Abstract
Recirculating aquaculture systems (RAS) are good candidates for the sustainable development of the aquaculture sector. A current limitation of RAS is the production and accumulation of nitrogenous waste, which could affect fish health. We investigated the potential of the anaerobic ammonia oxidation (anammox) process to treat marine wastewater from a cold-water RAS. We show that the marine anammox bacteria Candidatus Scalindua is a promising candidate. However, its activity was affected by unknown compounds in the RAS wastewater and/or the sub-optimum content of essential trace elements (TEs). Anammox activity dropped to 2% and 13% in NH4+ and NO2− removal, respectively, when NO3-rich RAS wastewater was used as a medium in the absence of TE supplementation. A TE supplementation was added to the RAS wastewater in a subsequent phase, and a recovery in anammox activity was shown (25% and 24% in NH4+ and NO2− removal, respectively). Future studies need to identify the unknown factor and determine the specific needs regarding TE for optimal RAS wastewater treatment by Candidatus Scalindua.
Highlights
The world population is expected to reach 9.7 billion by 2050 [1]
At the end of Phase 2, the removal efficiencies of NH4+ and NO2− were only 2% and 13%, respectively (HRT 2.4 h), and the total nitrogen (TN) removal rate was 0.09 g-TN L−1 day−1. These results clearly indicate that there was a negative effect of the recirculating aquaculture systems (RAS) wastewater and/or the absence of trace elements (TEs) on the activity of anammox bacteria
Scalindua rather than its relative abundance was affected by unknown compounds in the RAS wastewater and/or an imbalance in certain TEs
Summary
The world population is expected to reach 9.7 billion by 2050 [1]. there is an urgent need to increase nutritious and sustainable food production [2]. The production methods’ intensification has led to environmental concerns regarding, e.g., eutrophication, caused by the leakage of nutrients to the environment, especially in open-water systems [4] Closed containment systems such as recirculating aquaculture systems (RAS) allow for a high degree of water reuse as well as ensuring better control of the farming environment, resulting in reduced ecological impact [5,6,7]. NO3– can accumulate over time in an RAS and can reach concentrations of up to 100–1000 mg L−1 depending on the RAS design and management [9,10] Over time, such levels may negatively affect fish health and welfare if not appropriately managed through denitrification or regular water exchanges [11,12]. Ambient levels below 10 mg NO3−-N L−1 (freshwater) and 20 mg Parameter Value
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