Disturbance-based management of ecosystem services and disservices in partial nitritation anammox biofilms

Abstract

The resistance and resilience provided by functional redundancy, a common feature of microbial communities, is not always advantageous. An example is nitrite oxidation in partial nitritation-anammox (PNA) reactors during wastewater treatment, where suppression of nitrite oxidizers like Nitrospira is sought. In these ecosystems, biofilms provide microhabitats with oxygen gradients, allowing the coexistence aerobic and anaerobic bacteria. We designed a disturbance experiment where PNA biofilms treating water from a high rate activated sludge process removing organic matter (mainstream wastewater), were constantly or intermittently exposed to the effluent of anaerobic sewage sludge digestion dewatering (sidestream wastewater), which has been proposed to inhibit nitrite oxidizers. With increasing sidestream exposure we observed decreased abundance, alpha-diversity, functional versatility, and hence functional redundancy, among Nitrospira in the PNA biofilms, while the opposite patterns were observed for anammox bacteria within Brocadia. At the same time, species turnover was observed for the aerobic ammonia-oxidizing Nitrosomonas populations. The different exposure regimens were associated with metagenomic assembled genomes of Nitrosomonas, Nitrospira, and Brocadia, encoding genes related to N-cycling, substrate usage, and osmotic stress response, possibly explaining the three different patterns by niche differentiation. These findings imply that disturbances can be used to manage the functional redundancy of biofilm microbiomes in a desirable direction, which should be considered when designing operational strategies for wastewater treatment.