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 consumption measurements, were used to compare microbial parameters using a wastewater model system of a potato processing plant. The effects of the operating conditions in the continuous aerobic reactor on microbial growth and flora composition were also analysed. Continuous-feed experiments allowed for the calculation of the following biodegradation parameters: maximum substrate consumption specific rate (qSmax) = 0.19 mgCOD (mgVSS)-1·h-1, saturation constant (Ks) = 8.3 mgCOD·l-1, biomass yield (YX/S) = 0.61 mgVSS (mgCOD)-1, biomass decay constant (kd) = 0.04·h-1 and maximum oxygen consumption specific rate (qO2max) = 0.03 mgCOD (mgVSS)-1·h-1. The respirometric technique also allowed for the calculation of kinetic parameters. However, these parameters depended on dilution rate (D) and / or on dissolved oxygen concentration (DO). Values of qO2max and Ks increased with D; qO2max ranged between 0.05 and 0.13 mgO2 (mgVSS)-1·h-1 and Ks between 2 and 26 mgCOD· -1 for D values varying between 0.01 and 0.15·h-1. Microscope observations showed that sludge composition was a function of dilution rate. Low D values (low soluble organic matter (Ss) and high DO concentrations) 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 limit the growth of micro-organisms maintaining the initial physiological state of the original biomass, the observed differences in the respirometric parameters reflected the actual microbial composition. WaterSA Vol.27(2) 2001: 169-176