Development of polyaluminum chloride-based coagulants from aluminum scrap for the treatment of textile wastewater

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.