Influence of the sewage sludge stabilization process on the value of its oxidation-reduction potential

The paper presents the study of a sewage sludge subjected to the process of the autothermal thermophilic stabilization (autothermal thermophilic aerobic digestion (ATAD)), which occurs in a two-stage installation. This study was conducted at the municipal wastewater treatment installation in 2010 and 2011. A thickened sludge was examined in an intermediate tank from which it was next being transferred to successive ATAD installation reactors. The content of the dry mass and organic substances was checked in a raw sludge after the first installation stage and after the ATAD process. Also, the levels of the chemical oxygen demand, the pH and the temperature were measured. During the process, the redox potential was measured. Collected results were subjected to statistical analysis. Our main attention was focused on measurements of the redox potential and further the usefulness of this measurement for the evaluation of the process was considered. The way its values were changing was determined. In the thickened sludge prior to the ATAD process, the value of the redox potential oscillated from 329.90mV to-108.50mV. In the first-stage reactor, this value dropped significantly and held within a range between-509.80mV and-214.60mV. In the second installation stage, this value ranged between-561.60mV and-306.40mV. During the study, fully sanitized and stabilized sludge was obtained. The paper presents the evaluation of the conducted research and conclusions ensuing from it.