Water purification using crab shells

Scientists have discovered that crab shells are effective in removing copper and cadmium from polluted water

[Translation by Dr. Nachmani Moshe]

The metals copper and cadmium occur in nature normally, but human activities, including in industrial and agricultural processes, may increase their concentrations. In high concentrations, copper can cause adverse health effects such as nausea, and cadmium can be toxic to the kidneys.

Wastewater treatment methods help remove these metals from water sources intended for daily use. Common methods include, among others, chemical precipitation, coagulation, flocculation, ion exchange, membrane filtration, activated carbon and much more expensive technologies (for example, the use of carbon nanotubes). At the same time, waste materials that exist in nature, known as absorbent biomaterials, can purify the polluted water with the same efficiency, alongside their negligible impact on the environment and human health.

As part of a long-published paper in the scientific journal Pertanika Journal of Science and Technology, scientists from the University of Malaysia tested the effectiveness of using ground crab shells as absorbent biomaterials. These shells are suitable for the removal of copper and cadmium ions thanks to the fact that the substance calcium carbonate that makes up their outer shell forms strong bonds when exposed to copper and lead, and the substance chitin (one of the main components of the hardened exoskeleton of arthropods) absorbs the dissolved cadmium and copper ions . These shells themselves are a common waste material in the fishing industry, a fact that makes them excellent candidates as effective and cheap materials for removing metals.

The team of researchers performed several tests in water conditions similar to those existing in the fields of mining and refining using five different concentrations of copper and cadmium ranging from 20-1 percent. The researchers found that the crab shells are able to remove up to 95 percent of the copper ions and up to 85 percent of the cadmium ions, after only six hours.

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