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"Genius is one per cent inspiration, ninety-nine per cent perspiration"
Thomas Edison
7 ADSORPTION OF COLORED POLLUTANTS FROM
DISTILLERY SPENT WASH BY NATIVE AND
TREATED FUNGUS: NEUROSPORA INTERMEDIA
7. Adsorption of colored pollutants from distiUery spent wash by native
and treated fungus: Neurospora intermedia
7 .1. Introduction
Distillery effluent, a foul smelling, dark colored by-product of distillery industries
is perceived as one of the serious pollution source of the countries producing alcohol
from fermentation and subsequent distillation of sugar cane molasses. It contains
extremely high COD, BOD, soluble solids, inorganic solids, color and low in pH (Saha et
al., 2005) besides other caramelized and recalcitrant wastes. The characteristic
recalcitrance to decolourization of distillery effluent is due to the presence of brown
melanoidin polymers that are formed in Maillard reactions between amino acids and
carbohydrates (Wedzicha and Kaputo, 1992). These Maillard compounds have
antioxidant properties that render them toxic to aquatic micro and macroorganisms (Kitts
et al., 1993). Various physico-chemical methods/ treatment technologies such as
incineration, composting and biological treatments have been studied for distillery waste
wasters by various researchers (Sheehan and Greenfield, 1980; Hayase et al., 1984;
Gupta et al., 1990; Pena et al., 1996; Nandy et al., 2002).
Biological treatment is practiced in most of the Indian distilleries resulting in
reduction of BOD and COD. The biological treatment system includes anaerobic
treatment with recovery of biogas, followed by aerobic treatment for removal of residual
BOD and COD. However, the success rate of most of the biological methods increases if
applied after physicochemical treatments. The major problem encountered with distillery
effluent treatment is the color which remain present even after biological treatment due to
the presence of recalcitrant compounds viz. caramel, melanoidins, variety of sugar
decomposition products, anthocyanins and tannins, and other xenobiotic compounds. It is
difficult to remove ·these constituents from the disti1lery effluent through conventional
biological processes.
Several workers have attempted to remove these recalcitrant compounds by
physico-chemical methods using diluted distillery wastewater and biologically treated
130
distillery effluent. Among the physico-chemical treatment methods, adsorption on
activated carbon (AC) is widely used for removal of color and specific organic pollutants
(Bernardo et al., 1997).
Activated carbon is a well-known adsorbent due to its extended surface area,
microporus structure, high adsorption capacity and high degree of surface reactivity.
Previous studies on decolourization of distillery spent wash include adsorption on
commercial as well as indigenously prepared activated carbons (Satyawali and
Balakrishanan, 2007) but the relatively high cost restricts its usage. Low cost adsorbents
such as pyorchar (activated carbon both in granular and powdered form, manufactured
from paper mill sludge) and bagasse flyash have also been studied for this application.
Since the bagasse flyash has high carbon content and the adsorbed organic material
further increases its heating value, it is not considered as good alternative. Yet another
adsorbent that has been evaluated is the natural carbohydrate polymer chitosan derived
from the exoskeleton of crustaceans. Lalov et al. (2000) studied the treatment of distillery
wastewater using chitosan as an anion exchanger.
Biomass of some natural microbial species, including bacteria, fungi and algae, is
capable of removing the different textile dyes by biosorption, biodegradation or
mineralization (Carliell et al., 1995). Ever increasing demand for new sources of low-cost
adsorbent undoubtedly make chitosan-containing biomass as one of the most attractive
'materials for colored wastewater treatment (Babel and Kurniawan, 2003). Various
researchers have carried the biosorption studies of various organic pollutants and color
from wastewaters (Tsezos and Bell, 1989; Fu and Viraraghavan, 2001). Partial
elimination of Maillard colored compounds was obtained by using microbes like
Geotrichum candidum (Borja et al., 1993). Rhizoctonia sp. D-90 (Sirianutapiboon et al.,
1995). Electron microscopy revealed the presence of melanoidin like pigment, in the
form of electron dense material in the cytoplasm that was adsorbed by the mycelia. Color
removal from molasses spent wash through adsorption was also studied by Miranda et al.
