Fig. 5

Progress over time of the ecological richness, evenness and diversity calculated at the OTU level for bacteria (a–c) and archaea (d–f) for the LNR reference reactor and the free ammonia intoxicated reactors, HNR1, HNR2 and HNR3. For the (observed) richness (R) and diversity (Inv. Simpson), increased values indicate a higher richness and diversity of species, respectively. For the evenness (Simpson even), values range from 0 (uneven community; one or several dominant OTUs and many singlets) to 1 (perfectly even community, all OTUs present at the same relative abundance). “Process reconditioning I, II, III”, “Process recovery” and “Process stability test” refer to the stages and phases described in Table 1