Aquaculture wastewater is typically laden with organic matter, nitrogen, phosphorus, and other nutrients. Discharging untreated wastewater can exacerbate eutrophication in surrounding water bodies, disrupting ecological balance and degrading water quality. 

A team research led by Prof. Xie Yonghong from the Institute of Subtropical Agriculture, Chinese Academy of Sciences, pioneering developed a "Four Ponds and Two Dams" constructed wetland system, an innovative approach to aquaculture wastewater treatment. 

“This technology not only optimize water purification processes in intensive aquaculture systems, but also help us know more detailes in the synergistic interactions between aquatic plants and epiphytic biofilms, unraveling their crucial roles in removing pollutants from bullfrog aquaculture wastewater.” Prof. Xie Yonghong, the corresponding authors of the study said. Their new groundbreaking study findings were recently published in Microorganisms.

This efficient multi-stage treatment system integrates a sedimentation pond, a first filtration dam, an aeration pond, a second filtration dam, a biological filter pond, and a submerged plant stabilization pond, creating a comprehensive, eco-friendly wastewater remediation framework. A demonstration site was established at a bullfrog aquaculture facility in the Datong Lake region of Yiyang City.

The findings demonstrate that this constructed wetland system achieved a remarkable removal efficiency exceeding 60% for both total nitrogen (TN) and total phosphorus (TP) in bullfrog aquaculture wastewater, effectively mitigating a wide spectrum of pollutants. However, the treatment performance exhibited notable seasonal variations, with TN removal maintaining consistent stability, while TP removal fluctuated significantly across different seasons.

Furthermore, the aeration pond played a crucial role in enhancing dissolved oxygen (DO) levels, which provided optimal conditions for phosphorus removal in July and nitrogen removal in November. Within the aeration pond and biological filter pond, epiphytic bacterial α-diversity was significantly higher than in other treatment ponds, suggesting that these zones offer an enriched microenvironment conducive to bacterial colonization and activity.

Additionally, the bacterial community composition exhibited pronounced seasonal shifts. In July, Firmicutes were the dominant phylum, whereas in November, the microbial landscape shifted to be dominated by Nitrospiraceae and Acidobacteriota, reflecting dynamic microbial succession patterns influenced by seasonal factors. Furthermore, functional genes associated with sulfur metabolism, nitrogen fixation, and oxidative phosphorylation displayed marked temporal variations within the aeration pond, underscoring the direct impact of seasonal growth dynamics and process optimizations on biofilm functional gene expression.

These insights underscore the pivotal role of aeration and aquatic plants—especially submerged plants—in the efficient treatment of aquaculture wastewater. "The synergistic interactions between aquatic vegetation and epiphytic biofilms are fundamental to enhancing nutrient removal efficiency and sustaining long-term system performance," said Dr. Chao chuanxin, the first author of the paper. " From an application perspective, strategic aquatic plant management and continuous aeration emerge as key technical interventions to fully harness the potential of the "Four Ponds and Two Dams" constructed wetland system."

Contact: Chao chuanxin; Xie Yonghong

E-mail: chaochuanxin94@163.com; yonghongxie@163.com

"Four Ponds and Two Dams" constructed wetland purification system. (Image by Chao Chuanxin)