Unlocking Carbon Potential in Corncobs: Evaluating Acidic, Alkaline, and Ultrasonic Pretreatments

Abstract

In recent years, due to their significant economic and safety advantages, agricultural wastes have become sustainable external carbon sources for nitrogen removal through denitrification. This study investigated the carbon and nitrogen release characteristics of corncobs (CC) under different pretreatment methods (NaOH, HCl, CH3COOH soaking, and ultrasonic). The structural variations of CC under different soaking methods were also analyzed. The results demonstrated that 3% NaOH soaking was the optimal pretreatment method; the average released carbon by NaOH soaking was 630.53 mg·g−1, which was 43.64%–191.63% bigger than those of HCl and CH3COOH. Ultrasonic pretreatment exhibited a negligible effect (<5%) on carbon release. The carbon release process under all pretreatment methods followed first-order kinetics (R2=0.99) and the Ritger–Peppas equation (R2=0.86). NaOH can degrade lignin to break the skeletal structure, whereas HCl and CH3COOH cannot. The released carbon source by 3% NaOH soaking showed good denitrification performance; the dominate denitrifying genera consisted of Flavobacterium (5.3%), Acinetobacter (4.6%), and Acidovorax (2.8%). This study explored the mechanisms of carbon release by alkali soaking and ultrasonic treatment and verified that the released carbon source from CC could be used for nitrogen removal.