(1996) using Aspergillus niger
In this study, the native, heat-, acid- and alkali-treated biomasses of Neurospora
intennedia were used for the adsorption of colored components of distillery effluent in
batch cultures. The effects of experimental conditions such as effluent concentration,
131
temperature and pH were also investigated to obtain information on adsorption properties
of the fungal biomass. The possible mechanisms involved in the adsorption are discussed
on the basis of the treatment of the fungal biomass followed by Electron Microscopic and
.FTIR spectroscopic studies. Finally, equilibrium biosorption capacities were also studies
by using adsorption isotherm techniques. The experimental data was fitted into the
Langmuir, Freundlich equations.
7 .2. Material and methods
7 .2.1. Sorbate
For studying the process of adsorption by fungal biomass, the effluent, collected
from Modi distilleries, Modinagar, Uttar Pradesh, India, was diluted to desired dilution
·using MSM (minimum salt media) for adsorption studies. The pH of the sample was
adjusted using O.lM HCl or O.lM NaOH as required.
7 .2.2. Cultivation of fungus
The fungus "Neurospora intennedia (MTCC-9655)" was selected for adsorption
studies. It was observed in chapter 3 that this fungus played significant role in
decolorizing the distillery spent wash through adsorption rather than using its enzymatic
system. Thus, it was assumed that the process of adsorption was dominantly taking place.
The strain was maintained on PDA plates, stored at 4°C with routine transfers in a cycle
of 2 months (Kapoor et al., 1999). It was cultivated in liquid medium in PDB using the
shake flask method. Once inoculated, flasks were incubated on an orbital shaker at 125
rpm for 7 days at 30°C. After incubation, the biomass was harvested from the medium
and washed with distilled water. The washed biomass (live biomass) was used
immediately thereafter.
7 .2.3. Physical and chemical treatment of fungal biomass
Untreated fungus was called native fungus. Native fungus was soaked in 0.1M
HCJ at room temperature, in the ratio 1:10 w/v for 1 hour at 125 rpm. The biomass was
then washed with buffer saline. This fungus was called acid treated fungus. Similarly,
base treated fungus was prepared by treating it with O.lM NaOH. For preparation of heat
treated fungus, biomass was heated in water bath at 1 00°C in buffer saline for 10 min
(Bayramoglu et al., 2006).
132
7 .2.4. Adsorption studies
Batch adsorption studies were conducted by varying adsorbent (biomass),
adsorbate concentration (distillery spent wash), pH and temperature, to obtain rate and
equilibrium data. In each experiment, accurately weighed 10% fungal biomass (wet
weight) was added to 100 ml of distillery spent wash solution (MSM- effluent, 65oo·cu)
taken in a 250 ml conical flask along with necessary carbon (dextrose, 0.05%), nitrogen
(NaN03, 0.025%), for the fungus (chapter 3). The mixture was agitated at 125rpm in an
incubated shaker at constant temperature (30°C).
At the end of the equilibrium period, the contents of the flasks were analyzed for
residual concentration of adsorbate. The adsorption of the colored contaminants of
distillery spent wash on the native and heat-acid- and base-treated fungal biomass was
also investigated. The distillery spent wash having 65000 CU was served as stock
solution. Different concentrations were prepared from this stock solution. To determine
the effect of initial concentrations of the effluent on the adsorption rate and capacity on
the fungal preparations, the initial concentration of the effluent was varied between 1 000
CU to 6500CU in the bisorption medium. The effects of the medium pH on the
adsorption capacities of the fungal biomass preparations were later investigated in the
initial pH range 2.0-8.0 (which was adjusted with HCl or NaOH at the beginning of the
experiment) at 30°C. The effect of temperature was studied at varied temperature ranges
20- 40°C at pH 3.0.
