START-UP AND OPERATION OF ANAEROBIC DIGESTERS WITH AUTOMATIC BICARBONATE CONTROL

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.