The effects of low oxidation-reduction potential on the performance of full-scale hybrid membrane-aerated biofilm reactors

Nerea Uri-Carreño*, Per H. Nielsen, Krist V. Gernaey, Qian Wang, Ulla Gro Nielsen, Marta Nierychlo, Susan H. Hansen, Lisette Thomsen, Xavier Flores-Alsina

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Membrane-Aerated Biofilm Reactors (MABRs) are becoming a popular process intensification alternative within wastewater treatment plants (WWTP). Indeed, the nitrogen removal capacity of aerobic/anoxic/anaerobic reactors can be substantially enhanced with reduced energy consumption and footprint requirements. However, little is known about how oxidation–reduction potential (ORP) may impact their overall process performance. This study aims to report some of these effects by showing the results of almost three years of monitoring of two hybrid MABRs (R1, R2) adjacent to an existing Biodenipho™ facility. In Period 1 (P1), R1 and R2 were fed with anaerobic mixed liquor from the selector for the biological phosphorus removal zone. In Period 2 (P2), external aeration was introduced to increase ORP values (R1, R2), and membranes were replaced (R1) or cleaned (R2). Results show an increase in nitrification rates: from 0.27 and 0.33 g N m−2 d−1 in R1/R2 during P1 to 1.0 and 0.80 g N m−2 d−1 in R1/R2 during P2. 16 s rRNA amplicon sequencing analysis revealed that the relative abundance of nitrifying organisms increased from 0.2 to 6.7 % in R1 and 0.8 to 5.3 % in R2 in P2 (in detriment of microbes with fermenting capabilities). Energy dispersive X-ray spectroscopy confirmed the presence of coating substances under the lowest ORP (P1), which could be pyrite and its precursors like mackinawite. Overall, it is hypothesized that low ORP conditions (P1) had a detrimental effect on nitrification performance, as it promoted the reduction of different iron and sulfur compounds, which in turn a) precipitate in the biofilm as FeS increasing mass transfer limitations and competing with biomass for space; b) re-oxidize increasing the internal oxygen demand; c) inhibit nitrifiers growth.

Original languageEnglish
Article number138917
JournalChemical engineering journal
Publication statusPublished - 1 Jan 2023

Bibliographical note

Funding Information:
Nerea Uri-Carreño gratefully acknowledges the Industrial Ph.D. program's financial support from Innovation Fund Denmark, through the project “MANTRA” (Contract-No: 7091-00038A). Dr. Xavier Flores-Alsina and Prof. Krist Gernaey also thank the Danish Council for Independent Research in the frame of the DFF FTP research project GREENLOGIC (Contract-No:7017–00175A) and the Danida fellowship center (DFC) research project ERASE (Contract-No: 18-M09-DTU). Professor Ulla Gro Nielsen and Dr. Qian Wang thank The Danish Research Council - Technology and Production Science grant (Contract-No: 7017-00262).

Publisher Copyright:
© 2022 The Author(s)


  • 16s rRNA
  • Biofilm composition
  • Elemental composition
  • IFAS
  • MABR
  • Redox


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