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Candidatus Accumulibacter phosphatis clades enriched under cyclic anaerobic and microaerobic conditions simultaneously use different electron acceptors
Citation:
Camejo, P., B. Owen, J. Martirano, J. Ma, V. Kapoor, J. Santodomingo, K. McMahon, AND D. Noguera. Candidatus Accumulibacter phosphatis clades enriched under cyclic anaerobic and microaerobic conditions simultaneously use different electron acceptors. WATER RESEARCH. Elsevier Science Ltd, New York, NY, 102:125-137, (2016).
Impact/Purpose:
The removal of N and P from wastewater before being discharged into the environment has become a worldwide concern. In conventional biological nutrient removal (BNR) systems, N removal is achieved by a two-stage treatment, that is, aerobic nitrification followed by anoxic denitrification. BNR processes are typically operated under elevated levels of dissolved oxygen (DO) in the aeration basin to ensure complete nitrification and P removal. However, aeration is an energy-intensive operation, which can account for 60% or more of the overall power consumption at a wastewater treatment plant (WWTP). Simultaneous nitrification, denitrification, and P removal (SNDPR), achieved by alternating between anaerobic and low DO conditions, has the potential of significantly reducing both energy and carbon requirements in BNR. It has been hypothesized that oxic and anoxic zone formation within microbial flocs facilitates the occurrence of simultaneous nitrification and denitrification (SND), as nitrite and nitrate produced by nitrifying organisms can be reduced by denitrifying PAOs (DPAOs). The uncultured ‘Candidatus Accumulibacter phosphatis, the most abundant PAO in most full-scale EBPR systems and easily enriched in lab-scale reactors, seems to have the abililty to denitrify. This study aims to investigate the relevance of clade-level population dynamics of Accumulibacter to the removal of P and N under micro-aerobic conditions.
Description:
Lab- and pilot-scale simultaneous nitrification, denitrification and phosphorus removal-sequencing batch reactors were operated under cyclic anaerobic and micro-aerobic conditions. The use of oxygen, nitrite, and nitrate as electron acceptors by Candidatus Accumulibacter phosphatis during the micro-aerobic stage was investigated. A complete clade-level characterization of Accumulibacter in both reactors was performed using newly designed qPCR primers targeting the polyphosphate kinase gene (ppk1). In the lab-scale reactor, limited-oxygen conditions led to an alternated dominance of Clade IID and IC over the other clades. Results from batch tests when Clade IC was dominant (i.e., >92% of Accumulibacter) showed that this clade was capable of using oxygen, nitrite and nitrate as electron acceptors for P uptake. A more heterogeneous distribution of clades was found in the pilot-scale system (Clades IIA, IIB, IIC, IID, IA, and IC), and in this reactor, oxygen, nitrite and nitrate were also used as electron acceptors coupled to phosphorus uptake. However, nitrite was not an efficient electron acceptor in either reactor, and nitrate allowed only partial P removal. The results from the Clade IC dominated reactor indicated that either organisms in this clade can simultaneously use multiple electron acceptors under micro-aerobic conditions, or that the use of multiple electron acceptors by Clade IC is due to significant microdiversity within the Accumulibacter clades defined using the ppk1 gene.
