Micro-analysis of nitrogen transport and conversion inside activated sludge flocs using microelectrodes

Abstract

To investigate the nitrogen transport and conversion inside activated sludge flocs, micro-profiles of O₂, NH₄⁺, NO₂^–, NO₃^–, and pH were measured under different operating conditions. The flocs were obtained from a laboratory-scale sequencing batch reactor. Nitrification, as observed from interfacial ammonium and nitrate fluxes, was higher at pH 8.5, than at pH 6.5 and 7.5. At pH 8.5, heterotrophic bacteria used less oxygen than nitrifying bacteria, whereas at lower pH heterotrophic activity dominated. When the ratio of C to N was decreased from 20 to 10, the ammonium uptake increased. When dissolved oxygen (DO) concentration in the bulk liquid was decreased from 4 to 2 mg·L^-1, nitrification decreased, and only 25% of the DO influx into the flocs was used for nitrification. This study indicated that nitrifying bacteria became more competitive at a higher DO concentration, a higher pH value (approximately 8.5) and a lower C/N.

Keywords

nitrogen transport / activated sludge flocs / heterotrophic bacteria / nitrifying bacteria / microelectrodes

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Acknowledgements

This work was supported by Program for Changjiang Scholars and Innovative Research Team in University (No. IRT0853), State Commission of Science Technology of China (No. 2009ZX07212-002), State Key Laboratory of Western Architecture and Technology (No. 10KF08), and Foundation of Shaanxi Educational Committee (No. 11JK0759).

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg