Successful enrichment of anammox consortium in a single-stage reactor at full-scale: The difference in response of functional genes and transcriptional expressions

Abstract Anammox process is a cost saving biological nitrogen removal process. The shortage of anammox inoculum restricts the full-scale application. In the present study, an anammox consortium enrichment was successfully achieved in a single-stage reactor at full-scale with working volume of 117 m3. The external dosing of sodium nitrite (NaNO2) and sodium acetate (NaAc) for the increase in TN removal was successively operated during 261 days’ experiment. Multiple low-dose of NaNO2 stimulated the immediate responses of amoA and hzsA transcripts, and the high growth rates of those genes. The mRNA/DNA ratio of hzsA was 127 at the initial nitrite treatment, with the increase in the copy number of hzsA (growth rate of 0.20 d−1), and mRNA/DNA ratio decreased to 2 through 75 days’ nitrite treatment. Low-dosage of NaAc (207002D333 mgCOD/L) was beneficial for anammox enrichment at both gene and transcript levels. The anammox bacteria took the dominance with the abundance of 17.76%. However, over-dosage of NaAc (417 mgCOD/L) gave rise to heterotrophs (Armatimonadetes_gp5, Thauera and Comamonas) and decreased the abundance of hzsA transcript and Candidatus Kuenenia. With 261 days’ operation, TN removal rate and efficiency increased from 0 to 0.59 kgN/(m3 d), and from 0% to 92%, respectively. The anammox activity reached 0.41 kgN/(kgMLSS d). The external dosage of NaNO2 and NaAc showed positive correlation with TN removal rate and hzsA trancripts.