Durata- Achieving Complete PET Neutrality: Master Plan

11 min readMay 1, 2021

Plastic in our oceans is poisoning you.

In 2019, the global production of plastics reached an annual 368 million metric tons. PET plastic is one of the most widely used, present in your single-use water bottles, clothing, and containers. It is currently being produced at a rate of 73.39 million metric tons per year, and by 2026, that number will be 130 million.

We wondered why this was, considering by 2026, there will be at least 230.02 million tons of PET plastic in our oceans. That’s the same weight as 260 golden gate bridges stacked on top of each other.

Currently, we have almost 2 times the global PET plastic demand just sitting there in our oceans, killing 100,000 marine mammals every year and creating 500 dead zones, which will double every decade.

If you are wondering how that affects you, 1 in 3 fish for human consumption contains plastic, and the average seafood eater eats 11,000 pieces of toxic plastic every year. Suddenly, I love a nice ribeye steak.

However, if we could ensure that just 56% of PET plastic in the ocean was recycled per year, we could meet the entire global demand and eliminate the production of new PET.

According to the PET Resin Association, PET is the world’s packaging choice because it is hygienic, strong, lightweight, shatterproof, retains freshness, resistant. Current biodegradable plastics don’t have enough demand or the characteristics that make them a better alternative. PET is not going away anytime soon — but the Earth can. We want to create a sustainable cycle for PET recycling, giving the Earth a chance to breathe by reducing the demand for new PET to zero.

Plastic recycling is ineffective and too expensive.

There are two main ways that plastic is recycled currently:

Mechanical Recycling: this is the simplest and most common method of recycling plastic, and it occurs in 5 steps. The first three are collecting, sorting, and washing the plastic, which are pretty self-explanatory. Next, the plastic is ground up into flakes and can be turned into granulate as well. However, during this process, the quality of plastic may be compromised due to processing and/or lifetime degradation. Compared to a cheap-newly produced virgin plastic, any differences in quality entail fear of ruining a companies brand.
Chemical Recycling: this entails depolymerizing plastic into its monomer subcomponents (in the case of PET, it can be broken down into components such as TPA, EG, BHET, or other compounds depending on the method used). These can be used to reinforce new polymers or can be purified and sold independently. The main downfall to this process is its extremely high costs, mostly due to the amount of energy it takes to complete the process.

Our solution targets both problems with chemical recycling, specifically by using biodegradation. This minimizes net energy costs to zero, allowing us to sell recycled plastic at competitive prices with both virgin and recycled PET, while not compromising the plastic’s quality.

Our solution uses Microbial Fuel Cells that utilize biochemical reactions to self-sustain.

Microbial fuel cells (MFCs) are essentially biological batteries, utilizing biochemical reactions to generate electricity. One of the main pitfalls of chemical recycling is the extremely high energy costs when creating high temperatures, pressure, etc. However, MFCs can harvest electricity from PET degradation, creating a self-sustaining system that can continuously generate/use electricity to degrade PET and re-synthesize the monomers into recycled PET resin.

MFCs can achieve this in a few key steps:

Enzymes in bacteria can break down a given substrate, releasing electrons in the process. This is done in the anode (negative) compartment of the MFC.
In the cathode (positive) compartment of the MFC, a final electron acceptor with a high affinity for electrons (usually oxygen) is stored.
A conductive material between the two compartments allows the electrons to move freely to the positively charged cathode compartment, where oxygen atoms await to take them up. The electrons are combined with oxygen and protons to create water as a byproduct.
The flow of electrons between the anode and cathode compartments creates an electric current that can be stored.

MFCs require sustained electron release in the anode and electron consumption in the cathode. The attainable metabolic energy gain for bacteria is directly related to the difference between the anode potential and the substrate redox potential. The optimal design for MFC is still under investigation, and different materials for the electrodes as well as more selective membranes for proton exchange are being currently developed to enhance their performance. Small cells connected in series offer higher potentials than bigger reactor volumes.

One of the main applications of MFCs currently is for wastewater treatment, and one has even been shown to power an urban wastewater treatment center successfully. Other applications include small biosensors, renewable electricity, bioremediation, and hydrogen gas production. Currently, the main drawback for the full-scale application of MFC is the cost of materials and the low buffering capacity of domestic wastewater.

