Abstract
•A new strategy was developed to enhance nutrient removal from low carbon-wastewater.•A FNA-based nitrifying-sludge treatment was used in a two-sludge system.•1.9mgN/L FNA caused ∼67.8% of nitrite accumulation in the nitrifying reactor.•1.9mgN/L FNA caused ∼83% in nitrogen removal and ∼88% in phosphate removal.•FNA treatment reduced the abundance of nitrite oxidizing bacteria.
A new method to enhance nutrient removal from low carbon-wastewater was developed. The method consists of a two-sludge system (i.e., an anaerobic-anoxic-oxic reactor coupled to a nitrifying reactor (N-SBR)) and a nitrifying-sludge treatment unit using free nitrous acid (FNA). Initially, 65.1±2.9% in total nitrogen removal and 69.6±3.4% in phosphate removal were obtained without nitrite accumulation. When 1/16 of the nitrifying sludge was daily treated with FNA at 1.1mgN/L for 24h, ∼28.5% of nitrite was accumulated in the N-SBR, and total nitrogen and phosphate removal increased to 72.4±3.2% and 76.7±2.9%, respectively. About 67.8% of nitrite was accumulated at 1.9mgN/L FNA, resulting in 82.9±3.8% in total nitrogen removal and 87.9±3.5% in phosphate removal. Fluorescence in-situ hybridization analysis showed that FNA treatment reduced the abundance of nitrite oxidizing bacteria (NOB), especially that of Nitrospira sp.