Moderate temperature increase leads to disintegration of floating sludge and lower abundance of the filamentous bacterium Microthrix parvicella in anaerobic digesters

Filamentous bacteria such as Microthrix parvicella can cause serious foaming and floating sludge problems in anaerobic digesters fed with sewage sludge. The sewage sludge and oil co-fermenting laboratory-scale biogas digesters in this study were fed with substrates from a foaming-prone full-scale biogas plant containing the filamentous bacterium M. parvicella. At 37 degrees C, in both pneumatically mixed digesters a highly viscous and approximately 3 cm thick floating sludge was observed. A gradual increase of the temperature from 37 degrees C to 56 degrees C led to a significant decrease in the floating sludge thickness, which correlated with a strong decrease in the abundance of M. parvicella in the digestate. Furthermore, the stepwise temperature increase allowed for an adaption of the microbial community and prevented process failure. The study indicates that already a moderate temperature increase from 37 degrees C to 41 degrees C might help to control the M. parvicella abundance in full-scale biogas plants. (C) 2014 Elsevier Ltd. All rights reserved.