7 .2.5. Analysis
Before analysis of the remaining color concentration in the adsorbate, the sample
was centrifuged at 5000 rpm for 20 min. The supernatant was analyzed for estimation of
color by cobalt-platinate method (Chapter 3). Coloring unit of the effluent was
considered a measure of amount o:( chemicals present in the effluent. Such approach has
been followed in other studies also where COD as a measure of effluent concentration
was used (Srivastava et al., 2005, Devi et aL, 2008). The readings were taken in duplicate
for each individual solution to check repeatability and the average of the values were
taken.
133
Percentage color removal was calculated using the formula
%Color removal =(Co- C1 )/C0 x 100
C0=lnitial color of spent wash
C1 =Final color of spent wash at time t
The amount of biosorbed coloring material per unit fungal biomass (g wet biomass) was
obtained by using the following expression:
qe =(Co- Ce) ·VIM
qe is the amount adsorbed at equilibrium, Co is the initial concentration of the sorbate, Ce
is the equilibrium solution concentration, V the volume, and M the mass of adsorbent.
7 .2.6. Characterization of the fungal biomass
Changes in fungal biomass was studied before and after adsorption by SEM and
FT-IR. The changes in the fungal mycelium due to physico-chemical treatments (acid,
base and heat) were also studied by Ff-IR.
Scanning Electron Microscopy
The fungal mycelium before and after adsorption was analyzed by fixing and
soaking it overnight in O.lM phosphate buffer saline having 1% glutaraldehyde and 2%
paraformaldehyde at 4°C. Fixed mycelium was smeared over the coverslip coated with
poly-L-lysin for 30 min in wet condition. The specimen was washed with buffer,
dehydrated in a series of ethanol-water solution (30, 50, 70, and 90% ethanol, 5 min
each) and critical point dried under a C02 atmosphere for 20 min. Mounting was done on
aluminium studs provided with adhesive disk, a line of silver paint was applied on two
sides of each sample. A thin layer of gold was coated using Bio-rad Polaron Gold/Silver
Sputter coating unit for 30 min. Coated cells were viewed at 10 kV with scanning
electron microscopy (ZEISS Scanning Electron Microscope EVO 50). Working distance
was 10mm and SEl detector was used. Rate of scanning and magnification varied with
the sample (Srivastava and Thakur, 2006; Srivastava and Thakur, 2007).
Fourier Transform Infrared Spectroscopy (FT-IR)
The IR spectra of native, acid-, base- and heat-treated N. intennedia were
obtained by using a Ff-IR spectrophotometer. For FTIR spectra, fungal biomass (0.01 g
dry weight) was mixed with KBr (0.1 g) and pressed into a tablet form by pressing the
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ground niixed material with the aid of a bench press. Scan was recorded from 450nm to
4000nm with Perkin-Elmer 1600 series Ff-IR spectrophotometer (Nujol, KBr disks).
7 .2. 7. Equilibrium models
To optimize the design of a sorption system to remove the sorbates, it is important
to establish the most appropriate correlation for the equilibrium curves. These
equilibrium sorption capacity curves can be obtained by measuring the sorption isotherm.
The experimental data of the amount of sorbate adsorbed on the sorbent are substituted
into an equilibrium isotherm model to determine the best-fit model for the sorption
system. Using this relationship, any variation in the concentration of sorbent with the
concentration of sorbate in solution is correlated. The Freundlich and Langmuir
adsorption isotherm models are widely used to analyse data for water and wastewater
treatment applications. Hence, in this study, the experimental data were fitted with the
Freundlich and Langmuir models.
Freundlich model
The Freundlich equation can be written as:
K C 1/n qe= F e
Where KF is a constant indicative of the relative adsorption capacity of the adsorbent
(mg1-0/n)L11ng-1) and n is the constant indicative of the intensity of adsorption. The
Freundlich expression is an exponential equation and therefore, assumes that as the
adsorbate concentration increases, the concentration of adsorbate on the adsorbent
surface also increases.
