Effect of exogenous folate addition on the start-up process of single-stage partial nitritation-anammox system

In this study, two lab-scale reactors were operated to evaluate the impact of exogenous folate on the start-up process of single-stage partial nitritation-anammox (SPNA). Folate at a dose of 0.5, 1.0, and 1.5 mg/L was continuously added into the experimental reactor (RI) at different operation stages. The highest nitrogen removal rate was 0.26 kg N/(m3 center dot d) in RI with a nitrogen loading rate of 0.45 kg N/(m3 center dot d), which was higher than that in the control reactor (RII) of 0.20 kg N/(m3 center dot d). Moreover, the extracellular polymeric substances production in RI with 1.5 mg/L folate dosage was 264.24 +/- 6.74 mg/gVSS, enhancing by 0.5-fold that of the RII, and the activity of hydrazine oxidase increased to the highest level of 0.37 +/- 0.01 mu mol cyt-c/(gVSS center dot s). Meanwhile, the activity of dehydrogenase in RI was enhanced from 796.39 +/- 2.19 mu g/(gVSS center dot min) to 819.17 +/- 24.47 mu g/(min center dot gVSS). The relative abundance of Candidatus Brocadia was 0.64 % at the end of phase 5 in RI whereas it remained at 0.25 % in RII. Function prediction showed that the nitrogen-related genes highly increased with the folate addition.