Center for Environment and Energy Research and Studies (CEERS)
Abstract
Thermophilic aerobic digestion (TAD) is a possible alternative for
rapid sludge degradation and producing Class A biosolids. Aeration rate
and detention time are two of the important parameters in TAD processes
due to rapidly growing thermophilic bacteria population, limited
solubility of oxygen at high temperatures and the need to prevent
cooling of TAD process. Also the current knowledge and understanding of
dewatering TAD biosolids are limited and incompelet.The objectives of
this study were to investigate the effects of various aeration rates
and detention time on some characteristics of mixed sewage sludge. Four
glass-cylindrical digesters with 7 liters of sludge in each, placed in
a water bath and were operated at 55 °C with the aeration rates of
2.14, 3.00, 3.86 and 4.71 volume of air per volume of sludge per hours.
It was found the increase in aeration rate decreased the required
detention time in order to meet the Class A sludge regulations to
reduce vector attraction. The values of Oxidation-Reduction Potential
(ORP) were changed from negative values to positiv ones and the values
of pH were increased from around neutral to slightly basic, but this
increases were occured at different detention times. TAD affected
dewaterability of mixed sewage sludge and produced biosolids with
higher specific resistance to filtration (lower dewaterability) than
undigested sludge. Thermophically digested sludge has a good setteling
behavior and air drying on sand bed