Development of wastewater treatment plant for Firlej agglomeration in the city of Serock

The project aiming at the development of a wastewater treatment plant in Serock, Firlej commune is to:


Improve the quality of discharged wastewater by:

  • developing a new waste storage point for transferred sewage together with equalisation tank,
  • modernising the pumping station,
  • developing a mechanical pretreatment station,
  • developing an wastewater equalisation tank with a pumping station,
  • developing an anaerobic chamber with a separation chamber,
  • developing two bioreactors including anaerobic and aerobic tanks,
  • developing two secondary settling tank with a floating sludge removal system,
  • installing an aeration control system (oxygen probes in oxygen chambers).

Improve the quality of sludge by:

  • developing a aerobic sludge stabilisation chamber,
  • developing a sludge treatment facility with a storage place for sludge pellets).


The primary purpose of developing and modernisation of the wastewater treatment plant is to treat wastewater from Firlej agglomeration in accordance with the current regulations of the Polish laws regarding the quality of treated wastewater that is discharged into a receiver, as well as disposal of sludge that is a byproduct of the treatment process. For the past few years, the amount of wastewater has been increasing. The increase is seasonal and is correlated with the inflow of tourists visiting the region in spring and summer time (May – September).


Details about wastewater treatment technology and sludge disposal:
1. The wastewater treatment plant will be a flow-type plant working with two process lines i.e. two bioreactors and two separate secondary settling tanks.
2. The wastewater treatment plant will operate with low-loaded activated sludge.
3. Sludge age in activated sludge chambers will be no less than 10 days.
4. The active capacity of activated sludge chamber will be no less than 800 m3.
5. Sludge concentration in activated sludge chamber will not exceed 4.0 kg sm/m3 – as calculated.
6. Activated sludge chamber aeration process – fine bubble aeration.
7. Aeration process in activated sludge chamber is controlled by aeration and mixing equipment with blowers working in start/stop mode.
8. The hydraulic load of the secondary settling tank (for Qh max) – not more than 0.8 m3/m2 x h, and maximum sludge surface load ≤300 l/(m2 x h),
9. External recirculation regulated in the range of 70-120 Qh average.
10. Two pumps (1 working + 1 spare) will recirculate the sludge. Excess sludge will be pumped out by a specially designed pump.
11. Internal recicrulation between aerobic and anoxic chambers ≥ 450%.
12. The wastewater treatment station will have a discharge point with a screen for transferred wastewater, a supplier identification computer system and a measurement and control system preventing discharge of wastewater that does not meet preset parameters (conductivity and pH level).
13. The wastewater treatment station will be equipped in screenings, sand and oil removal installations (an aerated sand trap with a separate chamber, an oil pump and a grit washer).
14. Sieve clearance in the sieved grit chamber and manual screen (emergency) not more than 6 mm, sieve throughput – not less than 60 m3/h; screenings hydration – not more than 70 %.
15. Sieved grit chamber throughput – not less than 60 m3/h.
16. Sand scrubbers will produce sand with hydration not exceeding 65 %, containing not more than 3% of organic matter (compared with dry product).
17. Screenings and sand will be collected in separate containers. Layers of screenings will be covered with chlorinated lime/quick lime. A specialist company will dispose of screenings, sand and oil.
18. Excessive sludge stabilisation will undergo aerobic digestion in a separate chamber with compacting function.
19. The time spent in digestion chamber will be minimum 15 days.
20. A belt press with two flocculators will dewater the sludge. Belts will be cleaned using the resulting effluent or treated wastewater.
21. The end-product of sludge processing will be a lime-sludge granulate containing at least 75% of dry matter. The dewatered sludge will be mixed with quick lime in a mixer that will mix both ingredients fast enough to create high temperature that will result in obtaining a stable and hygienically safe granulate.
22. Foul air from odour emitting facilities will be directed to a deodorising installation.