Full-scale deammonification system for reject-water treatment at Tartu WWTP
Tartu Waterworks Company is the second biggest municipal wastewater treatment plant in Estonia (100 000 PE) and one of the many WWTPs in the Baltic Sea Region where anaerobic digestion of sludge is applied. Nitrogen-rich reject-water produced in anaerobic digestion is commonly recirculated back to the process thus increasing the nitrogen load and challenging the main treatment process in keeping the discharge limits. This increases the amount of external carbon to be added to the main nitrification-denitrification process. A full-scale deammonification technology was developed and installed with regard to demonstrate in-situ start-up of deammonification without external seed.
In the framework of constructing the anaerobic digester (2013-2015) in Tartu WWTP, the tanks were designed for nitritation of the sludge water before releasing it back to the influent of the plant. Ammonium nitrogen is oxidized to nitrite nitrogen during nitritation process, however, nitrogen removal process is still performed in main wastewater treatment process. In order to enhance nitrogen removal with cost efficient investment, a full-scale deammonification system was implemented for reject-water treatment using existing infrastructure. The deammonifying microbiological consortium was grown in-situ without a need of buying the sludge externally. In-situ start-up of the process without external inocculum decreases the budget and gives valuable competence on start-up of deammonification technology. The installation reduces amounts of external carbon to be added and thereby operational costs.
As it is the first reject-water deammonification system in Estonia, operators of Tartu WWTP receive continuous support from the University of Tartu to achieve optimal process efficiency. As a result, competence will be established and a case-study will be available for other interested stakeholders. Operating a full-scale deammonification system will be continued after the project lifetime. Additionally, as start up without purchasing an inoculum is not widespread, current installation demonstrates that deammonification without external seed is a cost-efficient process. Piloting that process has transnational relevance as a proof of applicability and sustainability of deammonification technology.