Langmuir model
The langmuir model assumes uniform energies of adsorption on to the surface and
no transmigration of adsorbate in the plane of the surface. The langmuir equation may be
written as:
qe = qmbCe
1+ bCe
where qe is the amount of solute adsorbed per unit weight of adsorbent at equilibrium (mg
g-1), Ce the equilibrium concentration of the solute in the bulk solution (mg L-1
),. qm· the
maximum adsorption capacity (mg g-1), and b is the constant related to the free energy of
the adsorption.
135
The linearized form of these models was used for calculations (Table 7.1).
Langmuir is converted into five different linear equations (Hamdaouia and Neffrechoux,
2007).
· Table 7.1. Isotherm model and their linear forms
Isotherm Equation Linear form
Freundlich q=KcYn 1 e F e lnqe = lnKF +-lnCe
n
Langmuir- I 1 1 1 1 -=----+-qe bqm ce qm
Langmuir-2 ·{; 1 1 _e =-C +--
Langmuir-3 qmbCe qe=l+bCe
Langmuir-4
Langmuir-5
7 .3. Results
7.3.1. Characteristics of fungal biomass
Scanning Electron Microoscopy (SEM)
qe qm e qmb
1 qe qe =bC+qm
e
!b._= -bq +bq C e ,m e
1 1 -=bq --b Ce m qe
Plot
lnqe vs. znce
1 1 vs.
qe C,
C, vs. ce
qe
qe vs. qe
C,
q, vs. q,
C,
1 1 VS.
ce q,
The surface morphology of the native fungus N. intennedia mycelia was
exemplified by the Scanning Electron micrograph in Figure 7 .1. As shown in the SEM
micrograph, the fungal mycelia have rough and porous surface. After adsorption the
mycelia looses its structure and wear and tear due to the particles present in the effluent is
evident. (Figure 7.1)
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Figure 7.1. Scannaing electron microscopy of (a) native fungal mycelium N. intermedia
(top) (b) biosorbed fungal mycelium (Bisorption of distillery effluent) (bottom)
Fourier Transform Infrared Spectroscopy (FTIR).
In order to confirm the existence of functional bioadsorption groups (i .e., amino,
carboxyl and phosphate) on the fungal biomass and its different preparations, the FTIR
spectra of the finely powdered dried fungal biomasses were obtained. The spectra for
native fungal biomass is shown in Figure 7.2(A). The broad stretching adsorption band at
3356 cm- 1could be assigned hydroxyl groups stretching vibrations. The-NH stretching of
the protein and the acetamido group of chitin fraction stretching vibrations bands are
superimposed on the side of the hydroxyl group band at 3500-3200 cm- 1• The band at
1659 em - I is a consequence of CO stretching vibration conjugated to NH band. The peaks
at around 1411 and 1248 em - I are caused by the CO stretching band of carbonyl groups.
137
The moderately strong absorption bands at 1030 could be assigned to the -CN stretching
vibration of the chitin-chitosan and protein fractions. Strong absorption bands at 2925
cm-1 could be assigned to the -CH stretch. These data show the presence of C, H, N and
0 elements with their functional groups.
The FfiR spectra bands of bioadsorption studies by native fungi shows that the
broad overlapping peak shift to 3391cm-1 after adsorption of distillery spent wash, which
may be due to hydroxyl or amine groups present in the effluent itself. Additionally, the
peak at 1659 cm-1 assigned to the CO stretching shifted to 1634 cm-1 suggesting its role
in adsorption. However, the peak stretching at 1411 and 1248 shifted to 1434 and 1358
respectively, after adsorption indicating the presence of additional carboxyl groups in the
effluent (Figure 7.2 B).
