Optimizing nitrogen and phosphorus removal at Jurmala WWTP, Latvia

Solution to which problem

Exceeding of the phosphorus HELCOM recommendation of 0,5 mg/l. This was mostly due to nitrate being transported to the anaerobic zone and disturbing the EBPR (enhanced biological phosphorus removal).

Accumulation of surface sludge and foam. In addition Jurmala is a touristic area, this means that the WWTP is receiving varying flows and loads during the year. 

Technical conditions

Jurmala Sloka wastewater treatment plant treats the water of 32 400 PE, using conventional primary treatment without primary sedimentation, activated sludge process for enhanced biological phosphorus and nitrogen removal and sludge treatment by mechanical thickening and dewatering.

There are two biological treatment lines. The biological process consists of two round basins. First, there is an anaerobic zone followed by the main anoxic (D) zone, aerobic (N) zone and two switch zones, which can be operated either anoxically (warm period) or aerobically (cold period). The purified waste waters are discharged from Sloka to river Lielupe that flows to the Gulf of Riga. 


Within PURE project, a technical study was commissioned at Sloka to identify ways to further improve the waste water treatment performance of the plant. Jurmala Water together with investment coordinator John Nurminen Foundation and the project consultant decided to realize the following investments at Sloka WWTP within PURE project:

• to purchase and install new measurement and control instrumentation;

• to divide the anaerobic and aerobic zone to internal zones and to lower the walls between the anaerobic and aerobic zones, this will enable surface sludge to be transported to the aerobic basin, where it may be disintegrated by aeration;

• to purchase and install a new polymer unit to improve sludge treatment (separate chemical dosing to the thickening and dewatering equipment).

The air flow meters (2 pcs), a pressure sensor and the polymer unit (SL1500) were supplied and installed between August and November 2012. The whole project, including the installation of new walls in anaerobic and aerobic zones, was ready on December. The same subcontractor installed the polymer unit, the new walls and the air flow meters as well delivered the control valves (4 pcs). The dynamic simulation software BioWin for wastewater treatment process and BW Controller software for online process management were installed on December 2012.


These investments helped the Sloka treatment plant operators to balance the nitrogen and phosphorus removal performance and to achieve more constant results, to prevent problems with bulking sludge and sludge washouts and to achieve better energy efficiency.

The dynamic simulation software BioWin for wastewater treatment process and BW Controller software for online process management were purchased.

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