BACKGROUND: This study focused on the effectiveness of the zero-valent iron (ZVI) pre-treatment for enhancing the biodegradability of 2-chloronitrobenzene (2-ClNB), and further to evaluate the performance and mechanism of a coupled ZVI column-sequencing batch reactor (SBR) system treating 2-ClNB contained wastewater. RESULTS: 2-ClNB was readily transformed into 2-chloroaniline (2-ClAn) with the efficiency over 99.9% by ZVI column, and its biodegradability was significantly enhanced via ZVI pretreatment. The transformed effluent was subsequently fed into the SBR followed by 2-ClAn loading of 3.4-117.2 g m(-3) d(-1) and COD loading around 1000 gm(-3) d(-1). A 2-ClAn removal efficiency over 99.9% and COD removal efficiency of 82.0-98.1% were obtained. Moreover, 91.9 +/- 0.1% TOC removal efficiency and 107.1 +/- 6.0% chloride recovery efficiency during one cycle confirmed the complete biodegradation of 2-ClAn in the coupled system. 16S rDNA PCR-DGGE analysis suggested that ZVI pretreatment enhanced the diversity of the microbial community and promoted enrichment of the functional microorganisms degrading 2-ClAn in the following SBR. CONCLUSION: ZVI pretreatment significantly enhanced the biodegradability of 2-ClNB, and the coupled ZVI-SBR system demonstrated excellent performance when treating wastewater containing 2-ClNB. (C) 2011 Society of Chemical Industry