Brasov wastewater treatment plant (Brasov county, Romania), designed to treat a dry weather maximum daily flowrate of 205.805 m³/day (500.000 PE), is an existing treatment facility that encountered difficulties in achieving its treatment goals.

Due to recent wastewater quality changes, the biological treatment has started to unsuccessfully remove nutrients such as nitrogen and phosphorus.

At this point, the Operator sought professional expertise to assess the required modifications the biological treatment needs to undergo to lower the effluent’s N and P concentrations to the compliance limits (NH4-N: 1,55 mg/L; NO3-N: 5,65 mg/L, NO2-N: 0,30 mg/L; TP: 1,0 mg/L).

The modelled process was a 3-stage Modified Bardenpho (A20 – Anaerobic, Anoxic, Oxic) treatment scheme that incorporated the already well established EPBR (Enhanced Phosphorus Biological Removal) for biological phosphorus removal and pre-denitrification for biological nitrogen removal.

The proposed model is based on the ASM2d Model (Activated Sludge Model 2d) of the IWA (International Water Association) for basic biological removal of carbon, nitrogen, and phosphorus, UCTADM1 Model (UCT Anaerobic Digestion Model) for anerobic fermentation process and Musvot model for the inorganic components precipitation.

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Glina-Bucharest wastewater treatment plant site is located in the nearby of Bucharest Municipality, in the village of Glina, Romania. At the present (following Stage I plant modernization implementation, 2011), the plant operates a mechanical treatment process that includes coarse screens, fine screens, grit and grease removal chambers and primary clarifiers.

The mechanical treatment is followed by a biological treatment process which is based on AS (‘Activated Sludge’) and ARS (‘Activated Return Sludge’) bioreactors technology for biological organic matter and nitrogen removal through intermittent denitrification procedure and enhanced phosphorus Biological Removal (EPBR).

Phosphorus is biologically removed in an organic matter side-stream hydrolysis process of the return activated sludge. The phosphorus balance is then subsequently polished to compliance through chemical precipitation using Ferric Chloride (FeCl₃).

The plant was designed to treat maximum 10.0 m³/s mechanically with only 4.0 m³/s treated biologically, the equivalent of 2.500.000 PE (population equivalent). The flow rate balance of 6.0 m³/s is bypassed to the receiving water with no biological treatment.

The biological treatment modeling goal was to confirm the AS /ARS treatment scheme feasibility in attaining effluent compliance for organic matter, nitrogen and phosphorus.

The modelled process included an intermittent denitrification treatment scheme for biological nitrogen removal and the already well established EPBR (Enhanced Phosphorus Biological Removal) model for phosphorus removal in conjunction with an ARS (“Activated Return Sludge) biological process.

The proposed model was based on the ASM1 Model (Activated Sludge Model 1) of the IWA (International Water Association) for basic biological carbon, nitrogen removal while the biological and chemical phosphorous removal was modelled through a conventional model.

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