[Nitrate removal from recirculating aquaculture system using polyhydroxybutyrate-co-hydroxyvalerate as carbon source...

Nitrate accumulation in recirculating aquaculture systems (RAS) remains a persistent challenge. While conventional methods rely on chemical or biological treatments, their long-term effectiveness and environmental impact are not fully understood. Prior research has shown that biofilm-based denitrification can reduce nitrate levels, but the role of specific carbon sources in this process is less clear. This gap motivated the investigation into the use of biodegradable polymers as a sustainable alternative. PHBV, a biodegradable polymer, has been proposed as a potential carbon source in denitrification systems. However, its effectiveness in RAS and the microbial communities it supports remain understudied. Understanding how PHBV influences microbial dynamics could improve system design. This study aimed to explore the feasibility of PHBV in nitrate removal. The findings may contribute to more efficient and eco-friendly RAS management strategies.

The study aimed to assess the effectiveness of polyhydroxybutyrate-co-hydroxyvalerate (PHBV) as a solid carbon source and biofilm carrier in a denitrification reactor connected to a recirculating aquaculture system (RAS). The researchers wanted to determine whether PHBV could support microbial activity sufficient to reduce nitrate levels. They also sought to identify the microbial communities forming on the PHBV surface over time. By comparing systems with and without the denitrification reactor, the team aimed to quantify the nitrate removal capacity. The study focused on the dynamics of microbial populations in biofilms. The researchers were particularly interested in the succession patterns of dominant bacterial species. The results could inform the design of more sustainable RAS. This approach could reduce reliance on chemical treatments and improve water quality.

The researchers used a denitrification reactor packed with PHBV as a solid carbon source. They monitored nitrate levels in RAS connected to the reactor over time. A control RAS without the reactor was also tested for comparison. To analyze microbial communities in the biofilm, they used PCR-DGGE. This method allowed them to identify dominant bacterial species. They isolated bacteria from the biofilm using pure culture techniques. The isolated strains were then classified based on phylogenetic analysis. The study spanned 150 days to observe long-term microbial changes. The researchers tracked shifts in microbial populations at 40 and 150 days. This approach provided insights into how the biofilm evolved over time.

Nitrate levels in the RAS connected to the denitrification reactor dropped significantly. In contrast, nitrate levels in the control RAS increased continuously. The microbial community in the biofilm was dominated by Proteobacteria, Firmicutes, and Bacteroidetes. At 40 days, Acidovorax and Bacillus were the most abundant species. By 150 days, Clostridium and Desulfitobacterium became more prevalent. Other notable species included Dechloromonas, Pseudoxanthomonas, and Flavobacterium. The researchers isolated four PHBV-degrading bacterial strains. These included Acidovorax, Methylibium, Pseudoxanthomonas, and Dechloromonas. The results suggest that PHBV supports a diverse and dynamic microbial community.

The study suggests that PHBV can serve as an effective carbon source for nitrate removal in RAS. The denitrification reactor packed with PHBV significantly reduced nitrate levels compared to the control. The microbial community in the biofilm changed over time, indicating dynamic population shifts. At 40 days, Acidovorax and Bacillus were dominant, while Clostridium and Desulfitobacterium became more prevalent by 150 days. The researchers propose that these shifts reflect the adaptation of microbial populations to the PHBV environment. The isolated PHBV-degrading bacteria included Acidovorax, Methylibium, Pseudoxanthomonas, and Dechloromonas. These findings suggest that PHBV supports a functional denitrifying community. The results may inform the development of more sustainable RAS designs.