Evaluation of dewatered sludge properties from a selected municipal sewage treatment plant

摘要

An incorrectly maintained sludge management in wastewater treatment plants, may cause a major threat to the natural environment. Sewage sludge and supernatant, as by-products of the sewage treatment process, generate various chemical substances, including toxins. The aim of the study was to determine the physicochemical characteristics of sludge, sampled from a selected municipal wastewater treatment plant of a throughput of 9000 m~3/d. The supernatant and water extract of tested sludge were also determined. The tests were carried out in compliance with the accredited methods for municipal sewage sludge. The heavy metal content of tested sludge does not exceed the amounts specified for their use in agriculture and for land reclamation. Taking into consideration the use of polyelectrolytes in the sludge conditioning process, some examinations were performed using a gas chromatography electron-capture detector to determine the polyacryloamide content. Thus the concentration of this compound in the water extract from the sludge after the press was 1.62 μg/L, while in the supernatant from the pressed sludge it was at a level of 0.98 μg/L. In the examined water extract from the pressed sludge, a very high level of dissolved organic carbon was found (TOC = 128.5 mg C/L) as against the permissible value (TOC = 30mg C/L). For this reason, the waste (pressed sludge) should not be disposed on a landfill site other than the one designed specifically for non-hazardous and neutral wastes.