A positive effect on SSA activity caused by CLX is shown in Fig. 2a. Acceleration in SRB of 19.9% and 39.7% was found for intact and disrupted sludge respectively. Fig. 2b shows that TC caused a 28.6% and 40.0% increase in the relative SSA for intact and disrupted sludge. In order to investigate whether this acceleration was caused by stimulation or antimicrobial disintegration, the activity test was repeated without a carbon source. No activity appeared either to MPA or SRB, which demonstrates that CLX and TC cannot be used by microorganisms as a carbon source (data not shown). The acceleration observed may have been caused by a stimulation effect.