Effects of Elevated Fe (III) on Anaerobic Ammonia Oxidation Biofilm Process: Inhibition and Recovery

Abstract

To investigate the treatment performance of employing the anaerobic ammonia oxidation (anammox) biofilm process to treat the iron-containing industrial wastewater with a low carbon–nitrogen ratio and obtain an optimal condition, the effects of elevated exposure to Fe (III) (ranging from 0 to 1.5 mM) on the anammox biofilm process were explored. The findings indicated that the performance of anammox nitrogen removal remained unaffected when exposed to low levels of Fe (III) (0.1 mM and 0.3 mM). However, high concentrations (higher than 0.5 mM) showed a negative effect. The semi-inhibitory concentration (IC50) of Fe (III) was 1.32 mM. Additionally, under exposure to high levels of Fe (III), a remarkable accumulation of Fe (III) was observed within the anammox system. The total iron concentration increased from 30 mgFe·gVSS−1 to a saturation point of approximately 300 mgFe·gVSS−1. This accumulation led to a decrease in extracellular polymeric substance (EPS) from 221.4 mg·gVSS−1 to 91.3 mg·gVSS−1 and specific anammox activity (SAA) from 0.0482 gN·(gVSS·d)−1 to 0.018 gN·(gVSS·d)−1. Consequently, the activity of anammox bacteria (AnAOB) was inhibited, leading to a decline in the average total nitrogen removal efficiency (TNRE) from 86.9% to 38.3%. However, it was discovered that the inhibitory effect of continuous Fe (III) could be reversed by introducing the ferric ion complex EDTA·2Na into the system. As a result, the TNRE recovered to 60%. The findings would be useful to optimize the anammox biofilm process by adjusting the concentration of Fe (III) in the practical industrial application.