Removal of Organic Dyes from Industrial Effluents: An Overview of Physical and Biotechnological Applications - Green Chemistry for Dyes Removal from Wastewater - page 18

1.3.2.5 ElectrokineticCoagulation
Electrokinetic coagulation is an economically feasible method for dye
removal. It involves the addition of ferrous sulphate and ferric chloride,
allowing excellent removal of direct dyes from wastewaters. Unfortunately,
the poor results with acid dyes; as well as the high cost of the ferrous sul-
phate and ferric chloride, mean that it is not a widely used method.
The optimum coagulant concentration is dependent on the static charge
of the dye in the solution, and the difficulty in removing the sludge formed
as part of the coagulation is a problem. Production of large amounts of
sludge occurs, and this causes high disposal costs [146,53].
1.3.3 BiologicalMethods
In recent years, an enormous amount of attention has emerged on bio-
logical methods with some microorganisms such as fungi, bacteria and
algae, which are highly capable of biodegrading and adsorbing dyes
from wastewater [155]. The application of biological processes for dye
wastewater removal offers many considerable advantages such as being
relatively low cost, environmentally friendly, and producing less second-
ary sludge and nontoxic end products of complete mineralization [11].
Much of the research conducted on the use of microorganisms for dye
wastewater removal has proven the potential of microorganisms such as
Cunninghamella elegans [12], Aspergillus niger [13], Bacillus cereus [14],
Chlorella sp . [15] and also Citrobacter sp . [16]. The adaptability and the
activity of each microorganism are the most significant factors that
influence the effectiveness of microbial decolorization [156]. Hence, to
develop a practical bioprocess for dye wastewater treatment, it is need to
continuously examine the microorganisms that are capable of degrading
azo dyes [17].
However, the application of microorganisms is often restricted because
of technical constraints. Bhattacharyya and Sharma [157] have suggested
that biological treatment requires a large land area, and is constrained by
sensitivity towards diurnal variation, as well as the toxicity of some chemi-
cals, and less flexibility in design and operation. Further biological treat-
ment is not able to provide satisfactory color elimination using current
conventional biodegradation processes [48]. Moreover, although many
organic molecules are degraded, many others are not degradable due to
their complex chemical structure and synthetic origin [158].
The biological processes, which can be implemented for both municipal
and industrial wastewaters, are classified as aerobic and anaerobic.