The power generated from an MFC is limited by the internal resistance of the system components. Though the anode potential is hard to vary since it depends on the respiratory enzymes of the bacteria, most innovation in system design is designed to maximize cathode potential, through differences in final electron acceptors, cathode architecture, proton exchange membranes, and electrode spacing.

We target a specific bacterial enzyme to break down PET.

As previously mentioned, MFCs rely on bacteria to break down the substrate and release electrons. Thus, to break down PET, we set out to find a bacteria that could break down this seemingly indestructible plastic.

In 2016, Japanese scientists discovered a bacterium, Ideonella sakaiensis, that can break down PET plastic. Specifically, the bacterium developed an enzyme dubbed “PETase” that was able to depolymerize PET into its subcomponents. However, it wasn’t efficient enough to break down PET at an industrial scale. To achieve our goal on a large enough scale, we turned to a similar, yet more effective enzyme to break down PET plastic.

A 2019 report describes a more efficient PET hydrolase, LCC, that vastly outperforms other PET hydrolase enzymes:

After adding some improved modifications to the LCC enzyme, ICCG was engineered that could maximize PET degradation:

“Here we describe an improved PET hydrolase that ultimately achieves, over 10 hours, a minimum of 90 per cent PET depolymerization into monomers, with a productivity of 16.7 grams of terephthalate per litre per hour (200 grams per kilogram of PET suspension, with an enzyme concentration of 3 milligrams per gram of PET).”

As shown in the graph, LCC is more than 10,000 times more effective than Is-PETase. ICCG is 33 times more effective than that, making it the most suitable to break down PET at an industrial scale. The ICCG enzyme breaks down PET into a compound called Terephthalic acid (TPA), and ethylene glycol (EG), both of which can be re-synthesized into PET under large amounts of heat and pressure.

We improve current MFC models by using ICCG and minimizing resistance.

We propose an MFC that utilizes ICC to break down PET, creating an electrical current that can then be reused to make the entire system of PET breakdown and recycling self-sustaining.

When constructing our MFC- we first begin with PET degradation. This is done by taking PET substrate (a mixture of PET pieces and water) and allowing the aforementioned ICCG enzymes to break it down. The products of the chemical reaction (TPA and EG) are then collected.

Next, to be able to harvest energy from this reaction, we need to create two compartments for our microbial fuel cell, the anode (negative) and cathode (positive).

Since the reaction between PET and ICCG releases electrons, once they are released they can be conducted to an external circuit.

As mentioned before, the cathode requires an electron acceptor that has a high affinity for them. That way, electrons would be more “willing” to travel over to the positive cathode compartment, where they are taken up by the electron acceptor. Though most MFCs use oxygen as their acceptor, potassium ferricyanide produces 50–80% higher power than oxygen due to increased mass transfer efficiencies and larger cathode potential (source).

This is a diagram of one module within an MFC, however, our MFC is made up of a stack of multiple parallel modules to maximize surface area, minimize resistance, and increase overall electron output. As mentioned before, minimizing internal resistance is key to boost our energy production.

We take into account factors such as electrode spacing, substrate concentration, anode/cathode material/concentration, and a parallel circuit configuration to altogether minimize resistance and boost power production.

Re-synthesizing TPA and EG to create PET resin provides high-quality product to sell to companies.

We use the TPA and EG generated as a byproduct of the FMC to create PET resin pellets, which is what companies melt and mold into the plastic shapes they want. To create the resin pellets, TPA and EG are combined at high temperatures and low vacuum pressure to create a bowl of “PET spaghetti” that can be cut up into pellets. We then sell these pellets to companies such as water bottle manufacturers, minimizing the production of new PET by using existing PET. Since biodegradable plastics are not going to be replacing PET anytime soon, we leverage existing PET supply chains and resupply the building block PET resin pellets using the waste that is destroying our planet.

The initial study on ICCG showed the results of using PET’s subcomponents to create plastic bottles:

“Bottles blown from this PET had similar mechanical properties (a displacement of 2.9 mm at a maximal top-load force of 176 N) to those of commercial PET bottles (a displacement of 3.0 mm at a maximal top-load force of 181 N). Moreover, their excellent lightness values of 87.5% are better than those of the minimal standard for PET bottles (greater than 85%).”

