Abstract

Cleaning the Oceans from plastic pollution

In just a few years of growth, world population has more than tripled, inevitably leading to mass consumption and therefore to plastic packaging. This resulted in the dumping of a huge amount of waste very difficult to degrade, which, for most of it, reaches the oceans. Guided by marine currents, plastic items accumulate and gather in each of the five oceans.  In the Pacific Ocean, this garbage patch is said to spread on an area which is 5 times larger than France, not without consequences on biodiversity as well as humans and their activities.

The goal of this study is to describe the life cycle of an aquatic plactic item, from its arrival into the ocean to its retrieval and reprocessing. North Atlantic Oceanic currents will be described and modelled. Then, two possible solutions to plastic pollution will be exposed:

  • The retrieval of water surface aquatic plastic waste and reprocessing into fuel or incineration. We will try to figure out whether this reprocessing could be enough to cover the extraction costs.
  • The increasing use of biodegradable bioplastics, such as PLA (polylactic acid). We will discuss whether this solution is environment-friendly.

ROMS AGRIF software uses primitive equations to model currents and represents the oceanic flow. This way, we can observe the four main currents of the gyre in the Atlantic Ocean.  Thanks to this modelling, combined with movement equations of plastic particles, we can understand their paths.  As soon as they enter the ocean, plastic items are carried by the main currents to the center of the gyre, where they accumulate. Retrieving them from this point might thus be interesting.

 

However, plastic extraction from the North Atlantic gyre doesn’t seem to be profitable. Indeed, in the three possible reprocessing solutions considered, the net present value, or NPV, is very negative. A project is usually accepted when this value is strictly positive. Moreover, comparative LCA (life cycle assessment) of both reprocessing solutions (conversion into fuel or incineration) doesn’t show any significant difference regarding environmental impacts. Conversion into diesel then appears to be the most acceptable answer, considering sustainable development requirements. Nevertheless, this result is strongly dependent on the amount of plastic which is really extractible, and this value is difficult to assess.

Downward solutions being hardly feasible, from an economic as well as a technical point of view, it may be more relevant to act upwards. For example, conventional plastics could be substituted by biodegradable ones. LCA clearly shows that for plastics ending on a marine environment, PLA is less dangerous to the environment than polyethylene which was retrieved and reprocessed. The role of recycling in avoiding or reducing the impact should also be noted. Because they directly depend on hypothesis, particularly regarding PLA biodegradability in the ocean, those results have to be analyzed with a critical mind. 

Ocean plastic pollution remains a complex and not well-known issue. Nowadays, the lack of information about those “plastic continents”, as well as the lack of technical means and political will, is an obstacle to setting up a project to depollute those areas. Upwards solutions such as recycling, bioplastics or taxes currently seem to be more realistic.