Performance and Microbial Ecology of a Low Temperature (15°C) Mainstream Anammox Moving Bed Biofilm Reactor (MBBR) Process

摘要

With the advantage of providing WWTPs the ability toward energy neutrality, mainstream nitrogen removal using anammox (anaerobic ammonium oxidization) based technologies has been increasingly explored these days. However, the decreased bacteria activities under temperature <20°C could reduce the nitrogen removal efficiency, which remains as a key issue for successful mainstream applications (Gilbert, Agrawal et al. 2014, Lackner, Welker et al. 2015). Enriched biomass with high AnAOB (anaerobic ammonium oxidization bacteria) ratio within the mainstream process was proved effective to mitigate the negative impact of low temperatures. Thus far, most documented studies of mainstream operation was initially direct seeding either with granular or biofilm biomass from sidestream deammonification/anammox (combining partial nitritation and anammox) processes, which are typically operated at higher temperatures (>30°C) and influent nitrogen loadings. In this study, a different enrichment method was applied, which entailed continuously feeding a mainstream MBBR (operated at 15±1°C) with the effluent from a sidestream deammonification MBBR (operated at 35 + l°C). By connecting the two reactors, the suspension biomass from the sidestream MBBR was transferred into mainstream anammox MBBR, so as to seed the mainstream reactor, and to enrich biofilm biomass under low temperature directly. The specific objectives in this study were to characterize the performance and microbial ecology of the enriched low-temperature mainstream anammox MBBR relative to that of the sidestream deammonification MBBR. As the results showed, successful enrichment was observed in the mainstream biofilms with a biomass concentration increased from 0.33 + 0.08mgCOD/carrier to 0.80 ± 0.05mgCOD/ carrier within 6 months. Microbial ecology in both sidestream and mainstream was analyzed through the next-generation sequencing technologies targeting 16S rRNA region. The sequencing data indicated a similar spatial distribution and microbial diversity of three major bacteria between sidestream and mainstream reactors. An extremely high fraction (>50%) of Candidatus "Kuenenia" related bacteria was founded to dominate the biofilm population in mainstream reactor, and an average fraction of 54.3 ± 9.38% of Nitrospira was presented in the suspensions. The overall results suggested this connecting method a good way for mainstream biomass enrichment.