Abstract: Aiming at the bottleneck in the treatment of high loaded pressing liquor generated during the centralized treatment of kitchen waste, the dose effect and enhanced performance of zero-valent iron on the anaerobic digestion of kitchen waste pressing liquor for methane production were investigated through the batch test of anaerobic digestion for methane production. The results showed that the optimal dose of zero-valent iron was determined to be 3 g/L, and the maximal methane production potential and the rate of the experimental group were enhanced by 24.91% and 475.99%, respectively, and the late period of gas production was shortened by 66.25%. Analysis of excitation emission matrix-parallel factor showed that the appropriate dose of zero-valent iron was able to slow down the humification of the system and promote the secretion of extracellular polymers by bacteria, which acted as an electron transfer medium to promote the direct interspecies electron transfer of microorganisms, and enhanced the biofilm formation ability of microorganisms on the surface of the carriers by enhancing the hydrophobicity of the microbial surface. Analysis of sludge characterization showed that the addition of zero-valent iron increased the ETS activity of the sludge electron transport system by 397.68%, and the concentration of coenzyme F420 by 24%, which confirmed that it could enhance the methane production rate of the system by strengthening the methanogenic metabolic pathway of hydrogen trophicity and constructing the direct interspecies electron transfer channel in microorganisms at the same time.

Key words: kitchen waste pressing liquid, direct interspecies electron transfer in microorganisms, zero-valent iron, excitation emission matrix-parallel factor