In recent years, partial denitrification-anammox (PDA) technology has emerged as an efficient and energy-saving solution for nitrogen removal in municipal wastewater treatment. However, challenges such as the retention of anammox bacteria (AnAOB), unstable nitrogen removal performance, high inoculation costs, and competition with heterotrophic bacteria hinder its widespread implementation. This chapter addresses these challenges by exploring the integration of PDA technology into traditional denitrifying biofilters (DNBFs). A partial denitrification filter was developed by inoculating conventional activated sludge to produce nitrite as a substrate for AnAOB growth. Two methods for inoculating anammox sludge were assessed, and the feasibility of in situ enrichment of AnAOB in single-stage and two-stage filter systems was examined. The results demonstrated the feasibility of applying anammox in DNBFs, although achieving self-enrichment of AnAOB remains difficult. In a single-stage system, NH₄⁺-N removal was limited to 0.55 mg/L after 111 days, while a two-stage system achieved 6.45 mg/L after 164 days. Metagenomic analysis confirmed successful enrichment of Candidatus Brocadia in the secondary biofilter, with key AnAOB enzymes present. This study lays a foundation for advancing PDA technology in municipal wastewater treatment.