NON-FILAMENTOUS ACTIVATED-SLUDGE BULKING CAUSED BY ZOOGLOEA

An abundant growth of zoogloeal colonies was observed periodically dur ing some experiments carried out on a bench-scale plant fed with a com plex synthetic wastewater. The plant had a configuration with an enhan ced regeneration-denitrification-nitrification (R-D-N) activated sludg e process for low alkalinity wastewaters. Several operational changes were undertaken in order to suppress the excessive growth of zoogloeal colonies. They included: (1) changes in the wastewater composition, ( 2) volume changes in the compartmentalization of the anoxic selector, (3) increase of D.O. concentration in the regeneration and nitrificati on tanks. Conclusions from the plant operation observations give rise to a hypothesis that none of the operational changes provoked a signif icant restriction in the abundant zoogloeal growth. When a temporary i mprovement was observed, after acclimatization on the new operational conditions the microorganisms culture returned to its previous state a nd continued to grow in a wave-mode. The reason for the appearance of this type of sludge might be closely related to the composition of the synthetic wastewater.