Unionized Acetate Degradation at 45°C Anaerobic Digestion: Kinetics and Inhibition

This study demonstrated the degradation of unionized acetate in anaerobic digestion at 45 degrees C through the identification of kinetics and inhibition parameters. The kinetic parameters, K-s and r(max), were determined using Monod-based model for three different conditions, namely uninhibited, inhibited, and systems with high substrate condition. The K-s values for uninhibited condition were in the range of 0.124 to 0.191 mg/L as unionized HAc. K-s value of inhibited condition were at 0.027 mg/L as unionized HAc. K-s values for systems with high substrate condition were found to be in the range of 0.237 to 0.279 mg/L as unionized HAc. As for r(max), a 35 degrees C anaerobic digestion system showed the highest value at 0.166 mg/L/day - greater than the values of all 45 degrees C systems under all experimental conditions. Additionally, the inhibition parameter K-I was also determined using the Michaelis-Menten model. The parameter was determined for inhibitory conditions resulting from high free NH3 content. The inhibition type was uncompetitive with K-I value of 0.072 mg/L as unionized HAc. The outcomes suggested that the methanogens responsible for the digestion process at 45 degrees C were thermo-tolerant acetate-utilizing methanogens of Methanosarcinaceae species, and the system will be totally inhibited with the presence of high free NH3 content.