Pilot-scale Recirculating Aquaculture Systems Research Articles

Influence of dietary phosphorus on orthophosphate accumulation in recirculating aquaculture systems with rainbow trout (Oncorhynchus mykiss)

Dietary phosphorus (P) levels affect the excretion of orthophosphate (PO4-P) from fish. Since most recirculating aquaculture systems (RAS) do not specifically remove PO4-P within the recirculating loop, dietary P levels may influence PO4-P concentrations in RAS water. A feeding trial was performed in freshwater RAS, aiming to determine the relationship between dietary P levels and PO4-P accumulation in RAS water, and to examine potential effects of dietary P levels on microbial activity and abundance in RAS water given that P is an essential mineral for all microorganisms. Three diets with 1.49% (HiP), 1.20% (MeP), and 0.89% (LoP) total P, respectively, were each fed to triplicate pilot-scale RAS with juvenile rainbow trout (Oncorhynchus mykiss) for five weeks, applying a daily feed loading of 1.67 kg feed/m3 make-up water. Digestible dietary P levels correlated significantly with the PO4-P concentrations in RAS water at the end of the trial, while no similar correlations with microbial abundance or activity were observed. Nitrate-N concentrations measured by the end of the trial matched predicted equilibrium concentrations. In contrast, measured PO4-P concentrations were approximately 40 – 50% lower than predicted regardless of diets, suggesting that PO4-P was likely utilized by RAS microbes. We therefore speculate whether lowering dietary P levels could become an effective tool for microbial management in RAS.

Evaluation of biofilter performance with alternative local biomedia in pilot scale recirculating aquaculture systems

Plastic is commonly used as biofilter media in recirculating aquaculture systems. Because plastic is relatively expensive and may erode and emit microplastics to the environment, efforts are being made to test and develop more sustainable materials. Five alternative locally available biofilter media were compared with commercial plastic media and evaluated in duplicate in 1 m3 two pilot scale Recirculation aquaculture system. Ammonium chloride and sodium nitrite were added to the systems for 4 weeks followed by stocking 20 kg of Nile tilapia in each system. Volumetric total ammonia nitrogen (TAN), nitrite and oxygen conversion rates were assessed for ten weeks. All biofilters with local media matured and reached full capacity after six weeks, while commercial plastic biomedia matured after seven weeks. This study found that the performance of commercial plastic biomedia was similar to performance of coconut shells in terms of volumetric TAN conversion rate (VTR), volumetric nitrite conversion rate (VNR) and volumetric oxygen conversion rate (VOCR). The highest VTR recorded in this study was 599 ± 15.8 g TAN/m3/d from coconut shells while the lowest was 343 ± 8.9 g TAN/m3/d from cattle horns. Biofilters with commercial plastic media had the highest VNR (704 ± 50.3 g NO2–N/m3/d) while media made of cattle horns was the lowest (457 ± 46.1 g NO2–N/m3/d). Biofilters containing coconut shells demonstrated the highest oxygen consumption around 3.0 g/m3/d and biofilters containing charcoal consumed less than 1.0 g/m3/d of oxygen. This study suggests that coconut shells can be used in place of plastic materials in simple recirculation aquaculture system biofiltration. This study also recommends further studies on comparing coconut shells with other biomedia and assessing its effects on water quality parameters and durability.

Trace elements, anions, and carbohydrates in the recirculating aquaculture system using woodchip denitrification, constructed wetland, and sand infiltration

Abstract A recirculating aquaculture system (RAS) aims to achieve fish production with negligible discharge into the environment. RASs have been applied for fish production in several countries, but nitrate removal is often a limiting factor for production increases. In this study, a pilot-scale RAS (10 tons of fish/year) was connected to a water treatment field which consisted of a denitrifying woodchip bioreactor (9 m × 14 m) filled with birch woodchips (Betula pendula), a constructed wetland (7.5 m × 6 m), and sand infiltration (16 m × 31 m) to achieve high water quality with low-maintenance treatment units. In the constructed wetland, a perennial common reed (Phragmites australis) was used in a well-drained soil for nutrient re-use. Concentrations of different elements, diluted anions, and selected hydrocarbons were monitored and quantified. Some Mn leaching occurred during the sand infiltration stage. However, Mn concentrations decreased towards the end of the experiment. Concentrations of total-Fe increased up to 2.75 mg L−1 and Mn up to 5 mg L−1 in the sand infiltration stage of the water treatment field, probably due to anoxic conditions and leaching of fine particles. This type of process design offers effective but low-maintenance treatment of circulating water.

