SYNCHRONIZED DIVISION OF ACTIVATED-SLUDGE MICROORGANISMS

Two laboratory continuous activated sludge units were run. One unit was an OSA system with anaerobic stabilization of returned sludge and the other a conventional activated sludge (CAS) system, operated as a control unit. Excess biomass from both systems was used as inoculum for batch experiments in order to study the kinetic behaviour of microorganisms originally grown in oxic-anaerobic conditions. All experiments were carried out with synthetic wastewater. Biomass growth, substrate removal, oxygen uptake and carbon dioxide production were measured using a quadrupole mass spectrometer (Inficon IQ 200) coupled to a 15-1. fermentor (Biolafitte). The results showed that at initial S0/X0 ratios higher than 2, cell division occurred, which was demonstrated by an acceleration of substrate removal and biomass growth rates. This division was synchronized (simultaneously occurring cell multiplication) in the case of activated sludge from the OSA unit. The synchronization was induced by periodical exposure of the microorganisms to unfavourable conditions of growth due to starvation under anaerobic conditions. The primary aim of this paper is to point out the existence of synchronized cell division in certain laboratory activated sludge systems and to determine the conditions under which this phenomenon can occur.