Potential for performance enhancement of biological wastewater treatment by bacterial community shift and adaptation of ammonia-oxidizing bacteria: a case study on the nitritation of pig slurry

The bacterial groups responsible for nitrogen elimination in biological wastewater treatment are diverse and ubiquitous. This diversity implies the possibility for the enhancement of biotechnological processes by natural selection (adaptation and community shift) in the activated sludge under conditions usually considered unfavourable. The 1-year operation of a partial nitritation reactor - seeded with sludge from a municipal single-stage deammonification reactor and fed with liquid pig slurry (high NH₄-N and salinity) - revealed a combined functional and structural change in the activated sludge and the ammonia-oxidizing bacteria (AOB) community to cope with the process's conditions. The relative abundance of AOB within the living microbial biomass increased from 22 to 35%. Initially, the AOB community consisted of <i>Nitrosomonas europaea/eutropha</i> and <i>Nitrosomonas communis</i>. Following adaptation, members of the <i>Nitrosomonas marina</i> lineage and <i>Nitrosococcus mobilis</i> were also identified within the sludge. AOB maximum activity (expressed as autotrophic specific oxygen uptake rate, SOUR) increased from 66.3 to 139.2 mgO₂/gVSS/h, while the FA concentration associated with half-maximum SOUR (IC₅₀) rose from 21.7 to 25.4 mg/L NH₃ and 62.0 to 73.7 mg/L NH₃. Natural selection acting on the microorganisms in the nitritation reactor helped to form a highly specialized and productive activated sludge.