Tunable carbon release from melt-blended carbon source particles for simultaneous denitrification in low-C/N wastewater

Achieving simultaneous carbon release and denitrification (SCRD) remains a key challenge for solid carbon sources (SCSs) in low-C/N wastewater treatment. In this project, novel melt-blended advanced carbon sources (MB-ACSs) with tunable compositions were developed to regulate SCRD through structural design, where MB-ACSs were engineered to form interpenetrating networks with controllable porosity and diffusivity based on the different compositions of corn cob (CC) and polyhydroxybutyrate (PHB) within a polyethylene (PE) matrix. Among them, MB-433 (40 ​wt% PE, 30 ​wt% PHB, 30 ​wt% CC) exhibited the most balanced structure, integrating rapid CC-derived dissolution, PHB-mediated sustained release, and PE-supported stability. All MB-ACSs displayed a biphasic release pattern – initial surface dissolution followed by internal diffusion – whereas MB-433 maintained a steady carbon supply ideally synchronized with microbial demand. Denitrification assays conducted across a wide range of nitrate loads (25–1000 ​mg NO₃⁻-N/L) and C/N (0, 1.5, 3) showed that MB-433 consistently achieved 60–80 ​% nitrate removal under moderate conditions (25–50 ​mg NO₃⁻-N/L), avoided inhibition under high-loading and high-carbon conditions (1000 ​mg NO₃⁻-N/L, C/N ​= ​3), and maintained complete denitrification even in the absence of external carbon (C/N ​= ​0). Logistic and exponential fittings confirmed MB-433's superior capacity on SCRD, while Monod modeling revealed high denitrification potential ( V _max ​= ​0.172 ​mg/L d) and strong nitrate affinity ( K _s ​= ​8.42 ​mg/L).