Effect of Fe (II) on nitrogen removal of anammox under organic matter inhibition

Abstract

The purpose of this study is to investigate the effect of Fe2+ on the nitrogen removal efficiency of anammox under the inhibition of organic matter. In the experiment, the influent C/N was controlled at about 2.25 by synthetic water, and the up-flow anammox reactor was run at 0.15, 1.5, 3.0, and 4.5 mg/L Fe2+, respectively. The number of denitrifying bacteria and the characteristics of microbial community in the reactor were analyzed by most probably number method and high-throughput sequencing method. The results show that when the influent C/N and Fe2+ are controlled at 2.25 and 0.15 mg/L respectively, the TN removal efficiency can reach 82.15%. When Fe2+ concentration increased to 1.5, 3.0 and 4.5 mg/L, TN removal efficiency increased by 4.00%, 6.89% and 7.77%, respectively. In terms of microbes, the abundance of denitrifying bacteria and anammox bacteria increased collectively with the addition of Fe2+. When the Fe2+ increased from 0.15 mg/L to 3 mg/L, the number of denitrifying bacteria in the bottom and middle of the reactor increased from 1.62 × 108 and 2.74 × 107 to 8.06 × 108 and 3.76 × 107 respectively. In the middle of the reactor, the abundance of Planctomycetota and Candidatus_Jettenia with anammox function increased from 4.01% and 2.18% to 4.87% and 3.17%, respectively. Therefore, appropriate Fe2+ addition can promote the growth of denitrifying functional bacteria and anammox bacteria in the anammox reactor inhibited by organic matter, thus improving the denitrification efficiency of the reactor. It can provide a reference value for the anammox reactor to treat actual municipal wastewater containing organic matter.