Please use this identifier to cite or link to this item: https://hdl.handle.net/10321/4866
Title: Biosorption of Fe2+ from potable water using natural and modified sugarcane bagasse
Authors: Ndebele, Nompumelelo Lindi Gelsiah 
Keywords: Sugarcane bagasse;Heavy metals;Cellulose;Lignin;Hemicellulose
Issue Date: May-2023
Abstract: 
Even though some metals are crucial for the health and development of human bodies, their
presence in higher concentrations is worrisome because it has a detrimental effect on people's
health. These heavy metals cause cancer and cannot be broken down by biological processes. The
removal of heavy metals from water using traditional techniques; such as reverse osmosis,
precipitation, ion exchange; has been the subject of extensive investigation. However, because
these processes are so expensive to run, a lot of research is currently focusing on using agricultural
biomasses to remove these heavy metals. Dumping of this agricultural waste (sugarcane bagasse)
in landfills creates dangers of spontaneous combustion, because of microbial activities.
The functionality of circular economy depends on waste resources being utilized to their fullest
potential, with almost no production of recoverable waste. In a circular economy, sugarcane
bagasse is utilized as a fuel source for the boilers that generate process steam and electricity in the
sugar mill facilities. Sugarcane bagasse is used in the manufacturing of paper and paper goods, as
well as in the agricultural sector. Stakeholders across the value chain, from product design to waste
management, This study fulfils the functionality of the circular economy where it looks at
extracting the valuable components of the sugarcane bagasse, then further using the sugarcane
bagasse to remove heavy metals from potable water.
In this study, the adsorption capacities of unmodified and modified sugarcane bagasse for
removing Fe2+ from potable water were investigated in batch experiment studies. Sugarcane
bagasse comprises cellulose, hemicellulose and lignin. In order to determine the effect of
removing/ extracting each component from the sugarcane bagasse, sugarcane bagasse was
pretreated with different concentrations of sodium hydroxide and sulphuric acid, ranging between
0.5 wt% and 2.5 wt%, predominantly used to extract lignin and hemicellulose.
A cellulosic structure was left behind after the simultaneous removal of both amorphous
components (the lignin and the hemicellulose) using the combined pretreatments of sodium
hydroxide and sulfuric acid. The advantages of extracting or eliminating these components came
from their high value in many sectors. Lignin is used in the paper business and costs between R11
300 and R17 420 per ton, hemicellulose is used in the pharmaceutical sector and costs between
R500 and R1000 per ton, and cellulose is utilized in the textile sector. The concentrations of all chemical pretreatments used on the sugarcane bagasse ranged from 0.5
to 2.5%, with alkaline pretreatments intended to extract lignin, acid pretreatments intended to
extract hemicellulose, and combination pretreatments intended to remove both lignin and
hemicellulose. While cellulose content increased from 32.02 to 65.65% after sodium hydroxide
pretreatment, lignin and hemicellulose content reduced from 22.30 and 24.30% to 7.56% and
13.63%, respectively. Lignin and hemicellulose concentration for the sulphuric acid pretreatment
went from 22.30 and 24.30% to 14.90% and 13.63%, respectively, while cellulose content went
from 35.02 to 65.65%.
After the sugarcane bagasse underwent chemical pretreatments, batch studies were conducted on
both the natural and chemically pretreated sugarcane bagasse in order to determine how the
removal of lignin, hemicellulose, and cellulose affected the performance of the biosorbents in the
biosorption of Fe2+ from drinkable water. To assess the efficacy of natural and modified sugarcane
bagasse on the Fe2+ removal, the operational parameters investigated in the batch experiments were
initial concentration ranging from 1 to 30 mg/L; pH ranging from 2 to 7, contact time ranging from
5 -100 minutes, and adsorbent dose ranging from 0.2 to 1.4 g.
For every variation investigation, one variable was varied at a time while keeping the other
variables constant. The experimental runs done were repeated thrice and average values are
reported throughout the study. According to the biosorption results, 1% NaOH was the best
performing biosorbent for the alkali-pretreatment. The most effective biosorbent for the acidpretreatment variation was 2.5% H2SO4. The optimal combination for the pretreatment was (0.5%
NaOH + 0.5% H2SO4).
