Synergetic decolorization of reactive blue 13 by zero-valent iron and anaerobic sludge

•Zero-valent iron (ZVI) enhanced anaerobic bioreduction of reactive blue 13.•Sludge morphology and microbial community were changed by ZVI addition.•pH and salinity were two important influential factors of the process.•The mechanism of synergy between ZVI and sludge was elucidated. Efficient decolorization of reactive blue 13 was achieved by a combined use of anaerobic sludge and zero-valent iron (ZVI), and the underlying mechanism of this process was elucidated, Addition of 1.0g/L ZVI into sludge accelerated the decolorization, with the decoloration ratio after 1-h treatment increased by 29.4% compared with the sum of the individual systems, indicating a synergy between the sludge and ZVI. Meanwhile, substantial changes in sludge morphology and microbial community were observed. The increased dye removal by ZVI was mainly attributed to: (1) a directly chemical reduction and aggregation; and (2) creation of a more favorable pH and anaerobic environment for microorganisms. The acid production by acidogens also partially offset the pH rise in ZVI corrosion and would alleviate ZVI deactivation. This work might offer valuable implications for the optimization and practical application of ZVI-anaerobic sludge processes for treatment of azo dyes or other recalcitrant pollutants.