Environmental Engineering Reference
In-Depth Information
They concluded that the Langmuir and the pseudo-second-order mod-
els appropriately described the equilibrium and kinetics of the dye bio-
sorption process, respectively. Kinetic studies showed that the suggested
biomaterial offered fast decolorization kinetics. Biosorption equilibrium
was established within 40 min. The possible interaction of Thamnidium
elegans -RR198 was clarified by the FTIR and zeta potential analysis. It was
found that -OH and -NH groups on the Thamnidium elegans surface con-
tributed to dye binding.
8.3
Factors Affecting Biosorption
The biosorption process is affected by various factors, including pH, tem-
perature, biosorbent dosage, particle size, contact time, initial dye con-
centration and stirring rate [2-13]. The selection of the more adequate
operation ranges for these factors is a crucial study in the biosorption field
[6,9,12,13]. From this study, it is possible to improve the biosorbent poten-
tial and also the performance of the biosorption system. Thus it is very
important to know how these variables can affect the biosorption process.
In this section, the effects of pH, temperature, biosorbent dosage, particle
size, contact time, initial dye concentration and stirring rate are discussed
in details.
8.3.1 pH
One of the most important factors that affects the biosorption process is
the pH, which is a measure of acidity (pH < 7) or basicity (pH > 7) of an
aqueous solution [9,11,12]. This factor influences the surface charge of the
biosorbent, the degree of ionization of the material present in the solution,
the dissociation of functional groups on the active sites of the biosorbent
and the chemistry of the dyes [9]. In relation to the biosorbent, the point of
zero charge (pH zpc ) is indicative of the surface charge as a function of pH
[19]. When the pH of the solution is lower than pH zpc , the surface of the
biosorbent surface is positively charged and the biosorbent surface is nega-
tively charged at pH values higher than pH zpc [19,25,31,44]. As a result, the
biosorption of cationic dyes is increased at high pH values and the anionic
dyes biosorption is favored at low pH values [3]. Regarding the dyes, pH
affects the structural stability of dye molecules (in particular the dissocia-
tion of their ionizable sites), and therefore their color intensity. Hydrolysis,
protonation, deprotonation, complexation by organic and/or inorganic
Search WWH ::




Custom Search