A first step towards integrating marine plastics into urban recycling

In response to the millions of tonnes of marine litter, mostly plastics, floating on the oceans, the need to manage this waste effectively is more urgent than ever. Faced with this reality, the UPV/EHU’s Materials + Technologies research group decided to take a first step. “We assessed a practical approach: the possibility of integrating plastics collected from the sea into the urban waste system. This pioneering study, which is part of a PhD thesis, explores the possibility of managing this waste efficiently in current urban recycling infrastructures,” explained Cristina Peña, lecturer in the Department of Chemical and Environmental Engineering at the Faculty of Engineering, Gipuzkoa (UPV/EHU) and author of the work.

Unlike municipal solid waste, marine litter does not yet have a systematised management system; it is managed on a very ad hoc basis and within the framework of very specific projects. “It is important to bear in mind that this waste, having been at sea, has a level of degradation that is significantly different from, for example, a bottle deposited in a yellow container under normal conditions. So our starting point and key question was precisely this: Does the level of degradation of marine waste prevent it from being classified in an urban waste management process?” as Amaia Mendoza, a researcher in the UPV/EHU’s Materials + Technologies research group, pointed out.

PET plastic bottles

“In this work,” Amaia Mendoza went on, “we used identical PET plastic water bottles of the same brand to assess the effects of various environmental conditions. We divided the bottles into two batches: the first batch was left in the open air for nine months, simulating exposure on a beach or rocky coast, and the second batch was submerged in the sea for the same period. We saw that the submerged bottles underwent increased chemical degradation, while those exposed to the open air on the “shore” remained in a better state”. This approach allowed them to analyse how the degradation process varies according to marine conditions and how each type of waste responds in different environments.

We then “simulated how these materials would be managed in an urban solid waste treatment plant” by comparing them with the same bottles that had not undergone degradation to see if the automatic separation equipment in these plants would be able to identify and separate the plastic bottles of marine origin. “To find out, we conducted tests using an optical separation system, a type of technology that automatically classifies materials according to their composition,” and they saw that the effectiveness of separating the bottles of marine origin –both those exposed to the open air and those submerged in the sea– “was very high, comparable to that of bottles from urban waste”, said Amaia Mendoza. “These results indicate that the treatment of marine bottles in these plants is feasible and could be successfully implemented. The state of degradation is crucial when determining the feasibility of subsequently recycling them,” stressed the UPV/EHU researchers.

The authors of the work say that “the study has achieved an important breakthrough by demonstrating that PET plastic bottles of marine and urban origin can be separated in a joint process, thus establishing a first step in an area with huge potential for development”. It also “opens up the way to exploring the automatic separation of other plastics present in marine litter, such as polypropylene or polyethylene, in urban waste treatment plants”, added Amaia Mendoza.

The UPV/EHU team stresses that this work set out to evaluate the possibility of upgrading marine litter by making it attractive as a usable raw material. “If we manage to find practical applications and encourage the industrial development of these materials, collecting them will also become attractive. The more efficient and viable the management of this litter is, the greater the incentive to use it and, consequently, the greater the interest in collecting it from the sea,” said Cristina Peña.