Developing a robust and sensitive analytical method to detect off-flavor compounds in fish

In recirculating aquaculture systems (RAS), off-flavors that accumulate in fish muscle tissue can be problematic in terms of consumer acceptance and the reputation of farmed fish products. Although off-flavors are not toxic at low concentrations, they often give fish muscle earthy, muddy, or other unwanted flavors. Traditionally, muddy off-flavors caused by geosmin (GSM) and 2-methylisoborneol (MIB) have been detected, but a variety of other compounds and flavors have also been identified. In this study, a method based on solid phase micro extraction (SPME) coupled with gas chromatography and mass spectroscopy was developed to identify and quantify 14 off-flavor–inducing compounds in RAS–farmed fish. The selected off-flavors were quantified in circulating water and in fish from a pilot-scale RAS rearing rainbow trout (Oncorhynchus mykiss). The method showed high accuracy and precision with limits of detection and quantification at a low ng L−1 level. In this study, 13 compounds were found in the fish muscle which decreased in concentrations during the 15-day depuration period. This study showed that off-flavors in fish can also be induced by other compounds besides GSM and MIB. This emphasizes the need for sufficient off-flavor control in the RAS, but also the importance of an accurate and reliable analytical quantitation method.

Integrating Microbial Protein Production and Harvest Systems into Pilot-Scale Recirculating Aquaculture Systems for Sustainable Resource Recovery: Linking Nitrogen Recovery to Microbial Communities.

In aquaculture, it is important to raise the nitrogen recovery efficiency (NRE) to improve sustainability. To achieve this, recovery of microbial protein (RMP), instead of nitrification/denitrification in conventional wastewater treatment, is a promising approach whose microbiological mechanisms must be characterized. Here, periodic RMP was conducted in an in situ biofloc-based aquaculture system (IBAS) and a separating assimilation reactor-based recirculating aquaculture system (SRAS). Kinetic analysis indicated that a microbial biomass level of 3 g L-1 was optimal for inorganic N removal, and excess biomass was harvested to improve the NRE. Unlike the IBAS, the SRAS eliminated the fluctuation in water quality caused by the RMP. Periodic RMP significantly increased the NRE to 44-57% by promoting the filamentous bacterium Herpetosiphon and suppressing anaerobic denitrifiers. Aerobic chemoheterotrophy was the main microbial metabolic process for energy. After RMP, nitrate reductase-encoded functional genes (napA and narG) significantly decreased, while nitrite reductase-encoded functional genes, especially nirK, significantly increased. Co-occurrence networks analysis indicated that the cooperation and competition among organic matter degraders, filamentous bacteria, nitrifiers, and denitrifiers determined the microbial protein yield. These results provide fundamental insights into the influence of the RMP on microbial communities and functions, which is important for realizing sustainable aquaculture.

Changes in rearing water microbiomes in RAS induced by membrane filtration alters the hindgut microbiomes of Atlantic salmon (Salmo salar) parr

