Abstract
The aerobic thermophilic treatment process of sewage sludge was studied at different bioreactor scales in a pilot plant installation. Since, for a satisfactory sludge disinfection, the Swiss legislation requires minimal incubation times of all volume elements, the bioreactors were operated in repetitive batch mode (draw and fill). Different retention times and frequencies of the volume changes were applied in order to prove the capability of the particular operation modes in assuring high degradative potential. The main enzymatic activity involved during the aerobic treatment was proteolysis: the RQ values ranged between 0.8 and 0.9 depending on the applied operating conditions. Although not in a linear manner, the efficiency of the microflora decreased as the bioreactor scale increased, when this increase corresponded with a reduction of the specific power input. The sludge oxidation rates can be tuned by some process operating conditions such as the volume change frequency, the changed volume quantities and the retention times. It was possible to improve the microbial degradative efficiency by an increased frequency of the changes, while the mean retention time influenced in particular the ultimate product quality, described as residual organic matter content of the sludge. The microflora present was also satisfactorily active at mean hydraulic retention times of less than 10 h. The organic matter concentration of the inlet sewage sludge plays an important role: it influences the aerobic degradation process positively.
Published Version
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