%T
3391.2
926.9 518.7
3356.4 1642.3
4000 3000 2000 1500 1000 450 cm-1
Figure 7.2. FfiR spectra of {A) dried unadsorbed (B) effluent adsorbed. N. intermedia
biomass
138
The FfiR spectra of these treated fungal biomasses shows that these treatments
have modified surface chemistry of the fungi. As shown in Table 7.2 there was loss of
some functional groups along with presence of some additional binding sites for the same
groups, while at the same time there was a change in the intensity for others (Figure 7.3).
(C)
3335.1
4000 3000
1606.8 1658.5 1456.7
1512.2
1645.6
2000 cm-l 1500
547.0
1000 450
Figure 7.3. FfiR spectra of (A) base (B) acid and (C) heat treated fungal biomass
preparations
139
Table 7.2. Comparative analysis of functional groups present in native, acid base and
heat treated mycelium
S. No. IR band Native Acid Base Heat
1 3500-3200 [(N-H) and 0-H] 3356 3319 3401 3335
2 2925, (C-H) 2924.4 2924.1 2925.1 2925.2
3 1659, [(N-H) amine and CO)] 1659.2 1651.8 1658.5 1645.6
4 1411, (C=O) 1411.4 - 1456.7 -
5 1248, (C=O) 1248.8 1250.8 1253.2 1252.7
6 1029, [(C-OH) and (P=O)] 1029.2 1039.5 1051.9 1034.2
7 518, (protein structure) 518 547 545.5 546.7
7.3.2. Effect of pH and temperature on adsorption
The effect of temperature on the equilibrium sorption capacity was investigated in
the temperature range of 20-40°C. The adsorption of distillery spent wash was enhanced
with raising the temperature up to 30°C and the time taken to reach the equilibrium
decreases with increasing temperature, however beyond that there was a decrease in the
further adsorption potential of the fungi with the increase in temperature (Figure 7.4a).
The pH of the aqueous solution is a controlling factor in the adsorption process. In
this study, the role of hydrogen ion concentration was examined at pH values ranging
between 2-9. The influence of pH on the bioadsorption potential of the fungi (N.
intennedia) is shown in Figure 7.4b. The most suitable pH for bioadsorption was 3 and
there was a decrease in the extent of bioadsorption potential with increase in the pH of
the solution. Hence fm1her studies were conducted at pH 3.
140
120
~ 100
> 0 E 80 Q) ... ... 0 60 0 (.)
tf. 40
20 15 20 25 30 35 40 45 2 3 4 5 6 7 8 9
Temperature pH (a) (b)
Figure 7.4. (a) Effect of temperature and (b) pH on adsorption potential of N. intennedia
7.3.3. Effect of contact time
It was found that the removal of colored pollutant from distillery spent wash
increases with increase in contact time to some extent. Further increase in contact time
does not increase the uptake due to deposition of colored pollutants on the available
adsorption sites of native fungal biomass. Preliminary investigations on the uptake of
pollutants on the adsorbent material at their optimum pH values and temperature values
indicated that the process was quite rapid. Typically, 80% of the total adsorption occurs
within the first four hours at the effluent concentration of 10% (v/v). This initial rapid
adsorption subsequently gives way to a very slow approach to equilibrium and saturation
was reached in 5-6h. For further optimization of other parameters, this contact time was
considered as the equilibrium time.
7.3.4. Biosorption isotherms
Equilibrium data, commonly known as adsorption isotherms, are the basic
requirement for the design of adsorption systems. The shape of the isotherms is the first
experimental tool to diagnose the nature of a specific adsorption phenomenon. The
amount of biosorbed coloring material onto the fungal biomass preparations was studied
and plotted as a function of the equilibrium concentration of colored material in the
biosorption medium. Several mathematical models can be used to describe experimental
data of adsorption isotherms. In this study, the equilibrium data were modeled with the
Langmuir (five linearized expressions) and Freundlich models.