Regarding initial concentration variations, all biosorbents were most effective at a concentration
of 1 mg/L, where natural sugarcane bagasse was able to remove 50% of Fe2+, 1% NaOH was able
to remove 99.7% Fe2+, 2.5% H2SO4 removed 75.93% Fe2+, and the combined-pretreated
biosorbent of (0.5% NaOH + 0.5% H2SO4) removed 87.17% Fe2+
.
The increase in biosorbent dose led to an increase efficiency of the natural and chemically
pretreated biosorbents. The highest removal of Fe2+ was obtained at 1 g (both for the natural and
for all the pretreated biosorbents), with 32.2% for the natural; 79.04% for the 1% NaOH; 58.79%
for the 2.5% H2SO4 and 70.73% for (0.5% NaOH + 0.5% H2SO4). Results of the study also showed that the highest removal of Fe2+ for the pH variation of 2-7 was
at pH “6” for both the natural and pretreated biosorbents. For the variation of the agitation speed,
the highest Fe2+ removal was at 160 rpm with 52% Fe2+ removal for the natural sugarcane bagasse.
The Langmuir and Freundlich adsorption isotherms were used to study the biosorption
mechanisms. Good correlation coefficients (R
2
) of > 0.95 were obtained for both the Langmuir
and Freundlich isotherms for both the natural and modified sugarcane bagasse, indicating that the
biosorption followed both homogeneous and heterogeneity interaction between Fe2+ ions and
active functional groups of the surface and pores of the biosorbents. Biosorption results for the
natural sugarcane bagasse best fitted with the Langmuir isotherm with qmax of 0.770 mg/g, R
2
of
0.987 and RL of 0.938. The alkali and acid-pretreated biosorbents favoured both the Langmuir and
Freundlich isotherms with R
2 > 0.95; RL < 1 and 1
𝑛
< 1. The highest qmax of 9.199 and 5.743 mg/g
was obtained at 1% NaOH and 2.5% H2SO4, respectively. The combined pretreatment fitted best
with only the Langmuir isotherm with R
2
of 0.987, the R
2
of the Freundlich isotherm was less than
0.9. The biosorption of Fe2+ followed both the pseudo-first-order and pseudo-second-order kinetic
reactions with 𝑞𝑒(𝑒𝑥𝑝)
in close proximity to 𝑞𝑒(𝑐𝑎𝑙𝑐)
and R
2 > 0.9. These results showed that
sugarcane bagasse had great adsorption capacity after removing the valued components, namely,
lignin and hemicellulose.
Characterization studies, which included FTIR, XRD, BET and SEM, were also carried out on the
natural and pretreated bagasse before and after adsorption experiments. FTIR confirmed the
existence of carbonyl, hydroxyl and carboxyl functional groups as major groups responsible for
the adsorption of Fe2+ onto the natural and pretreated sugarcane bagasse. XRD revealed that the
natural structure of the sugarcane bagasse was of native cellulose consisting of both amorphous
and crystalline regions; this structure became more crystalline after the chemical pretreatments as
the crystallinity index increased from 39.04% to 66.85% at 1% NaOH; 57.47% at 2.5% H2SO4;
and 57.92% at (0.5% NaOH + 0.5%H2SO4).
The natural sugarcane bagasse structure featured rough surfaces, according to SEM data, and the
main constituents were silicon (Si), carbon (C), and oxygen (O). According to the BET data,
employing 1% NaOH, 2.5% H2SO4, and (0.5% NaOH + 0.5% H2SO4), respectively, the initial
surface area of 0.904 cm3
/g rose to 1.503, 1.233, and 1.376 cm3
/g and the pore size of 56.33 ̊A
increased to 99.63, 93.680, and 99.10 ̊A. According to the EDS data, sodium hydroxide
pretreatment performed better in terms of adsorption, followed by combined pretreatment and sulphuric acid. The natural sugarcane bagasse, 1% NaOH, 2.5% H2SO4, and (0.5% NaOH + 0.5%
H2SO4) were able to biosorb 0.77, 7.89, 1.63, and 3.8% Fe2+, respectively.
Description: 
Submitted in fulfillment of the requirements of the degree of Master of Engineering, Durban University of Technology, Durban, South Africa, 2022.
URI: https://hdl.handle.net/10321/4866
DOI: https://doi.org/10.51415/10321/4866
Appears in Collections:Theses and dissertations (Engineering and Built Environment)

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