The fight against plastic pollution has become a major challenge for the health of our oceans. It is estimated that 200 million tonnes of waste are currently present in them. Yet, the majority of this pollution does not float.
The famous « 7th continent » of plastic, although iconic, actually represents only about 800,000 tonnes. So where is the rest hiding?
For many scientists, the answer is clear: at the bottom of the waters. Images from IFREMER and other institutes confirm this — vast fields of macro-waste cover the ocean depths. The pollution visible at the surface is only the tip of the iceberg.
While capturing this pollution in the deep sea is technically unrealistic today, it is relevant to focus on its areas of origin and transit, particularly on the seabed of shallow coastal zones.
This is precisely what the Blue Odyssey Initiative has been working on since 2021.
Ports: Overlooked Passage Zones
Beyond rivers and streams — well identified as waste vectors — our expeditions have revealed flows of marine macro-waste in certain bays, but also a strategic, accessible, yet untreated transit point: port entrances.
Ports are natural waste traps. Pedestrians, bins, winds, currents, ships — the concentration of sources is considerable. This phenomenon is well documented and the subject of many studies on marine pollution originating from ports. In France, many efforts have been made: regulation, education, labeling (such as « Clean Port »). The country prides itself on being at the forefront in protecting port basins.
Numerous articles discuss topics such as:
- Pollution by marine debris
- Macro-waste pollution in ports
- Macro-waste pollution at sea
But one phenomenon remains little known: the “waste vacuum” effect produced by some ports. They not only emit waste but also attract it from surrounding areas. This behavior, repeatedly observed by divers and specialists (notably during Blue Odyssey South 2022 and Corsica 2023 expeditions aboard the Platypus), has never been formally studied — yet it deserves full attention.
Three Hydrodynamic Phenomena at Work
The “waste vacuum” effect in ports can be explained by a combination of three phenomena, well known in navigation but rarely linked to pollution:
- Venturi effect: when water flows from a large volume (the sea) to a narrow passage (the entrance) and then to another large volume (the port), it accelerates and sucks in suspended particles.
- Coastal currents and winds, often combined, which push floating or semi-submerged waste toward port structures.
- Tides, weak in the Mediterranean but strong elsewhere, whose effects on sediment transport are known but rarely applied to macro-waste.
When currents reverse, waste trapped in ports can be released back into the sea, damaging surrounding water quality.
What Current Solutions Do Not Address
Today, two main types of solutions exist to combat port pollution:
- Upstream (on land) solutions, such as filters on stormwater outlets and sewers, widely deployed by our partner Pollustock, especially through the Hydro Rescue system.
- Surface solutions, with floating recovery devices. Among the most effective is the D-Pol, developed by Ekkopol, a low-tech skimmer designed to recover surface waste.
These solutions are relevant, proven, and contribute effectively to reducing surface pollution.
However, one fact is clear: no device currently addresses submerged waste resting on the seabed, even though it is estimated that 40% of waste sinks upon arrival, and up to 90% eventually settles on the bottom.
Note: seabed clean-up operations do exist — led by divers or committed associations (such as Stéphane Mifsud or Mer Veille) — but they do not constitute permanent capture devices.
THE FINDING
PolluSub was born from this finding. Rather than waiting for waste to settle in the sea, PolluSub acts upstream, at the transit point. It transforms rivers, bays, or ports — already partially cleaned at the surface — into active underwater depollution actors.
THE CONCEPT
- Sensors detect submerged waste flows at port entrances (or other areas: rivers, bays, estuaries…).
- A passive underwater net, inspired by a tennis net, is placed on the seabed, perpendicular to the flow, without disturbing marine life. It is held by floats and weighted by a chain.
- It is easily lifted, emptied, and repositioned following a simple protocol adapted to each site.
Note: only certain geological configurations are concerned by this phenomenon, not all! Preliminary studies are therefore essential.
A Missing Link in Pollution Control
PolluSub addresses a previously ignored need: capturing submerged macro-waste before it permanently settles or is released back into the sea.
Simple, robust, economical, and scalable, this device complements existing solutions by adding the underwater dimension to a comprehensive port depollution strategy.
A Strategic Alliance
PolluSub is driven by a complementary partnership:
- Blue Odyssey Initiative: design, coordination.
- Pollustock: co-design, manufacturing, distribution.
- Ekkopol: operational expertise, hydrodynamic analysis, management.
This trio pursues a clear goal: turning ports into anchors for sustainable underwater depollution.
Call for Collaboration
Ahead of UNOC 2025 in Nice, we wish to open this project to:
- Pilot ports and local authorities;
- Public or private partners (CSR, sponsorship, joint deployment);
- Sea-related stakeholders ready to promote and support this new approach.
Source : Blue Odyssey Initiative:
