• • Corncob-based carbon sources with PHBV:cellulose ratio of 1:1 (CC4) achieved release durations exceeding 134 h, ensuring stable carbon supply for denitrification, outperforming straw and sawdust systems in bioavailability.
• • Increasing straw or sawdust proportion (e.g., PHBV:cellulose ratio from 4:1 to 4:5) accelerated release rates and increased total DOC release, while reducing aromaticity (SUVA254) and molecular weight, enhancing DOM bioavailability.
• • Optimal formulations JG5, MX5, and CC4 exhibited low theoretical maximum release (M∞) and high mass transfer coefficients (k), balancing sustained release and availability, critical for long-term denitrification.
• • EEM-PARAFAC revealed that protein-like components (C1, C2) dominated released DOM, with relative abundance far exceeding humic-like C3; higher straw/sawdust ratios promoted simultaneous release of both protein-like and humic-like substances, while corncob ratio had minimal effect on component distribution.