The roles of Paracoccus huijuniae for enhancing denitrification with N-methyl pyrrolidone as the electron donor

A strain of Paracoccus huijuniae was isolated from acclimated denitrifying biomass. It was tested for denitrification activity alone or by bioaugmenting it into the denitrifying biomass when N-methyl pyrrolidone (NMP) was the electron donor. The nitrate removal rate was increased by 22 % when P. huijuniae was bioaugmented into the denitrifying biomass, since the nitrate-reduction rate by P. huijuniae was 3.2-fold greater than that for the denitrifying biomass alone. P. huijuniae alone achieved 100 % nitrate conversion to nitrite, but nitrite was not reduced unless nitrate disappeared completely, and then nitrite reduction was slow. Stoichiometric nitrite accumulation can be attributed to the activity of nirK in P. huijuniae being inhibited by the presence of nitrate. Thus, bioaugmentation with P. huijuniae enhanced overall denitrification kinetics by accelerating nitrate reduction to nitrite, but subsequent denitrification steps were completed by other denitrifying strains in the community. • Nitrogenous N-methyl pyrrolidine (NMP) was used as electron donor for denitrification. • A strain of Paracoccus huijuniae was isolated from NMP acclimated biomass. • Adding 10 % P. huijuniae accelerated nitrate removal rate by 22 %. • Its nitrate-reduction kinetics was 3.2-fold faster than that for the denitrifying biomass alone. • P. huijuniae only reduced nitrate to nitrite, and other denitrifiers completed reduction to dinitrogen gas.