Ø by filtering the contents using whatman filter paper

Ø Isolation,
culturing and biomass preparation of Blue green algae (Oscillatoria):

 Micro algal
samples were collected from various ponds of Surat district. The material so
collected was identified under microscope and serial dilution was carried out
for isolation and then obtained algae were added to various synthetic medium in
order to check which media was able to support the best growth of alga. The
medium with below mentioned constituents showed maximum growth and thus was
further used for culturing and multiplication. After required growth was
observed it was filtered through whatman filter no.1 and oven dried at 60°C and
the powder was further used for biosorption process.

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Ø Marine
algae collection and preparation of biomass:

 Fresh and mature
thalii of Sargassum and Ulva sp. were collected from Veraval
coast in Junagadh district along the west coast of Gujarat. Algal material was
brought to laboratory in polythene bags. Then it was cleaned, washed with
distilled water to remove dust and impurities. After washing it was sun dried
for 24 hours and then kept in oven at 60°C for further drying until it attained
constant weight. After complete drying it was ground and sieved to powder of
equal size. The powdered material was stored in plastic, air tight bottles at
room temperature. This biomass powder was used for biosorption experiments.

Ø Preparation
of metal solution:

Metal solution was prepared using nitrate salt of the
metal. Heavy metal salt of analytical grade viz Pb(NO3)2 was
used to prepare stock solution of  lead
nitrate having concentration of 1000mg/L. Solutions of varying concentrations
were produced through dilutions of stock solution until desired concentrations
were reached. 

Ø Biosorption
experiment:

 Batch experiment was carried out in 250 ml
Erlenmeyer flask containing weighed biomass and 50 ml stock solution. The flask
were sealed with cotton plugs and kept on rotary shaker at room temperature.
The metal solution was agitated at a constant speed of 120 rpm per minute.
After a desired time interval the biomass was separated by filtering the
contents using whatman filter paper no.1. The amount of metal adsorbed on to
the biosorbent was calculated from the difference between metal ion
concentration in solution before and after biosorption process. Initial and
final concentration of metal was measured on Atomic Adsorption Spectroscopy.
Process parameters related to biosorption such as pH, time of contact,
concentration of metal, biomass dosage, temperature were varied and their
uptake was recorded.

       i.           
Effect of pH:

Batch process was carried out with series of 250 ml
Erlenmeyer flask containing 50 ml of metal solution and 100 mg of biomass.
Experiment was carried out at different pH values ranging from 2.0 to 6.0 by
keeping all other parameters constant. The pH of the metal solution was
adjusted to the desired value by adding either 0.1 N NaOH or Hcl. The samples
were run for 120 min and then filtered to determine the concentration of metal.
Optimum pH giving maximum metal removal was determined by analyzing the metal
concentration using AAS. All the experiments were carried out in duplicates.

     ii.           
Effect of contact time:

In order to understand the effect of time on the process
of biosorption the agitation period was varied from 0 to 120 min using 100 mg
biomass in 50 ml of metal solution, adjusted to optimum pH at which maximum
biosorption of metal ion occurred. The samples were removed after every 10 min
interval and filtered and analyzed for metal concentration on AAS.

  iii.           
Effect of metal ion concentration:

 Batch experiments were carried out in 250 ml
Erlenmeyer flask containing 50ml of selected stock solution. The metal
concentration of solution was ranging from 10 to 70 mg/L.  The experiment was set up at optimum pH using
100 mg biomass and run for optimum time as occurred. Later the samples were
filtered and analyzed for residual metal content on AAS.

  iv.           
Effect of Biomass dosage:

The weight of biomass added in each experiment was varied
from 0.1 to 2.0 gm. The optimum concentration of the metal was used and it was
maintained at optimum pH. The experiment was carried for optimum time interval
as occurred and the samples were filtered and the filtrate was analyzed for
metal concentration on AAS.

     v.           
Effect of temperature:

The effect of temperature on the sorption of metal ion
was studied at temperature range from 20°Cto 45°C. The pH, biomass
concentration metal concentration and contact time were maintained constant by
varying the temperature. The supernatants were analyzed for Pb uptake using
AAS. All the components were conducted I duplicates.

Ø Determination
of Pb+2 ions in the solution:

Biosorption experiments were carried out in duplicates
and average values were used in the analysis. The removal efficiency was
determined by computing the % sorption using the formula:

% Sorption =

Where Ci = initial metal concentration

            Ce = final metal
concentration

Atomic adsorption spectroscopy (AAS) was used
to determine amount of heavy metal in aqueous solution before and after the
equilibrium was established.

