It seems that DECA as a co-substrate in an optimum ratio might increase methane production of digesters that stabilize excess sludge from aerobic wastewater treatment. The concentration of total solids in all assays of this batch was w8 g/kg which was reduced to 20-34% with a corresponding decrease of the VSS to 12e35% from the initial 4.3 g VSS/kg. During the course of the experiment the pH remained constant at 7.5-7.6 and only a minimal fatty acid production was observed.