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

Abstract

A modified three-stage system was developed for the rapid production of methane from food wastes. The primary stage was a semianaerobic hydrolysis/acidogenic system, in which approx 4100 mg/L of volatile fatty acids (VFAs) was produced at a hydraulic retention time (HRT) of 2 d. The operation temperature and pH were 30 degrees C and 5.0-5.5, respectively. The non-degraded materials were removed through a hole at the bottom of the reactor. The secondary stage was an anaerobic acidogenic system equipped with an upflow anaerobic sludge blanket (UASB) type of fermentor. VFA was accumulated up to 6100 mg/L by the addition of Clostridium butyricum to the reactor at an HRT of 2 d. The optimum temperature and pH range were 35 degrees C and 5.0-5.5, respectively. The tertiary methanogenic stage produced CH4 and CO2 from the VFA in the UASB reactor. Methane content was 72% of the total gas volume, and the yield was 0.45-0.50 m3/kg of volatile solids at an HRT of 12 d. The 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 mg/L of total phosphorus remained in the final effluent.