Biofilm colonization and succession in a full-scale partial nitritation-anammox moving bed biofilm reactor

Journal article, 2024

Background Partial nitritation-anammox (PNA) is a biological nitrogen removal process commonly used in wastewater
treatment plants for the treatment of warm and nitrogen-rich sludge liquor from anaerobic digestion, often
referred to as sidestream wastewater. In these systems, biofilms are frequently used to retain biomass with aerobic
ammonia-oxidizing bacteria (AOB) and anammox bacteria, which together convert ammonium to nitrogen gas. Little
is known about how these biofilm communities develop, and whether knowledge about the assembly of biofilms
in natural communities can be applied to PNA biofilms.

Results We followed the start-up of a full-scale PNA moving bed biofilm reactor for 175 days using shotgun
metagenomics. Environmental filtering likely restricted initial biofilm colonization, resulting in low phylogenetic
diversity, with the initial microbial community comprised mainly of Proteobacteria. Facilitative priority effects allowed
further biofilm colonization, with the growth of initial aerobic colonizers promoting the arrival and growth of anaerobic
taxa like methanogens and anammox bacteria. Among the early colonizers were known ‘oligotrophic’ ammonia
oxidizers including comammox Nitrospira and Nitrosomonas cluster 6a AOB. Increasing the nitrogen load in the bioreactor
allowed colonization by ‘copiotrophic’ Nitrosomonas cluster 7 AOB and resulted in the exclusion of the initial
ammonia- and nitrite oxidizers.

Conclusions We show that complex dynamic processes occur in PNA microbial communities before a stable
bioreactor process is achieved. The results of this study not only contribute to our knowledge about biofilm assembly
and PNA bioreactor start-up but could also help guide strategies for the successful implementation of PNA
bioreactors.