This work in this thesis was conducted in partnership with the company ÁGUAS DO ALGARVE, and had as main objective to characterise the performance of the enhanced biological phosphorus removal wastewater treatment in Boa vista, through the utilisation of an activated sludge model and aim to test various operating factors to optimize the process. Characterization of the sewage influent and effluent was performed in order to evaluate the content of organic matter (i.e., chemical oxygen demand - COD) and its biodegradability (Biological Oxygen Demand - BOD) as well as nutrients (such as nitrogen (N) and phosphorus (P)). The influent COD was also characterized in terms of particulate, biodegradable and inert fractions. This information was used as input in the GPS-X program, where the ASM2d model was tested.
The biological treatment system of the Boavista plant consists of an extended aeration activated sludge system with nitrification/denitrification and biological phosphorus removal.
For model calibration purposes, a through, 6-day sampling campaign was conducted in June 2015, where all relevant flow rates and CDO, N and P fractions were measured in the influent, effluent and recycles. The calibrated model was able to describe very well the performance during this period. This calibration model was then applied to describe the performance data during the year 2014. A substantial deviation was found between the model predicts and the measured process data. This derivation is likely at least partially attributable to the different aeration regimes employed in 2014 vs 2015, as well as the cessation of iron coagulant addition in 2015, which could necessitate recalibration of the ASM2d model.
A simulation study carried out with and without iron sulfate addition suggested that the Boavista plant could eliminated iron sulfate addition without an appreciable increase in effluent phosphorus concentration.
This hypothesis was indeed supported by the effluent phosphorus data achieved at Boavista, which actually experienced a decrease in effluent p levels after ceasing iron sulfate addition in 2015 as compared to 2014, thereby lowering operational costs at theWWTP
