Anammox brings WWTP closer to energy autarky due to increased biogas production and reduced aeration energy for N-removal

TLDR

Municipal WWTPs originally used 2–3 h HRT primary clarifiers, but the addition of nitrogen removal increased BOD demand and shortened HRT to under one hour, reducing biogas yield. The study investigates whether treating digester liquid with autotrophic nitritation/anammox can restore longer primary clarifier HRT, boost biogas production, and cut aeration energy while preserving overall nitrogen removal. The authors applied an autotrophic nitritation/anammox process to 15–20 % of the digester liquid, eliminating the need for organic carbon and halving aeration energy, thereby permitting longer primary clarifier HRT. Implementation of the anammox process allows primary clarifier HRT to be increased, leading to higher biogas yields and lower aeration energy consumption while maintaining nitrogen removal.

Abstract

Fifty years ago when only BOD was removed at municipal WWTPs primary clarifiers were designed with 2–3 hours hydraulic retention time (HRT). This changed with the introduction of nitrogen removal in activated sludge treatment that needed more BOD for denitrification. The HRT of primary clarification was reduced to less than one hour for dry weather flow with the consequence that secondary sludge had to be separately thickened and biogas production was reduced. Only recently the ammonia rich digester liquid (15–20% of the inlet ammonia load) could be treated with the very economic autotrophic nitritation/anammox process requiring half of the aeration energy and no organic carbon source compared to nitrification and heterotrophic denitrification. With the introduction of this new innovative digester liquid treatment the situation reverts, allowing us to increase HRT of the primary clarifier to improve biogas production and reduce aeration energy for BOD removal and nitrification at similar overall N-removal.