Strengthened attachment of anammox bacteria on iron-based modified carrier and its effects on anammox performance in integrated floating-film activated sludge (IFFAS) process.

Moving-bed biofilm reactor (MBBR) or integrated floating-film activated sludge (IFFAS) process has been proved to be one of the ideal candidates for anammox application. However, the slow development of anammox bacteria (AnAOB) biofilm and unstable bioactivity always limit their wide application. This study developed a type of novel zero-valent iron (ZVI)-based modified carrier for strengthening AnAOB attachment and enhancing anammox performance. Surface properties analysis indicated the iron-based modified carrier revealed electropositive, less hydrophobic, and higher surface free energy compared with conventional high density polyethylene (HDPE) carrier. These surface parameters were positively correlated with total biomass attachment, anammox biofilm development, EPS secretion and heme-c production. IFFAS process filled with iron-based modified carriers could keep relatively stable and high anammox activity at different influent TN loadings (varied from 0.6 to 1.4 kg/(m3∙d)) and showed potential to keep and recover AnAOB bioactivity after six-months-freeze. Microbial analysis confirmed that anammox genus, Candidatus Kuenenia, had a significant niche preference on iron-based modified carrier than conventional HDPE carrier. As a result, the population of Candidatus Kuenenia in IFFAS process filled with modified carriers that contained 2 wt% or 3 wt% ZVI was 1.34 × 106-1.55 × 106 copies/ mg DNA, increased by 20.7-39.6% comparing with that in the control reactor (1.11 × 106 copies/ mg DNA). This study demonstrated AnAOB could be enriched and maintained in situ with high abundance and bioactivity on the iron-based modified carriers, which would be significant for anammox process wide application in full-scale.