Modelling of Nitrogen Removal Using a Microalgal-Bacterial Consortium Under Different SRTs

130Mathematical modelling of the microalgal-bacterial consortia was presented in Chapter 5, and shown to be an efficient tool to evaluate the removal mechanisms within the consortia. In this Chapter, further improvement of the model was achieved using the experimental data from Chapter 4. The complete set of experimental data, which included hourly logs of ammonium, nitrite, nitrate, COD and oxygen concentrations at different SRTs, allowed to calibrate and validate the model for different processes. The SRT of 26 days was used for the calibration, while the SRTs of 52 and 17 days were selected for validation. The most sensitive parameters were the maximum growth rate of algae ( μ_m,p ) and light extinction coefficient ( k ). After calibration and validation, the μ_m,p was found to be 2.00 (± 0.05) d⁻¹, the maximum growth rate of heterotrophic biomass ( μ_m,H ) was 5.5 (± 0.01) d⁻¹, ammonium oxidizing bacteria maximum growth rate ( μ_m,AOB ) was 1.1 (± 0.02) d⁻¹ and the maximum growth rate of nitrite oxidizing bacteria ( μ_m,NOB ) was 1.3 (± 0.01) d⁻¹. Furthermore, the minimum SRT for nitrification was calculated using the validated model, and it was found to be between 5 and 10 days. Overall, the model identified the critical point at which the reactor starts to fail, and the limiting conditions when reducing the SRT.