An important step in water treatment in recirculating aquaculture systems (RAS) is the removal of particulate organic matter. While commonly applied treatment technologies remove most of the particles, fine particulate organic matter typically accumulate in RAS, and serve as substrate for heterotrophic bacteria in the system. Membrane ultrafiltration has been shown to reduce the concentrations of total organic carbon and to counteract blooms of opportunistic bacteria in periods with high organic loading. The potential influence of such opportunistic bacteria on the fish microbiomes and fish welfare is poorly understood. In this study, we investigated the effects of high organic loading on the water and hindgut microbiomes in RAS with Atlantic salmon parr. Two pilot-scale RAS, one with membrane ultrafiltration of a 10–15% side-stream (mRAS), and one without (cRAS), were operated in periods with low and high organic loadings, and the water and hindgut microbiomes were characterized by Illumina sequencing of 16S rDNA amplicons. At the end of the experiment, after a period of high organic loading, two OTUs representing Mycobacterium and Spartobacteria dominated the water microbiomes in cRAS, with relative abundances as high as 24 and 17%, respectively. In the mRAS water they were rare (relative abundances of 1.9 and 0.1%). The membrane ultrafiltration stabilized the water microbiota and efficiently prevented the growth of these bacterial populations in RAS. The parr hindgut microbiomes were generally highly distinct from the RAS water microbiomes and were dominated by the bacterial phyla Bacilli and Firmicutes. Furthermore, an OTU probably representing Carnobacterium inhibens, originally isolated from the gut of adult salmon, was highly abundant in the gut microbiomes, with relative abundances reaching over 30%. However, for the cRAS fish after a period with high organic loading, the relative abundance of this Carnobacterium OTU was reduced, and an increased similarity between the gut and the water microbiomes was observed. The Mycobacterium and Spartobacteria OTUs that were abundant in the cRAS water were also abundant in the cRAS hindgut samples. This indicates a direct influence of the water microbiomes on the gut microbiomes, and that high organic loading in the cRAS resulted in growth of opportunistic bacteria that were able to colonize the fish gut. The present study shows that membrane filtration is an applicable strategy to counteract growth of opportunistic bacteria in RAS and to promote positive fish – microbe interactions.

Foam fractionation and ozonation in freshwater recirculation aquaculture systems

Foam fractionation is often considered an ineffective way of removing organic matter from freshwater due to the low surface tension of the water. There is, however, a lack of studies testing foam fractionation efficiency in replicated freshwater recirculating aquaculture systems (RAS). Foam fractionation can be applied with or without ozone. Ozone is a strong oxidiser previously shown to improve water quality and protein skimmer efficiency. To test the efficiency of foam fractionation and ozonation (20 g O3 kg-1 feed) separately and in combination in freshwater RAS, a two-by-two factorial trial was conducted with each main factor at two levels (applied or not applied). Each treatment combination was carried out in triplicates using 12 replicated pilot scale RAS stocked with juvenile rainbow trout (Oncorhynchus mykiss) and operated at a feed loading of 1.66 kg feed m-3 make-up water. The trial lasted 8 weeks and samples were obtained once a week. Ozone applied by itself significantly reduced the number of particles (83%), bacterial activity (48%) and particulate BOD5 (5-days biochemical oxygen demand; 54%), and increased ultra violet transmittance (UVT; 43%) compared to the untreated control group. Foam fractionation by itself lead to significant reductions in particle numbers and volume (58% and 62%, respectively), turbidity (62%), bacterial activity (54%) and total BOD5 (51%). A combination of both treatments resulted in a significant additional improvement of important water quality variables, including a 75% reduction in total BOD5, 79% reduction in turbidity, 89% reduction in particle numbers and 90% reduction in bacterial activity compared to the control. The removal efficiencies were within the same range as those observed in previous studies conducted with foam fractionators in saltwater systems (with or without ozone), corroborating that foam fractionation may become a useful tool for controlling organic matter build-up and bacterial loads in freshwater RAS.

