The short-term and long-term effects of Fe(II) on the performance of anammox granules.

Fe(II) is one of the commonly used additives in wastewater treatment and proved to be benefit for promoting microbial activity. In this study, the effects of Fe(II) on the specific anammox activity (SAA) and reactor performance were proved to be concentration-depended. In the short-term experiment, low concentration of Fe(II) (5-80 mg/L) significantly enhanced the SAA while high concentration of Fe(II) (120-300 mg/L) inhibited the SAA. It was confirmed that anammox can be domesticated after long-term exposure to low Fe(II) concentration, and the SAA could be further enhanced by higher Fe(II) concentration in the following phases. In addition, as an important factor for anammox granulation and maintaining the SAA, the extracellular polymetric substance (EPS) was also affected by Fe(II) addition. In spite of the effects on SAA and EPS, Fe(II) was proved to be the key factor that enhancing the N2 O emission via abiotic pathway in the anammox reactor.