295
reactive red 239 and reactive blue 250 (Alver and Metin 2012; Ozdemir et al. 2004).
Moreover zeolites are characterized by low permeability; therefore in the continuous systems (column studies), additional artificial support is needed. Retention of
dyes on zeolites is the result of ion-exchange mechanism. The yield of removal
process is usually lower that in the case clays adsorbents. In literature many examples of zeolites application for dyes removal could be found but here was mentioned
only some of them. High sorption capacity toward basic dyes was obtained using
zeolites synthesized from electrolytic manganese residue, raw and functionalized
by iron oxide clinoptilolite for removal of methylene blue (Li et al. 2015; Wang
et al. 2006; Badeenezhad et al. 2018) and crystal violet and rhodamine B (Wang
et al. 2006). The adsorption capacity for dyes under discussion is in order of methylene blue > crystal violet ∼ rhodamine B. Adsorption of basic dyes could be
described well by pseudo second-order model. Film diffusion plays a meaningful
role, too. Not only the Langmuir but also the Freundlich isotherms fit good the equilibrium data. Retention of cationic dyes is an endothermic in nature (Wang et al.
2006). Li et al. (2015) also found that pseudo second-order and Langmuir models
are proper for methylene blue sorption description. pH and temperature greatly
affected the sorption efficiency of methylene blue. The adsorption of methylene
blue on electrolytic manganese residue is endothermic and spontaneous process.
Methylene blue removal by unmodified clinoptilolite was pH dependent and gives
26.86% and 48% removal at pH 3 and 9, respectively. Methylene blue retention on
the impregnated clinoptilolite was much higher (96.4–98.6%) and not pH and initial
dye concentration dependent. Freundlich isotherm model fit well the experimental
results.
11.4.4 Biosorbents
Biosorption is physicochemical process and is described as accumulation and concentration of pollutants using biological materials (Crini 2006). The use of biosorbents in dyes removal seems to be very promising (Asgher 2012; Crini 2006). It
results above all from the fact that biosorbents as low-cost sorbents, with easy
accessibility even in large quantities, are sometimes characterized by a much higher
sorption capacity in relation to metal ions than commercial activated carbons or ion
exchangers (reduction of dyes concentration to ppb levels could be obtained).
Chitosan molecule modification by inserting functional groups (grafting) or crosslinking reactions leads to the formation of chitosan derivatives of superior sorptive
properties results in enhancement of adsorption capacity and resistance (Kyzas
et al. 2017). This process is effective and competitive, requires little processing, and
is inexpensive. During the biosorption different mechanisms could be responsible
for dyes sorption, e.g., physicochemical adsorption, ion exchange, complexation,
electrostatic interaction, and micro-precipitation (Asgher 2012). As biological
materials for wastewaters decolorization, chitin, chitosan, peat, yeasts, white rot
fungi, algae, and dead or living biomass are applied. Chitin and chitosan are
11 Characteristics and Adsorptive Treatment of Wastewaters Containing Dyes
reactive red 239 and reactive blue 250 (Alver and Metin 2012; Ozdemir et al. 2004).
Moreover zeolites are characterized by low permeability; therefore in the continuous systems (column studies), additional artificial support is needed. Retention of
dyes on zeolites is the result of ion-exchange mechanism. The yield of removal
process is usually lower that in the case clays adsorbents. In literature many examples of zeolites application for dyes removal could be found but here was mentioned
only some of them. High sorption capacity toward basic dyes was obtained using
zeolites synthesized from electrolytic manganese residue, raw and functionalized
by iron oxide clinoptilolite for removal of methylene blue (Li et al. 2015; Wang
et al. 2006; Badeenezhad et al. 2018) and crystal violet and rhodamine B (Wang
et al. 2006). The adsorption capacity for dyes under discussion is in order of methylene blue > crystal violet ∼ rhodamine B. Adsorption of basic dyes could be
described well by pseudo second-order model. Film diffusion plays a meaningful
role, too. Not only the Langmuir but also the Freundlich isotherms fit good the equilibrium data. Retention of cationic dyes is an endothermic in nature (Wang et al.
2006). Li et al. (2015) also found that pseudo second-order and Langmuir models
are proper for methylene blue sorption description. pH and temperature greatly
affected the sorption efficiency of methylene blue. The adsorption of methylene
blue on electrolytic manganese residue is endothermic and spontaneous process.
Methylene blue removal by unmodified clinoptilolite was pH dependent and gives
26.86% and 48% removal at pH 3 and 9, respectively. Methylene blue retention on
the impregnated clinoptilolite was much higher (96.4–98.6%) and not pH and initial
dye concentration dependent. Freundlich isotherm model fit well the experimental
results.
11.4.4 Biosorbents
Biosorption is physicochemical process and is described as accumulation and concentration of pollutants using biological materials (Crini 2006). The use of biosorbents in dyes removal seems to be very promising (Asgher 2012; Crini 2006). It
results above all from the fact that biosorbents as low-cost sorbents, with easy
accessibility even in large quantities, are sometimes characterized by a much higher
sorption capacity in relation to metal ions than commercial activated carbons or ion
exchangers (reduction of dyes concentration to ppb levels could be obtained).
Chitosan molecule modification by inserting functional groups (grafting) or crosslinking reactions leads to the formation of chitosan derivatives of superior sorptive
properties results in enhancement of adsorption capacity and resistance (Kyzas
et al. 2017). This process is effective and competitive, requires little processing, and
is inexpensive. During the biosorption different mechanisms could be responsible
for dyes sorption, e.g., physicochemical adsorption, ion exchange, complexation,
electrostatic interaction, and micro-precipitation (Asgher 2012). As biological
materials for wastewaters decolorization, chitin, chitosan, peat, yeasts, white rot
fungi, algae, and dead or living biomass are applied. Chitin and chitosan are
11 Characteristics and Adsorptive Treatment of Wastewaters Containing Dyes