The use of trace organics in anaerobic digestion

Earlier work has demonstrated that the addition of small quantities of some organic compounds can have a significant effect on the performance of the activated sludge process. This paper examines the effect of some of these trace organics on an anaerobic digester inhibited by gallic acid and by fluoride ions. An anaerobic contact digester was operated with a 24 hour hydraulic retention time and a starch-based feed. After the reactor had reached steady state, the digestion was inhibited with gallic acid (10 mgl(-1)). When glucose was added as a growth factor, at a concentration of 10 mgl(-1) the inhibitory effects were largely reversed. Increasing the glucose concentration to 15 mgl(-1) improved the reversal effect only very slightly. The concept that glucose acted, in some way, through pyruvate was then tested by adding fluoride, which is known to prevent the formation of phospho-enol-pyruvate, to a gallic acid-inhibited/glucose counter-acted digester. This caused a reduction in the specific gas yield (19% of the control). The subsequent addition of pyruvate (20 mgl(-1)) largely reversed this inhibition.