SRT increases with biofilm thickness in MBBR systems

SRT is a key operational parameter that can impact the functionality of biological treatment systems. Little is known about SRTs of organisms in attached growth systems, though due to higher biomass retention it is likely that these systems would exhibit higher SRTs than suspended growth systems. We calculated the SRT of individual sequence variants (SVs) (referred to herein as taxon-SRT) in nitrifying MBBR reactors in which we controlled biofilm thickness using Veolia/ ANOX ™ Z-carriers with maximum biofilm thicknesses of 50 μm, 200 μm, 300 μm, 400 μm and 500 μm. We find that average residence time of microbes in nitrifying MBBRs are long, exceeding 38 days, and that taxon-SRTs generally increased as biofilm thickness increased with lowest average Taxon-SRT in the thinnest biofilms. Differences in the patterns of taxon-SRT with biofilm thickness within the nitrifying guild point towards variations in ecological strategies of individual nitrifiers.