In this paper, anaerobic-process control based on bicarbonate alkalini
ty addition and regulation during start-up and overload operation is d
escribed. The experiments were performed with laboratory-scale hybrid
digesters fed on olive-mill effluents. An automatic instrument monitor
ed bicarbonate concentration and controlled its value in each reactor
by alkali addition. Two different start-up procedures were tested: ste
p-increases of substrate concentration at constant feedflow rate and s
tep-increases of flow rate at constant feed-concentration, keeping in-
reactor bicarbonate alkalinity constant by automatic control. Two over
load experiments were carried out. In the first case, the volumetric l
oading rate was increased, as described above, up to 8 kg TOC m3 d kee
ping both reactors under automatic control. No major differences were
observed in the performance of the reactors. In the second case, overl
oad was induced by a 100% step-increase of the substrate concentration
as acetic acid and alkalinity was controlled in one reactor only. As
expected, the system without control became unstable and sour conditio
ns developed.