Microbe-Mediated Degradation of Synthetic Dyes in Wastewater - Microbial Degradation of Synthetic Dyes in Wastewaters - page 220

important, the process produces a large quantity of sludge (Robinson et al. 2001 ).
Coagulation followed by adsorption was reported to produce ef uent of reuse

standard, apart from cutting down the coagulant consumption by 50 %. Hence, it
lowers the volume of sludge formed, in comparison to coagulation process done
(Papic et al. 2004 ). Coagulation in combination with advanced oxidation processes,
either in sequential or in concurrent manner, has been reported for dye wastewater.
Investigation on sequential use of coagulation and ozonation revealed the superi-
ority of the scheme involving ozonation preceded by coagulation over the reversed
scheme (Tzitzi et al. 1994 ). Multi-stage application of coagulation, followed by
ozonation, was proved to be superior to their single pass sequential application
(total ozonation time the same) (Hsu et al. 1998 ). The advantage of the multistage
application was more convincing in case of wastewater with high recalcitrant
composition.

2.4.2 Adsorption Based Combinations

Adsorption techniques, specially the excellent adsorption properties of carbon-
based supports, have been utilized for the decolorization of dyes in the industrial
ef uents (Forgacs et al. 2004 ). Activated carbon, either in powder or granular form,

is the most widely used as adsorbent for this purpose due to its extended surface
area, micro porous structure, high adsorption capacity and high degree of surface
reactivity (Malik 2003 ). It is very effective for adsorbing cationic, mordant, and
acid dyes and to a slightly lesser extent for dispersed, direct, vat, pigment and
reactive dyes (Robinson et al. 2001 ). However, the use of carbon adsorption for
decolorization of the raw wastewater is impractical because of competition between
colored molecules and other organic/ inorganic compounds. Hence, its use has been
recommended as a polishing step or as an emergency unit at the end of treatment to
meet the discharge color standards (Hao et al. 2000 ). There has been considerable
interest in using low-cost adsorbents for decolorization of wastewater. These
materials include chitosan, zeolite, clay; certain waste products from industrial
operations, such as

y ash, coal, oxides; agricultural wastes and lignocellulosic
wastes and so on (Naim and Abd 2002 ; Babel and Kurniwan 2003 ). Adsorption
concurrent with ozonation (Lin and Lai 2000 ), UV-H 2 O 2 (Ince et al. 2002 )or
microwave induced oxidation (Lin and Lai 2000 ) has been reported to yield mutual
enhancements like catalysis of AOP by adsorbent and simultaneous regeneration of
adsorbent. A rather elaborate method, involving solvent extraction and catalytic
oxidation, has been documented in the literature (Hu et al. 2005 ; Muthuraman and
Palanivelu 2005 ). The method consists of dye extraction, using an economical
solvent followed by dye recovery through chemical stripping. In this way, the
solvent is also regenerated. Finally, treatment of the extraction raf

nate can be

achieved by the catalytic oxidation.