Changes in hydrogen ion exponent of sewage sludge in the process of autothermal thermophilic aerobic digestion

This paper presents a study on the evaluation of digested sewage sludge during the process of Autothermal Thermophilic Aerobic Digestion (ATAD), taking place as a three-tank process at a municipal waste water treatment plant in Luban, Poland. ATAD installation was manufactured by FUCHS Enprotec GmbH Mayen-Deutschland. Over the period from June 2006 to February 2010 sewage sludge digested by tha ATAD-Process was examined. The hydrogen ion exponent was measured in every tank. The results obtained indicated changes in the composition of the digesting sludge at successive stages of the process. Over the study period the ATAD-installation was in both a two- and a three-stage process. pH of sludge under study during the process of the thermophilic stabilisation changes and its value grows significantly, with the installation working in a two-stage arrangement from 6,63 to 7,99, and when the installation was operated as a three-stage system from 6,60 to 8,14. The results collected were subject to the statistical analysis. The paper presents conclusions drawn from the study and own experience.