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Tlenowa stabilizacja termofilowa osadów ściekowych

Borowski S.

Ochrona Środowiska

2000

nr 4

21-25

The aerobic thermophilic stabilization (ATS) process was investigated on sludge samples collected at the Municipal Treatment Plant of Tomaszów Mazowiecki, serving a population of about 70,000 inhabitants. Mixed (primary and waste activated) sludge, pre-thickened to an approximately 5% dry solids concentration, was treated in a laboratory setup under semicontinuous conditions. Maximum stabilization rate, paralled by an over 39% reduction of mixed liquid volatile suspended solids, was obtained at a hydraulic retention time (HTR) of eight days. The minimum HTR to provide complete stabilization turned out to be six days, partial stabilization being achieved after four days of the ATS process. In the course of ATS, large amounts of nitrogen were released into the supernatant. A certain portion of the nitrogen converted into ammonia, thus accounting for an unpleasant odour of the outlet gas. The highest nitrogen concentration (1568 gN/m3) in the supernatant and the most objectionable odour of the outlet car were recorded at the HTR of four days. Phosphorus followed a slightly different pattern: it entered the supernatant (like nitrogen), but also cumulated in the sludge; the highest phosphorus concentration (327 gP/m3) in the supernatant was recorded at the HTR of four days, whereas the maximum phosphorus cumulation (over 60%) in the dry solids portion of the sludge was achieved at the HRT of 6 to 8 days. Apart from phosphorus, they were also heavy metals that accumulated in the sludge. Maximum concentrations of iron, cadmium, copper and lead in the dry solids portion (208%, about 100% and 61%, respectively) were measured at the HRT of eight days. The ATS process noticeably deteriorated the dewaterability of the sludge, which was measured by a capillary suction timer. Following completion of the process, the capillary suction time increased almost tenfold. To upgrade the dewaterability of stabilized sludge, conditioning was carried out with organic flocculants, of which the onion polyelectrolyte Magnafloc was found to be the most effective.