Low-technology recirculating aquaculture system integrating milkfish Chanos chanos, sea cucumber Holothuria scabra and sea purslane Sesuvium portulacastrum

Closed recirculation aquaculture systems (RAS) in combination with integrated multi-trophic aquaculture (IMTA) are considered best management practices, but high material costs and difficult maintenance still hinder their implementation, especially in developing countries and the tropics. Few case studies of such systems with tropical species exist. For the first time, an extremely low-budget system was tested combining the halophyte sea purslane Sesuvium portulacastrum and a detritivore, sandfish Holothuria scabra, with finfish milkfish Chanos chanos over 8 wk on Zanzibar, Tanzania. In a 2 m3 RAS, milkfish and sea purslane showed good growth, producing an average (±SD) of 1147 ± 79 g fish and 1261 ± 95 g plant biomass, while sea cucumber growth was variable at 92 ± 68 g. The system operated without filter units and did not discharge any solid or dissolved waste. Water quality remained tolerable and ammonia levels were reliably decreased to <1 mg l-1. A NO2- peak occurred within the first 30 d, indicating good biofilter performance of the different system compartments. Changes in dissolved inorganic nitrogen (DIN) species support the notion that the sea cucumber tank was the main site of nitrification, while the hydroponic halophyte tank acted as a net sink of NO3-. A nitrogen budget accounted for 63.7 ± 5.3% of the nitrogen added to the system as fish feed. Increasing the plant to fish biomass ratio to 5:1 would fully treat the DIN load. The experiment provides proof-of-concept of a simple pilot-scale RAS, integrating tropical species at 3 trophic levels.

Effects of reduced organic matter loading through membrane filtration on the microbial community dynamics in recirculating aquaculture systems (RAS) with Atlantic salmon parr (Salmo salar)

A key challenge in recirculating aquaculture systems (RAS) is the accumulation of particulate organic matter, especially the fine and colloidal fraction due to low removal efficiency of today's technology. The supply of organic matter is typically the limiting resource determining the carrying capacity (CC) of heterotrophic bacteria in the system. An appropriate and stable CC is proposed as a strategy for an optimal microbial environment in RAS with less blooms of opportunistic bacteria and more stable community dynamics. In this study, we investigated the effects of including a membrane for ultrafiltration in the RAS water treatment loop (treating 10–15% of the total water flow) to reduce the amount of fine and colloidal organic matter. Atlantic salmon parr (Salmo salar) were reared in two pilot-scale RAS (mRAS: membrane, cRAS: conventional). To evaluate the bacterial dynamics with and without membrane filtration at different organic loadings, the water exchange rates of the systems were manipulated equally to create periods with high and low loading of organic matter. The results showed that in the mRAS water, the level of organic matter was more stable throughout the experiment for the changing organic matter loadings. As a consequence, water in mRAS had higher microbial diversity, lower and shorter bacterial blooms and generally lower bacterial densities than in cRAS. All variables indicate a better microbial environment in the water of the system with membrane filtration. Also, the physicochemical water quality was better in mRAS in terms of lower turbidity and particulate organic matter (POC), and slightly lower concentrations of total ammonia nitrogen (TAN). The composition of the microbial communities was significantly different between the two systems, and temporal variations in the community dynamics were observed in both systems during the periods with different organic loadings. At high organic loading, the genus Mycobacterium had high relative abundance in the cRAS water (up to 0.25) compared to mRAS (0.01–0.03). The fish in mRAS were significantly bigger (14%) than fish in cRAS at the end of the experiment, however it is hard to conclude whether the better growth in mRAS was due to higher temperatures (caused by membrane operation) or better water quality, as it was probably a combination of both. We can conclude that membrane filtration gave more stable and better physicochemical and microbial water quality, which will reduce the probability for microbially related accidents in RAS.

UV irradiation and micro filtration effects on micro particle development and microbial water quality in recirculation aquaculture systems

