Development of a modified three-stage methane production process using food wastes

A modified three-stage system was developed for the rapid production of met hane from food wastes. The primary stage was a semianaerobic hydrolysis/aci dogenic system, in which approx 4100 mg/L of volatile fatty acids (VFAs) wa s produced at a hydraulic retention time (HRT) of 2 d. The operation temper ature and pH were 30 degrees C and 5.0-5.5, respectively. The nondegraded m aterials were removed through a hole at the bottom of the reactor. The seco ndary stage was an anaerobic acidogenic system equipped with an upflow anae robic sludge blanket (UASB) type of fermenter. VFA was accumulated up to 61 00 mg/L by the addition of Clostridium butyricum to the reactor at an HRT o f 2 d. The optimum temperature and pH range were 35 degrees C and 5.0-5.5, respectively. The tertiary methanogenic stage produced CH, and CO, from the VFA in the UASB reactor. Methane content was 72% of the total gas volume, and the yield was 0.45-0.50 m(3)/kg of volatile solids at an HRT of 12 d. T he operation temperature and pH were 41 degrees C and 7.6-7.9, respectively . The three-stage process exhibited an unusually high total chemical oxygen demand reduction rate up to 95%. Total nitrogen decreased to 96% and <10 m g/L of total phosphorus remained in the final effluent.