Kinetic comparisons of mesophilic and thermophilic aerobic biomass.

Kinetic parameters describing growth and decay of mesophilic (30 degrees C) and thermophilic (55 degrees C) aerobic biomass were determined in continuous and batch experiments by using oxygen uptake rate measurements. Biomass was cultivated on a single soluble substrate (acetate) in a mineral medium. The intrinsic maximum growth rate ( micro (max)) at 55 degrees C was 0.71+/-0.09 h(-1), which is 1.5 times higher than the micro (max) at 30 degrees C (0.48+/-0.11 h(-1)). The biomass decay rates increased from 0.004 h(-1) at 30 degrees C to 0.017 h(-1) at 55 degrees C. Monod constants were very low for both types of biomass: 9+/-2 mg chemical oxygen demand (COD) l(-1)at 30 degrees C and 3+/-2 mg COD l(-1)at 55 degrees C. Theoretical biomass yields were similar at 30 and 55 degrees C: 0.5 g biomass COD (g acetate COD)(-1). The observed biomass yields decreased under both temperature conditions as a function of the cell residence time. Under thermophilic conditions, this effect was more pronounced due to the higher decay rates, resulting in lower biomass production at 55 degrees C compared to 30 degrees C.