Recent studies have focused on micro particle build-up in recirculation aquaculture systems (RAS), and a correlation between micro particles and microbial activity has been shown. This study evaluated how micro particle build-up and microbial activity are affected by UV irradiation and micro filtration. Using 12 identical pilot scale RAS stocked with rainbow trout (Oncorhynchus mykiss), a two-factor factorial experiment was carried out testing in triplicate systems the effect of UV irradiation (systems with or without) in combination with cartridge filtration (1 or 200 μm pore size) on selected water quality parameters. The trial ran for 13 weeks. Water samples were obtained once a week, and the number and size distribution of micro particles was analysed. Microbial activity was derived from the hydrogen peroxide degradation rate, and concentrations of total and dissolved organic matter were measured as chemical oxygen demand (COD).Overall, both UV and cartridge filtration had significant effect (<0.05) on micro particle distribution and microbial activity in the systems. By the end of the trial, a two-way Anova showed that UV treated RAS, independently of cartridge filtration pore size, were significantly (p < 0.05) lower in micro particle numbers (74% reduction), micro particle surface area (54% reduction), and dissolved COD (34% reduction) compared to systems without UV. Similarly, microbial activity was reduced up to 89% independently of cartridge filtration. UV thus appeared to reduce micro particle numbers by destroying bacteria. In addition, the effect of UV on dissolved COD suggested a possible feedback mechanism between microbial activity and substrate release in the systems. For micro filtration, a 1 vs. 200 μm pore size significantly reduced the number of micro particles (by 50%), micro particle volume (by 83%), and micro particle surface area (by 73%) independently of UV treatment. This was accompanied by a significant reduction in particulate COD (80%) and microbial activity (approximately 54% reduction independent of the use of UV). Hence, cartridge filtration appeared to reduce a build-up of micro particle by directly removing bacteria and bacteria substrate. In conclusion the study sustains that combining UV and particle removal is a potential viable tool for managing microbial water quality in RAS.

Reducing environmental impact of recirculating aquaculture systems by introducing a novel microaerophilic assimilation reactor: Modeling and proof of concept

Use of recirculating aquaculture systems (RAS) to grow fish is on the rise. Fish feed typically contains 25–60% protein and is the only significant input in RAS. Fish recover 20–30% of the applied feed as biomass, and the unassimilated nitrogen is released into the water, mainly as ammonia, which is toxic to fish. Nitrification is the most common treatment practice, converting ammonia to the less toxic nitrate, and nitrogen removal is achieved by either water exchange or denitrification. The aim of this study was to develop and test a novel approach to remove nitrogen based on a microaerophilic assimilation side-reactor. In the suggested system, fish solid waste and dissolved nitrogen are assimilated into protein-rich microbial biomass, which has the potential to partially offset fish feed input. Initially, a theoretical model based on the system’s nitrogen mass balance was established. Then, an intensive pilot-scale RAS was constructed, growing ∼50 kg fish/m3. The system consisted of a fish tank, solids filter, and microaerophilic assimilation reactor based on activated sludge treatment. Intrinsic solid waste and wheat-flour waste were used as carbon source. After a trial run of about 2.5 months, the RAS was tested for 101 days. Average total ammonia nitrogen, nitrite, and nitrate removal were 89.1, 69.4 and 100%, respectively. Of the introduced solids, over 82% were lost as carbon dioxide by respiration, 11.7% were recovered as microbial biomass and 6.5% as fish biomass, and only 0.6% remained in the water. Biomass organic content was similar to aquafeed and nitrogen content was equivalent to 40% crude protein. Daily energy demand for the system’s designed capacity of 80 kg/m3 would result in a low energy consumption of 7.72 kW h/kg fish. Overall, a novel concept for sustainable production in intensive aquaculture was developed and successfully demonstrated in a pilot-scale RAS.

Microbial dynamics in RAS water: Effects of adding acetate as a biodegradable carbon-source

