Back to the basics: high-loaded activated sludge

Degradation of organic substances in municipal wastewater is conventionally performed in the activated sludge process in presence of enhanced nitrogen removal processes. In the future, new nitrogen removal processes could demand a wastewater already treated for organics. The project "Back to the basics: high-loaded activated sludge" aims to make the high-loaded activated sludge process more efficient.

Without the presence of enhanced nitrogen removal processes, it is possible to decrease the solids retention time for the organics, including the microorganisms. Therefore is the degradation of the organics in the produced sludge not so extensive in a high-loaded activated sludge process, which decreases the need of oxygenation of the activated sludge and increases the biogas production during anaerobic digestion of the sludge.

Still, even if the activated sludge process was invented 100 years ago and the first 80 years almost excluded enhanced nitrogen removal processes, there are several challenges to make the high-loaded activated sludge process more efficient since the focus on energy-efficiency is much stronger today.

A short solids retention time increases the risk of bad effluent quality and causes often foaming problems, which increases the need of good operational strategies. Also, today’s mathematical models of the activated sludge process are not well suited for short solids retention times.