NonBio: Non-biological ammonia removal

Description

Is a future without biofilters in RAS possible? The NonBio project explores whether recirculating aquaculture systems (RAS) can operate effectively without traditional biofilters, which rely on nitrifying bacteria to convert ammonia (TAN) into nitrate (Ebeling and Timmons 2012).

Today's RAS biofilters can be grouped into four categories (Lekang 2013), which differ in water flow and oxygen supply: flowthrough systems, bioreactors (moving/fixed bed), fluid bed/active sludge and granular filters/bead filters.

While these biofilters are technologically simple, low-cost, biologically effective, and have a biofilm shielding for pathogens, they come with notable drawbacks: long maturation periods, sensitivity to temperature and loading fluctuations, risk of harmful microbiota, and challenges in hygiene and automation (Navada, Gaumet et al. 2021).

Contrary to the RAS industry, the water and wastewater treatment sector has adopted other, non-biological methods in addition to the conventional biofiltration technologies (Lekang 2013, Lekang and Lekang 2013). These emerging non-biological ammonium removal technologies — including electrochemical, chemical, and physical methods or combinations thereof — offer promising alternatives to biofilters (Loh, Zaidi et al. 2022, Magen 2023, Singh Parmar 2023, Ben Asher, Gendel et al. 2024).

These solutions eliminate the need for biofilm maturation, potentially reduce nitrate accumulation, and enable better system automation and control. Early-stage developments in electrochemical applications show potential for ammonia removal without forming nitrite or nitrate, though field data remain limited (Ben‐Asher, Gendel et al. 2024).

However, replacing biofilters would impact RAS design, microbial ecosystems, and fish health. Additionally, some biofilters have additional positive effects, including degassing CO2 and removing fine solids. Thus, evaluating non-biological alternatives (NBA) requires careful assessment of operational costs, environmental effects, and overall system performance (Interdonato 2012), which the proposed NonBio project aims to provide.