(A) study on the anaerobic digestion of Korean food waste and its mathematical modeling

Abstract

The objective of this study is to apply anaerobic digestion system, which can recover energy in the form of methane, to food waste treatment and develop a model for stable operation and proper design of an anaerobic digestion system. The elemental composition of the standard food waste sample used in this study was 48.2, 7.2, 39.3, and 3.9 % in the order C, H, O, and N, respectively. Total solid (TS) out of wet waste was 18.9 % and volatile solid (VS) out of total solid was 94.9 %. The anaerobic digestion system was operated using acclimated microorganisms from the sludge of the anaerobic digester in the Taejon Sanitary Plant and the methane production rate was maximum at 35℃ . Methane production rate and volatile fatty acids (VFA) concentration were observed to study the effect of initial pH and initial substrate concentration on methane production. The initial pH tested were 7.65, 7.40, and 6.70 and initial substrate concentration were 2, 5, 10, and 20 g VS/L. When the initial food waste concentration was 2 g VS/L, there was no accumulation of VFA in the digester and there was little inhibition in methane production because the pH values were maintained above 7.0. But there was a trend that as the initial pH became low and as the initial food waste concentration was increased, inhibition in methane production was more serious and the exhaustion time of VFA was longer. When the initial food waste concentration was 10 g VS/L with initial pH of 6.70, the accumulation of VFA was so high that it halted the process. This was also the case when the initial food waste concentration was 20 g VS/L with initial pH values of 6.70 and 7.40. When the initial pH was 7.65, there was some inhibition of methane production with an initial food waste concentration of 20 g VS/L, but the process did not stop. Anaerobic digestion with repeated input of food waste was carried out to find the proper input amount for continuous process operation with high efficiency. When the input ra...