The accumulation of both forms of butyric acid (HBu) has been used as
an indicator of digester failure. However; the present experimental re
sults indicated that the normal- and iso- HBu-degradation activities o
f the methanogens increase by 14-25% and 17-43%, respectively, for eac
h gram of the biomass coming into contact with 0.02-3.89 mg of Mn, Zn,
Ni, Fe and Cu. These results imply that in the presence of these heav
y metals care should be taken in using HBu accumulation as an indicato
r of digester failure. (C) 1998 Elsevier Science Ltd. All rights reser
ved.