Enhancing Nitrogen Removal in Marine Recirculating Aquaculture Systems by Optimized Carbon Addition in a Circulating Airlift Fluidized Bed (CAFB) Bioreactor

Jia, Lei; Sun, Yue; Yang, Xiaohan; Li, Xian; Shang, Xiaodi; Yin, Xiaoya; Wang, Gang; Song, Xiefa

doi:10.3390/w18121426

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Enhancing Nitrogen Removal in Marine Recirculating Aquaculture Systems by Optimized Carbon Addition in a Circulating Airlift Fluidized Bed (CAFB) Bioreactor

by

Lei Jia

^1,2,

Yue Sun

²,

Xiaohan Yang

^3,*,

Xian Li

¹,

Xiaodi Shang

²,

Xiaoya Yin

²,

Gang Wang

² and

Xiefa Song

^1,*

¹

Key Laboratory of Mariculture (Ministry of Education), Fisheries College, Ocean University of China, Qingdao 266001, China

²

Tianjin Fishery Research Institute, Tianjin 300221, China

³

College of Fishery, Tianjin Agricultural University, Tianjin 300384, China

^*

Authors to whom correspondence should be addressed.

Water 2026, 18(12), 1426; https://doi.org/10.3390/w18121426

Submission received: 7 May 2026 / Revised: 26 May 2026 / Accepted: 6 June 2026 / Published: 10 June 2026

(This article belongs to the Special Issue Research on Wastewater Treatment, Recycling and Reuse)

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Abstract

The treatment of high-salinity, low-carbon marine aquaculture wastewater poses significant challenges for biological denitrification. This study systematically evaluated the performance of a polycaprolactone (PCL)-based aerobic denitrification biofilter under varying temperatures (15 °C and 25 °C) and PCL addition levels (282, 564, 846, 1128, and 1410 g). Optimal nitrogen removal, total nitrogen (TN) removal efficiency exceeding 92%, was achieved with 1128 g PCL at 15 °C (HRT 10 h) and 1410 g PCL at 25 °C (HRT 8 h), significantly outperforming the low-PCL baseline treatment. Microbial community analysis revealed that increased PCL dosage promoted the dominance of the hydrolytic genus Flavobacterium over Simplicispira, enhancing polymer degradation capacity and system stability. Metagenomic sequencing further elucidated the complete PCL degradation pathway, wherein hydrolysis products were oxidized to generate NADH and FADH₂, serving as electron donors for denitrification. Key functional genes (narG, nirK, nosZ) and enzymes associated with both PCL decomposition and nitrate reduction were significantly enriched in high-performance reactors (e.g., AT15H6, AT25H6, ET15H10, ET25H10), correlating strongly with observed nitrogen removal rates. By integrating reactor performance with microbial ecology and functional genetics, this work provides a comprehensive “material–microorganism–gene–performance” framework, offering both practical strategies and mechanistic insights for enhancing denitrification in saline aquaculture systems.

Keywords: aerobic denitrification; marine aquaculture wastewater; nitrogen removal; microbial community; functional genes

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MDPI and ACS Style

Jia, L.; Sun, Y.; Yang, X.; Li, X.; Shang, X.; Yin, X.; Wang, G.; Song, X. Enhancing Nitrogen Removal in Marine Recirculating Aquaculture Systems by Optimized Carbon Addition in a Circulating Airlift Fluidized Bed (CAFB) Bioreactor. Water 2026, 18, 1426. https://doi.org/10.3390/w18121426

AMA Style

Jia L, Sun Y, Yang X, Li X, Shang X, Yin X, Wang G, Song X. Enhancing Nitrogen Removal in Marine Recirculating Aquaculture Systems by Optimized Carbon Addition in a Circulating Airlift Fluidized Bed (CAFB) Bioreactor. Water. 2026; 18(12):1426. https://doi.org/10.3390/w18121426

Chicago/Turabian Style

Jia, Lei, Yue Sun, Xiaohan Yang, Xian Li, Xiaodi Shang, Xiaoya Yin, Gang Wang, and Xiefa Song. 2026. "Enhancing Nitrogen Removal in Marine Recirculating Aquaculture Systems by Optimized Carbon Addition in a Circulating Airlift Fluidized Bed (CAFB) Bioreactor" Water 18, no. 12: 1426. https://doi.org/10.3390/w18121426

APA Style

Jia, L., Sun, Y., Yang, X., Li, X., Shang, X., Yin, X., Wang, G., & Song, X. (2026). Enhancing Nitrogen Removal in Marine Recirculating Aquaculture Systems by Optimized Carbon Addition in a Circulating Airlift Fluidized Bed (CAFB) Bioreactor. Water, 18(12), 1426. https://doi.org/10.3390/w18121426

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Enhancing Nitrogen Removal in Marine Recirculating Aquaculture Systems by Optimized Carbon Addition in a Circulating Airlift Fluidized Bed (CAFB) Bioreactor

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