This study evaluated the effect of an abrupt increase in easily biodegradable carbon (acetate) on bacterial activity and abundance in the water of recirculating aquaculture systems (RAS). The study included a batch experiment with RAS water only, and an experiment at system level where twelve pilot scale RAS were used. The batch experiment was made to test how acetate concentration would influence the microbial state in RAS water. Further, we wanted to observe if the selected microbial analysis tools would be able to detect these changes. The second experiment was carried out in twelve identical and independent RAS that had been operated under constant loading conditions (1.6 kg/m3 make-up water) for five months prior to the trial. The twelve RAS were divided into four treatment groups in triplicates: i) control with submerged biofilter (Ctrl + bf); ii) control without submerged biofilter (Ctrl-bf); iii) acetate addition in RAS with submerged biofilter (Ac + bf); and iv) acetate addition in RAS without submerged biofilter (Ac-bf). The biofilter media from the groups without submerged biofilter (Ac-bf and Ctrl-bf) was removed just 5 h prior to the start of the trial. The two acetate treatment groups (Ac + bf and Ac-bf) were spiked with 40 mg/L of acetate three consecutive times (0, 24 and 48 h). Consumption of acetate, bacterial abundance and bacterial activity were followed for 72 h after the first acetate spike for both experiments. Bacterial activity was quantified by BactiQuant® and hydrogen peroxide (HP) degradation assay. Bacterial abundance was assessed by quantifying micro-particles and free-living bacteria. In the batch experiment we observed a significant increase in bacterial activity proportional to the amount of acetate added, and a corresponding significant increase in microparticles (1–3 μm). In the pilot scale RAS experiment, the acetate addition in RAS with submerged biofilter did not cause an increase in bacterial activity, or in the number of microparticles in the water phase but a significant increase in bacterial activity and number of microparticles were observed in the RAS without submerged biofilter (Ac-bf). These changes were particularly pronounced shortly after each acetate spike.In RAS with submerged biofilters, the acetate was presumably consumed primarily by the bacterial community within the biofilm, and consequently, only minor changes were observed in densities of free-living bacteria in the water phase. The results of the study suggest that heterotrophic bacteria in the submerged biofilter have a high capacity to handle fluctuation of organic matter loading in RAS, thereby stabilizing the abundance and activity of bacteria in the water column.

Evaluation of membrane filtration and UV irradiation to control bacterial loads in recirculation aquaculture systems

Ultraviolet (UV) irradiation is commonly used to control pathogen loads in recirculation aquaculture systems (RAS), although these micro-organisms can be shielded by particles in the water, and some species tolerate very high UV doses. The objective of this study was to evaluate membrane filtration (MF) as an alternative, or complimentary, treatment to UV irradiation for pathogen control in RAS, as well as examine the operation and cost of each treatment. In a pilot-scale RAS, both MF and UV were used to treat wastewater for 30 days and water samples were collected biweekly and analysed for culturable bacteria, suspended solids, UV transmittance and other parameters. Bacterial control efficiencies were similar between both MF and UV treatments, which removed 99% of total bacteria and 98% of heterotrophic bacteria, respectively. Surface fouling was negligible for the UV while MF required biweekly cleaning to maintain operation. However, MF had the additional benefit of removing 96% of suspended solids, which resulted in increased UV transmittance. Capital and operating costs of MF were similar to UV, but only when MF treated a fraction of the wastewater compared with UV. We conclude that MF represents a potential complimentary technology to enhance UV irradiation, especially to minimise pathogens in RAS that are shielded by particles or tolerate UV.

Changes in microbial water quality in RAS following altered feed loading

Intensive recirculating aquaculture systems (RAS) with its hyper-eutrophic water offer ideal conditions for bacterial growth, abundance and activity, potentially affecting fish and system performance. Feed composition and feed loading in particular will have significant impact on organic and inorganic nutrients available for microbial growth in RAS. How these nutrient inputs affect and regulate bacteria in RAS water is, however, unclear. To investigate this relationship and the associated water quality dynamics, the effects of altered feed loading on microbial water quality in RAS was studied.The study included six independent, identical pilot-scale RAS, each with a total volume of 1.7 m3 (make-up water: 80 L/day) stocked with juvenile rainbow trout (Oncorhynchus mykiss). All systems had been operating with constant and identical feed loading of 3.13 kg feed/m3 make-up water for a period of three months before the experiment was initiated. Three controlled levels of feed loading where established in duplicates: no feed (0 kg feed/m3), unchanged feeding (3.13 kg feed/m3), and doubled feeding (6.25 kg feed/m3). The experimental period was seven weeks, where microbial and chemical water quality was monitored weekly. Bacterial activity was measured using Bactiquant®, and microbial hydrogen peroxide degradation. Bacterial abundance was quantified by flow cytometry, and water quality parameters by standardized methods The study showed that water quality as well as bacterial activity and abundance were affected by the changes in feed loading. The microbial water quality parameters, however, did not respond to feed loading changes as quickly and straightforward as the physicochemical parameters such as nitrate, chemical oxygen demand and biological oxygen demand. It was presumed that the fixed bed biofilter suppressed microbial response in the water phase. Hydrogen peroxide degradation assay proved to have considerable potential for assessing overall bacterial load in RAS water although further adjustments and standardization procedures are required.

