Among the many technologies and initiatives developed over the years to remove plastic from seas and rivers, it is now possible to take stock, that is, identify the most promising and effective solutions. To this end, we report here the analysis and results of this study published this year in the prestigious journal “Ocean and Coastal Management.”
What are the main strategies for removing plastic from seas and rivers?
Let’s first explore a selection of innovative strategies to eliminate the harmful presence of macro-plastics and micro-plastics from our precious water resources.
Beach plastic collection
Naturally, we begin with the commitment of heroic operators and volunteers who dedicate themselves to waste collection from beach to beach, including the dreaded plastic. This action frees the beaches from macro-plastics and can be done through manual methods, using bags, gloves, and rakes, or with the help of beach cleaners towed by powerful tractors.
Rainwater filters
These devices are used for the treatment of drainage water from impermeable surfaces, such as roads, parking lots, and roofs. These filters are designed to remove pollutants, sediments, and other substances from drainage water before it is discharged into the sewer system or surrounding water bodies, such as rivers, lakes, or oceans.
Municipal wastewater filters
As we know, municipal wastewater is collected in sewage networks, which transport it to a treatment plant. Here, it undergoes a series of treatment processes to remove contaminants and pollutants before being discharged into the environment. The good news is that these processes are usually able to remove a considerable percentage of microplastics 69-99%. These microplastics are mostly microfibers and remain accumulated in sewage sludge, the proper disposal of which is essential to avoid environmental contamination from plastic.
Floating barriers
These devices (called booms in English) are barriers that trap floating macro-plastics on the surface. They can be strategically positioned, for example, anchored to the banks of a river at the delta or near sensitive areas, such as bridges or dams. Their design must include suitable anchors and positioning according to weather conditions and prevailing currents, and a regular maintenance plan will be necessary for the removal of collected waste.
Sea bins
Sea bins are devices that remain semi-submerged in the water at specific anchor points. Thanks to an electrically powered pump, they create a forced circulation of water into and out of the bin. In passing through the bin, residues and macro-plastics are trapped while the rest flows through. Here and here are two examples. Sea bins fall into the category of immobile skimmers, devices that remain fixed and remove plastic near the surface.
Specialized vessels
Over time, vessels capable of removing plastic have been developed. These include dredger boats: these vessels can dredge the bottom of water bodies for limited depths for various purposes, including maintenance and trash removal. Another type of initiative that makes use of vessels is that of ships equipped with nets, which can mechanically filter the first meters or tens of centimeters of water surfaces, as in this and this example. In this case, we are talking about mobile skimmers, mobile devices that, like sea bins, act as “scoops,” trapping waste and letting the rest pass, but in this case, they can move.
What are the best strategies?
Let’s see what the most promising strategies are for plastic removal from water bodies, according to the aforementioned study. For this work, researchers were able to contact over a dozen companies active in this sector in Europe, America, and Canada and obtain from them 14 datasets suitable for analysis. Of course, to identify the best method, it is first necessary to clarify the evaluation criteria. The study is based on the use of various indicators, including cost-benefit analysis, which allows evaluating the benefit (i.e., plastic removed from the environment over a period) compared to the cost, i.e., initial investment, operating costs, and maintenance costs. Costs include, for example, the removal of plastic from floating barriers or sea bins.
Study results
The study first reports that removing plastic from beaches, floating barriers, and rainwater filters are the strategies with the lowest investment and operational cost. The use of vessels, both dredgers and mobile skimmers, requires the highest investments (up to almost €1 million in investment and €0.2 million/year in operating and maintenance costs).
However, considering the effectiveness of the systems, i.e., introducing into the equation the amount of plastic removed annually and thus considering the euros spent to remove each kilogram of plastic, it turns out that vessels are among the most cost-effective solutions, while rainwater filters and floating barriers are heavily penalized precisely for the reduced amount of plastic removed. While vessels can remove thousands of tons of plastic per year (4960-6791 tons/year), floating barriers and filters have much more limited capacities, and their effectiveness is closely tied to their positioning. Finally, sea bins are quite promising because they show a limited investment cost but still allow for the removal of significant amounts of plastic (185 tons/year).
How authoritative are the sources?
The article is published in the “Ocean & Coastal Management” journal, an international journal that publishes scientific articles on coastal and ocean conservation. The published articles are “peer-reviewed,” meaning they must undergo quality control by other experts in the field, who can reject the article or propose modifications before its publication. It is important to note, however, that the treatment, although rigorous, is based on data provided by the same companies contacted by the researchers, and therefore may be influenced by this difficult-to-eliminate bias, given that databases on the subject are currently very limited.
Conclusions
In conclusion, the issue of collection and disposal from the seas is still a field of discoveries, where different companies and governments launch initiatives, with more or less success. Certainly, the solution to the problem is not simple, as we are talking about huge areas to be cleaned, with debris of plastic of various sizes, floating and non-floating.
Ranking may seem like a useless activity, but in reality, this type of work will help direct efforts (both economic and non-economic) in the coming decades. On the other hand, should we stop plastic upstream or collect it downstream? Reduce consumption, as proposed by the first of the 3R of sustainability? Unfortunately, it will be necessary to do all this and more.
What to remember
There are various technologies and initiatives that have been pursued over the years to remove plastic from seas and rivers. As one can imagine, not all of them have the same degree of effectiveness and costs. According to an analysis conducted by researchers from around the globe, if we focus solely on investment costs, floating barriers and filters placed on stormwater have excellent results. However, when considering the amount of plastic removed, specialized vessels have an edge.
Additional Information
The article “Assessing the performance of marine plastics cleanup technologies in Europe and North America” (in English) can be found here.
