Preparation of solid-phase carbon sources with different ratios and their carbon release properties

Given the widespread occurrence of low C/N ratios in treated wastewater effluent and the instability of conventional liquid carbon sources， it is necessary to investigate solid-phase carbon sources in terms of composition and design. The goal is to optimize both the quantity and quality of carbon release for denitrification under low C/N conditions and to extend research into the environmental behavior of emerging contaminants. In this study， nine composite solid-phase carbon sources were prepared from straw， sawdust， and corncob as natural cellulose materials with different PHBV-to-cellulose mass ratios. Their carbon release characteristics were evaluated via dynamic release experiments combined with dissolved organic carbon （DOC） analysis， UV-Vis spectroscopy， and excitation-emission matrix （EEM） fluorescence spectroscopy. The results showed that with identical carbon-source components， increasing the proportion of cellulose caused corncob-based solid-phase carbon sources to exhibit release patterns that differed from， and in some cases were opposite to， those of straw- and sawdust-based systems. When the carbon-source composition was the same， increasing the proportion of straw or sawdust accelerated the release rate， increased total release and release duration， reduced the aromaticity and molecular weight of the released dissolved organic matter （DOM）， and promoted the release of protein-like DOM such as tryptophan and tyrosine， indicating that material ratios can synergistically regulate DOM bioavailability. Under identical ratio conditions， corncob-based composite carbon sources outperformed straw- and sawdust-based systems on multiple parameters： they achieved a moderate total carbon release while maintaining release durations exceeding 134 hours， thereby ensuring a stable carbon supply. The DOM they released exhibited lower aromaticity， smaller molecular weight， and a lower proportion of humic substances， indicating higher bioavailability. Overall， the corncob-based system demonstrated significant advantages in both bioavailability and engineering application potential.