Modelling of biological nitrogen removal from the liquid fraction of pig slurry in a sequencing batch reactor

Biological nitrogen removal through nitrification–denitrification is a treatment alternative that can be considered for scenarios in which there is a nitrogen surplus linked to pig manure management. Studies found in the literature referring to the treatment of the liquid fraction of pig slurry using sequencing batch reactors (SBRs) were reviewed and typified. Mathematical modelling of this treatment was carried out considering: nitrite and pH as state variables; nitrification and denitrification as two-step processes; surface-limited kinetics for hydrolysis and dependence for the heterotrophic biomass yield, as well as for the anoxic maximum growth rate, on the electron acceptor. Sensitivity analysis permitted identification of the parameters that had the greatest influence on the response of the model under specific test conditions. These were subsequently assessed, principally using respirometry. Finally, model-based predictions were contrasted with results obtained in a lab-scale SBR following two different operational strategies. The availability of biodegradable organic substrates for complete denitrification was identified as one of the main limiting factors of the treatment, even when treating raw waste. Low aeration intensity during oxic periods made it possible to mainly conduct the process along the nitrite route and to thereby reduce the organic and oxygen requirements of the process.