141
Validation of models
The experimental values of qe and Ce detennined in adsorption isotherms were
initially treated with linearized equations of Freundlich and Langmuir to find out the
model parameters. After detennining the best model, the values of qe were recalculated
using linear equation of the model. The reconstitute isothenns were compared with initial
isothenns to evaluate the error in the models. Linear correlation coefficients (r) showed
the fit between experimental data and linearized fonns of isothenn equations while the
average percentage errors (APE) calculated according to given equation indicated the fit
between the experimental and predicted values of adsorption capacity used for plotting
isothenn curves (Hamdaouia and Neffrechoux, 2007).
APE%= 4\-1 { (ge)experimental-(qe) predicted} I (ge) experimental X 100
N Where N is the number of experimental data.
Langmuir isotherm
The adsorption data obtained for colored pollutants in the distillery spent wash
was analyzed by regression analysis to fit the five linearized expressions of Langmuir
isothenn models. The details of these different fonns of linearized Langmuir equations
and the method to estimate the Langmuir constants qm and b from these plots are shown
in Table 7.3. The favorable nature of adsorption can be expressed in terms of
dimensionless equilibrium parameter of Hall (Hall et al., 1996).
RL= lfl+bC0
Where b is the Langmuir constant and C0 is the initial concentration of the adsorbate in
the solution. The values of RL indicates the type of isothenn to be irreversible (RL=O),
favorable (O<RL<l), linear (RL=l) or unfavorable (RL>l) ((Hamdaouia and Neffrechoux,
2007. The values for RL were 0.54, 0.81, 0.42 and 0.79 for native, acid, base and heat
respectively. RL values were less than 1 and greater than zero indicating favorable
adsorption.
In order to check the validity of the Langmuir model, it is interesting and essential
to recalculate the adsorbed amounts using the equilibrium concentration values and
Langmuir parameters detennined using the five linearized fonns of the equation. The best
142
' fitting model for native, acid and heat was Langmuir- I with r-values 0.8819, 0.9988 and
0.9298, respectively and Langmuir-2 was best fitting model for base treated fungi
(r=0.9777) The calculated average percentage errors for Langmuir 1,2 and 3 are shown in
Table 7.3. It is clear from the average percentage errors shown in Table 7.3 that inspite of
the lowest value of average percentage errorin Langmuir-2 for acid treated fungi, this·
model does not describe perfectly the equilibrium data because of the lower values of
coefficients of correlation. Thus, it is not appropriate to use the coefficient of correlation
of the linear regression method for comparing the best~fitting isotherms. The qm values
based on Langmuir 1 model shows that maximum adsorption was in the series native>
heat >acid, base (Table7 .3). The values of qe, Ce and graphs of initial isotherms and
reconstituted isotherms are given in appendix I.
Freundlich isotherm
The equilibrium data was further analyzed using the linearized form of Freundlich
equation using the same set experimental data, by plotting lnqe versus lnCe. The
calculated Freundlich isotherm constants and the corresponding coefficient of correlation
values were shown in Table 7.3. The fitness of Freundlich model for all the four types of
experimental data was in the order of acid> base> native> heat. The magnitude of the
exponent n gives an indication on the favorability of adsorption. The n values are > 1 for
all the tested fungal biomass preparations, indicating a favorable adsorption process.
However, heat treated fungal biomass preparation showed poor adsorption capacity as the
n value was less than one (0.98) along with lowest value of coefficient of correlation.
143
Table 7 .3. Summarized values of various isotherm parameters for adsorption of effluent
on Neurospora intennedia
~sotherm NATIVE ACID BASE HEAT !Freundlich ...
