Nanoscale zero-valent iron integrated with bioreactor for recalcitrant antimony-Congo red dyeing wastewater treatment

Antimony (Sb) and recalcitrant organic dyes often coexist in dyeing wastewater, and the simultaneous removal of Sb and dyes has been a challenge for traditional biological method in the treatment of Sb-dyeing wastewater. Nanoscale zero-valent iron (nZVI) is particularly suitable for separating heavy metals and enhancing the biodegradability of recalcitrant organic compounds. Herein, nZVI is integrated with bioreactors (nZVI-bio system) to achieve enhanced removal of Sb and degradation of Congo red (CR) in wastewater. The nZVI-bio system achieves a reduction in Sb levels from 2.5 g L-1 to 0.064 mg L-1, with a color removal efficiency of up to 98.60 % and a reduction in COD from 167 mg L-1 to 55 mg L-1. The excellent performance is mainly attributed to nZVI pretreatment, which removes Sb and degrades CR into smaller and more biodegradable organic compounds, providing favorable environmental conditions for the subsequent biotreatment system. This suggests that integrated nZVI-bio system has potential for the treatment of complex wastewater containing heavy metals and recalcitrant organic dyes.