 Metal
uptake during biosorption experiment was determined using above mentioned
percentage sorption formula, in order to calculate equilibrium concentration
following formula is used:

Where qe represents amount of adsorption at equilibrium
(mg/g), M is mass of biosorbent (mg/g), C0 and Ce are initial and final
(equilibrium) concentration of metal ion (mg/L), V is the volume of metal (ml).

Ø Continuous
flow column experiment:

          The adsorption experiment was carried
out in column made up of glass. The column was equipped with a stopper for
controlling column flow rate. To enable a uniform inlet flow of solution into
the column glass beads of 1.5mm diameter were packed to attain a height of 2
cm. A known quantity of biomass of Sargassum,
Ulva and Oscillatoria were placed in respective column to yield desired
sorbent bed height of 10 cm, maintaining constant flow rate of 1.5ml/ min. Lead
solution of different concentrations (10, 20, 30, 40, 50) ppm with pH: 5.0 were
fed upward inside the column to get desired flow rate. Lead solutions at the
exit of the column were collected at different time interval and were analyzed
on AAS.

 

 

Ø Characterisation
of biosorbent before and after metal sorption :

·       
SEM/EDX:

SEM is used for studying surface morphology of materials.
The changes in the surface microstructures of the biosorbent due to chemical
surface modification and biosorption are studied using SEM.

Dried biomass of three different algae namely
Sargassum, Ulva and Oscillatoria
were coated individually with thin layer of gold under vacuum and examined
under scanning electron microscope. To determine chemical composition and
inorganic elements present on biosorbents energy dispersive X- ray spectrometer
(EDX) is used which is compatible with SEM. The samples were prepared as per
SEM and the compositions present on biosorbent were determined before and after
the process of biosorption. Both the analysis was performed simultaneously.

·       
FTIR:

It is a technique which is used to determine vibration
frequency changes in functional groups present on the biosorbent surface. In
order to study the functional groups present on the dried biomass of algae (Sargassum, Ulva and Oscillatoria)
FTIR was carried out. The samples were first mixed with KBr and then ground in
an agate motar to prepare a mixture. Then the mixture was pressed at 10 tonnes
for 5 min to obtain pellets. The pellets were used to record spectrum on IR
spectrum within the range of wave number 400-4000 cm-1. IR analysis
of all the 3 algae dried biomass was done before and after the biosorption
process in present study.

Ø Desorption
studies:

  For desorption studies, the column containing
11 gm of algae was contacted with 120 ml of Pb+2 metal solution of
known concentration. After biosorption experiment, the biomass was treated for
desorption. Then 120 ml of disodium EDTA solution of 0.1 N was allowed to pass
through the column. Then at 30 min time interval for 3 times the filtrate was
taken and were analysed to determine the concentration of Pb+2 after
desorption.

Desorption efficiency was calculated from the ratio
between the amount of metal ion adsorbed on biomass and the final metal ion
concentration in desorption medium as shown in following equation:

Ø Modelling
of heavy metal biosorption:

Sorption Isotherm: Several models of isotherms have been used.
In this context two different isotherm models (Langmuir and Freundlich) were
used in order to determine the biosorption of lead.

The Langmuir model describes quantitatively the formation of a
monolayer adsorbate on the outer surface of the adsorbent, and after that no
further adsorption takes place. The model assumes uniform energies of adsorption
onto the surface and no transmigration of adsorbate in the plane of the
surface.  (Vermeulan et al.,1966). Based on these assumptions, Langmuir represented the
following equation:

Langmuir
adsorption parameters were determined by transforming the above equation into
linear form.                                 

Where
Ce is the equilibrium concentration of adsorbate (mg/L), qe is the amount of
metal adsorbed per gram of adsorbent at equilibrium (mg/g), Qo is maximum
monolayer coverage capacity (mg/g), KL is Langmuir isotherm constant
(l/mg). The Langmuir plots obtained by plotting 1/qe Vs 1/Ce are linear showing
the applicability of Langmuir adsorption isotherm for metal adsorption using adsorbents
selected for this study. The isotherm feasibility can also be expressed as a
best fit by linear equation as seen from correlation coefficient values (R2).
The values of qmax and KL were computed from the slope
and intercept of the Langmuir plot of 1/qe and 1/Ce. (13)

Even
the separation factor (RL) which is a dimensionless constant is an
essential factor of Langmuir isotherm. It can be expressed I following way
(Weber and Chakrabarti, 1974).

 

Where
Co = initial concentration, KL = constant related to
energy adsorption.

 RL values indicate the adsorption
nature and feasibility of isotherm:     

RL values                                   Type of
isotherm

RL >1                                            
Unfavourable

RL=1                                               Linear

RL