Effect of Anaerobic Stabilization of Activated Sludge on its Production under Batch Conditions at Various S_o/X_o Ratios

The effect of anaerobic stabilization of returned activated sludge in a continuous system on biomass production under batch conditions at various S_o/X_o ratios was studied. A system without anaerobic sludge stabilization was also operated as a control unit. All experiments were carried out with Toulouse settled 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-liter fermentor (Biolafitte). The results confirmed that one of the most important parameters in batch cultivation is the initial S_o/X_o ratio. It was found that anaerobic treatment of activated sludge changed its behaviour during batch cultivation. As a consequence, the observed biomass yield (Y_obs) decreased with increasing S_o/X_o while it remained constant with the sludge from the control unit. In the anaerobic reactor, microorganisms are subject to a physiological shock due to lack of oxygen and food. Under the above conditions, they use ATP as a source of energy. After they are returned to aerobiosis and supplied with exogenous substrate, they rebuild energy reserves at the expense of growth.