Efficient water treatment achieved in recirculating aquaculture system using woodchip denitrification and slow sand filtration.

For a recirculating aquaculture system (RAS), a passive water treatment system was designed for efficient discharge nutrient removal and water reuse in RAS production. Denitrification in a woodchip bioreactor filled with birch wood (Betula pendula) followed by sand filtration was introduced into a side-loop of an experimental RAS rearing rainbow trout (Oncorhynchus mykiss). Denitrification efficiency remained high (96%) throughout the experiment and reached a nitrogen removal rate of 15 g NO3-N m-3 per day. Sand filtration was used to remove dissolved and particulate matter and improve water quality before being returned to water circulation. To ensure the absence of harmful substances in the system, heavy metals were quantified. Additionally, off-flavor-inducing compounds were quantified in the circulating water and in fish flesh. Significantly higher concentrations of geosmin (GSM) (p<0.05) were observed in the controls compared to side-looped systems, but a similar effect was not observed in the case of 2-methylisoborneol (MIB). Among heavy metals, concentrations of Co (30 µg L-1), Ni (40 µg L-1), and Pb (140 µg L-1) decreased to below 10 µg L-1 in the side-loop water after the start-up of the system. Only low concentrations of Cu (5-30 µg L-1) were found in the rearing tank water, in both the side-loop and controls. The results indicated that this type of process design is suitable for safely producing fish of high quality.

Solids management in freshwater-recirculating aquaculture systems: Effectivity of inorganic and organic coagulants and the impact of operating parameters.

Coagulants are widely used for solids (uneaten food, faeces, etc.) management in recirculating aquaculture systems (RAS), but no recent research has been performed on the effectiveness of different coagulants in treatment of aquaculture sludge. This study examined the effectivity of selected inorganic (polyaluminium chloride, PAC) and organic products (polyamine- and starch-based) as coagulant agents for solids management in RAS. Reductions in residual concentrations of total phosphorus (tot-P), phosphate­phosphorus (PO4-P), suspended solids (SS) total nitrogen (tot-N), nitrate­nitrogen (NO3-N), ammonium­nitrogen (NH4-N), aluminium (Al) and chemical oxygen demand (COD) in reject water were determined. The effect of process parameters (coagulant type, dose, mixing and sedimentation time) on sludge treatment was also evaluated. The PAC products tested were most effective at concentrating pollutants (Tot-P, PO4-P, SS, COD) in RAS sludge into the solid phase. The organic products tested, especially a high-molecular-weight polyamine product (pAmine1), achieved good performance and can be considered a valid alternative to inorganic salts. At optimum dose, PAC (dose 32 mg/L) and pAmine1 (dose 15 mg/L) removed, respectively, 99.4% and 82.8% of turbidity, 98.2% and 65.4% of PO4-P and 97.7% and 73.6% of SS. The mixing time applied in flocculation and the time allowed for sedimentation had significant effects on coagulant performance, with the organic coagulants being most affected. Flocculation times of 5-15 min and sedimentation times of 15-60 min showed good results and can be used as a starting point in process optimisation with both inorganic and organic coagulants. The use of coagulants for treatment of RAS sludge enhances flock formation and improves particle settling characteristics, substantially decreasing nutrient, organics and solids concentration in reject water.

A comparison of photolytic, photochemical and photocatalytic processes for disinfection of recirculation aquaculture systems (RAS) streams.

The development of technologically advanced recirculation aquaculture systems (RAS) implies the reuse of water in a high recirculation rate (>90%). One of the most important phases for water management in RAS involves water disinfection in order to avoid proliferation of potential pathogens and related fish diseases. Accordingly, different approaches have been assessed in this study by performing a comparison of photolytic (UV-LEDs) at different wavelengths (λ = 262, 268 and 262 + 268 nm), photochemical (UV-LEDs/H2O2, UV-LEDs/HSO5- and UV-LEDs/S2O82-) and photocatalytic (TiO2/SiO2/UV-LEDs and ZnO/SiO2/UV-LEDs) processes for the disinfection of water in RAS streams. Different laboratory tests were performed in batch scale with real RAS stream water and naturally occurring bacteria (Aeromonas hydrophyla and Citrobacter gillenii) as target microorganisms. Regarding photolytic processes, higher inactivation rates were obtained by combining λ262+268 in front of single wavelengths. Photochemical processes showed higher efficiencies by comparison with a single UV-C process, especially at 10 mg L-1 of initial oxidant dose. The inactivation kinetic rate constant was improved in the range of 15-38%, with major efficiency for UV/H2O2 âˆ¼ UV/HSO5- > UV/S2O82-. According to photocatalytic tests, higher efficiencies were obtained by improving the inactivation kinetic rate constant up to 55% in comparison with a single UV-C process. Preliminary cost estimation was conducted for all tested disinfection methods. Those results suggest the potential application of UV-LEDs as promoter of different photochemical and photocatalytic processes, which are able to enhance disinfection in particular cases, such as the aquaculture industry.

