Effect of particle size and sodium ion concentration on anaerobic thermophilic food waste digestion

Serial basic tests were conducted for the determination of fundamental kinetics and for the actual application of kinetic parameters to food waste digestion with precise measurement of methane production. The effects of food particle size and sodium ion concentration on the anaerobic thermophilic food waste digestion process were investigated. Results of serial tests for the determination of fundamental kinetic coefficients showed the value of k (maximum substrate utilization rate coefficient) and K_S (half-saturation coefficient) as 0.24 hr⁻¹ and 700 mg/L, respectively, for non-inhibiting organic loading range. The substrate inhibition coefficient (K_i) was 1000 mg/L for inhibiting organic loading range. No inhibition effect was shown until 5g/L of sodium ion concentration was applied to the serum bottle reactor. However, the volume of methane gas was decreased gradually to the concentrations of more than 5 g/L of sodium ion applied. All sizes of food waste particle had the same constants (A:0.45) but the maximum substrate utilization rate constant (k_HA) was inversely proportional to particle size. As average particle size increased from 1.02 mm to 2.14 mm, k_HA decreased from 0.0033 hr⁻¹ to 0.0015 hr⁻¹. Result reveals that particle size is one of the most important factors in anaerobic food waste digestion.