Functional robustness and gene pools of a wastewater nitrification reactor: Comparison of dispersed and intact biofilms when stressed by low oxygen and low pH

Yuejian Mao, Lars R. Bakken, Liping Zhao, Åsa Frostegård

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

The functional robustness of biofilms in a wastewater nitrification reactor, and the gene pools therein, were investigated. Nitrosomonas and Nitrosospira spp. were present in similar amounts (cloning-sequencing of ammonia-oxidizing bacteria 16S rRNA gene), and their estimated abundance (1.1 × 109 cells g-1 carrier material, based on amoA gene real-time PCR) was sufficient to explain the observed nitrification rates. The biofilm also had a diverse community of heterotrophic denitrifying bacteria (cloning-sequencing of nirK). Anammox 16S rRNA genes were detected, but not archaeal amoA. Dispersed biofilms (DB) and intact biofilms (IB) were incubated in gas-tight reactors at different pH levels (4.5 and 5.5 vs. 6.5) while monitoring O2 depletion and concentrations of NO, N2O and N2 in the headspace. Nitrification was severely reduced by suboptimal O2 concentrations (10-100 μM) and low pH (IB was more acid tolerant than DB), but the N2O/NO3- product ratio of nitrification remained low (<10-3). The NO 2- concentrations during nitrification were generally 10 times higher in DB than in IB. Transient NO and N2O accumulation at the onset of denitrification was 10-103 times higher in DB than in IB (depending on the pH). The contrasting performance of DB and IB suggests that the biofilm structure, with anoxic/micro-oxic zones, helps to stabilize functions during anoxic spells and low pH.

Original languageEnglish (US)
Pages (from-to)167-180
Number of pages14
JournalFEMS microbiology ecology
Volume66
Issue number1
DOIs
StatePublished - Oct 2008
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Microbiology
  • Ecology
  • Applied Microbiology and Biotechnology

Keywords

  • Biofilm
  • Denitrification
  • Nitrification
  • Wastewater treatment
  • amoA

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