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The conventional methods of nitrogen removal are typically based on a two-part process. Ammonia is first oxidized to nitrite and subsequently to nitrate under aerobic conditions by the autotrophic microorganisms. Nitrate is then dissimilatively reduced to nitrogen gas under anoxic conditions by the heterotrophic bacteria.

This paper describes a method (the SymBio™ process, protected by USA patents 5,506,096, 5,557,415, 5,700,370 and 5,906,746) of maintaining simultaneous nitrification and denitrification in a single tank at very low dissolved oxygen concentrations. Bacterial content of the reduced forms of coenzymes nicotinamide adenine dinucleotide (NADH) changes with the metabolic condition of the biomass. The NADH concentration is monitored on-line by a sensor that takes advantage of the fluorescent properties of NADH. The changes in fluorescence signal are used to control the dissolved oxygen concentrations at the desired level. This allows each sludge floc particle to maintain a balance between the nitrifying and the denitrifying fraction, thus achieving both simultaneously in the same basin

If the operating conditions vary, the measurement of NADH will detect changes in the energy state. Armed with this information, it is possible to decide whether the biological process is in a state of balance or imbalance. This knowledge can then be put to immediate use to control one or more critical process parameters such as the level of aeration the rate of sludge return, the MLSS concentration or the end of the denitrification phase. Actual case studies are discussed.

Document Type: Research Article


Publication date: January 1, 2000

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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