Dual role of organic matter in Feammox-driven nitrogen and phosphate removal
Yi Liu, Jiachen Dong, Xiaohui Cheng, Xiaotong Cen, Yan Dang, Kangning Xu, Min Zheng
Abstract
• Organic matter inhibits ammonium oxidation but enhances nitrate removal in Feammox. • Fe(II)-mediated precipitation forms vivianite, improving phosphorus removal. • Adding Fe(III) could alleviate organic matter inhibition on nitrogen removal. • Optimized Fe(III) and COD levels are critical for Feammox-driven nutrient removal. Feammox is a novel microbial process that enables simultaneous nitrogen and phosphorus removal in wastewater treatment. This study investigated the role of organic matter in Feammox-driven nutrient removal during long-term bioreactor operation by gradually increasing the influent chemical oxygen demand (COD) concentration from 0 to 50, and then to 100 mg/L. The results revealed that the ammonium removal efficiency was reduced from 60.5 % to 20.7 % with COD concentration increasing from 0 to 100 mg/L. In contrast, organic matter enhanced nitrate removal through heterotrophic denitrification, which outcompeted nitrate-dependent Fe(II) oxidation. Phosphorus removal was increased up to approximately 90 % via Fe(II)-mediated precipitation, forming vivianite crystals, evidenced by X-ray diffraction analysis. Continuous addition of Fe(III) alleviated the inhibitory effect of organic matter on ammonia oxidation by serving as an alternative electron acceptor, reducing competition. Therefore, optimizing organic matter levels and ensuring sufficient Fe(III) availability are crucial for achieving efficient nutrient removal in Feammox systems, particularly for treating wastewater with a low carbon/nitrogen ratio. Graphical abstract