Agar-plated bacteria found in the activated sludge of lab-scale SBR and CFSTR systems

We identified and compared the predominant agar-plated bacteria in the activated sludge of two popular wastewater treatment systems, the sequencing batch reactor (SBR) and the continuous-flow stirred tank reactor (CFSTR). All tests had the same feed composition except for the buffer intensity. It was found that Corynebacterium sp. seemed to prefer growing under lower buffer condition, and Arthrobacter sp. grew dominantly in the system with higher buffer intensity. Gram-negative bacteria appeared more sensitive to an environment with unstable organic loading, such as in the SBR system. On the contrary, the SBR system was more selective to the Gram-positive genera with a special rod-coccus-cycle characteristic, such as Arthrobacter, Corynebacterium, or Brevibacterium.