SYNTHESIS OF DENITRIFICATION ENZYMES IN ACTIVATED-SLUDGE - MODELING WITH STRUCTURED BIOMASS

Three mechanisms are responsible for microbiological elimination proce sses in activated sludge: the survival of qualified organisms in the e cological selection process, the expression of specific enzymes and th e absence of inhibitors limiting enzyme activity. A mathematical model with structured biomass has been formulated to improve the descriptio n of data from denitrification experiments. The model includes synthes is and decay of denitrification enzymes and is able to predict nitrate , nitrite and N2O concentrations. Kinetic parameters have been estimat ed and used to simulate the effect of cell saturation with enzymes in a waste water treatment process. Low dissolved oxygen concentrations i n the anoxic reactor reduce the denitrification efficiency equally by inhibiting enzyme activity and enzyme synthesis: at 0.5 gm(-3) O-2 enz yme decay causes a cell saturation of below 40 %. Enzyme synthesis can take place in the sludge blanket of a secondary sedimentation tank an d improve denitrification efficiency. The benefit of modelling with st ructured biomass is shown. The comprehension of experimental observati ons has been improved, and plant design and operation can be optimized . However, the multitude of unknown parameters still may restrict the validity of complex models.