The Role of Biofilters in Aquaculture Systems

Effective water quality management is essential in aquaculture, where fish live in continuous contact with their aquatic environment. Since everything that enters the fish as feed exits as waste, maintaining clean water is crucial for fish health and welfare.

AKVA Group has focused on advancing biofilter technology to address these challenges, offering solutions like the Zero Water Concept (ZWC) to optimize water treatment.This need becomes even more critical in Recirculating Aquaculture Systems (RAS), where water exchange is minimized to conserve resources and enhance sustainability. 

Biofilters: A Key Component in AKVA’s Water Treatment Approach

Central to AKVA Group’s water treatment systems are biofilters—specialized compartments housing microscopic organisms that convert harmful waste products into non-toxic compounds. In AKVA’s Zero Water Concept (ZWC), biofilters play a dual role. The nitrifying biofilter facilitates the conversion of toxic ammonia into relatively harmless nitrate through nitrification. In the next stage, AKVA’s denitrifying biofilter removes the accumulated nitrate, transforming it into nitrogen gas (N2) in a process known as denitrification.

These two processes rely on distinct types of microbes. Nitrifying bacteria, known as autotrophs, grow slowly, require oxygen, and use CO2 as their carbon source. In contrast, denitrifying bacteria are fast-growing heterotrophs that thrive in oxygen-free environments and depend on organic carbon for growth. Together, these processes achieve biological nitrogen removal—a method long employed in wastewater treatment and adapted by AKVA Group for aquaculture.

Precision Control for Consistent Biofilter Performance

Managing biofilters in RAS involves more than just monitoring ammonia and nitrate levels. Water in RAS contains a variety of compounds, each influencing the microbial community within the biofilter. As Dutch microbiologist Baas Becking noted in 1934, “Everything is everywhere, but the environment selects.” This principle holds true today, as the environment within a biofilter determines which microbes thrive.

To ensure consistent water quality, AKVA Group emphasizes precision control. Even slight changes in water parameters can significantly impact biofilter performance. For instance, raising pH can increase ammonia toxicity while reducing the toxicity of hydrogen sulfide (H2S). Similarly, excess organic carbon from overfeeding promotes the growth of heterotrophic bacteria, which can outcompete nitrifiers and lead to oxygen depletion. In some cases, increased organic loading can shift the microbial process toward dissimilatory nitrate reduction to ammonia (DNRA), producing ammonia instead of nitrogen gas.

Advancing Biofilter Technology with Data-Driven Insights

Recognizing these complexities, AKVA Group is refining biofilter design to facilitate easier water and biofilm sampling. This approach enables more precise monitoring and control of microbial activity. Recent studies have shown that nitrifying bacteria constitute only up to 12% of the microbes found on biofilm carriers in various RAS facilities. This raises important questions: What functions do the remaining 88% serve? How do water quality parameters shape the microbial community? Can the microbiome be intentionally shaped to improve water quality? Can beneficial bacteria be encouraged to occupy the remaining microbial space?

To address these questions, AKVA Group needs to integrate data from microbiome analyses, water quality metrics, biofilter operation, and fish performance. This approach moves beyond basic monitoring, leveraging advancements in chemical and microbial analysis to optimize biofilter performance and overall system health.

Ongoing Developments in Biofilter Operation

Currently, most commercial water quality monitoring systems for RAS focus solely on chemical parameters, overlooking the critical role of microbial water quality. Since microbes drive water treatment, understanding their dynamics is important for future water quality models. In response, AKVA Group is optimizing biofilter backwashing protocols to prevent activity loss and off-flavor issues—demonstrating that biofilter optimization encompasses both design and operation.

By supporting the management of the microbial community, AKVA Group aims to enhance the role of the nitrifying biofilter from a simple water treatment component to a central element in RAS functionality.