MODELLING AND PARAMETERS CALIBRATION OF A BIOLOGICAL TREATMENT FOR NUTRIENTS REMOVAL AFTER DIRECT MEMBRANE FILTRATION OF URBAN WASTEWATER

At present, wastewater is addressed like a dirty stream to treat with the most cost-effective technologies in order to stay within the effluent limits imposed by law. This approach leads current centralised wastewater treatment plants to be not environmentally sustainable and to waste many resources. In particular, in the conventional activated sludge process, energy potential is wasted through the aerobic conversion of the organic matter into carbon dioxide through an energy intensive system. A promising solution consists in applying direct membrane filtration to raw wastewater, in order to redirect the carbon mass flow to anaerobic digestion for its energetic valorisation, and treat the permeated flow with low energy footprint technologies. This thesis is focused on the evaluation, through modelling, of the feasibility of a biological treatment for the permeate of direct ultrafiltration deriving from a pilot plant set in Alboraya, Valencia. Because of the low COD/N ratios characteristic of the permeate stream, the biological methods suitable for its treatment are those based on partial nitrification, in which nitrite is accumulated to be directly denitrified. In the first part of this work a dynamic calibration is carried out in the model BNRM2. The value of anoxic heterotrophic growth yield is assessed together with the biomass distribution, furthermore deviations in permeate quality data are adjusted. In the second part of the work the implementation of a partial nitrification process to treat the permeate is evaluated, performing different sets of simulations. The final configuration, selected as optimal to set up the process in the sequencing batch reactor, is a single stage configuration operated with a dissolved oxygen concentration of 0.7 mgO2/l and a sludge retention time of 8 days. The influence of the addition of an external inhibitor to speedup the start-up of the process is also studied.