Journal
WATER RESEARCH
Volume 106, Issue -, Pages 518-530Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.watres.2016.10.028
Keywords
Stratification; pH gradient; Nitrobacter; Nitrospira; Mainstream conditions
Funding
- Marie Curie Intra European Fellowship (GreenN2) [PIEF-GA-2012-326705]
- SIAM Gravitation Grant [024.002.002]
- Netherlands Organization for Scientific Research
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Partial nitritation was stably achieved in a bench-scale airlift reactor (1.5L) containing granular sludge. Continuous operation at 20 degrees C treating low-strength synthetic wastewater (50 mg N-NH4+/L and no COD) achieved nitrogen loading rates of 0.8 g N-NH4+/L.d) during partial nitritation. The switch between nitrite-oxidizing bacteria (NOB) repression and NOB proliferation was observed when ammonium concentrations in the reactor were below 2-5 mg N-NH4+/L for DO concentrations lower than 4 mg O-2/L at 20 degrees C. Nitrospira spp. were detected to be the dominant NOB population during the entire reactor operation, whereas Nitrobacter spp. were found to be increasing in numbers over time. Stratification of the granule structure, with ammonia-oxidizing bacteria (AOB) occupying the outer shell, was found to be highly important in the repression of NOB in the long term. The pH gradient in the granule, containing a pH difference of ca. 0.4 between the granule surface and the granule centre, creates a decreasing gradient of ammonia towards the centre of the granule. Higher residual ammonium concentration enhances the ammonium oxidation rate of those cells located further away from the granule surface, where the competition for oxygen between AOB and NOB is more important, and it contributes to the stratification of both populations in the biofilm. (C) 2016 Elsevier Ltd. All rights reserved.
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