<p>To address the challenge of deep denitrification in wastewater treatment plants, this study innovatively constructed an integrated closed-loop process combining “biological-ion exchange-electrocatalysis-biological” to achieve efficient removal of nitrate. The nitrate removal rate using the Gandu composite bacterial agent reached 86%, with the effluent reduced to 14.0&#xa0;mg·L⁻¹. After 180&#xa0;min of adsorption on trimethylamine-loaded D301 resin, the treated effluent (14.0&#xa0;mg·L⁻¹ NO₃⁻) achieved a removal rate exceeding 94%, with the effluent concentration as low as 0.84&#xa0;mg·L⁻¹, below the threshold for causing water eutrophication (1.0&#xa0;mg·L⁻¹) and regulatory standards (WHO &lt; 10&#xa0;mg·L⁻¹ NO₃⁻), and consistent with the Langmuir model and the pseudo-second-order kinetic model. For high-salt regenerated solution (5000&#xa0;mg·L⁻¹ NO₃⁻, 10% NaCl), the phosphate-modified foam iron-nickel electrode (P-FeNi-foam) achieved a nitrate removal rate of 97.61% within 6&#xa0;h, with a small amount of byproduct NH₄⁺, significantly outperforming microbial methods (15.3%) and Pd-Cu bimetallic catalysts (44.67%). This advantage stems from the O–H…OPO₃ structure on the electrode surface, which reduces the adsorption potential and dissociation potential of H₂O, promoting the generation of hydrogen radicals from a kinetic perspective, inhibiting Fe corrosion, and thereby facilitating nitrate reduction. Additionally, the consumption of Cl⁻ during the electrocatalytic process suppresses the formation of byproduct NH₄⁺. This process achieves a total nitrate removal rate of 99.16% and creates favorable conditions for biological reuse by electrocatalytically consuming Cl⁻, forming a closed-loop treatment system. The integrated “biological-ion exchange-electrocatalytic-biological” process holds broad application prospects in the treatment of nitrate wastewater.</p>