Roles of waste iron scraps in anammox system treating sulfide-containing wastewater: Alleviating sulfide inhibition, promoting novel anammox bacteria enrichment, and enhancing nitrogen removal capacity

In this study, waste iron scraps (WIS) were exerted to alleviate sulfide inhibition on anammox bacteria and promote anammox nitrogen removal from sulfide-containing wastewater.Short-term batch experiments showed that WIS-addition led to the anammox bacteria activity increasing by 124.8 % at an initial sulfide concentration of 40 mgS/L. During the long-term experiments, the nitrogen removal rate (NRR) reached to 8.76 kg/(m³·d) in the WIS-added reactor, while the maximum NRR was only 3.77 ± 0.31 kg/(m³·d) in the non-WIS reactor. In contrast to anammox bacteria development in the non-WIS reactor, the relative abundance of Candidatus Kuenenia (1.4-3.7 %) declined significantly in the WIS-added reactor, but novel potential anammox bacteria Brocadiaceae_unclassified (60.1 %-78.6 %) were highly enriched. Overall, the experimental evidence suggested that WIS-addition not only mitigated the sulfide inhibition on anammox bacteria, but also promoted novel anammox bacteria proliferation. The findings of this work provide a promising solution for wide engineering applications of anammox treating sulfide-containing wastewater.