Beyond Conventional: Sustainable Denitrification with Solid Carbon

This study examines the dissolution behavior and biodegradability of biodegradable plastics, mainly focusing on polycaprolactone (PCL) along with polylactic acid (PLA), polyhydroxyalkanoate (PHA), and polybutylene adipate terephthalate (PBAT). These bioplastics serve as slow-release carbon sources in solid-phase denitrification systems, where limited carbon availability can reduce nitrate removal efficiency. A series of experiments was performed to assess how key operational parameters, such as temperature, surface area, solvent type, bead reuse, and hydraulic retention time (HRT), affect the release of soluble chemical oxygen demand (SCOD) from these materials. Among the bioplastics studied, PCL showed a moderate, temperature-sensitive dissolution profile, characterized by a quick initial release followed by a plateau, consistent with its dual amorphous-crystalline structure. PLA exhibited a rapid yet limited SCOD release, while PHA released high initial SCOD levels but decreased with reuse. PBAT displayed the lowest SCOD release, likely due to its dense structure and limited porosity. The dissolution behavior of PCL, in particular, was effectively modeled using the Noyes-Whitney and Higuchi equations. Complementary structural analyses, including FTIR, BET, TGA, and DSC, provided further insight into these trends by revealing material-specific properties. In addition to physical dissolution assessments, biological tests were conducted to evaluate the denitrification potential of PCL compared to methanol. Using acclimatized biomass, the yield and maximum specific growth rate were measured for both carbon sources. The results highlighted differences in microbial utilization patterns and underscored the importance of combining physical solubility characteristics with biological performance metrics.
Overall, these findings offer a comprehensive framework for optimizing bioplastics in solid-phase denitrification applications.