Environmental Engineering Reference
In-Depth Information
adsorption processes, the distillation process does not get affected with exhausted capac-
ity of adsorbents. Also, any problems in the distillation can be identiied by the absence of
water exiting the device. Energy consumption is the major challenge, and a lot of efforts
have been made to design and develop energy-eficient distillation stills. The material
that is removed from water gets deposited in the distillation compartment of the unit,
which needs regular cleaning and is sometimes tedious. Chemicals are commonly used
to effectively help remove these deposits, and the frequency of cleaning is obviously
dependent on the amount and nature of the material dissolved in the input water used
for distillation. Distillation can remove F and almost all other constituents in water; there-
fore, essential salts may need to be supplemented. Household-sized distillation systems
are available, while solar stills are also being considered for cleaner energy and low cost.
In this way, although distillation offers effective removal of luoride, high-energy cost
and the removal of useful water constituents are major limitations, so this is not a popular
option for deluoridation.
17.6 Electrochemical Methods
Electrochemical methods have also been extensively used for removal of luoride. This
method involves electrosorption of luoride on electrogenerated aluminum hydroxide loc,
produced by the anodic dissolution of aluminum or its alloys, in an electrochemical cell
(Lounici, 2004). However, the process is energy intensive, which can be overcome by using
electricity generated by solar panels. Another disadvantage is that signiicant quantity of
luoride-rich sludge is generated, which is sometimes dificult to dispose.
17.6.1 Electrolytic Defluoridation Technique of CSIR-NEERI
A deluoridation technique based on the principle of electrolysis has been developed in
NEERI, and the irst plant based on this technique was installed in 2002 at Dongargaon
village, Chandrapur district, Maharashtra, India. This technique requires simple equip-
ment and is easy to operate and controlled electrically with no moving parts, thus requir-
ing less maintenance. It can be conveniently used in rural areas where electricity is not
available, as solar panels can be coupled to the unit. The technique avoids use of chemicals,
and there is no problem to neutralize excess chemicals, and it produces palatable, clear,
colorless, and odorless water. The process is found effective in removing excess luoride
and also bringing down the bacterial load of the raw water. The deluoridation process is
based on the principle of electrolysis, using aluminum plate electrodes placed in the raw
water containing excess luoride. During the electrolysis, the anode gets ionized and luo-
ride is removed by complex formation, adsorption, precipitation, coagulation, and settling
(Gwala et al., 2012).
An electrolytic deluoridation unit basically consists of an electrolytic reactor having an
aluminum anode and cathode. When a direct current (DC) source is applied across the
electrodes, the anode dissolves and hydrogen gas is released at the cathode. During the
dissolution of the anode, various aqueous metallic species are produced, which depend on
the solution chemistry. These metallic species act as a coagulant by combining with the
luoride ions present in the water to form large-size loc, which can be removed by sedi-
mentation or iltration. The electrolytic deluoridation process using sacriicial aluminum
