Organic composition of starch wastewater steers denitrifying microbiomes for enhanced nitrogen removal

Two-stage corn starch wastewater, specifically hydrolysis acidification wastewater (HAW) and vertical flow sedimentation wastewater (VSW), was assessed as an external carbon supplement to enhance denitrification in low C/N municipal wastewater. In the initial rapid phase, NOx-N reduction rates reached 15.91 and 18.04 mg N g^-1 MLVSS h^-1 for HAW and VSW, respectively, slowing significantly to 3.57 and 8.02 mg N g^-1 MLVSS h^-1 during the subsequent nitrite reduction phase. EEM-PARAFAC indicated preferential depletion of a tyrosine-like component linked to fast NOx removal. Nir-gene profiling showed nirK denitrifiers were more carbon-sensitive than nirS, and Rhizobium dominated nirK under VSW addition. Thirty-day operation remained stable with low effluent nitrate and limited nitrite accumulation. This work supports the feasibility of recycling corn starch process wastewaters, particularly VSW, as external carbon sources for nitrogen removal and proposes an engineering pathway for implementation.