Anaerobic digestion is promising technology to recover energy from waste activated
sludge. However, the sludge digestion is limited by its low efficiency of hydrolysis
eacidification. Zero valent iron (ZVI) as a reducing material is expected to enhance
anaerobic process including the hydrolysiseacidification process. Considering that, ZVI
was added into an anaerobic sludge digestion system to accelerate the sludge digestion in
this study. The results indicated that ZVI effectively enhanced the decomposition of protein
and cellulose, the two main components of the sludge. Compared to the control test
without ZVI, the degradation of protein increased 21.9% and the volatile fatty acids production
increased 37.3% with adding ZVI. More acetate and less propionate are found
during the hydrolysiseacidification with ZVI. The activities of several key enzymes in the
hydrolysis and acidification increased 0.6e1 time. ZVI made the methane production raise
43.5% and sludge reduction ratio increase 12.2 percent points. Fluorescence in situ hybridization
analysis showed that the abundances of hydrogen-consuming microorganisms
including homoacetogens and hydrogenotrophic methanogens with ZVI were higher than
the control, which reduced the H2 accumulation to create a beneficial condition for the
sludge digestion in thermodynamics.