Does it rot?
Various bioplastics have been developed to address environmental issues associated with conventional petroleum-derived plastics. However, bioplastics are associated with some shortcomings. It should be understood that similar to petroleum-based plastics, some bio-based plastics cannot be recycled. Consequently, many biodegradable bioplastics end up in landfills, which decompose gradually and produce methane gas. We confirmed this when meeting with Belinda Li, a bioplastics expert, who demonstrated that bioplastics can contribute to just as much pollution as plastics and stressed the importance of considering the degradability of our bacterial cellulose. To address this issue within Cellucoat, we tested the biodegradability of compostability of our bacterial cellulose coated in PHB by sending a sample to our city’s composting facility.
In an attempt to create sustainable packaging alternatives to plastic while still maintaining the cost, strength, and variability advantage that traditional plastic materials have, companies have turned to biodegradable plastics, such as PLA (1). According to Belinda Li, an environmental engineer and an expert on the impact of bioplastics, the environmental friendliness of biodegradable materials is overstated. Belinda Li indicated this is because, in combination with very effective marketing and poor public knowledge, it is believed that biodegradable materials can be composted, but the opposite is actually true.
All compostable materials are biodegradable, while not all biodegradable materials are compostable (2). This is because biodegradable materials do not degrade within the set amount of time in city-wide compost facilities, thus getting placed back into the landfill stream with plastics (2). Therefore, with the current production and use of single-use plastics and inadequacies in city-wide composting programs, biobased plastics will contribute to pollution to a similar degree to that of plastic (2).
Hence, Cellucoat must be designed to not only be biodegradable and adhere to the industrial certification of compostability, but it must also be compostable within city compost facilities so it can be processed and degraded rather than being thrown into the landfill.
Our team reached out to Natalia Gonzalez, Waste Management Specialist at Calgary Waste Services to discuss how materials are diverted from landfills, what materials can be composted, and lastly if Cellucoat is compostable. From this discussion, our team came out with three key findings:
Using these three considerations, our team went through three iterations of the Cellucoat design and proposed implementation.
During the initial prototyping phase, our team wanted to choose a material that could be both made from produce and composted in the same manner. Bacterial cellulose became an attractive material choice because it was made of pure cellulose, which naturally degrades in three months, which is half the time that other peels such as banana and apple peels take to compost
We thought that our material choice was sufficient to assume its compostability, however, we were reminded by Belinda Li that post-production treatments can compromise the degradability of naturally compostable materials. The post-processing treatments of autoclaving, washing in 0.5 M sodium bicarbonate and air drying were tested in a solution of cellulase. The results indicated that the BC material treated with sodium bicarbonate was resistant to degradation from cellulase compared to the untreated control. This was good news for the longevity of the material, but not ideal for a compostable material as microorganisms rely on internal cellulases to break down the BC substrate.
The decomposition process in compost is mediated by aerobic bacteria that break down and use food waste as energy (3). To break down organic materials, aerobic bacteria produce numerous, extracellular enzymes (3). With many types of enzymes within the decomposing bacteria with the purpose of breaking down different types of cellulose, our post-production treatment would not compromise the compostability of the material.
Even though the primary packaging material was compostable, the other components of Cellucoat, like PHB and the AMPs, must also be compostable. According to literature, both PHB AMPs are, as they can be broken down by intracellular enzymes within decomposing bacteria. However, biodegradability does not guarantee compostability in industrial compost conditions.
Our team once again reached out to Calgary Waste Management to see what criteria materials must meet to be compostable in industrial compost conditions.
To test if different materials can be degraded, Calgary Waste Management conducts trials to test the compostability of new materials that have the potential to be diverted to be composted. Hence, our team was able to get both BC alone and PHB integrated into BC samples sent to the Calgary compost facilities to undergo the 60-day compost cycle with the rest of the test materials.
Figure 2: After delivering the samples to be tested for their compostability, the 2022 iGEM Calgary team was given a tour of the Shepard Compost Facility and learned how waste is diverted to compost and recycling streams to reduce and repurpose waste that would otherwise go to the landfill.
Our team sent in the two BC and BC enriched with PHB samples to the Calgary Waste Facilities in Early August, and by the end of September, results were available. The BC samples were degraded to a slightly larger extent compared to the BC enriched with PHB samples.
After further correspondence with Natalia Gonzalez, she stated that as long as the material appears to be a part of normal and high quality fertilizer it is still capable of being diverted to the compost facilities. Since both samples were evidently degrading and had a rich black color to them, it was evident that the materials blended into the compost substrate and will be permitted to be placed into the compost bins.
