Nitrate concentrations exceed standards in many drinking water sources. Solid carbon source (SCS) is usually used to increase the biological denitrification in waters with a low carbon‑nitrogen ratio. However, there is a lack of research on the enhanced denitrification in drinking water sources with nitrate exceeding limits by the introduction of SCS. In this study, a SCS composite was prepared using agricultural waste corncob and polybutylene succinate and the SCS carbon release performance, denitrification effect and potential chemical and biological risks were investigated via a series of batch and column experiments. The SCS composite presented a long-term, stable carbon release performance and good microbial utilization capability for denitrification: SCS composite has a sustained release capacity for over 28 days in dynamic waters. Short-chain fatty acids accounted for over 60 % of the released carbon, and predominant fluorescence compounds were protein organic compounds and soluble microbial metabolites. The introduction of SCS composite evidently improved bio-rope biomass and its denitrification effect. The removal percentage of NO₃⁻ by SCS reactor pretreatment reached 90.9 %, remaining stable within 28 days. The SCS pretreatment increased formation potentials of trihalomethanes, but formation potentials of haloacetonitriles with higher toxicity were effectively reduced, so the comprehensive toxicity risk of disinfection by-products was reduced. The SCS pretreatment has slight negative impact on drinking water biological stability only during the first 10 days, which needs attention. This study demonstrated that the prepared SCS composite has excellent carbon release performance and denitrification effect, and its chemical and biological risks were controllable.