Bio-based plastics can reduce waste – but only if we invest in systems to get rid of them

Waste plastic. Image: Getty.

With news that companies like Starbucks, Hyatt and Marriott have agreed to ban plastic straws, it’s a fitting time to consider the role of plastic in our daily lives. Plastics are an often overlooked modern wonder – cheap and multipurpose substances that can be fashioned into myriad products.

Drinking straws are just the literal tip of humanity’s plastic addiction. In 2016 global plastic resin production reached nearly 335m metric tons. By some estimates, it could grow to approximately 650m metric tons by 2020, roughly 100 times the weight of the Pyramid of Giza.

Our lab is one of a number of research teams looking for potential solutions to society’s plastic problems. We study a tiny photosynthetic bacteria, which we are using as a production platform to convert light and carbon dioxide into renewable compounds, including bioplastic alternatives. Bio-based plastics are a promising option for reducing plastic waste, but scaling them up will require substantial investments, both in making them and in special facilities for disposing of them.

Worldwide, only 14 per cent of plastic packaging is recycled. Image: Ellen MacArthur Foundation/creative commons.

Long-lived waste

Much of the world’s plastic output is manufactured into single-use objects, such as drinking straws. Indeed, food packaging and food-related objects, such as cups, carryout containers, shrink wrap and plastic bags, account for a large proportion of all plastics made.

Less than 10 per cent of all waste plastic is recycled worldwide. Most plastic food packaging cannot be easily recycled if it has any food remnants stuck to it, because these residues can interfere with various stages of processing. As a result, many recycling plants will not accept food packaging.

What about other plastic waste? About 12 per cent is incinerated, but nearly 80 per cent ends up in landfills or the environment. In the ocean, currents aggregate plastic trash in large floating “islands” of garbage.

A NASA simulation shows how ocean currents steer plastic waste into huge floating garbage patches.

Whether they are buried or floating at sea, plastics can take hundreds of years to break down. In the process they can wash up on shore, creating litter and tourism headaches. Furthermore, large plastic objects, and even the microparticles they can wear down into, are harmful to a variety of wildlife, including seabirds, marine life and corals.

Plastic from plants

A wide variety of bio-based plastics made from renewable biological compounds have been under study for many years. Today, many can serve as drop-in replacements for the fossil-fuel based plastics that most of us are familiar with, such as polystyrene and polyethylene.

Most bioplastics are currently made by taking sugars derived from plants, such as corn and sugarcane, and using microorganisms to convert them into raw materials that can be eventually formed into plastic resin. But there is a trade-off between making bioplastics biodegradable on the one hand and still durable enough for their purpose on the other. A straw and cup that disintegrate halfway through your road trip are not much use at all.

Many of the most promising bioplastics in production and in development can be rapidly degraded under controlled conditions, such as those in a large-scale composting facility. Here, bioplastics may be intermingled with other organics and mixed regularly to ensure that there is adequate aeration to promote rapid decomposition. One such facility that is particularly engaged in testing and improving the degradation of bioplastics is Cedar Grove, operated out of Washington state. The end result is a rich compost that is suitable for fertilising gardens and crops.

At Jepsen Prairie Organics in Vacaville, California, shredded organic waste is laid out in rows and covered to conserve heat as bacteria convert the materials into compost. Image: San Francisco Department of the Environment.

However, even bio-based plastics will still languish for decades or centuries if they are thrown in the trash and buried in landfills. Below the surface layer of a landfill, the conditions are often dry, cool and lacking in oxygen. All of these factors discourage the growth of microbes that can accelerate the breakdown of bioplastics. By contrast, compostable plastics are largely degraded within three months inside industrial compost facilities, where conditions are managed to promote aeration and temperatures are often substantially higher because of all of the microbial activity.

Similarly, it is unlikely that any developed materials will be biodegradeable under all environmental conditions. For example, they may not break down in the Arctic or at the bottom of the ocean. Conditions in such environments, such as low temperatures and oxygen levels and high pressure, can inhibit the growth of organisms that act to break the bonds within plastic polymers, leading to much slower rates of breakdown.

This means that any breakthroughs in materials science need to be coupled with sustainable methods for bioplastic production and a well-oiled system to direct bioplastic goods into composting facilities.


Using microbes to make bioplastics

Making plastic from plant sources is certainly more sustainable than fossil fuel-based approaches, but it requires land and fresh water to grow and process the feedstock materials. Our research lab is looking for ways to train photosynthetic microbes (cyanobacteria) that can naturally harness the sun to make these same bioplastic compounds.

In this process, these microbes perform the same role as plants, using sunlight and carbon dioxide to create sugars that can be converted to bioplastics. In fact, cyanobacteria are more efficient solar converters and don’t require soil or fresh water, so this approach could reduce competition for land and resources.

