Operation and dynamic modeling of a novel integrated anaerobic–aerobic–anoxic reactor for sewage treatment

• A small footprint integrated column reactor for wastewater treatment was developed.
• High COD removal efficiency in short HRT was obtained.
• Stable nitrification process with nitrite accumulation was obtained.
• A validated dynamic model was used for the reactor operation and design.

Integrated reactors (IR) combining anaerobic, aerobic and nitrogen removal processes are a viable alternative to reduce operational costs and footprint compared to conventional wastewater treatment plants. An integrated bench scale (6.4 L) anaerobic–aerobic–anoxic column reactor (ICR) is developed to remove carbon and nitrogen compounds from sewage of our university campus. The ICR is comprised of an up-flow anaerobic sludge blanket reactor (UASB), a membrane aerated biofilm reactor (MABR) and a denitrifying biofilm reactor (DNB). The global COD removal efficiency (ηC-Global) is ~82% at hydraulic retention time (HRT) of 8.4 h. The partial nitrification (PN) process is obtained with an ammonia/nitrite ratio (Ra/n) of 4. The experimental data were used to calibrate and validate an integrated carbon-nitrogen removal model (ICNRM), in order to determine operating conditions for the improvement of the ICR performance, considering the hydrodynamic profile and reaction kinetics. A good agreement between the measured and modeled results is obtained with a least square error function (S) lower than 0.09. The model predicts that the COD removal efficiency at the MABR (ηC-MABR) and nitrite accumulation at the DNB are influenced by the volumetric oxygen transfer coefficient (kLa) and oxygen concentration, respectively. The optimal operation zone for ηC-MABR>90% and Ra/n of 1.32 were reached for kLa between 1.26 and 1.36 1/h, and an inlet DO concentration of 1.5 to 1.6 mg/L respectively, standing out the importance of calibrating hydrodynamic behavior and kinetics.

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