Achieving high-level nutrient removal and wastewater treatment capacity through iron-mediated microbial process and sludge granulation

This study aims to develop and demonstrate a novel integration of anammox with zero-valent iron (Fe-0) for highly efficient wastewater treatment. The process enables not only enhanced phosphorus removal but also favored sludge granulation to reduce footprint, and more importantly, leads to a combination of microbial iron (Fe)-based denitrification for high-level nitrogen removal. In an integrated laboratory system, superior perfor-mances of nitrogen and phosphorus removal and treatment capacity were achieved over one year. With low-strength mainstream wastewater (NH4+-N = 58.2 +/- 0.6 mg/L) as influent, total nitrogen (TN) removal efficiency stabilized at 97.4 +/- 1.6 %, with effluent TN concentration of <2.0 mg N/L. Phosphorus removal was also high above 90 %, attributed to the formation of chemical precipitates in sludge granulation with a mean volume diameter of similar to 1 mm. The formation of granular sludge was due to that the Fe0 served as carriers to support microbial attachment and growth, and stimulated the secretion of extracellular polymeric substances to accel-erate microbial aggregation. A 16S rRNA gene sequencing analysis, together with a series of batch activity tests revealed that the added Fe-0 enriched nitrate removal pathway and improved the activity of denitrifiers, thereby successfully polishing effluent with a very low TN level. Overall, this proposed integrated process is proved to be a promising technology of simultaneously achieving high-level nitrogen, phosphorus removal and capacity for next-generation wastewater treatment.

Automated summary

This study develops and demonstrates a novel integration of anammox with zero-valent iron (Fe-0) for efficient wastewater treatment. The process not only enhances phosphorus removal and sludge granulation but also combines microbial iron-based denitrification for high-level nitrogen removal. The integrated laboratory system achieves superior nitrogen and phosphorus removal, with stable total nitrogen removal efficiency of 97.4 +/- 1.6% and phosphorus removal above 90%.