The application of different techniques to determine activated sludge kinetic parameters in a food industry wastewater

In the present work, a continuous-feed system under steady state conditions (classical method) and a respirometric technique based on oxygen consumpti on measurements, were used to compare microbial parameters using a wastewat er model system of a potato processing plant. The effects of the operating conditions in the continuous aerobic reactor on microbial growth and nora c omposition were also analysed. Continuous-feed experiments allowed for the calculation of the following bi odegradation parameters. maximum substrate consumption specific rate (q(Sma x)) = 0.19 mgCOD (mgVSS)(-1).h(-1), saturation constant (Ks) = 8.3 mgCOD.t( 1), biomass yield (Y-X/S) = 0.61 mgVSS (mgCOD)(-1), biomass decay constant (kd) = 0.04.h(-1) and maximum oxygen consumption specific rate (q(O2max)) = 0.03 mgCOD (mgVSS)(-1).h(-1). The respirometric technique als allowed for the calculation of kinetic para meters. However. these parameters depended on dilution rate (D) and/or on d issolved oxygen concentration (DO). Values of q(O2max) and Ks increased wit h D; q(O2max) ranged between 0.05 and 0.13 mgO(2) (mgVSS)(-1).h(-1) and Ks between 2 and 26 mgCOD.t(1) for D values varying between 0.01 and 0.15.h(-1 ). Microscope observations showed that sludge composition was a function of di lution rate. Low D values (low soluble organic matter (Ss) and high DO conc entrations) yielded sludges mainly formed by floc-forming bacteria: high D values (high Ss and low DO concentrations) yielded sludges mainly formed by filamentous micro-organisms. Since the low substrate/biomass ratios used in the respirometric method lim it the growth of micro-organisms maintaining the initial physiological stat e of the original biomass, the observed differences in the respirometric pa rameters reflected the actual microbial composition.