2003 Volume 34 Issue 2 Pages 91-100
In this study, the effects of process configuration on acidogenic performance were evaluated via system parameters such as volatile acid (VA) production, volatile solids (VS) degradation and particle size distribution under mesophilic conditions and an HRT of 20 days. Using fresh soybean meal or okara as substrates, two process configurations-the cascade process and the solid recycle process-were employed to perform the experimental estimation. An apparent first-order hydrolysis rate constant of 9.0×10-3/d for the cascade process at pH values of 4.5-4.6, which was higher than that obtained by a previous study (7.2×10-3/d), and 5.0×10-3/d for the solid recycle process at a pH of 4.4, which was lower than that obtained in a previous study, were obtained. The apparent VS degradation ratio ranged from 9.6 to 16.5% and total VA (as acetic acid) from 10.8 to 16.7g/L. Occupying ratios for ionized VA in both process configurations increased from 27.5% to 30.8% for the solid recycle process and to 35.5% for the cascade process. The acetic acid ratios also were elevated from 86.0% to 94.3% for the cascade process and to 93.3% for the solid recycle process. As regards the distribution of VS particle size, the addition of milling balls caused the mechanical breakdown of the large particles whereas generation of soluble solid was not significantly affected.
