Revealing the mechanisms for potassium ferrate affecting methane production from anaerobic digestion of waste activated sludge

[Display omitted] •Potassium ferrate promoted both methane production potential and rate of sludge.•Potassium ferrate accelerated sludge disintegration.•The biodegradability of organics liberated from sludge flocs was improved.•Potassium ferrate enhanced the digestion of humus and lignocellulose. This study investigated the issue of potassium ferrate (PF) affecting anaerobic methane generation from sludge by a set of experimental and model analyses. Experimental results indicated that the methane production was significantly promoted from 164.7 to 204.1 mL/g VSS (volatile suspended solids) with PF dosage enhanced from 0 to 0.05 g/g TSS (total suspended solids). Further enhancement of PF dosage reduced methane production, which even decreased to 135.4 mL/g VSS when PF dosage increased to 0.1 g/g TSS. Model-based analysis showed that except for methane production potential, the methane production rate was also promoted by PF treatment, which was sufficiently enhanced from 8.80 to 11.88 mL/g VSS/d when PF dosage was 0.05 g/g TSS. Mechanism studies indicated that PF not only promoted sludge disintegration, but also enhanced the proportion of biodegradable organics in sludge liquor, and the digestion potential of the non-biodegradable humus and lignocellulose were promoted.