Associate Professor Soo Han Sen holding a vial of chemical mixture that can dissolve plastic under sunlight. Photo credit: NTU Corporate Communications.
Our planet is drowning in plastic pollution. It is estimated that more than 8.3 billion tonnes of plastics have been produced since the 1950s [1], of which around 60% has ended up in landfills or the natural environment.
In 2020, Singapore generated almost 6 million tonnes of solid waste, of which 868 thousand tonnes were plastic waste [2]. Plastic waste management in Singapore occurs mainly through incineration at waste-to-energy plants, with the incineration ash sent to Singapore’s only landfill on Pulau Semakau. At the current rate of waste growth, this landfill space will run out by 2035, and a new landfill will be needed every 30 to 35 years, a tall demand for a land-scarce country [3].
A revolutionary approach to plastic waste
A new vision for managing plastic waste is being explored by the research team of Associate Professor Soo Han Sen at NTU’s School of Physical and Mathematical Sciences. They are attempting to implement large-scale “upcycling” of plastic waste — using renewable energy to convert the waste into chemical feedstocks that can be used to create useful chemicals.
They are currently seeking crowdfunding for their project, which is called Sustainable Plastics RepUrposing for a Circular Economy (SPRUCE).
The group’s technology, which is still undergoing development but has been patented by Associate Professor Soo, is the only currently known way to harness light energy to completely process a wide range of plastics. It employs vanadium photocatalysts to break down plastic waste into chemical acids, which are suitable for the manufacturing of fuel cells, preservatives, and other useful products.
The plastic waste and vanadium photocatalyst are combined in a solvent, and circulated through a reactor with an automated pumping system. This circulation process is repeated until the plastics are completely converted into the desired chemical acids.
Facing up to the planet of plastic
Existing recycling strategies for managing plastic waste are “downcycling” approaches, meaning that they produce products of lower value compared to the original plastics (or no value at all). Since most plastics in Singapore are incinerated, and the ash buried in a landfill, they are lost forever as potential resources.
Moreover, the practice of incinerating plastics has many drawbacks. Burning plastic waste produces greenhouse gases such as carbon dioxide, as well as toxic air pollutants. Although incineration plants can filter out many pollutants before they are released into the atmosphere, the process still consumes precious energy and resources. Singapore’s sophisticated waste-to-energy plants recover a significant portion of the expended energy by using heat from the combustion process to generate electricity, but the recovery far from completely efficient [4].
These built-in limitations have driven many scientists and engineers to explore upcycling schemes for plastic waste. However, at present there is no scalable commercial technology that can do this.
There are a few other technologies for catalytic plastic upcycling currently being developed. However, these all use heat to break down the plastics, which is less appealing since the required heat is often generated from either burning fossil fuels or combusting the plastics. By contrast, Associate Professor Soo’s process can be powered by sunlight.
According to Associate Professor Soo’s research team, the method is still not commercially viable, but with the right of funding and manpower, a prototype process can be demonstrated within five years.
An illustration on how SPRUCE will create a new circular economy value chain in Singapore. Image credit: Soo Han Sen.
If this comes to pass, then the use of plastics need no longer be a zero-sum game. With plastic upcycling, we can turn the crisis of plastic waste into an opportunity to benefit the planet, by providing an alternative source of inputs for the chemical manufacturing industry, which accounts for about a quarter of Singapore’s GDP. In the event that 80% of the plastic waste in Singapore can be upcycled, this would translate to a 2 million tonne reduction in carbon dioxide emissions, or around 4% of Singapore’s total greenhouse gases emissions [5]. Globally, plastic reuse and recycling could generate as much as US$60 billion for the chemical industry [6].
In the not-too-distant future, we may be able to relish the conveniences that plastics offer without sacrificing the health of our planet.
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References
[1] Fast facts about plastic pollution, National Geographic (2018).
[2] NEA Waste Statistics.
[3] Zero Waste Nation initiative.
[4] Consumer Plastic and Plastic Resource Ecosystem in Singapore, Singapore Environment Council (2018).
[5] The estimation uses monetary values adjusted to 2020 prices in Singapore, and publicly available data from public agencies like NEA. Please contact the project team for details.
[6] How plastics waste recycling could transform the chemical industry, McKinsey & Company (2018).