To control buoyancy, ships, tankers and cargo carriers store ballast water. Ballast water is released into the sea when cargo is loaded and, when it is unloaded, water is pumped in as ballast.
Studies report that 12 billion tonnes of ballast water is dumped into the sea each year. This water contains a substantial amount of biological and other contaminants. One such contaminant poses a threat to marine fauna. Microplastics, plastic pieces of size less than five millimetres, disrupt the ocean food chain, causing plastic accumulation in the body, especially in predators.
Ravidas K Naik and team from the National Centre for Polar and Ocean Research, Goa recently collaborated with researchers from other Indian institutes to develop a simple method for reducing microplastic pollution from global oceans.
To control bioinvasion and pollution in the ballast, when pumping water in, ships usually filter out organisms and particles greater than 50 micrometres. The researchers now devised a screening chamber at the discharge point of the water that is flushed back into sea.
The chamber made of non-corrosive stainless steel has screens of different mesh sizes. The researchers designed the chamber such that the back-flushed water first falls over a plate of 10 millimetre mesh size. Then it passes through a series of three more layers of screens with reducing mesh sizes, ending in a mesh size of only 100 micrometres, to filter out the microplastics. Then, before discharge into the sea, the filtered water enters the bottom chamber which has a mesh size of twenty millimetres.
The researchers claim that the technique can gather up to 204 metric tonnes of microplastics per day, on a global scale.
“If the International Maritime Organisation collaborates with the shipping industry to put this suggestion for a filter at the ballast water outlet, global reduction in microplastics in oceans can be achieved in a short time”, says Ravidas K Naik, NCPOR Goa.
Environmental Pollution, 283: 117070(2021);
Meera K M
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