For the nitritation–anammox, full-scale implementation at municipal wastewater treatment plants (WWTPs) is constrained to nitrogen removal of sludge digester supernatant in sidestream. The characteristics of digester supernatant facilitate the growth of aerobic ammonium-oxidizing bacteria (AerAOB) and anammox as well as the inhibition of nitrite-oxidizing bacteria (NOB) and heterotrophic denitrifiers [3]