Ozonation control and effects of ozone on water quality in recirculating aquaculture systems

To address the undesired effect of chemotherapeutants in aquaculture, ozone has been suggested as an alternative to improve water quality. To ensure safe and robust treatment, it is vital to define the ozone demand and ozone kinetics of the specific water matrix to avoid ozone overdose. Different ozone dosages were applied to water in freshwater recirculating aquaculture systems (RAS). Experiments were performed to investigate ozone kinetics and demand, and to evaluate the effects on the water quality, particularly in relation to fluorescent organic matter. This study aimed at predicting a suitable ozone dosage for water treatment based on daily ozone demand via laboratory studies. These ozone dosages will be eventually applied and maintained at these levels in pilot-scale RAS to verify predictions. Selected water quality parameters were measured, including natural fluorescence and organic compound concentration changes during ozonation. Ozone reactions were described by first order kinetics. Organic matter, assessed as chemical oxygen demand and fluorescence, decreased by 25% (low O3), 30% (middle O3) and 53% (high O3), while water transmittance improved by 15% over an 8-day period. No fish mortality was observed. Overall, this study confirms that ozone can improve RAS water quality, provides a better understanding of the ozone decay mechanisms that can be used to define further safe ozone treatment margins, and that fluorescence could be used as a monitoring tool to control ozone. This study might be used as a tool to design ozone systems for full-scale RAS by analysing water sample from the specific RAS in the laboratory.

Particle surface area and bacterial activity in recirculating aquaculture systems

Suspended particles in recirculating aquaculture systems (RAS) provide surface area that can be colonized by bacteria. More particles accumulate as the intensity of recirculation increases thus potentially increasing the bacterial carrying capacity of the systems. Applying a recent, rapid, culture-independent fluorometric detection method (Bactiquant®) for measuring bacterial activity, the current study explored the relationship between total particle surface area (TSA, derived from the size distribution of particles >5μm) and bacterial activity in freshwater RAS operated at increasing intensity of recirculation (feed loading from 0.043 to 3.13kgfeedm−3 make-up water). Four independent sets of water samples from different systems were analyzed and compared including samples from: (i) two individual constructed wetlands treating the effluent system water from two commercial, freshwater rainbow trout (Oncorhynchus mykiss) farms of different recirculation intensity; (ii) an 8.5m3 pilot scale RAS; and (iii) twelve identical, 1.7m3 pilot scale RAS assigned one of four micro-screen treatments (no micro-screen, 100, 60, or 20μm mesh size micro-screens) in triplicate. There was a strong, positive, linear correlation (p<0.05) between TSA and bacterial activity in all systems with low to moderate recirculation intensity (i.e. feed loading ≤1kgfeedm−3 make-up water). However, the relationship apparently ceased to exist in the systems with highest recirculation intensity (feed loading 3.13kg feedm−3 make-up water; corresponding to 0.32m3 make-upwaterkg−1 feed). This was likely due to the accumulation of dissolved nutrients sustaining free-living bacterial populations, and/or accumulation of suspended colloids and fine particles less than 5μm in diameter, which were not characterized in the study but may provide significant surface area. Hence, the study substantiates that particles in RAS provide surface area supporting bacterial activity, and that particles play a key role in controlling the bacterial carrying capacity at least in less intensive RAS. Applying fast, culture-independent techniques for determining bacterial activity might provide a means for future monitoring and assessment of microbial water quality in aquaculture farming systems.

