Biosorption of Heavy Metals

1. A Greener Cleaner:
Investigating a Potential Biosorbent
for the Removal of Heavy Metals
from Aqueous Solutions
Ananya Karthik
Saint Francis High School

2. Problem
 Heavy metal contamination of water poses a serious threat to the global
ecosystem
 Conventional methods of removal are expensive and may generate toxic
sludge
 A need exists for a low-cost and effective biosorbent for the removal
of heavy metals from wastewaters

3. Objective
 Spent coffee grounds (SCG)
 abundantly available
 currently disposed of as solid waste
 Scientific literature on using SCG as a biosorbent is limited
Can SCG be used as a potential biosorbent for the removal of
heavy metals from aqueous solutions?

4. Research
HEAVY METALS:
 Natural components of the Earth's crust that cannot be degraded or
destroyed and are toxic even at low concentrations
 Rapid urbanization has increased their disposal into the environment
due to their wide use in several industries
 Dangerous since they tend to accumulate in the environment and in
food chains, causing disruption in biological processes
 Lead, copper, and chromium have been classified as priority
pollutants by the U.S. EPA, and their accumulation in the body may
cause disorders, including brain damage, cancer, and developmental
problems in children

5. METHODS OF REMOVAL:
 Conventional methods
 relatively expensive
 may generate toxic sludge
 less feasible to use in developing countries
 Adsorption
 the ability of the adsorbate to adhere or attach to the adsorbent
 well-established separation technique to remove dilute pollutants
 Biosorption
 relatively new process that is promising for the removal of heavy
metals from aqueous solutions
 biomass naturally concentrates and binds contaminants onto its
cellular structure

6. SPENT COFFEE GROUNDS:
 Various agricultural wastes
 investigated as adsorbents for the removal of contaminants from
aqueous solutions
 their success has been attributed to different functional groups and
structural compounds like cellulose, hemicellulose, and lignin
 SCG
 solid residues generated by the processing of coffee
 USDA data shows the global production capacity of coffee beans in
2015 was greater than 9 billion kilograms, and in the future more
production and waste of spent coffee grounds are expected
 The utilization of spent coffee grounds as an adsorbent of metal
ions may therefore represent an attractive strategy for the effective
reduction and reuse of this type of waste

7. ATOMIC ABSORPTION SPECTROSCOPY:
 A technique for determining the concentration of a particular metal
element within a sample
 The liquid sample is aspirated and atomized in the flame, through which
radiation of a chosen wavelength (using a hollow cathode lamp) is sent;
the amount of absorbed radiation gives the concentration of the element
in the sample
REMOVAL EFFICIENCY:
 Extent of biosorption in percentage is given by the following equation:
RE% = [(Ci – Cf) / Ci] × 100
where Ci and Cf are the initial and final metal ion concentrations (ppm),
respectively, and RE is the removal efficiency

8. Hypothesis
Based on research, the hypothesis was formed:
 SCG can be used as a potential biosorbent for the removal of
heavy metals from aqueous solutions

9. Experimental Design
 Independent Variable: pH value, contact time, adsorbent dose,
initial metal ion concentration
 Levels
 pH values (3, 4, 5, 6, 7)
 Contact times (30, 60, 90, 120, 150 minutes)
 Adsorbent doses (0.5, 1.0, 1.5 g)
 Initial metal ion concentrations (10, 25, 50 ppm)
 Trials: 3
 Dependent Variable: Biosorption of lead, copper, and chromium
from aqueous solutions
 Operational Definition: remaining concentration (ppm) of heavy
metal in solution, attained using Atomic Absorption Spectroscopy

10. Experimental Design
 Constants: temperature (37.5°C), agitation rate (100 rpm), type of
biosorbent (SCG – Arabica)
 Controls
 Positive control: aqueous solutions of 10, 25, and 50 ppm of
lead, copper, and chromium without SCG
 Negative control: deionized water

11. Overview of the Process
Coffee Beans Cup of Coffee Spent Coffee Grounds
Test SolutionsSample Analysis

12. Preparation
 Preparation of the Adsorbent
 SCG were air-dried for a week, washed with DI water to remove
dust or other particles, and oven-dried at 100°C for four hours
 Ground into a fine powder with a kitchen grinder to increase
surface area and the number of available adsorption sites
 Sieved to maintain uniformity in particle size (<= 0.25 mm)
 Preparation of Test Solutions
 Prepared 1000 ppm stock solutions of the heavy metals using lead
nitrate, copper sulfate, and potassium chromate
 Made dilutions to achieve 10, 25, and 50 ppm in 50 mL solutions
 Adjusted pH with hydrochloric acid and sodium hydroxide

13. Adsorption Experiments
 Adsorption experiments were conducted in triplicates by treating the
metal solutions with SCG
 Samples were agitated at 100 rpm and 37.5°C for different pH
values, contact times, adsorbent doses, and initial metal ion
concentrations
 Samples were filtered and then analyzed using Atomic Absorption
Spectroscopy
 The removal efficiency of the SCG for each sample was calculated

