. It might be feasible to use sugar, or first generation resources to produce styrene, but this does not fit into our view of a better world.

The second step was to calculate the carbon footprint of recycled toilet paper. The carbon footprint of a feedstock in a certain phase of the Life-Cycle analysis is proportional to the monetary value the feedstock holds in that particular phase. Since the recycled toilet paper is derived from paper, we looked into the monetary value of recycled toilet paper in combination to the resource, paper. After this we looked at the price of the toilet paper, and compared to the price of wood. This way, we could make a parallel to the toilet paper CO2-eq. The cradle to grave carbon emission of paper is 0.9 CO2-eq per kg paper (Croezen & Lieshout, 2015; figure 2 gives a visual representation of the factors determining the carbon emission of paper feedstock).

The cost of paper is €150 per ton. Due to the fact that toilet paper recycling is still in its infancy, it was hard to define the representative price for this resource. However, after talking to several experts(as you see here), we came to a price estimate of €15 per ton. Since, toilet paper holds 10% of the monetary value of paper, we divided the CO2-eq by 10 as well, giving our recycled toilet paper feedstock a carbon footprint of 0.09 CO2-eq per kilogram.

Next we need to know how much energy (and therefore, how carbon emissions) is required to produce 1 kilogram of StyGreen. The energy requirement is based on the following formula (see table 2):

From the energy requirements we can now derive the process emissions in CO2 per kg StyGreen by means of the following formula (see table 2):

This brings us the a process emissions of 1.229 CO2 per kg produced StyGreen. If our genetically engineered yeast had a 100% conversion rate, we would need 10 kilograms of recycled toilet paper to produce 1 kg of StyGreen (based on the theoretical maximum yield). Which would mean that the carbon footprint of our StyGreen would be 2.129 CO2-eq per kg.

This is a lot better than 7.8 CO2-eq per kg for petroleum-based styrene. However, at this point in time our conversion are not yet 100%. For each kilo of styrene we produce, we need 263 kilograms of cellulose (recycled toilet paper) right now. This would result in 24.89 CO2-eq per kg, which is way worse than regular (petroleum-based) styrene. This partly due to the assumptions made in the flux model, which assumes that yeast needs have a net biomass gain at all times. While, that is not necessary in our bioreactor. Moreover, the first version of our yeast is just a proof of concept. There are still a lot of parts that can be optimized. Both in the yeast strain itself, in the form of knock-outs, and in the bioreactor, by reducing the process emissions.

Conclusions

1. Toilet paper waste is used as the primary raw material in the biorefinery to produce styrene. The reason for this it is not used for feeding humans. The other reason is we can add value to this product.
2. Currently the process is not sustainable (based on flux model, with mass balance of 263 : 1)
3. We could still optimize our process a lot, so we should be able to decrease the mass balance by a lot. And starting from a mass balance of 33 : 1 we are cleaner than petroleum-based styrene
4. We can also improve the process emissions, lower process emissions means our mass balance can be higher (at the moment the process emissions are more than 28% of the total emissions of petroleum-based styrene).

Safety should be a cornerstone of every project, taken into account during every phase. For this reason the Dutch Governmental Institute for Public Health and Environment (RIVM) has challenged us to participate in their Safe-by-Design assignment. The goal of this assignment is to demonstrate how our team has taken safety into account throughout our project, in every aspect. Of particular importance is the human practices part, where our ideas get taken outside the lab and into the world surrounding us. Of special interest is the iterative process, where the direction of the project is adjusted based on input from stakeholders and experts in relevant fields, safety and ethical guidelines, and considerations regarding the upscaling of our project. We have had 2 Skype meetings with staff members of the RIVM, and using their tips and guidance we made some more adjustment. The final product, an infographical timeline describing the iterative process of our project, is pictured below.

References

Boonniteewanich, J., Pitivut, S., Tongjoy, S., & Lapnonkawow, S. (2014). Evaluation of Carbon Footprint of Bioplastic Straw compared to Petroleum based Straw Products. Energy Procedia, 56, 518–524. https://doi.org/10.1016/j.egypro.2014.07.187

Croezen, H. J., & Lieshout, M. van. (2015). Handleiding CO2-waarden voor biobased grondstoffen volgens MJA3/MEE-methodiek. CE Delft, 73.