0.8766 0.9898 0.9434 0.8678 V\PE% 15.17121 4.542265 12.02121 13.572929 !KF(CU 1-ltnLIIng-1) 1.743 1.142 11.279 2.233
~ 1.141422 1.214477 1.550628 0.9801039 !Langmuir 1
0.8819 0.9988 0.9636 0.9298 APE% 15.77206 4.723965 7.327218 16.462239 Qm(CU g-1
) 33300 5000 5000 10000 b(LCU-1
) 0.00016 0.000067 0.0002 0.000049 Langmuir2
0.2625 0.9053 0.9777 0.006 APE% 28.33244 3.505215 6.237372 13.40558 qm(CU g-1) 16700 5000 5000 100000 b(LCU-1
) 0.000034 0.000067 0.0002 0.0000044 1Langmuir3 lr 0.0282 0.849 0.8562 0.1438 V\PE% 42.83899 17.94081 9.241919 41.200438 lqm(CU g-1
) 4008.9 5165.4 5330 220.78 lb(LCU-1
) 0.00018 0.000064 0.00018 -0.00052 Langmuir4
0.0282 0.849 0.8562 0.1438 qm(CU g-1
) 27500 4700 1594.35 -17900 b(LCU-1
) 0.00002 0.00006 0.0002 -0.00003 Langmuir5
0.8819 0.9988 0.9696 0.9298 lqm(CU g-•) 12000 5720 1594.35 7760 lb(LCU-1) 0.00004 0.00005 0.0002 0.00005
7 .4. Discussion
Various workers have investigated the biosorption of various organic pollutants
and color from wastewaters (Tsezos and Bell, 1989; Fu and Viraraghavan, 2001).
Biosorption of heavy metals in aqueous solutions has received increasing attention in
recent years (Kac,ar et al., 2002; Bai and Abraham, 2003; Abu Al-Rub et al., 2004). As
an efficient, cost-effective and environmentally friendly technique, biosorption for heavy
metals and various organic pollutants has emerged as a potential alternative to the
144
conventional techniques. Phanerochaete chrysosporium is a well-known white-rot fungus
and it has a strong ability to biosorb various xenobiotics (Benoit et al., 1998). A few
studies have been carried out with P. chrysosporium for detoxifying chlorophenol
bearing effluents (Aksu and Yener, 1998; Benoit et al., 1998). Most studies about
biosorption have focused on the use of dead biomass in powdered fonil. Microbial
biomass is inexpensive and many fungal and bacterial species have been shown as
potential biosorbents. Certain basidiomycetes, Phanerochaete chrysosporium, Bacillus
cereus, Plasiomonas achromobacter, Rhodococcus sp. were tested as dye degrading
microorganisms. Other biomasses such as Aeromonas sp. and Fomitopsis carnea have
been used to successfully adsorb reactive and cationic dyes respectively (Hu, 1992; .
Mittal and Gupta 1996).
The scanning electron microscopy of untreated fungi shows extremely rough and
porous morphology of the fungi. This surface property increases the total surface area and
thus improves adsorption capability of the fungus (Bayramoglu et al., 2006). The effluent
adsorbs on the surface of the mycelium ultimately destroyed the surface properties. The
suspended solids present in the effluent collide with the mycelium and wear and tear of
the mycelium takes place (Figure 7.1 ).
The biosorption potential of the fungi Neurospora intermedia has been identified
in chapter three. From the results of FT-IR it is clear that it contains chitin and chitosan
(Figure 7.2). These chemical compounds are involved in biosorption (Saiano et al.,
2005). Similar studies has been shown by using Rhizopus sp. (Volesky and May-Philips,
1995). FTIR studies also showed that the bands associated with colorants/ compounds in
distillery effluent were also observed in the effluent treated mycelium (Pandey, 1999;
Hoareau et al., 2004). Both native and physically (heat)- chemically (acid, base) treated.
fungal biomasses have been used to remove colored pollutant from aqueous medium
(Vandeviverae et al., 1998; Ozer et al., 2005). In our study of FT-IR, data revealed that
the chemical moieties associated with the fungal mycelium underwent changes when
mycelium was given acid, base and heat treatment (Figure 7.3, Table 7 .2). This change
was positive or negative. Treatment of mycelium led to loss of some functional groups.
