The present day wastewater treatment practise can be significantly improved when new microbial processes are introduced. In this paper a new concept is discussed along general lines. The concept consists of a first stage in which a maximal sludge production is achieved. In this way COD is removed as sludge and aeration requirements minimized. This sludge can be digested to yield methane for energy generation. The nitrogen removal is based on a partial oxidation to nitrite and subsequent denitrification with ammonium as electron donor.