Removal of Organic Dyes from Industrial Effluents: An Overview of Physical and Biotechnological Applications - Green Chemistry for Dyes Removal from Wastewater - page 17

bioreactor (MBR) with a gravity drain was designed for the treatment of
dyeing and printing wastewaters and was tested on wastewater from a wool
mill. The MBR was used continuously as a gravity-controlled system with-
out chemical cleaning for 135 days. The average removal ratios of BOD 5 ,
COD, turbidity and color were found to be 80.3%, 95%, 99.3% and 58.7%
respectively.
Hai et al. [151] developed a submerged membrane fungi reactor for tex-
tile wastewater treatment. A submerged microfiltration membrane biore-
actor implementing the white rod fungi, Coriolus versicolor , was developed
for the treatment of textile dye wastewater with different fouling preven-
tion techniques. It was found that the color removal ratio from synthetic
wastewater by the reactor is about 99%.
1.3.2.3 IonExchange
In this method, wastewater is passed over the ion exchange resin until
the available exchange sites are saturated. Both cationic and anionic
dyes can be removed from dye-containing effluent this way. Advantages
of this method include no loss of adsorbent on regeneration, reclama-
tion of solvent after use and the removal of soluble dyes. Ion exchange
is not widely used for the treatment of dye-containing effluents. This is
because the ion exchange resins are not effective for a range of a wide
variety of dyes [50]. A major disadvantage is cost. Organic solvents are
expensive, and the ion exchange method is not very effective for dis-
perse dyes [146].
Commercial anionic exchange resins were applied to the water contami-
nated with a broad range of reactive dyes by Karcher et al. [152,153], and
they reported that anionic exchangers possess excellent adsorption capac-
ity (200-1200 μmol/g) as well as efficient regeneration property for their
removal and recovery.
1.3.2.4 Irradiation
Sufficient quantities of dissolved oxygen are required for organic sub-
stances to be broken down effectively by radiation. The dissolved oxygen
is consumed very rapidly, and therefore for photocatalyzed oxidation a
constant and adequate supply of oxygen is required. Dye-containing efflu-
ent may be treated in a dual-tube bubbling rector. An application of this
method showed that some dyes and phenolic molecules can only be oxi-
dized effectively at a laboratory scale [154].