This paper describes the results from a study carried out to investigate the feasibility of upgrading Parada wastewater treatment plant (WWTP) for biological nitrogen removal. The biological treatment of Parada WWTP is a conventional activated sludge process. Since 1992 only one of the three available aeration tanks has been used.

Activated Sludge Model No.1 was used as a base for modelling of the activated sludge system. To accomplish all the calculations, AQUASIM software was applied. The model was calibrated and verified with data from Parada WWTP operation. Very good correlations between measured data and simulation results were achieved using stoichiometric and kinetic parameter values proposed by the authors of IAWQ Model No. 1. However, characterisation of the actual wastewater was necessary.

Computer simulations with a verified and extended model were done to study whether the capacity of the treatment plant is enough for biological nitrogen removal. Very high effluent quality can be achieved if the first tank volume is used for denitrification, the second and third tank volumes are used for BOD removal and nitrification, the recirculating effluent flow ratio is 1.5 and the sludge age is 15 days.

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