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/Fe3O4 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.

Initiating an anaerobic ammonium oxidation reactor by inoculation with starved anaerobic ammonium oxidation sludge and modified carriers.

Prolonged starved anammox sludge (SAS) obtained during initial rejuvenation was inoculated into a reactor together with activated sludge (AS), anaerobic granular sludge (AGS) and modified carriers consisting of honeycomb carrier with high biological interception and activated carbon carrier with high adsorption performance. SAS accounted for 5% of the inoculated sludge. The anammox process was started and operated at around 25℃. After 160 days, the nitrogen loading rate and nitrogen removal rate reached 1.12 kgN·m-3·d-1 and 0.97 kgN·m-3·d-1, respectively. Obvious red anammox biofilms were observed on the modified carriers. Microbial community analysis showed that the relative abundance of anammox bacteria increased from < 0.1% to 22.96%. Candidatus Jettenia and Candidatus Brocadia were the dominating anammox species. This work demonstrates the potential to reuse SAS to improve the start-up efficiency of anammox reactors, which makes good economic sense.