| During the biological wastewater treatment, especially in the biological phosphorus removal, the biologically induced phosphorus precipitation has been observed in some stages of the process. This is due to the local conditions in certain points of the plant (pH, phosphate and metal cations concentration, etc.) which are suitable for solids formation. This chemical mechanism of fixation of phosphorus can represent up to 80% of the suspended phosphorus in the system.;On the other hand, mathematical modelling has been revealed as a very useful tool for designing and simulating biological nutrient removal systems. There are different models proposed in the literature to simulate biological phosphorus removal. However, most of these models do not consider the biologically mediated phosphorus precipitation process.;The aims of this thesis are: the development of a mathematical model that allows to simulate the biologically induced precipitation and dissolution processes during the wastewater treatment, and the study of the influence of calcium on the biological phosphorus removal.;The proposed model considers that: the acid-base and ion pairing reactions quickly achieve the chemical equilibrium and that the solid formation is governed by the kinetic of the reactions.;In order to check the predictive capacity of the precipitation model together with the biological processes, this model was included in the mathematical structure of the BNRM1 model, developed for the design and simulation of wastewater treatment plants.;This model, which incorporates the biological processes, the pH calculation and the precipitation processes, was able to reproduce satisfactorily the results obtained in the experiments carried out in a SBR operated for enhanced biological phosphorus removal (alternating anaerobic and aerobic conditions).;The study of the effect of the wastewater calcium concentration on the enhanced biological phosphorus removal process, pointed out an important influence. The higher calcium concentrations the lower phosphorus release/acetic acid uptake relation during anaerobic conditions (YPO4) was obtained. These results suggest that the increase in calcium cause the decrease of the internal polyphosphate available for the acetic acid uptake, favouring the GAO metabolism opposite to the PAO metabolism. |
