Protozoan predation on nitrification performance and microbial community during bioaugmentation

► About 58% of ammonia uptake rate and 80% nitrite uptake rate of the seed source was lost in the seeded reactors. ► The population of nitrifiers increased immediately after bioaugmentation. ► The activity of nitrifiers increased gradually after bioaugmentation. ► Predation did not have a significant effect on the activity of nitrifiers. ► K-strategist is more vulnerable to predation than r-strategist.