doi:10.1038/nindia.2016.130 Published online 3 October 2016
Researchers at National Environmental Engineering Research Institute (NEERI) in Chennai have reported desalination of sea water using a microbial desalination cell (MDC) that utilizes activated carbon from coconut shells1, a biomass waste widely available in India.
Sea water is salty due to the presence of sodium chloride. Technologies, such as reverse osmosis, are currently used to make such water potable. These technologies are energy intensive and expensive.
MDC, a modified microbial fuel cell, has a middle compartment to hold saline water with an anode chamber and a cathode chamber on either sides. It has graphite rods acting as electrodes. Its working principle is as follows: the anode chamber is filled with a liquid medium to support microbial growth. Microorganisms growing on the anode surface form a biofilm and oxidize the organic matter in the medium releasing electrons, which move towards the cathode. To maintain electro neutrality, cations (positively charged sodium ions) of the saline solution migrate into the cathode chamber and anions (negatively charged chlorine ions) move into the anode chamber. The saline water in the middle chamber is thus desalinated.
The authors loaded activated carbon derived from coconut shells into the anode chamber to find higher desalination and power generation than that from a normal anode chamber. The researchers say further research using different types of carbon from other biomass sources might yield interesting results. This may lead to techno-economically feasible designs that can be used for simultaneous salt removal from sea water and electricity generation, they say.
1. Sophia, A. C. & Bhalambaal, V. M. Microbial water desalination and bio-electricity generation – role of biomass carbon. Curr. Sci. 111 (2016) doi: 10.18520/cs/v111/i6/1077-1083