A thermophilic anaerobic digester (AD) was combined with a microbial fuel cell (MFC) to evaluate whether either component had increased stability when operated in combination as a hybrid system, perturbed by the addition of acetic acid. The MFC and the anaerobic digester were able to operate effectively together. The MFC was more susceptible to high acetic acid load than the AD. The hybrid system did not have increased resilience compared to the solitary systems in the conditions tested. However, the low pH had a relatively delayed effect on the MFC compared to the AD, allowing the hybrid system to have a more stable energy output. Also, at very low pH, when operating as a hybrid, the AD component was able to recover pH to normal levels when the MFC component failed. These results demonstrate that there are synergies that can be gained from this hybrid system. (C) 2010 Elsevier Ltd. All rights reserved.