Effect of sludge fasting/feasting on growth of activated sludge cultures

Reduction of excess sludge in an oxic-settling-anoxic (OSA) activated sludg e process might be attributed to a "sludge fasting (insufficient food under an anoxic condition)/feasting (sufficient food under an oxic condition)" t reatment. This paper was to examine this explanation by investigating both the sludge fasting/feasting phenomenon and the effect of a fasting/feasting treatment on sludge growth. In this study, five different activated sludge cultures cultivated using synthetic wastewater composed of mainly glucose and other necessary nutrients: (1)an aerobic batch culture, (2) an intermit tently aerated batch culture, (3) an anoxic batch culture, (4) a continuous aerobic culture, and (5) an OSA culture, were employed. It was found that only the aerobic batch culture and the aerobic continuous culture are fasta ble when the oxidation reduction potential (ORP) level is below 100 mV unde r no-food condition during a 2-h fasting treatment. showing that both the b iomass and carbohydrate storage of these two cultures were reduced after th e treatment. When the fasted cultures were treated in a feasting environment, an accumul ation of carbohydrate storage did not occur, while specific oxygen uptake r ates (SOUR) showed a sharp increase. Both the substrate utilization and bio mass growth rates were also accelerated. It was therefore confirmed that a sludge feasting did occur after a fasting treatment for the fastable cultur es. However, an increase in sludge ATP content was not brought about by the feasting treatment. The sludge fasting/feasting treatment in this paper co uld not induce a reduction of the observed growth yield (Yobs) in all the c ultures cultivated with glucose-based synthetic wastewater. (C) 2001 Elsevi er Science Ltd. All rights reserved.