Abstract: A process for treatment of waste activated sludge from a BNR process, which includes the steps of: (a) concentration of the activated sludge from a total solids content (dry weight) of 0.1-1.0% w/v to an increased solids content of 1.5-5.0% w/v, wherein said solids largely contain bacterial biomass from prior aeration of the activated sludge; (b) disrupting bacterial cells contained in the biomass so as to release fermentable nutrients from said bacterial cells; (c) passing the activated sludge from step (b) through an anaerobic digester system; and (d) removing N and/or P from the residue obtained after step (c).