Kinetic Properties of Separated Solid-Liquid Fractions of Blended Swine Waste Slurry

Abstract

The kinetic properties ultimate methane yield (Bo) and substrate Inhibition coefficient (K) of separated solid-liquid fractions of blended surface-scarped swine waste were evaluated from data on batch digestion and semi-continuous high-rate digestion.

Results showed that the solid fraction had a lower Bo (0.373 li CII₄/gm VS added) than the liquid fraction  (0.498 Ii CII₄/gm VS added) due to its higher concentration of refractory materials.

K was evaluated using Chen and Hashimoto’s model for continuous well-mixed anaerobic systems at steady-state. The relationship between influent substrate concentration (So) and K was found to be exponential. Empirical equations derived at different combinations of organic loading rate (OLR), Hydraulic retention time (HRT) and temperature are as follows:

Solid Fraction:
K = 0.429 + 0.00177 exp (0.187 So), r² =0.0997

Solid Fraction:
K = 0.798 + 9.43x10⁻⁸ exp (1.808 So), r² = 0.863

The threshold substrate concentration where inhibition might start was approximately 30 gm / VS/Ii for the solid fraction and 8 gm VS/Ii for the liquid fraction.