Assessing nitrogen transformation processes in a trickling filter under hydraulic loading rate constraints using nitrogen functional gene abundances.

A study was conducted of treatment performance and nitrogen transformation processes in a trickling filter (TF) used to treat micro-polluted source water under variable hydraulic loading rates (HLRs), ranging from 1.0 to 3.0 m 3 /m 2 d. The TF achieved high and stable COD (97.7–99.3%) and NH 4 + -N (67.3–92.7%) removal efficiencies. Nitrification and anaerobic ammonium oxidation were the dominant nitrogen removal processes in the TF. Path analysis indicated that amoA /anammox and amoA /( narG + napA ) were the two key functional gene groups driving the major processes for NH 4 + -N and NO 2 − -N, respectively. The analysis also revealed that anammox/ amoA and nxrA /( nirK + nirS ) were the two key functional gene groups affecting processes associated with the NO 3 − -N transformation rate. The direct and indirect effect of functional gene groups further confirmed that nitrogen transformation processes are coupled at the molecular level, resulting in a mutual contribution to nitrogen removal in the TF. [ABSTRACT FROM AUTHOR]