Biochemical processes mediated by iron-based materials in water treatement: Enhancing nitrogen and phosphorus removal in low C/N ratio wastewater

Wastewater with low carbon-to-nitrogen (low C/N) ratio has led to residues of nitrogen and phosphorus contaminants due to insufficient carbon source, which received increasing attention. Recently, iron-based materials have been widely used to enhance denitrification and considered to be one of the potential methods for efficient treatment of low C/N ratio wastewater. However, the substance cycles between iron, nitrogen and phosphorus are complicated, the reviews about iron-enhanced nitrogen and phosphorus removal performance needs to be further concluded. The objective of this review is to discuss the role of iron in nitrogen and phosphorus removal, and to provide theoretical support for improving effiencies of wastewater treatment to a certain extent. Firstly, the biological or biochemical processes of iron-mediated nitrogen and phosphorus removal were briefly summarized. The iron-mediated nitrogen removal efficiencies were significantly associated with some conditions affecting biological processes such as iron dosage, or the addition of electron shuttles. The removal pathways and iron dosage were the main factors related to N2O emission. In addition, iron had a great influence on phosphorus accumulating organisms (PAOs) which participated in phosphorus removal. On subsequently, the effects of iron on microbial activity, including promotion and inhibition, were revealed, with the pathways through which iron affected microbes way discussed simultaneously. Thirdly, the combination of iron with other materials was introduced, with the removal efficiencies of composite materials summarized. It was found that iron-based materials showed several advantages when combined with available materials such as activated carbon and metals. Finally, as the challenges for the processes of iron-enhanced nitrogen and phosphorus removal were still present, some suggestions for future research were proposed in this paper. Overall, this review suggests that iron-based materials play a critical role in the biological removal process of nitrogen and phosphorus, which may improve the potentiality of their applications in biological technology.