| Summary: | Tertiary wastewater treatment could provide a reliable source of water for reuse. Amongst these types of wastewater treatment, deep-bed filtration of secondary effluents can effectively remove particles and organic matter; however, NH<sub>4</sub><sup>+</sup> and NO<sub>2</sub><sup>−</sup> are not easily removed. This study examined the feasibility of stimulating microbial activity using hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) as a bio-specific and clean oxygen source that leaves no residuals in the water and is advantageous upon aeration due to the solubility limitations of the oxygen. The performance of a pilot bio-filtration system at a filtration velocity of 5−6 m/h, was enhanced by the addition of H<sub>2</sub>O<sub>2</sub> for particle, organic matter, NH<sub>4</sub><sup>+</sup>, and NO<sub>2</sub><sup>−</sup> removal. Hydrogen peroxide provided the oxygen demand for full nitrification. As a result, influent concentrations of 4.2 ± 2.5 mg/L N-NH<sub>4</sub><sup>+</sup> and 0.65 ± 0.4 mg/L N-NO<sub>2</sub> were removed during the short hydraulic residence time (HRT). In comparison, filtration without H<sub>2</sub>O<sub>2</sub> addition only removed up to 0.6 mg/L N-NH<sub>4</sub><sup>+</sup> and almost no N-NO<sub>2</sub><sup>−</sup>. A DNA metagenome analysis of the functional genes of the media biomass reflected a significant potential for simultaneous nitrification and denitrification activity. It is hypothesized that the low biodegradability of the organic carbon and H<sub>2</sub>O<sub>2</sub> addition stimulated oxygen utilization in favor of nitrification, followed by the enhancement of anoxic activity.
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