There are two main incentives why companies would prefer recycled PET resin pellets:

There is no compromise in plastic durability/ease to shape into products through our solution. Often, there is stiffness, brittleness, discoloration, and a lack of previous tensile strength in recycled PET.
Our solution offers a cheaper alternative to other recycled plastic methods.

We talked to Melanie Condon, Director of Sustainability at Keurig Doctor Pepper to understand the economic incentives, benefits, and challenges for recycled plastics. We learned 3 key points:

From Keurig Green Mountain’s merge in 2018 with Dr. Pepper, the company prioritized sustainability because of reputation and pressure from investors. Additionally, climate change added risk to how they got their plastic. Finally, questions and pressure from consumers ultimately pushed KDP to aim higher with their sustainability goals. When asked, Melanie agreed that this followed a current trend, where companies are being pressured, specifically by Gen-Z, into becoming more eco-friendly. At KDP specifically, all Snapple bottles are made with recycled plastic rather than glass, a recent shift following this pressure. This also lightened the load of their trucks, allowing them to take 8500 trucks off the road and further lowering carbon emissions.
Companies have conservative claims on the word “recyclable” and “compostable”. In fact, only 3% of companies have access to compostable factories. Big companies also have legal risks to consider when trying to source recycle plastic. KDP missed several sustainable goals, as COVID prevented them from being able to send auditors to ensure responsible sourced recycled plastic.
Ocean plastic is a buzzword that if not done correctly, can cause more harm than good. KDP tried to use ocean plastic from a Taiwan supplier. However, the shipping wasn’t worth it for the carbon footprint.

As an alternative avenue that we can pursue, purifying the TPA monomers created it into “ a level higher than 99.8%, with an American Public Health Association (APHA) color number of 2.9”, and also produced 0.6 kg sodium sulfate per kg of TPA. This provides another possible avenue for revenue as the sodium sulfate market is 21.5 million tons a year with a 2.9% annual growth rate.

Our full economic breakdown:

According to the research paper that initially synthesized the ICCG enzyme, 1 ton of the enzyme cost $43.56 to produce. However, this was valued from the first time synthesizing the enzyme. If we can cut this cost by 1/2 by finding a way to synthesize it faster and using less labor, then this cost is $21.78 per ton of PET plastic.

Ocean plastic cleanup groups, such as the Ocean Cleanup, lose $5.00/kilogram for every ton of plastic that they collect from the ocean. It costs them $5.32 per kilogram for something that will, at best, be valued at $0.30 per kilogram. If we offered to make up 5% of this loss for every ton of PET plastic that we take off of their hands, then we will pay $227 per ton of PET plastic (this is 3.34x the amount they will make normally).

Using a case study of a small wastewater treatment MFC, the capital cost of a 200 L MFC system, made up of 96 modules in an array, was $6064 ($23.18 per module). This covered direct and indirect costs, such as materials, land, installation, and engineering. Variable costs would include $94.96/ton of PET plastic through the MFC system.

The total cost per ton through this method is $343.74 per ton of PET plastic. When compared with the current cost of production for recycled PET plastic $1114.64 / ton, we gain money per ton while the recycled plastic industry as a whole loses money, as the current selling price of PET plastic is $1112.50.

This calculation of cost does not capital the costs of re-synthesizing PET. However, the only variable costs in this process would be labor and maintenance. There would be net-zero energy costs due to MFC energy production.

Durata revolutionizes the way we produce plastic.

There would no longer be a reason to produce millions of tonnes of plastic each year. Instead, MFCs would ensure a self-sustaining recycling process, allowing us to eliminate trillions of ocean plastics.

By leveraging MFC technology, we can directly implement our solution to recycle 260 golden gate bridges worth of plastic waste. By just recycling 56% of that, we ensure that no new plastic bottles, or PET products as a whole, are made again.

TL;DR

By 2026, the weight of PET plastic in our oceans will be equal to 260 golden gate bridges stacked together. However, just 56% of that plastic would be enough to meet global demand.
Current plastic alternatives are more expensive and are of lower quality than current PET plastic.
We propose an MFC system that chemically recycles PET plastic, and generates electricity from degradation to power the reformation of PET resin pellets.
That way, the main cost of the energy needed to create extremely high temperatures and low vacuum pressure is minimized, and the system is self-sustaining.
We sell this to companies at their current price or even lower- which is much cheaper than current recycling/plastic alternatives.
If we can expand this to just half of the ocean’s plastic- we could minimize new PET production to zero