Aerobic Thermophilic Stabilization of Sludge versus Anaerobic Digestion and Other Kinds of Sludge Treatment at Middle-Sized Plants with Respect to Power Conservation and Economy

Operating data concerning energy balances are collected by a state bureau from a sewage treatment plant with aerobic–thermophilic stabilization and also from plants with anaerobic sludge digestion and energy recovery. On the basis of this data power and heat balances as well as cost–benefit–calculations have been obtaineu for treatment plants of different sizes with different biological and sludge treatment processes. In spite of high and rising energy costs in plants utilizing the aerobic-thermophilic stabilization process the results show an overall economic benefit for this process at small and middle-sized treatment plants compared to those utilizing anaerobic sludge digestion. The evaluation of data indicates that this economic benefit is due to high capital costs and little efficiency of energy recovery under process conditions at small and middle-sized plants applying anaerobic digestion.