Ql. Zhao et G. Kugel, THERMOPHILIC MESOPHILIC DIGESTION OF SEWAGE-SLUDGE AND ORGANIC WASTES/, Journal of environmental science and health. Part A: Environmental science and engineering, 31(9), 1996, pp. 2211-2231
The performance of treating a mixture of sewage sludge and high streng
th food processing organic wastes was investigated by running a pilot-
scale plant of two-stage anaerobic thermophilic/mesophilic digestion.
Temperature and hydraulic detention time were controlled at 75 degrees
C and 2.5 days for the first thermophilic digester and at 37 degrees
C and 10 days for the second mesophilic digester, respectively. It was
found that at the mesophilic stage, 16.8-53.2% of total solids (TS) a
nd 33.8-57.6% of volatile solids (VS) were removed when the organic lo
adings were 6.62-16.32 kg VS/m(3)d and 1.65-2.92 kg VS/m(3)d for the f
irst and second stages, respectively. Daily gas production was 10.02-2
3.73 m(3)/m(3) (equivalent to 1.511-1.861 m(3)/kg VS removed), 65-73%
of which was methane in the mesophilic digester. Volatile fatty acids
of 2600-9000 mg HAc/L produced at the first stage was removed down to
43-433 mg HAc/L in steady state mesophilic effluent. The ratio of vola
tile fatty acids to bicarbonate was less than 0.4 in mesophilic digest
er.This study showed that the proposed two-stage thermophilic/mesophil
ic digestion system was effective to treat sewage sludge combined with
20-50% potato processing concentrates, or 10% pig blood or 10% sausag
e processing floats.