Water quality in recirculating aquaculture system using woodchip denitrification and slow sand filtration.

In recirculating aquaculture system (RAS), ammonium excreted by the fish is typically transformed to less toxic nitrate by microbial activity in bioreactors. However, nitrate-nitrogen load can be harmful for the receiving water body when released from the RAS facility. A new type of water treatment system for a RAS was designed, including a passive woodchip denitrification followed by a sand filtration introduced into a side-loop of an experimental RAS, rearing rainbow trout (Oncorhynchus mykiss). In the process, woodchips acted as a carbon source for the denitrification, aiming at a simultaneous nitrogen removal and reduction of water consumption while sand filtration was used to remove organic matter and recondition the circulating water. A variety of chemical analyses and toxicological tests were performed to study the suitability of the process and to ensure the absence of harmful or toxic substances in the system. The results did not show increased toxicity, and no increased mortality was reported for the raised species. After the start-up of the system, the concentrations of fatty acids (e.g., hexadecanoic acid

The Fate of Bacteriophages in Recirculating Aquaculture Systems (RAS)-Towards Developing Phage Therapy for RAS.

Aquaculture production has increased tremendously during the last decades, and new techniques have been developed, e.g., recirculating aquaculture systems (RAS). In RAS, the majority of water volume is circulated via mechanical and biological filters and reused in the tanks. However, the prevention and treatment of diseases in these systems are challenging, as the pathogens spread throughout the system, and the addition of chemicals and antibiotics disrupts the microbiome of the biofilters. The increasing antibiotic resistance has made phage therapy a relevant alternative for antibiotics in food production. Indeed, as host-specific and self-replicating agent they might be optimal for targeted pathogen eradication in RAS. We tested the survival and spread of Flavobacterium columnare -infecting phage FCL-2 in recirculating aquaculture fish farm with rainbow trout (Oncorhynchus mykiss) in a fully controlled study. After a single addition, phage persisted in water samples collected from tank, fixed bed, moving bed, and aeration unit up to 14 days, and in the water of rearing tanks, rainbow trout mucus, and bioreactor carrier media from the fixed and moving bed biofilters for 21 days. Furthermore, phage adsorbed preferentially to moving bed carrier media, which contained biofilm attached and from which higher phage numbers were recovered. This study shows phages as a potent strategy for maintaining biosecurity in RAS systems.

The efficacy of two immunostimulants against Flavobacterium columnare infection in juvenile rainbow trout (Oncorhynchus mykiss).

Bacterium Flavobacterium columnare is the causative agent of columnaris disease in many wild and farmed fish species. Immunostimulants are used with success in aquaculture against many pathogens, but the ability to improve innate resistance to columnaris disease has not been studied. Fingerling rainbow trout were treated with two immunostimulants, yeast beta-glucan and beta-hydroxy-beta-methylbutyrate (HMB). Selected innate immune function parameters, the production of reactive oxygen species (ROS) by whole blood and by isolated head kidney leukocytes, plasma lysozyme activity and complement bacteriolytic activity, were determined to assess the immune status of fish. The fish were then bath challenged with virulent F. columnare bacteria, and the mortality of fish was recorded. Given orally both stimulants raised the levels of immune function parameters, but did not improve survival in challenge at any concentration of the stimulants used. Intra peritoneal injection of beta-glucan increased parameter values several fold, but no beneficial effect of injected glucan on survival was noted. As a control, antibiotic medication administered prior to and during the challenge infection prevented the mortality. Innate immune mechanisms, even when induced to high levels with immunostimulants, as evidenced here, were not able to increase resistance against F. columnare. This may be connected to the external character of the infection. The results from the treatments with beta-glucan and HMB suggest that there is little prospect of preventing columnaris disease by means of immunostimulants in early life stage of rainbow trout. However, the efficacy of other immune stimulants remains open.