Performance, kinetics characteristics and enhancement mechanisms in anammox process under Fe(II) enhanced conditions

In order to explore the performance, kinetics characteristics and enhancement mechanisms in anammox process under ferrous iron enhanced conditions, a laboratory-scale UASB anammox reactor has been built up and operated for 534 days. Experimental results showed that the Anammox process was successfully started up in a short operation period and the TNRE reached 83.34 ± 2.96% with a maximum total nitrogen removal rate of 14.4 kg m^-3 d^-1 after long-term operated under influent Fe(II) concentration of 5.3 mg L^-1. Simulation results using different kinetic models showed that the Stover-Kincannon model and the Grau second-order model were useful for describing the anammox performance under Fe(II) enhanced conditions. Extracellular polymeric substance (EPS) act a pivotal part in the granulation of Anammox sludge and the improvement of anammox activity. Iron improved the hydrophobicity of the sludge by reducing the PN/PS ratios, and also increased the Anammox granular diameter. The granular diameter of higher than 2.00 accounted for 58.3% of the total sludge. At the same time, the presence of iron decreased EPS levels, and also decreased the iron adsorption ability to sludge. More iron was transported into Anammox, which improved the nitrogen removal ability in the Anammox reactor.