In Psy’s latest anthem “That That”, the international pop star jubilantly celebrates a post-pandemic future. But while many countries are reopening their borders and lifting social distancing measures, Psy might have jumped the gun on getting the party started.
Covid-19 has led to a surge in medical waste. How can we deal with discarded Personal Protective Equipment (PPE) such as masks, gloves, and gowns sustainably? By converting plastic into water and fuel, that’s how.
Professors from the University of Auckland and Cornell University break down the science behind these methods and share how they can help to minimise Covid-19 pollution.
Turning plastic into vinegar
Engineers at the University of Auckland are converting discarded PPE into water and acetic acid (more commonly known as vinegar) in a process known as hydrothermal deconstruction technology.
This involves adding shredded plastic waste into a reactor, and applying pressurised water and compressed air to the contents at a temperature between 200-300°C.
The end product of dilute acetic acid is commonly found in cleaning and disinfectant products. It is also possible to extract pure acetic acid from its dilute form, which is a key component of inks, paints, and coatings.
With large amounts of water involved in this process, some may have concerns about wasting this precious and scarce resource.
But engineers have already thought one step ahead by “reusing the water after each cycle to conserve it,” Saeid Baroutian, Associate Professor in Chemical and Materials Engineering at the University of Auckland, says.
There is also no wastewater generated because the only products are pure water and acetic acid, which greatly minimises any pollution to water bodies.
Everything great about…
The benefits of hydrothermal deconstruction technology are manifold.
First, the process helps to reduce the formation of toxic pollutants.
The New Zealand government prohibits high-temperature incineration as it emits dioxins and particulate matter. “But as hydrothermal systems involve lower temperatures, we can avoid producing these harmful substances,” Baroutian explains.
Second, even though the cost of this technology is comparable to that of New Zealand’s existing waste management practice, it has the added benefit of eco-friendliness.
Currently, waste facilities sterilise garbage before dumping them into landfills. The rubbish not only takes up unnecessary space but also releases a slew of toxins and greenhouse gases into the environment.
By contrast, hydrothermal deconstruction technology allows governments to deal with much cleaner by-products such as oxygen and carbon dioxide without having to break the bank.
Third, the process is very efficient. “It only takes about an hour for a small prototype machine to completely dissolve plastic waste into water and acetic acid,” Baroutian shares. In comparison, rubbish in landfills takes years to break down and never really goes away.
Reduce, reuse, and recycle
But there are limitations as well. Once hydrothermal systems have broken down PPE into water and acetic acid, recovery facilities are unable to recycle any plastic.
Disinfecting PPE can open up some room for reuse. This allows hospitals and healthcare facilities to conserve supply in the event of equipment shortages.
Recycling facilities can also convert disinfected PPE into other products, such as plastic shipping pallets, storage containers, and outdoor furniture.
However, it is not always possible to reuse or recycle damaged or contaminated PPE. This is when hydrothermal deconstruction technology comes in handy as it can sustainably decompose any unusable product.
Back to basics
Engineers at Cornell University are riding on the same train of thought. But instead of converting plastic into vinegar, they are reverting it back to its basic form – fuel.
First, engineers sterilise, shred, and remove moisture from PPE waste. Second, pyrolysis takes place. This is when a reactor breaks down these tiny plastic particles into basic chemicals at a temperature of about 650°C.
The industrial applications of these chemicals are far-reaching and attach some form of economic incentive to pyrolysis. For example, propane and butane fuel gas ovens and portable heaters.
For pyrolysis, the same benefits as hydrothermal deconstruction technology hold as well.
“This method can reduce about one-third of fossil energy consumption and one-third of total greenhouse gas emission compared to incineration,” You Fengqi, Professor in Energy Systems Engineering at Cornell University says.
Pyrolysis also frees up a lot of space in land-scarce New York because “we are not retaining any solid waste and transporting them to landfills,” You shares. Even with incineration, the state needs to deposit the ash generated somewhere. But for pyrolysis, “the by-products have productive uses,” he adds.
You estimates that the entire state only requires two or three pyrolysis facilities to capture and convert all the PPE waste into fuel. This is a huge improvement from the 25 landfills that New York currently accommodates, according to the State Department of Environmental Conservation’s website.
One step closer to reality
You’s team will first look at processing PPE waste from New York’s hospitals and medical centres. But several roadblocks still stand in the way of expanding this project city-wide.
First, it would be great if the government can put in place some incentives to encourage the adoption of pyrolysis. The method may be expensive, “but the environmental cost is even heftier to bear,” You warns.
Second, the government needs to coordinate a collection mechanism that re-routes all waste to the pyrolysis facilities.
Finding a sustainable answer to waste management is not something that private companies can handle alone, both Baroutian and You concur. The government needs to step in to overcome this insidious problem.
Psy’s depiction of a post-pandemic world may not be so pink and rosy after all, but we can hopefully get there one day if we decide to sustainably deal with PPE waste here and now.