Abstract
The pollution of water by potentially toxic elements (PTEs) constitutes a substantial
threat to the environment and subsequently to animals and humans. It is essential to
develop effective methods to ensure that these PTEs are detected and removed with
the utmost sufficiency. In this study, sugarcane bagasse (SCB) and orange peels
(OPS) have been investigated as low-cost biosorbents, individually and in combination
for the removal of Cr(VI) and Pb(II) from simulated and real water samples.
Biosorbents were characterised using Fourier transform infrared (FTIR) spectroscopy,
thermogravimetric analysis (TGA), scanning electron microscopy (SEM) coupled to
energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy
(TEM), powder X-ray diffraction (pXRD), and Brunauer–Emmett–Teller (BET). The
FTIR spectroscopy identified the critical surface oxygen-bearing functional groups
involved in Pb(II) and Cr(VI) adsorption. The FTIR spectra for SCB and OPS were
matched with natural materials containing structural components such as cellulose
and hemicellulose. The TGA studied the thermal stability of SCB and OPS. Information
gathered in TGA described the degradation of structural components found in SCB
and OPS with increased temperature. The SEM and TEM microphotographs were
used to examine the surface morphology of SCB and OPS. Elemental analysis by
SEM-EDS revealed high oxygen concentrations in both SCB and OPS.
Characterisation by pXRD revealed that both biosorbents are amorphous and showed
diffractogram peaks characteristic of cellulosic plant material. Analyses of SCB and
OPS by BET revealed that SCB has a larger surface area, pore size, and pore-volume
than OPS.
Batch adsorption studies were explored under several experimental conditions to
optimise the removal efficiency of the selected PTEs. The pH study revealed optimum
removal efficiencies of Pb(II) at pH 7 for SCB and OPS. The optimum pH for the
removal of Cr(VI) was pH 7 and pH 8 using SCB and OPS, respectively. The optimum
contact time for Pb(II) and Cr(VI) removal by isolated and homogenised SCB and OPS
was found between 10 and 240 minutes. The adsorbent dosage study was capped at
0.17 g for OPS and 0.2 g for SCB to preserve the aesthetic quality of detoxified water.
Optimum experimental conditions could achieve up to 100% removal efficiencies for
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10 mg/L and 20 mg/L of Pb(II) using SCB and OPS, respectively. The highest
concentration of Cr(VI) that could be removed by SCB and OPS with an efficiency of
100% was 1 mg/L. The potential of the homogenised combination of 0.2 g SCB and
OPS (5:5) demonstrated 100% removal efficiencies for 10 mg/L of Pb(II) and 1 mg/L
Cr(VI). The removal of 10 mg/L Pb(II) and 1 mg/L Cr(VI) in real water samples
remained at 100% for SCB and OPS in isolation and homogenised combination.
The sustainability performance of SCB, OPS, and homogenised SCB and OPS
presented Pb(II) removal efficiencies above 90% for 2, 3, and 2 adsorption-desorption
cycles, respectively. The removal efficiency of 1 mg/L Cr(VI) remained at 100% for all
adsorption-desorption cycles. The application of these agricultural by-products
compared to conventional water treatment techniques offers reduced operational
costs, high removal efficiencies, lower sludge production, and a noble application for
organic load deemed agriculturally futile.