Full Scale Experiences with Thermophilic Aerobic Digestion of Primary-Chemical Sewage Sludge

A full scale demonstration project with thermophilic aerobic digestion (TAD) of primary-chemical sludge was started in May 1993 at Vårnes wastewater treatment plant (7300 p.e.). The project is partly funded by the Norwegian State Pollution Control Authority. The main objective is to document plant performance and characteristics of treated sludge when handling primary-chemical sludge.The demonstration plant is a standard two-stage facility from the German manufacturer Fuchs Gas- und Wassertechnik operating with a batch (once a day) feeding of sludge. A comprehensive monitoring programme has been established and this paper presents data on volatile solids reduction, pathogen reduction, sludge dewaterability and sludge nutrient content.A general conclusion so far is that the TAD process investigated here seems to be appropriate for stabilisation and disinfection of primary-chemical sludge, and that plant performance corresponds well with the long-term experiences from German plants treating biological or primary + biological sludges.