Inhibition of tetrachloroethene and trichloroethene on methanogenesis in anaerobic sludges from various origins.

Nine anaerobic sludges were screened to obtain the most effective methanogenic inoculum for the anaerobic treatment of groundwater that is contaminated with tetrachloroethene (PCE) or trichloroethene (TCE). The selection was based on the toxicity of PCE or TCE to acetoclastic methanogens in different sludges. The effects of two biological factors, sludge origin and specific acetoclastic methanogenic activity, and a physical factor, specific surface area of sludge, on the degree of inhibition were examined and compared. The fifty percent inhibition concentrations (IC50) of PCE and TCE that were obtained from 30 °C batch inhibition tests ranged from 0.18 to 0.41 and 1.71 to 3.31 mM, respectively, for the examined sludges. The toxicity of the contaminants to anaerobic sludges did not depend on the two biological factors but was closely correlated with the specific surface area of sludge. Suspended sludges, which have higher specific surface areas than granular sludges, suffered much greater inhibition. This paper suggests the use of anaerobic granular sludges as inocula in bioreactors for treating PCE- and TCE-contaminated groundwater to reduce the effect of their inhibition.

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.