Modeling of degradation of solutions containing nitrogen and carbon compounds in aerated submerged fixed-film (ASFF) bioreactors

The biodegradation reaction rates of waste-water solutions containing nitrogen and carbon compounds were studied in an aerated submerged fixed film (ASFF) reactor with four compartments. A solution containing sucrose (carbon source) and ammonium chloride (nitrogen source) was considered in this study. The kinetic models considered in the analysis were the variable order model and the Monod model. Measurements and analysis were performed as a function of organic and hydraulic loading for the reactor. Analysis of the kinetic data was carried out in the first compartment and in the combined section of the reactor which included the second, third, and fourth compartments. The reaction order for carbon removal in the first compartment was found to vary over a range of 1-2 and drops to a range of 0.7-1.2 in the combined section. Lower reaction orders were obtained for nitrogen removal which varied from 0.6-1 in the first compartment and the combined section. Upon application of the Monod model for the two reactions, similar trends to those of the variable order model were obtained for carbon and nitrogen removal in both sections of the reactor. The calculated Monod constants for carbon removal were one to two orders of magnitudes larger than those for nitrogen removal. Measured removal rates of carbon in the first compartment were two orders of magnitudes higher than the nitrogen removal rates in the same compartment. However, the removal rates of both components are comparable in the combined section, especially at high feed flow rates. This behaviour was consistent with literature data on simultaneous removal of carbon and nitrogen compounds, where high concentrations of carbon resulted in severe reduction in the removal rates of nitrogen compounds.