Membrane Capacitive Deionization Technology and Reverse Osmosis for Fluoride Removal from Water – A Comparative Study

Abstract

Ion-exchange membranes (IEMs) are unique in combining the electrochemical properties of ion exchange
resins and the permeability of a membrane. They are being used widely to treat industrial effluents, and in seawater and
brackish water desalination. Membrane Capacitive Deionization (MCDI) is an emerging, energy efficient technology for
brackish water desalination in which these ion-exchange membranes act as selective gates allowing the transport of
counter-ions toward carbon electrodes. Rajasthan is the only state where all most all the districts are affected by high
fluoride (beyond the permissible limit). In 23 districts the fluorosis problem can be visualized at various intensity level
i.e. Dental fluorosis, skeletal fluorosis, nonskeletal manifestation etc. Various Technologies have been developed so far
for deflouridation. Many Reverse osmosis plants have been installed in Rajasthan for removal of fluoride from ground
water. But, it is associated with high power consumption, scaling and fouling of membranes and reduced water recovery.
This sets up a need for more energy efficient device with less maintenance and operational cost with overcoming
shortcomings of reverse osmosis. Membrane capacitive deionization is the emerging technology which utilizes constant
current method with varying voltage to remove salts from underground water. The pilot plant (CapDI) manufactured by
Voltea (Netherland) was provided by In Now India Pvt. Ltd for carrying out this study. It was found that Capacitive
deionization technique is very efficient in removal of low salinity feed water sources. Energy consumption is quite low
approximately only 20 to 30% of energy utilized by reverse osmosis. And flow recovery rate of CapDI plant is also high
than reverse osmosis plant.