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

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2023-01, Vol.451, p.138917, Article 138917
• Main Authors: Uri-Carreño, Nerea, Nielsen, Per H., Gernaey, Krist V., Wang, Qian, Nielsen, Ulla Gro, Nierychlo, Marta, Hansen, Susan H., Thomsen, Lisette, Flores-Alsina, Xavier
• Format: Article
• Language: English
• Subjects: 16s rRNA; Biofilm composition; Elemental composition; IFAS; MABR; Redox
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2022.138917

•Full-scale hybrid MABRs fed with anaerobic sludge were monitored for three years.•Nitrification performance was lowest at the lowest ORP.•Nitrifying organisms’ abundance was significantly higher at the highest ORP.•High abundance of Fe and S compounds in MABR biofilm under the lowest ORP. 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.