Milenko Roš, Gregor Drago Zupančič


National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia



Anaerobic thermophilic stabilization and degradation of waste activated sludge from a wastewater treatment plant was studied. The main parameter of research was the organic fraction reduction (expressed as VSS) and biogas production. The experimental part of the study was divided into two parts. In the first, the goal was determination of the degradation function in a batch study. This function was used to determine the kinetic model of the continuous process. A degradation function of order n=3 was applied. The second experimental part was a study of the continuous process, in which VSS degradation and biogas production were studied. It was found that VSS degradation was 25% at a retention time of 1 day, and 49.2% at a retention time of 10 days. Specific biogas production increased with longer HRT, from 59 l/kg VSS inserted at 1 day HRT to 565 L/kg at 10 days HRT. However, biogas production expressed as L/day per model reached a maximum of 20.9 L/day per model at 3 days HRT. From the degradation function applied in the batch study, the model parameters were calculated and the behavior of the continuous process was predicted. Comparison of model and experimental results for VSS reduction showed a very good match for all retention times.  For biogas production, the model results are accurate above 3 days HRT. Below 3 days the model results differ very much from the experimental, and in such cases biogas production must be predicted from other process parameters, such as COD.