15. Results
 pH: Maximum removal efficiency (RE%) was at pH 5 for lead and
copper and pH 3 for chromium
 Contact Time: RE% increased with the increase in contact time.
Rapid adsorption occurred in the first 30 minutes for all metal ions;
equilibrium was reached at 90 minutes. Further increase in contact
time did not show an increase in biosorption
 Adsorbent Dose: Increasing the adsorbent dose resulted in greater
RE%
 Initial Metal Ion Concentration: With the increase in initial metal
ion concentration, RE% decreased

16. 0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8
RE%
pH
The Effect of pH on Removal Efficiency
Lead
Copper
Chromium
Initial Metal Ion Concentration=25 ppm, Adsorbent Dose=0.5 g,
Contact Time=90 min., Temp.=37.5ºC, Agitation Speed=100 rpm

17. 0
10
20
30
40
50
60
70
80
90
100
0 30 60 90 120 150 180
RE%
Contact Time (minutes)
The Effect of Contact Time on Removal Efficiency
Lead
Copper
Chromium
Initial Metal Ion Concentration=25 ppm, Adsorbent Dose=0.5 g,
pH=5, Temp.=37.5ºC, Agitation Speed=100 rpm

18. 0
10
20
30
40
50
60
70
80
90
100
0 0.5 1 1.5 2
RE%
Adsorbent Dose (g)
The Effect of Adsorbent Dose on Removal Efficiency
Lead
Copper
Chromium
Initial Metal Ion Concentration=25 ppm, Contact Time=90 min.,
pH=5, Temp.=37.5ºC, Agitation Speed=100 rpm

19. 0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30 35 40 45 50 55
RE%
Initial Metal Ion Concentration (ppm)
Lead
Copper
Chromium
The Effect of Initial Metal Ion Concentration on Removal Efficiency
Adsorbent Dose=0.5 g, Contact Time=90 min., pH=5,
Temp.=37.5ºC, Agitation Speed=100 rpm

20. Results
 RE% for lead was the highest at 97.83%, followed by copper at
94.21% and chromium at 84.09%, respectively
 Removal efficiencies ranged from 76.64% to 99.02%, depending on
the solution composition and adsorption conditions

21. 0
10
20
30
40
50
60
70
80
90
100
Lead Copper Chromium
RE%
Type of Metal
The Effect of the Type of Metal on Removal Efficiency
Lead
Copper
Chromium
Initial Metal Ion Concentration=25 ppm, Adsorbent Dose=0.5 g,
pH= 5, Contact Time=90 min., Temp.=37.5ºC, Agitation Speed=100 rpm

22. Conclusion
 The hypothesis was supported
 The results of this experiment indicate that SCG can be used as a
potential biosorbent for the removal of lead, copper, and chromium
from aqueous solutions
 Functional groups on the surface of SCG and cell wall components
like cellulose, hemicellulose, and lignin are responsible for metal ion
adsorption
 Experimental data showed that removal efficiencies up to 99% can
be achieved when using SCG as a biosorbent, depending on the
adsorption conditions
 The removal efficiency depends on the pH, contact time, adsorbent
dose, and initial metal ion concentration

23. Effect of pH
 The biosorption of lead and copper was highest at pH 5 since there were
lower numbers of competing hydrogen ions. At low pH values, there is a
higher concentration of hydrogen ions, which are preferentially adsorbed
rather than metal ions
 In the case of chromium, the biosorption was highest at pH 3 because at
low pH values there is an excess amount of hydrogen ions, causing the
adsorbent sites to be positively charged. This causes a strong attraction
between these sites and the negatively charged chromium ions
Effect of Contact Time
 The removal of metal ions was rapid for 0-30 minutes; 30-90 minutes
showed gradual removal; and 90-150 minutes indicated the equilibrium
state. The metal uptake by the biosorbent surface decreases with the
decrease in the availability of active sites, slowing down the transfer of
metal ions from the solution to the adsorbent surface

24. Effect of Adsorbent Dose
 The increase in removal efficiency with adsorbent dose is an expected
result and can be attributed to greater adsorbent surface area and
availability of more adsorption sites
Effect of Initial Metal Ion Concentration
 The decrease in removal efficiency with an increase in initial metal ion
concentration can be explained. At low concentrations the ratio of
available surface to the initial metal ion concentration is high, so
removal efficiency is higher. However, in the case of higher
concentrations this ratio is low, so the removal efficiency is lower

25. Real World Applications
 Over 6 billion kilograms of coffee wastes are generated worldwide
every year and are of no commercial value
 Advantages of using SCG as a biosorbent:
 Low-cost (especially for use in developing countries)
 Easily available
 Environmentally-friendly
 Possibly reusable
 This novel approach can help solve two problems:
 The removal of heavy metals from wastewaters
 The utilization of abundant SCG and promoting this waste into a
new resource

26. Acknowledgements
 I would like to thank my family and school science teacher for their
constant support, Dr. Roger Terrill for giving me the opportunity to
use the AAS equipment in the lab, and Starbucks for providing me
with the SCG. Thank you!