Examples of energy self-sufficient municipal nutrient removal plants.

In Austria, two municipal WWTPs (the Strass TP and Wolfgangsee-Ischl TP) operated with nutrient removal and aerobic sludge digestion are now energy self-sufficient. This is the result of a longstanding and on-going optimisation process at both plants including optimal aeration control and control of the aerobic section of the aeration tank to optimise denitrification and prevent degradation of particulate organic matter that should be degraded in the digester. Both TPs are now equipped with energy-efficient CHP units. However, it is maybe more sustainable to use the biogas as biomethane/bio-fuel than in conventional CHP at the WWTP. It is shown that energy self-sufficiency should be in reach at other municipal WWTPs, too.