Removal of Organic Dyes from Industrial Effluents: An Overview of Physical and Biotechnological Applications - Green Chemistry for Dyes Removal from Wastewater - page 14

to its highly porous nature, activated carbon has a much larger surface
area, and hence has a higher capacity in terms of the adsorption.
Peat has a cellular structure that makes it an ideal choice as an adsorbent
for the adsorption of transition metals and polar organic compounds from
dye-containing effluents. Peat requires no activation, unlike activated car-
bon, and also costs much less [74].
Wood chips exhibit a high adsorption capacity toward acid dyes, although
due to their hardness they are not as good as other available sorbents and
longer contact times are required [75,76].
Fly ash and coal mixture is used as an adsorbent for dye adsorption from
colored wastewaters. A high fly ash ratio increases the adsorption capacity
of the mixture due to its increased surface area available for adsorption.
This combination may be substituted for activated carbon, with a ratio of
fly ash:coal, 1:1 [77].
Silica gel is an effective material for removing basic dyes, although side
interactions such as air binding and fouling with particulate matter prevent
its commercial use.
Natural clay s as well as substrates such as corn cobs and rice hulls are com-
monly used for dye removal. Their main advantages are widespread avail-
ability and cheapness. These substrates are more attractive economically
for dye removal, compared to the other ones [69,75,78].
Several adsorbents have been studied to determine their ability of adsorp-
tion toward dyes from aqueous effluents and are given in Table 1.3. Several
studies focused on the economic removal of dyes using different adsorbents
such as sawdust [79], banana and orange peels [80], wheat straw, corncobs,
barley husks [81], tree fern [82], eucalyptus barks [83,84], wood [85], peat
[86], rice husk [87], chitin [88], algal biomass, metal hydroxide sludge [90],
soil [91], clays [92,93] and fly ash [94], and coal [95].
A number of low-cost adsorbents were studied to determine their ability
to adsorb dyes from aqueous effluents. However, the most widely used and
the most easily reached adsorbent for dyes is activated carbon as granule
or powder [145].
1.3.2.2 MembraneFiltration
This process has the ability to clarify, concentrate and, most importantly, to
separate dyes continuously from effluent [52,146, 147]. It has some special