Team:Imperial College/Industrial Implementation

Products

Using mixed waste as a resource, our system has been designed to produce ethylene glycol and poly-3-hydroxybutyrate as commodities to be sold in industry.

Product description

P3HB is degraded by specialised microorganisms without releasing of toxic products or intermediates. Meanwhile, P3HB has a low water solubility [1] and medium-low water and CO2 permeability [2], as well as very good barrier properties, enabling application in packaging. This biopolymer also has a high degree of crystallinity, high melting temperature [3], and good tensile strength, making it comparable to one of the most common petroplastic isotactic polypropylene [3]. In addition, there are many processing methods for P3HB [4], such as injection molding and extrusion, which are required in manufacture of most plastic products. Although the impact strength is relatively weaker compared to petroplastics, P3HB nanocomposites have shown significantly improved impact strength as well as other properties [3].

Ethylene glycol is a valuable by-product obtained in the process of recycling PUR and PET. Due to the high affinity for water, ethylene glycol has been commercialised for a wide range of uses including desiccant and vaccine manufacture.

Technology

Our waste degradation system is designed to fit with and enhance current waste management practices. One of the main focuses of waste legislation is to move towards a circular economy, where resources in waste are completely reused and nothing is lost. This will minimise the amounts of virgin material we require and also how much we have to dispose of. Mixed wastes are some of the ones which are most difficult to tackle as they require different processes to recycle or recover the different components. A type of mixed waste called solid recovered fuel(SRF) is produced from recycling plant seeking to recover valuable products from waste. Hundreds of thousands of tonnes of this are produced each year in the UK. It is then shipped at great expense to Europe for incineration. From this we will extract the product ethylene glycol and produce a substrate which we can produce the commodity bioplastic, PHB from. We have also designed the first system for PHB recycling, taking responsibility for the end of life solutions to the commodity we are producing. Each step is designed to be carried out in bioreactors.

Mixed Waste Breakdown

We plan to operate the bioreactors for SRF breakdown at the recycling facilities which produce it originally. The purpose of these facilities is to recover anything of value from waste. A system which could efficiently produce valuable commodities from unrecoverable waste would be welcomed. The important addition to these bioreactors will be membranes capable of filtering ethylene glycol from the remaining material. This are placed downstream of the reactor and allow for the efficient and specific separation of the product.

Sourcing

Every year, about 320,000 tonnes solid recovered fuel (SRF) is produced per recycling site in the UK, from where SRF is shipped to other countries for incineration. SRF is a cost to these recycling companies as they pay approximately £65 per tonne for shipping. SRF contains at least 30% plastic. Therefore, we plan to use SRF from the recycling companies as the feedstock, and charge them less than incineration sites.

Bioreactor safety features to prevent accidental release of our engineered bacteria

We have come up with a few strategies to prevent release of our bacteria into the environment. Firstly, the bioreactor containing bacteria will have a kill switch that kills bacteria if the bioreactor is opened when operating. Secondly, we lyse the cells at the end of reactions to harvest our product. This also ensures living bacteria will not be released unexpectedly. The team is also considering to establish symbiosis between bacteria with different plastic-degrading enzymes, so that the bacteria only live when two or more strains are present.

Market analysis

Market for bioplastics

Plastics represent a large percentage of materials used, as they can be applied in products ranging from water bottles and EE (electrical and electronic) equipments to agricultural mulch film and textiles.

At the present, bioplastics are approximately twice the price of petroplastics, limiting large-scale implement of bioplastics. Although bioplastics count only a small percentage of the total plastics currently, the market for bioplastics is predicted to grow 30% per year [3], and market share is predicted to approach 25%-30% by 2020 [5]. This fast growth rate predominantly come from the increasing price of petroleum and consumer pressure of using greener products.

Competitive comparison

There are existing P3HB producing companies that utilise genetically modified plants or microbes to produce P3HB. However, the technologies they developed cost higher than our technology, as shown in the graph. Plant-based technology cost estimation is based on switchgrass, which shows the highest P3HB production efficiency (3.7% of total dry mass) compared to other plants [6]. Apart from the cost, many other problems are potentially associated with existing technologies. For instance, plant-based technologies require a large growth area, plants have slow growth rate compared to bacteria, and current microbe-based methods demands glucose produced from corn as the feedstock.

References

1. Terada, M. & Marchessault, R. H. (1999) Determination of solubility parameters for poly(3-hydroxyalkanoates). International Journal of Biological Macromolecules. . 25 (1-3), 207-215.
2. Miguel, O., FernandezBerridi, M. J. & Iruin, J. J. (1997) Survey on transport properties of liquids, vapors, and gases in biodegradable poly(3-hydroxybutyrate) (PHB).Journal of Applied Polymer Science.. . 64 (9), 1849-1859.
3. Pilla, S. (2011) Handbook of Bioplastics and Biocomposites Engineering Applications 1st edition. USA, Scrivener Publishing LLC.
4. EHuang, J. C., Shetty, A. S. & Wang, M. S. (2003) Biodegradable plastics: A review. Advances in Polymer Technology. 10 (1), 23-30.
5. Helmut Kaiser consultancy. (2010) Bioplastics market worldwide 2010/11-2015-2020-2025. [Online] Hong Kong. Available from http://www.hkc22.com/bioplastics.html. [Accessed: June 2013].
6. Somleva, M. N., Snell, K. D., Beaulieu, J. J., Peoples, O. P., Garrison, B. R. & Patterson, N. A. (2008) Production of polyhydroxybutyrate in switchgrass, a value-added co-product in an important lignocellulosic biomass crop. Plant Biotechnology Journal.6 (7), 663-678.