Key Takeaways & Executive Findings
- •• • The composite carbon source YP4 (CC:PCL = 3:2) achieved a nitrate nitrogen removal efficiency of 94.76% in livestock wastewater, demonstrating superior denitrification performance compared to single carbon sources. • • Carbon release from the composite materials followed Fickian diffusion (n < 0.45), ensuring sustained and controlled carbon supply for denitrifying microorganisms, which is critical for long-term reactor operation. • • Effluent ammonia nitrogen from YP4 treatment met the GB 18596-2001 discharge standard, indicating that the composite carbon source does not introduce secondary nitrogen pollution. • • YP4 significantly increased the relative abundance of key denitrifying and polymer-degrading genera (Aeromonas, Novosphingobium, Bacteroides, Clostridium sensu stricto), enhancing microbial community function and process stability.
Abstract
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.
1. Introduction
Livestock wastewater treatment faces a critical bottleneck: the carbon-to-nitrogen ratio (C/N) is typically as low as 1.0–2.0, far below the 4–6 required for efficient heterotrophic denitrification. This carbon deficiency severely limits nitrate removal, leading to elevated total nitrogen in effluents and subsequent eutrophication of receiving waters. Conventional liquid carbon sources such as methanol and glucose are effective but pose economic and safety challenges, and precise C/N control is difficult, often resulting in incomplete denitrification or excessive sludge production.
To address this, researchers have turned to composite solid carbon sources that combine synthetic biodegradable polymers with cheap natural materials. Polycaprolactone (PCL) offers excellent biodegradability and mechanical strength, but its high cost restricts widespread application. Corncob, an agricultural residue rich in cellulose, is inexpensive and abundant. Blending PCL with corncob not only reduces material cost but also enhances microbial attachment and provides a sustained carbon release. This study systematically evaluates different CC:PCL ratios to identify an optimal formulation that balances denitrification efficiency and economic viability, offering a practical solution for low C/N wastewater treatment.
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TANG Qiang, YAN Xiaoping, HE Xiao, LIU Siqi, ZHAO Shengwei, JIANG Rong, YANG Zhanbiao (2026). Removal of Nitrate from Livestock Wastewater Using Composite Carbon Sources of Corncob and Polycaprolactone. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202510071
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Frequently Asked Questions
What is the optimal mixing ratio of corncob to PCL for maximum nitrate removal, and how does it compare to single carbon sources?
The optimal ratio was found to be 3:2 (CC:PCL), designated YP4, which achieved a nitrate removal efficiency of 94.76% in livestock wastewater. This outperformed single carbon sources (PCL or CC alone) under identical conditions, indicating a synergistic effect that enhances denitrification performance.
How does the carbon release kinetics of the composite carbon source influence its suitability for long-term denitrification?
The carbon release index (n) was below 0.45, indicating Fickian diffusion-controlled release. This ensures a slow, sustained release of organic carbon, preventing rapid depletion and maintaining a stable carbon supply for denitrifying bacteria over extended periods, which is essential for continuous wastewater treatment processes.
Does the use of YP4 composite carbon source introduce any secondary pollution, particularly regarding ammonia nitrogen?
No. The effluent ammonia nitrogen concentration from YP4 treatment met the GB 18596-2001 discharge standard, confirming that the composite carbon source does not cause ammonia nitrogen accumulation. This is critical for meeting regulatory requirements and preventing eutrophication.
What microbial community shifts are induced by YP4, and how do they contribute to enhanced denitrification?
High-throughput sequencing revealed that YP4 increased the relative abundance of genera such as Aeromonas, Novosphingobium, Bacteroides, and Clostridium sensu stricto. These genera are known for denitrification and biopolymer degradation capabilities, which facilitate the breakdown of complex carbon sources and enhance nitrate reduction, thereby improving overall nitrogen removal.
What are the practical implications of using corncob-PCL composite carbon sources in terms of cost and scalability?
By incorporating corncob, a low-cost agricultural byproduct, the overall material cost is significantly reduced compared to using PCL alone. The composite maintains high denitrification efficiency, making it an economically viable option for large-scale livestock wastewater treatment. The preparation process is straightforward, and the materials are readily available, supporting scalability.
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