Effect of anoxic decay process on simultaneous nitrification denitrification in a membrane bioreactor operated without an anoxic tank

摘要

This study was focused on evaluating the role and the effect of anoxic decay on the extentnof simultaneous nitrification–denitrification (SNdN) process sustained in a single membranenbioreactor. The membrane bioreactor was fed with relatively strong domestic sewage andnoperated at steady state at a sludge age of 36 days at a corresponding suspended solids levelnmaintained in the range of 17,500–21,000 mg/L. The SNdN could be sustained due to diffusionnlimitation of oxygen into the flocs. The evaluation identified an MLSS threshold level of aroundn17,000–18,000 mg/L below which nitrogen removal was essentially controlled by denitrificationnand above, the rate limiting mechanism shifted to nitrification maintaining total nitrogen removalnefficiency of 85–95% for a typical domestic sewage. The contribution of anoxic decay process tonthe overall denitrification potential was evaluated as 60%, substantially higher than the remainingn40% associated with the anoxic growth during the SNdN process.