During the years 2012-2016, VA SYD carried out a pilot project to study the introduction of anaerobic ammonium oxidation (anammox) to make the nitrogen removal in the mainstream more efficient at the Sjölunda Wastewater Treatment Plant (WWTP).
An introduction of anammox bacteria, as a significant nitrogen removal process in the mainstream of WWTPs, could reduce electrical energy use, replace needs of external carbon source dosing, dramatically increase biogas production, and remove the need for nitrate recirculation at the WWTPs.
A functioning process with anammox requires that the desired microbial cooperation is favoured and that unwanted competition is reduced. The anammox process has been implemented at more than 100 WWTPs worldwide for the treatment of warm, highly concentrated liquors from the dewatering of digested sewage sludge and industrial effluents. But the challenge of successfully introducing the anammox process into the mainstream of municipal WWTPs remains.
The main purpose of the project was to introduce the anammox process in the form of a nitritation-anammox process after the high-loaded activated sludge plant at Sjölunda WWTP. The pilot reactors contained moving carrier material, and were so-called moving-bed biofilm reactors (MBBRs). The pilot included both a mainstream process and a sludge liquor treatment. During most of the pilot study, carriers were moved between the mainstream and the reject water treatment. Nitritation-anammox was studied both as a one-step and as a two-step process.
The main conclusions of the project were:
- The anammox bacteria managed to be maintained in the mainstream for more than 900 days.
- Nitritation and anammox failed to become the completely dominant nitrogen removal processes. Nitratation, i.e. the nitrite-oxidising bacteria (NOB) that need to be inhibited for a successful anammox process, was not fully inhibited despite different aeration strategies.
- The nitrogen removal rates were acceptable, but the nitrate residue was too high, which means that an external carbon source needs to be dosed.
The above conclusions and more are described in more detail in the publications below.