NOVELTY - Treating a waste stream comprising wastewater sludge, involves introducing feed sludge into a continuously-stirred, sealed, anaerobic digester, and drawing off sludge from the digester at a rate such that the mean cell residence time for the sludge in the digester is 10-15 days; maintaining the temperature of the sludge in the digester at 47-65 degrees C; and producing treated sludge having reduced volatile solids content and reduced fecal coliform content than the feed sludge introduced into the digester.    USE - For treating a waste stream comprising wastewater sludge (claimed) for producing methane gas used to fuel internal combustion engines and a turbine.    ADVANTAGE - The method produces treated sludge having volatile solids content that is 55%, preferably at least 38% less than the volatile solids content of the feed sludge introduced into the digester, a reduced fecal coliform content that 4 log (base 10), preferably at least a 2 log (base 10) reduction from the feed sludge introduced into the digester. The geometric mean of seven samples of the treated sludge shows that there is not greater than 2000000 most probable number/g total solid (dry weight basis) of fecal coliform in the treated sludge.    DETAILED DESCRIPTION - Treating a waste stream comprising wastewater sludge, involves introducing feed sludge into a continuously-stirred, sealed, anaerobic digester, and drawing off sludge from the digester at a rate such that the mean cell residence time for the sludge in the digester is 10-15 days; maintaining the temperature of the sludge in the digester at 47-65 degrees C; and producing treated sludge having: a volatile solids content that is at least 38% less than the volatile solids content of the feed sludge introduced into the digester, a reduced fecal coliform content that is at least a 2 log (base 10) reduction from the feed sludge introduced into the digester, and where a geometric mean of seven samples of the treated sludge shows that there is not greater than 2000000 most probable number/g total solids (dry weight basis) of fecal coliform in the treated sludge.