Formaldehyde toxicity in anaerobic systems

Formaldehyde toxicity during acetoclastic methanogenesis exerted a dual cha racter. It was in part reversible and in part irreversible. Toxicity was on ly reversible at very low formaldehyde concentration. The deg ee of irrever sible toxicity was proportionally related to the initial sludge concentrati on, but was independent of the initial specific acetoclastic activity. Form aldehyde conversion seemed to be dependent on the concentration of the vari ous trophic groups present in the anaerobic granular sludge used. Hence bio mass diversity may play an important role in the outcome of toxicity studie s and may furthermore contribute to the explanation of the controversies wi th respect to toxicity values reported in literature.