Nano zero-valent iron regulates the enrichment of organics-degrading and hydrogenotrophic microbes to stimulate methane bioconversion of waste activated sludge

[Display omitted] •nZVI enhanced CH4 yield of sludge in an anaerobic continuous stirred tank reactor.•nZVI promoted CH4 bioconversion by serving as trace element and electron donors.•Organics-degrading bacteria and hydrogenotrophic methanogens were enriched.•Subsequent digested sludge dewaterability were enhanced at nZVI 160 mg/g-TS. Underlying mechanism of continuous nano zero-valent iron (nZVI) supply in functional microbes enrichment and methane bioconversion of waste activated sludge were investigated in a lab-scale continuous stirred tank reactor (CSTR). Results indicated that methane productivity strongly relied on nZVI dosage (R = 0.998, p (0.05)