While it’s easy to malign the lowly plastic straw, it’s hard to come up with substitutes that are as cheap, lightweight and durable, and are environmentally benign. I believe progress is possible, but only if scientists can collectively come up with bioplastic alternatives and social policies support the composting infrastructure to dispose of them suitably.

The Conversation

Danny Ducat, Assistant Professor of Biochemistry and Molecular Biology, Michigan State University.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

Leeds is still haunted by its pledge to be the “Motorway City of the Seventies”

Oh, Leeds. Image: mtaylor848/Wikimedia Commons.

As the local tourist board will no doubt tell you, Leeds has much to be proud of: grandiose industrial architecture in the form of faux-Egyptian temples and Italian bell-towers; an enduring cultural legacy as the birthplace of Goth, and… motorways. But stand above the A58(M) – the first “urban motorway”  in the country – and you might struggle to pinpoint its tourist appeal.

Back in the 1970s, though, the city council was sufficiently gripped by the majesty of the motorways to make them a part of its branding. Letters sent from Leeds were stamped with a postmark proudly proclaiming the city's modernity: “Leeds, Motorway City of the Seventies”.

Image: public domain.

During the 1960s, post-war optimism and an appetite for grand civic projects saw the rapid construction of motorways across England. The construction of the M1 began in 1959; it reached Leeds, its final destination, in 1968. By the early 1970s the M62 was sweeping across Pennines, and the M621 loop was constructed to link it to Leeds city centre.

Not content with being the meeting point of two major motorways, Leeds was also the first UK city to construct a motorway through the city centre: the inner ring road, which incorporates the short motorway stretches of the A58(M) and the A64(M). As the council put it in 1971, “Leeds is surging forward into the Seventies”.

The driving force behind Leeds' love of motorways was a mix of civic pride and utopian city planning. Like many industrial cities in the North and Midlands, Leeds experienced a decline in traditional manufacturing during the 1960s. Its position at the centre of two major motorways seemed to offer a brighter future as a dynamic city open for trade, with the infrastructure to match. In response to the expansion of the roads, 1970s council planners also constructed an elevated pedestrian “skywalk” in an attempt to free up space for cars at ground level. Photos of Leeds from that time show a thin, white walkway running through blocky office buildings – perhaps not quite as extensive as the futuristic urban landscape originally envisaged by planners, but certainly a visual break with the past.

Fast forward to 2019 and Leeds’ efforts to become a “Motorway City” seems like a kitsch curiosity from a decade that was not always known for sustainable planning decisions. Leeds’s historic deference to the car has serious consequences in the present: in February 2019, Neville Street – a busy tunnel that cuts under Leeds station – was found to contain the highest levels of NO2 outside London.

City centre planners did at least have the foresight to sink stretches of the inner motorways below street level, leaving pedestrian routes largely undisturbed. Just outside the centre, though, the roads can be more disruptive. Sheepscar Interchange is a bewildering tangle of arterial roads, Armley Gyratory strikes fear into the hearts of learner drivers, and the M621 carves unsympathetically through inner-city areas of South Leeds with pedestrian access restricted to narrow bridges that heighten the sense of a fragmented landscape.

 

Leeds inner ring road in its cutting. Image: author provided.

 

The greatest problem for Yorkshire's “Motorway City” in 2019, however, is not the occasional intimidating junction, but the complete lack of an alternative to car travel. The dire state of public transport in Leeds has already been raised on these pages. In the early 20th century Leeds had one of the most extensive tram networks in the country. The last lines closed in 1959, the same year construction began on the A58m.


The short-sightedness of this decision was already recognised in the 1970s, as traffic began to build. Yet plans for a Leeds Supertram were rejected by successive Conservative and Labour governments unwilling to front the cost, even though smaller cities such as Newcastle and Sheffield were granted funding for light transport systems. Today, Leeds is the largest city in the EU without a mass transit system. As well as creating congestion, the lack of viable public transport options prevents connectivity: the city's bus network is reasonable, but weaker from East to West than North to South. As a non-driver, I've turned down jobs a short drive away that would be a logistical impossibility without a car.

Leeds' early enthusiasm for the motorway was perhaps premature, but there are things we can learn from the 1970s. Whatever else can be said about it, Leeds' city transport strategy was certainly bold – a quality in short supply today, after proposals for the supertram were watered down to a trolleybus system before being scrapped altogether in 2016. Leeds' rapid transformation in the 1960s and 70s, its grandiose visions of skywalks and dual carriageways, were driven by strong local political will. Today, the long-term transport strategy documents on Leeds City Council's website say more about HS2 than the need for a mass transit system within Leeds itself, and the council has been accused of giving up the fight for light rail and trams.

Whilst central government's refusal to grant funds is the greatest obstacle to Leeds' development, the local authority needs to be far more vocal in demanding the transport system the city deserves. Leeds' desire to be the Motorway City of the Seventies might look ludicrous today, but the political drive and utopian optimism that underpinned it does not.