Plastics

27/10/2017

We have previously introduced the plastic crisis we are currently facing. We have looked at a few solutions to reduce the amount of waste on land, but what about the plastic that already reached the oceans?

The Great Ocean Cleanup

The oceans are full of plastic. Up to 22 tons of plastic are dumped in the ocean every minute, and the amount of plastic, by weight, in the oceans is expected to exceed the weight of all fish by 2050. The average plastic bottle will take up to 450 years to degrade, meaning that this marine plastic is not going away any time soon. The sheer volume of plastic deposited in the seas and oceans is known to have consequences for sea life, and downstream consequences on human health as plastic accumulates in the food chain.

The New Plastics Economy

A new initiative called ‘The New Plastics Economy’ intends to clean up the seas by providing a vision of a global economy where plastics never become trash. The initiative aims to bring together key stakeholders across the plastics value chain (consumer companies, producers, manufacturers, policy makers, and NGOs) to reduce the pollution of oceans with plastics, and to establish effective pathways for plastics after their primary use. As well as establishing these collaborations, the report proposes the creation of a coordinating body that will create global standards, coordinate with key parties, and provide funds for innovation. So what innovations might they support?

The Seabin Project

The Seabin is a small-scale floating filtration device intended to be installed in marinas and ports. Debris that is trapped by the bin is then brought onto land to be disposed of appropriately.

How does it work?

The device contains a 220V pump that gently draws surface water into a filter, along with any floating debris. Since the mouth of the bin sits at the surface of the water, no sea life is drawn into the filter. The filter itself is composed of a removable mesh catch bag, made from recycled high density polyethylene (HDPE) plastics, and is equipped to catch plastics at a minimum size of 2 mm, as well as oils and certain detergents, thanks to an oil absorption technology.

Modified from CleanTechConcepts

What are its limitations?

The major limitation of the Seabin is its ability to be implemented at scale. The bin can catch up to 1.5 kg of waste each day, amounting to half a ton each year. With ocean deposits every minute of up to 44 times that amount, the Seabin will have little real impact on the problem. The bin currently costs around $1USD to run per day, and the plastic mesh catch bag also requires regular emptying, which from a practical perspective makes the bin difficult and expensive to implement en masse. A bigger bin that catches more and needs emptying less could be the next logical step for Seabin, although no such project has been announced. Nonetheless, the project provides a good starting point for larger scale projects, and has been implemented commercially for the first time in Portsmouth, UK.

The Ocean Cleanup

Due to ocean currents, a lot of ocean plastic coalesces in huge islands, several of which have been extensively monitored, including the Great Pacific Garbage Patch and the North Atlantic Garbage PatchOcean Cleanup has designed a novel technology to deal with these garbage patches. One of the key problems to cleaning up these patches is the low density of plastic in the water, but its extensive distribution across a huge space. Estimates have put the density of plastic in these patches at 5.1 kg per square kilometre of ocean, across an area of between 700,000 to 15,000,000 square kilometres. Ocean Cleanup aims to tackle this problem by concentrating the plastic into a small area, and collecting it into a vessel for transport back to mainland.

How does it work?

A large pipe made from HDPE acts as a floater, and is mounted onto a solid screen, made from thermostable polyurethane, rather than a net, to catch plastic. The screen extends several metres beneath the surface of the water, since this is the region where most plastic mass lies. The current flows beneath the screen, allowing organisms following the current to pass underneath.

The device is then arranged in an open U-shape, and placed strategically across an ocean current, or gyre, to catch and concentrate plastic. Importantly, the device is anchored to a so-called ‘drifting barrier’, rather than being fixed to the seafloor, thus preventing small plastics from passing underneath the screen, and preventing adding stress to the system in adverse weather. The anchor does not lie on the seafloor, but nearly 600m deep, where the water flows at a much slower rate. This slower rate of movement results in the rate of the current, and therefore plastic, moving faster than the barrier, effectively concentrating the plastic. Since the barrier is mobile, and therefore subject to the same forces affecting the waste, it will drift to areas where the plastic is most concentrated.

The U shape of the device results in the plastic moving into the centre, where it drifts into a central system that houses the waste until a shipping vessel arrives to collect it. Assessment of prototypes will provide key data on how quickly the system fills up, and therefore how often the waste needs to be collected. The vessel will transfer the waste using pumps and belts, where it will be taken back to the mainland to be processed, recycled, and ultimately turned into branded goods, with the aim of generating revenue to make the process self-sustainable.

What are its limitations?

The technology is still in the testing phase. A prototype has been deployed in the North Sea, but the innovation has yet to prove itself. And whilst Ocean Cleanup aims to make the process self-sustaining, it is not known whether the value of the waste can offset the costs of the equipment, collection, processing and recycling required for the project to function at scale.

Whilst the issue of plastic pollution may seem insurmountable, the Seabin project and Ocean Cleanup have demonstrated that the problem can at least in part be solved by innovations. Ultimately, as both companies acknowledge, real change needs to come through better regulation and education to prevent the release of waste into the oceans.

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