Abstract:
High volumes of wastewater generation have become a serious concern over the
last few decades worldwide. The discharge of untreated textile wastewater has severely
polluted water and soil, threatening the entire environment. The treatment of this
wastewater is important in preventing environmental pollution. The most effective
methods to treat textile wastewater are coagulation and flocculation. In chemical
coagulation, positively charged ions of metal salts are added for charge neutralization and
destabilization of colloidal particles. Polyaluminum chloride (PAC) is a highly effective
coagulant that has gained popularity over the last few decades for the treatment of textile
wastewater because of its apparent cost-effectiveness and availability. In the present
study, PAC was synthesized using aluminum scraps as a raw material. For the synthesis
of PAC, AlCl3 solution was vigorously mixed with NaAlO2 solution for 3 h in an
automated synthesis system at 70 ℃. The synthesized PAC was characterized using
Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM)
with energy dispersive X-ray spectrometry (SEM-EDX), wavelength dispersive X-ray
fluorescence (WD-XRF) spectrometry, X-ray diffraction (XRD), thermogravimetric
analysis (TGA), differential scanning calorimetry (DSC), Zetasizer. The synthesized PAC
was also characterized for its basicity and Al2O3 content.
To determine the coagulation behavior of scrap-derived PAC coagulant, a batch
study was conducted with a commercially used anionic dye (Novacron Navy S-G). The
optimized parameters of the PAC dosage, pH, contact time, shaking speed and
sedimentation time were found to be 2.5 mg, 6.0, 20 min, 150 rpm and 35 min,
respectively. At optimum conditions, the synthesized PAC coagulant was found to
remove 83.37 to 94.11% of dye from 50 mL of dye-containing wastewater. The
effectiveness of PAC and conventional alum for the reduction of turbidity and chemical
oxygen demand (COD) in textile wastewater has also been investigated. Batch studies
were performed to optimize different parameters for the successful removal of turbidity
and COD. The parameters tested in the batch studies were coagulant dosage, pH, contact
time, mixing speed and sedimentation time. Results revealed that at optimum conditions,
PAC removed 97 to 99% of turbidity and alum removed 94 to 98% of turbidity. On the other hand, the reduction of ii COD was found to be 42 to 51% with PAC and 33 to 45%
with alum. Even though the coagulants demonstrated more or less similar performance
with respect to turbidity and COD removal, the scrap-aluminum-derived PAC performed
at a lower dosage. Therefore, scrap-derived PAC might be a potential coagulant and good
alternative to alum for raw textile wastewater treatment.