This study has been conducted to optimum operating conditions for effective acid fermentation according to OLR(organic loading rate) in the mesophilic and thermophilic acid fermentation process. The results are summarized as follows. In order to obtain reasonable acid fermentation efficiency in performing acid fermentation of food wastes in thermophilic condition, organic loading rate was required below 20 gVS/L.d. As SCODCr/TKN, SCODCr/T-P of thermophilic acid fermented food wastes in organic loading rate 20 gVS/L.d were 18.9, 73.4 respectively, it was possible to utilize as external carbon source for denitrification in sewage treatment plant after solid-liquid separation as well as co-digestion of fermented food wastes and sewage sludge.

This study has been conducted to investigate biodegradation characteristics and optimum mixing ratio for co-digestion with thermophilic acid-fermented food waste and sewage sludge using batch anaerobic digester. As the basis operating conditions for anaerobic digestion, the reaction temperature was controlled 35±1℃ and stirrer was set 70rpm. Thermophilic acid-fermented food waste and sewage sludge were mixed at the ratio of 10:0, 7:3, 5:5, 3:7, 0:10 and 5;5(food waste : sewage sludge) as the influent substrates. In results of co-digestion according to mixing ratio of thermophilic fermented food wastes and sewage sludge in batch mesophilic anaerobic digestion reactor, 385mL CH4/g VSadded of methane production rate at 1:1 mixing ratio was more than that of any other mixing ratios. Compared with 293mL CH4/g VSadded of methane production rate at 1:1 mixing ratio of food wastes and sewage sludge, pretreatment of food wastes by thermophilic acid fermentation was more effective in co-digestion with sewage sludge.