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

Abstract

This study aims to develop and demonstrate a novel integration of anammox with zero-valent iron (Fe0) 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 performances 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 ∼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 accelerate microbial aggregation. A 16S rRNA gene sequencing analysis, together with a series of batch activity tests revealed that the added Fe0 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.