Sequential treatment of simulated textile wastewater using zero-valent aluminum under alkaline conditions and biodegradation

The azo dye reactive yellow 145 (RY145) is inherently recalcitrant due to the presence of azo, ethyl sulfone and monochlorotriazine groups. This study explored removal of RY145 using zero valent aluminum (ZVAl) treatment under alkaline conditions followed by aerobic degradation using the bacterial strains Pseudomonas aeruginosa (RS1) and Thiosphaera pantotropha. During pretreatment using 1 g L−1 ZVAl at pH 11, 59% decolorization was observed after 30 min for 50 mg L−1 dye. However, even after carbon source supplementation, the supernatant could not support microbial activity due to the high aluminum concentration in solution at pH 11. After pH adjustment to neutral and Al(OH)3 precipitation, complete decolorization occurred and subsequently microbial degradation of the intermediates could be achieved. ZVAl pretreatment followed by biological treatment could cause an overall TOC reduction of 65% within 96 h. Sorption of dye on the precipitate only contributed to 13% dye removal. The bacterial cultures could utilize nitrogen from the dye intermediates formed after alkaline ZVAl treatment. The sequential treatment also reduced the concentration of total amines and phytotoxicity to Vigna radiata seeds. When a simulated textile wastewater containing 200 mg L−1 of RY145 was subjected to this sequential treatment, complete dye decolorization and 99.2% overall TOC reduction was observed in 30.5 h. The other compounds present in the synthetic wastewater facilitated decolorization as well as mineralization of the dye. © 2022 Elsevier Ltd