Iron-modified carriers accelerate biofilm formation and resist anammox bacteria loss in biofilm reactors for partial denitrification-anammox.

The slow formation of anammox biofilms presents a bottleneck for resolving anammox bacterial loss and achieving stable performance in biofilm-based partial denitrification-anammox (PD-A) processes. This study utilized iron-modified (K1/Fe3 O4 NPs) carriers, which were prepared and used for the first time in PD-A processes. Parallel moving bed biofilm reactors (MBBRs) indicated that iron-modified carriers facilitated the formation of biofilms at a faster rate than K1 carriers, consequently improving the nitrogen removal performance of the process by over 40 %. 16S rDNA analysis showed that anammox bacteria were approximately four times more abundant in the iron-modified carrier biofilm than in the K1 carrier biofilm. XPS and zeta potential analysis suggested that the improved microbial affinity of the iron-modified carrier surface caused this. As a result, the iron-modified carriers facilitated the formation of anammox biofilms and enhanced PD-A performance.