Biosorption of Organic Dyes: Research Opportunities and Challenges - Green Chemistry for Dyes Removal from Wastewater - page 297

resistant to aerobic digestion, and stable to oxidation agents [3-7]. This is
why many efforts have been made by environmental researchers in order
to develop effective and low-cost technologies to remove dyes from indus-
trial effluents.

8.1.2 Technologies for Dye Removal

As reported in recent review articles [2-7,9-11], several technologies
have been developed to treat DCEFs such as coagulation-flocculation,
filtration, sedimentation, precipitation-flocculation, electrocoagulation-
electroflotation, biodegradation, photocatalysis, oxidation, electrochemical
treatment, membrane separation, ion-exchange, incineration, irradiation,
advanced oxidation, bacterial decolorization, electrokinetic coagulation
and adsorption on activated carbon. It is evident that each technique has
its own advantages and drawbacks. From the industrial viewpoint, no
single process provides adequate treatment, being that significant reduc-
tion of expenses and enhancement of dye removal can be achieved by the
combination of different methods in hybrid treatments [9,11]. So, there
is a need to develop alternative decolorization methods that are effective
and acceptable in industrial use [9]. Among the above-mentioned tech-
nologies, it is recognized that adsorption on activated carbon is one of the
most powerful to treat DCEFs, providing benefits such as ease of operation
and high efficiency [5,10]. However, its use is limited by the obtention and
regeneration costs of activated carbon [4,6,9]. Alternatively, biosorption
can be employed to treat DCEFs, because it combines the advantages of
adsorption with the use of natural, low-cost, eco-friendly and renewable
biosorbents [6,12,13].

8.1.3 General Aspects of Biosorption

Probably, the work of Adams and Holmes [14] represented an early attempt
at biosorption. They described the removal of Ca and Mg ions by tannin
resin, black wattle bark ( Acacia mollissima ) [14]. However, biosorption has
gained special attention from 1970 on, due to the increase in environmen-
tal awareness, which has led to a search for new techniques capable of the
inexpensive treatment of polluted effluents [15]. Two definitions are com-
monly accepted in literature for the term “biosorption”: 1) Biosorption is
the removal of materials (compounds, metal ions, organic dyes, etc.) by
inactive, non-living biomass (materials of biological origin) due to high
attractive forces present between the two [15]; 2) Biosorption is the passive