During our initial meeting with Natalia Gonzalez, Waste Management Specialist at Calgary Waste Services, we learned that Calgarians often struggle with sorting their waste properly. To mediate this, the Calgary Waste facilities have educational initiatives to help the public learn about how to organize their waste and ways to reduce personal waste through following the “reduce, reuse, recycle, repurpose” model. However, Natalia shared statistics collected by the Calgary Waste Management, where a staggering 38% of waste collected in family landfill bins (black bins) is food waste that can go into the compost bins (green bins), and 130 million kg of food waste goes into the green bins annually from Calgarians.
The purpose of Cellucoat was to not only repurpose food waste but to reduce it by prolonging the shelf-life of produce. Our team wanted to expand these values to not only reduce food waste by increasing the amount of time food can be used, but also reduce the amount of food waste Calgarians throw out.
Using the advice of Natalia Gonzalez on the importance of educating the public on how to organize their waste, our team worked with the Calgary Waste Management App-Calgary Garbage Day- to provide accessible and educational ‘tips’ that pop up on the screen when Calgarians look for their garbage schedules to improve behaviors and practices to reduce the amount of food that is thrown out. The tips were iteratively improved upon by discussing with Natalia Gonzalez what information would be useful for the average Calgarian to know, improving how the information is communicated, and ways that it can be integrated into the app to be accessible without interfering with the main purpose of the app, which is to tell Calgarians which day their garbage is being picked up.
An example of the app tip that we collaborated with the Calgary Waste Management:
Integrating the tips into the Calgary Garbage Day app ensured that when Cellucoat goes onto the market as a compostable packaging material, it will be properly diverted to compost facilities as the public will know what signs to look for on packaging to indicate that it is compostable, all while reducing personal food waste to reduce the amount of usable food waste that goes to the compost or landfills.
The degradability of bacterial cellulose has implications when moving to an industrial level. It has been found that most bioplastics require an industrial composting facility to actually break down quickly and less harmfully. These bioplastics are only compostable in industrial composting facilities. Thus, if they are not disposed of properly, they are not much better than regular plastics. Furthermore, if left in a backyard compost, it generally takes at least a decade to break down (4).
Through prior literature, it has been found that PHB and BC are both natural polymeric materials that have the potential to replace traditional, nonrenewable polymers (4). In particular, the nanofibrillar form of bacterial cellulose makes it an effective reinforcement for PHB (4). When tested, it was found that the PHB/BC composite biodegraded at a greater rate and extent than that of PHB alone, reaching 80% degradation after 30 days (4). In contrast, PHB did not reach this level of degradation until close to 50 days of composting (4).
Since there is minimal research on composting BC, PHB, and nisin, the process of degrading bioplastics, in general, will be explored.
Industrially compostable bioplastics provide the functionality we need from single-use plastics but can be transported to commercial facilities and turned into usable composts and fertilizers in under 180 days (5). These facilities can process large volumes of municipal compostable waste, allowing communities to not only invest in bioplastics but to reduce the amount of food waste that is transported to landfills.
Two smaller-scale composting methods are on-site composting and vermicomposting (5).
On a municipal scale, there are three types of industrial composting: aerated windrow, aerated static, and in-vessel. Each can process large volumes of compostable waste.
Overall, not only does composting provide a better end-of-life option for bioplastics and other materials, but it can also divert a huge volume of waste away from landfills, where that waste can be converted into something new and usable for agricultural and other purposes. Up to 50% of the waste currently being landfilled could be composted instead (5). When food waste breaks down in landfills, it does so anaerobically, meaning that it does so without oxygen present. This process releases methane gas, an extremely harmful greenhouse gas. The composting process brings oxygen into the equation, allowing carbon to be sequestered in the final compost material rather than released into the atmosphere.
Municipal composting saves money for communities by diverting food waste from landfills. It also promotes sustainability by reducing emissions of methane, a powerful greenhouse gas produced in landfills when waste breaks down in the absence of oxygen. With these monetary and environmental benefits of increasing waste divergence to compost facilities, Cellucoat was iteratively designed with the intent of being compatible with being compostable in municipal industrial compost facilities. Through direct collaboration with the City of Calgary Waste Management Facilities and experts in the field of bioplastics, our team not only gained a holistic understanding of how large-scale compost facilities work and what materials can be composted but also verified if Cellucoat could be composted in municipal composting conditions.