The effects of organic toxicants on methane production and hydrogen gas levels during the anaerobic digestion of waste activated sludge

Batch serum bottle assays were conducted to examine the response of the anaerobic digestion process to inhibition induced by the pulse addition of four organic toxicants [chloroform, bromoethanesulfonic acid (BES), trichloroacetic acid (TCAA) and formaldehyde]. The impact that increasing levels of inhibition of methane production had on hydrogen response and volatile fatty acid (VFA) accumulation were examined. All of the toxicants, with the exception of formaldehyde, appeared to elicit similar hydrogen response patterns and VFA accumulations for similar levels of inhibition. Results indicate that both the hydrogen and acetate catabolizing methanogenic populations were inhibited to approximately the same extent by chloroform, BES, and TCAA. Severe inhibition of methane production (>70% reduction of methane produced compared to controls) resulted in a rapid accumulation of hydrogen in the gaseous headspace. When inhibition was less severe, hydrogen accumulated to levels only slightly above controls. Based on these preliminary results, there appears to be some limits on the potential of using hydrogen as an early warning indicator of process upset. Results do indicate, however, that monitoring hydrogen in consert with conventional process indicators should improve digester monitoring and may provide more rapid indication of process upsets due to toxic shocks.