Feasibility of nanoscale zero-valent iron (nZVI) for enhanced biological treatment of organic dyes.

Biodegradation of recalcitrant organic contaminants such as organic dyes is a fundamental challenge in wastewater treatment. We report herein the integration of nanoscale zero-valent iron (nZVI) with membrane bioreactors (nZVI-bio system) to achieve enhanced degradation of Congo red (CR) in wastewater. nZVI pretreatment converts the large and bio-recalcitrant CR molecules into smaller and more biodegradable organic compounds in continuous flow stirred tank reactors (CFSTR). A nZVI-bio system was experimented continuously for 52 d with a color removal efficiency of 99% and a reduction of chemical oxygen demand (COD) from 167 mg L−1 to less than 70 mg L−1. However, a conventional biotreatment system treating identical wastewater achieved color removal efficiency of just 30–70% and the COD reduction to 116 mg L−1. This suggests that integrated nZVI-bio system has potential for the treatment of recalcitrant organic dyes. On-line measurements of pH and redox potential in the CSFTR can be conveniently used to monitor and regulate treatment performance. Image 1 • nZVI pretreatment reduced color, toxicity, and enhances biodegradability. • nZVI-bio system enhanced color removal and COD reduction. • nZVI-bio system was feasible for CR wastewater treatment. • pH and E h in nZVI reactor could be used to monitor CR removal efficiency. [ABSTRACT FROM AUTHOR]