Page 91 - Industrial Wastewater Treatment, Recycling and Reuse

66 Industrial Wastewater Treatment, Recycling, and Reuse

as salts, cyanides, nitrites, PCBs, phenols, heavy metals, hydrocarbons, and
fats. It uses only electricity and can operate at room temperature and atmo-
spheric pressure. The energy consumption may, however, depend on the
COD level of the wastewater. This method becomes relevant when removal
of heavy metals from industrial effluents from processes relating to, for
example, metallurgical, metal coatings, dyes, and batteries are concerned.
This technology can be used to recover precious metals such as Ag from
photographic materials, heavy toxic metals like Pb from battery industries,
and others. The recovery of metal is achieved by means of metallic deposi-
tion on the cathode in the electrochemical reactor. The innovative aspect of
this technology is that it can basically treat toxic waste of high organic con-
centration as well as recover metals with greater purity in an environmen-
tally friendly manner because it avoids emission of gases, sulfur, and metal
particles, unlike pyrometallurgy. The current state of the technology implies
that it is being tested at the pilot and pre-industry level with some installa-
tions working in some parts of world. Siemens Corporate Technology in
Erlangen uses an electrochemical method of wastewater treatment, where
water molecules are converted to hydroxyl radicals that act as cleaning agents
by attacking almost every carbon-containing structure of organic substances
(Waidhas, www.siemens.com/innovation/en/publikationen/publications_
pof/pof_fall_2008/rohstoffe/abwasser.htm). The resultant pollutant fragments
may be digested by bacteria. The reactors are generally steel shells where waste-
water is pumped between oppositely charged electrodes whose potential differ-
ence creates hydroxyl radicals at the positively charged electrode and liberates
hydrogen gas at the negative electrode. The process setup is expected for appli-
cation on an industrial scale because the pilot plant setup can effectively treat
200 L/h of wastewater. The electrochemical method is suitable for the highly
concentrated wastewater from the textile, paper, and pharmaceutical industries.
Thegreatertheconcentrationofpollutantsinthewater,themoreeffectiveisthe
process because at higher concentrations, more particles adhere to the electrode
surface, increasing the decomposition quota per kilowatt-hour. The electro-
chemical method did not gain much importance initially because of the exten-
sivecapitalinvestmentandexpensiveelectricityrequirement.However,inview
of stringent environmental regulations regarding wastewater discharge and
drinking water standards, the electrochemical method for wastewater has
gained importance over the past two decades.
The application of nanomaterials and nanotechnology in industrial
wastewater treatment also needs careful evaluation. Although this area
appears to hold much potential for future applications, only a few studies