Laboratory-Scale Biochar-Aerated Constructed Wetlands for Low C/N Wastewater: Standardization and Legal Cooperation from a Watershed Restoration Perspective

To address the problems of eutrophication exacerbation in water bodies caused by low carbon-to-nitrogen ratio (C/N) wastewater and the limited nitrogen removal efficiency of conventional constructed wetlands, this study proposes the use of biochar (Corncob biochar YBC, Walnut shell biochar HBC, and Manure biochar FBC) coupled with intermittent aeration technology to enhance nitrogen removal in constructed wetlands. Through the construction of vertical flow wetland systems, hydraulic retention time (HRT = 1&ndash:3 d) and influent C/N ratios (1, 3, 5) were regulated, before being combined with material characterization (FTIR/XPS) and microbial analysis (16S rRNA) to reveal the synergistic nitrogen removal mechanisms. HBC achieved efficient NH4+-N adsorption (32.44 mg/L, Langmuir R2 = 0.990) through its high porosity (containing Si-O bonds) and acidic functional groups. Under optimal operating conditions (HRT = 3 d, C/N = 5), the CW-HBC system achieved removal efficiencies of 97.8%, 98.8%, and 79.6% for NH4+-N, TN, and COD, respectively. The addition of biochar shifted the dominant bacterial phylum toward Actinobacteriota (29.79%), with its slow-release carbon source (TOC = 18.5 mg/g) alleviating carbon limitation. Mechanistically, HBC synergistically optimized nitrogen removal pathways through &ldquo:adsorption-biofilm (bacterial enrichment)-microzone oxygen regulation (pore oxygen gradient).&rdquo: Based on technical validation, a dual-track institutionalization pathway of &ldquo:standards-legislation&rdquo: is proposed: incorporating biochar physicochemical parameters and aeration strategies into multi-level water environment technical standards: converting common mechanisms (such as Si-O adsorption) into legal requirements through legislative amendments: and innovating legislative techniques to balance precision and universality. This study provides an efficient technical solution for low C/N wastewater treatment while constructing an innovative framework for the synergy between technical specifications and legislation, supporting the improvement of watershed ecological restoration systems.