Removal of Nitrate from Livestock Wastewater Using Composite Carbon Sources of Corncob and Polycaprolactone
Carbon source is a critical factor driving heterotrophic denitrification, yet the low carbon-to-nitrogen ratio (C/N) of livestock wastewater limits this process. This study developed novel composite carbon sources by combining corncob (CC) and polycaprolactone (PCL). Static carbon release and denitrification experiments were conducted to evaluate carbon release patterns and nitrogen removal performance. Results showed that the carbon release index (n) was below 0.45, indicating Fickian diffusion as the dominant release mechanism. The composite carbon source prepared at a CC:PCL mass ratio of 3:2 (denoted YP4) achieved a nitrate nitrogen removal efficiency of 94.76%, with effluent ammonia nitrogen meeting the discharge limits of GB 18596-2001. High-throughput sequencing revealed that YP4 increased the relative abundance of genera capable of denitrification and biopolymer degradation (e.g., Aeromonas, Novosphingobium, Bacteroides, and Clostridium sensu stricto), thereby enhancing heterotrophic denitrification and nitrogen removal. These findings provide a novel approach for selecting and preparing external carbon sources for biological heterotrophic denitrification of low C/N wastewater.