Due to the complex nature of the process of adsorption it is not possible to predict the
adsorption capability accurately depending on the chemistry of the mycelium
145
(Bayramoglu et al., 2006). The results of this study clearly showed that physical and
chemical surface modification methods can be used to maximize the color removal
efficiency of different preparations of fungal biomass Thus, further studies involved the
equilibrium isotherm study of all four types of mycelium preparations.
·· ·It was found that best performance was by base treated mycelium followed by -
acid, then native and finally heat. However, the band intensities showed different patterns
with different treatments. Variability in the response of fungi after acid, base and heat
treatment has been reported in case of Phanerocheate chrysosporium (Bayramoglu et al.,
2006). For the linear models, the coefficient of determination (r2) is widely used in
assessment of isotherm accuracies and is commonly determined by the least squares
method (Dagnelie, 1998). Among the tested isotherm models Langmuir models were
more applicable to the type of biosorption achieved by fungal biomass preparations.
These results suggested that different preparation of N. intennedia biomasses have
potential applications in biotreatment systems for color removal from different industrial
effluents. The value of constant n was greater than 1 hence, all the adsorption process
were favorable. From the model we can say that adsorption has uniform energies on the
surface and there is no transmigration of adsorbate in the plane of the surface. Moreover,
. as the adsorbate concentration increases, the concentration of adsorbate on the adsorbent
surface also increases.
Research indicates that there are many factors of the adsorbent and the adsorbate
that can affect the extent and rate of adsorption process. Surface chemistry and the
distribution of adsorption sites on the surface of the adsorbent play a significant role in
the adsorption process. Distillery spent wash contains complex polymeric organic
compounds having different aromatic rings and functional groups and thus have varying
ionization potentials at different pH ultimately showing varying biosorption potential at
different pH values. The fungal cell wall is composed of polysaccharides (i.e. chitin and
chitosan), proteins, lipids and melanin with several functional groups (such as amino,
carboxyl, thiol and phosphate groups) capable of binding various organic molecules
(Yesilada et al., 2003). The ionic forms of these organic compounds in solution and the
surface electrical charge of the biomass depend on the solution pH. Therefore, the
interaction between an adsorbate and biosorbent is mainly affected by ionization states of
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the functional groups on both the molecule and biosorbent surface (Maurya et al., 2006).
Low pH has been found to favor adsorption of dyes (Aksu and Donmez, 2002) and heavy
metals (Bai and Abraham, 2003) by the biomass of yeast and fungi and also by other
adsorbents such as eucalyptus bark (Morais et al., 1999). Our studies also showed that
· lower pH values were favorable for adsorption process. Similar results were alsn found
by Hu (1992) and Mahony et al. (2002) while carrying out adsorption studies of different
reactive dyes.
The biosorption of the colored pollutants increased with increasing temperature
till 30°C due to increased surface activity and increased kinetic energy of the dye
molecules. Similar observations were reported in the literature (Arica and Bayramoglu,
2005). Aksu and Cagatay reported that the adsorption capacity of.-Chlorella vulgaris for
Ramazol Black B dye was increased as the temperature increased (Aksu and Cagatay,
2006). However, beyond 30°C there was decrease in the percentage biosorption.
In our study the equilibrium for adsorption was reached very early in which 80%
biosorption was completed within first 4 hours. Similar studies were observed by Kiff
and Little ( 1986) while studying biosorption where A. oryzae was used and it reached
equilibrium in 1 hour with 90% biosorption taking place in the initial 10 min at pH 6.0.
On the contrary, biosorption of metal ions i.e. lead, cadmium, copper and nickel by A.
niger took a longer time to reach equilibrium at a pH of 4-6 (Kapoor et al., 1999). This
surface binding involves specific chemical sites or functional groups on the cell wall,
performance of which is affected by pH and other ions.
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