The anaerobic digestion of potato juice, used as a model complex wastewater. was investigated at extreme ammonia concentrations. Even at 11.8~ ammonia-N/litre methanogenesis occurred, but at 16g ammonia-N/litre methanogenic activity had become nil. 7"he adaptation potential of the granular sludge used in this study was 6.2. which means that after the adaptation process in which the sludge gained the ability to produce methane at ammonia concentrations exceeding the initial toxicio' threshold level, the maximum tolerable ammonia concentration was 6"2 times higher than the initial toxicit.v threshold level.
After more titan three weeks of exposure to 9"l g ammonia-N/litre the maximum specific methanogenic activity of granular sludge at 52~ ammonia-N/litre was .[ound to fit well in the general relationship between ammonia concentration and methanogenic activity established in the present research. This indicates that even at extremely high concentrations ammonia toxicity {~" reversible to a great extent.
It was also .found that contrary to methanogenesis, the production ~1 volatile fatty acids /'rom the complex substrate was hardly affected hy high ammonia concentrations.