Integration of energy audits in the Life Cycle Assessment methodology to improve the environmental performance assessment of Recirculating Aquaculture Systems

In Recirculating Aquaculture Systems (RAS), water is continuously treated and recirculated as opposed to being discharged untreated into the environment as in other type of fish production systems; the design and production parameters will determine the overall energy consumption. This energy-intensive nature hampers their sustainability and cost-effectiveness. This paper proposes a combination of two methods (i.e. Life Cycle Assessment (LCA) with energy audits) to: improve environmental performance of RAS, identify energy consumption and thus, its environmental and monetary effects in order to seek cost reduction. The proposed methodology was proved with a case study focused in a pilot-scale RAS unit used in codfish (Gadus morhua) production, located in the Basque coastal area (northern Spain). Feed and juvenile production/transportation, oxygen transportation and energy consumed during the whole experiment were considered as inputs for the assessment. Energy consumption was measured both continuously by an energy meter embedded in the RAS unit as well as with a portable energy analyzer to measure each of the energy-consuming devices independently. Although the system required an average of 29.40 kWh/kg fish for successful system operation, the energy consumption varied by season presenting maximum and minimum periods of 40.57 and 18.43 kWh/kg fish, respectively. Main consumers included the heat pump, followed by the main and secondary pumps, respectively. Energy audit's results show the success in identifying the devices that consumed the largest amount of energy, and recorded data served to feed the Life Cycle Inventory and perform a more complete and precise LCA. Fossil fuel based on-farm electricity for the on-growing of fish was shown to be the most environmentally unfriendly input; it was the major impact producer in the assessed impact categories. It showed a temporal variability depending on the water temperature, which resulted to be the main factor linked to the energy use. This aided performing a precise assessment including system-specific scenarios. The combination of LCA and on-farm energy audit represents a useful tool to secure a more complete assessment with a periodic assessment to design a less energy intensive, profitable and sustainable system; likewise, it increases the speed and transparency of governance and decision-making, taking into account the time-based fluctuation of the energy consumption throughout the production cycle.

Synergistic Effects of Micro-electrolysis-Photocatalysis on Water Treatment and Fish Performance in Saline Recirculating Aquaculture System

A new physico-chemical process for TAN (total ammonia nitrogen) removal and disinfection is introduced in saline recirculating aquaculture system (RAS), in which the biofilter is replaced with an integrated electrolysis cell and an activated carbon filter. The electrolysis cell which is based on micro current electrolysis combined with UV-light was self-designed. After the fundamental research, a small pilot scale RAS was operated for 30 days to verify the technical feasibility. The system was stocked by 42 GIFT tilapia (Oreochromis niloticus) fish with the rearing density of 13 kg/m3. During the experiments, the TAN concentration remained below 1.0 mg/L. The nitrite concentration was lower than 0.2 mg/L and the nitrate concentration had increased continuously to 12.79 mg/L at the end. Furthermore, the concentration of residual chlorine in culture ponds remained below 0.3 mg/L, ORP maintained slight fluctuations in the range of 190~240 mV, and pH of the water showed the downtrend. Tilapia weight increased constantly to 339.3 ± 10 g. For disinfection, the active chlorine generated by electrochemical treatment caused Escherichia coli inactivation. Enzyme activity assay indicated that the activity of glutamate dehydrogenase, carbonic anhydrase and glutamic pyruvic transaminase increased within the normal range. The preliminary feasibility was verified by using this physico-chemical technology in the RAS.

Alternative prophylaxis/disinfection in aquaculture - Adaptable stress induced by peracetic acid at low concentration and its application strategy in RAS

The application of peracetic acid (PAA) at low concentrations has been proven to be a broad-functioning and eco-friendly prophylaxis/disinfection method against various fish pathogens. However, there is lack of knowledge on how to apply PAA in a recirculating aquaculture system (RAS), and whether the application of PAA at low concentration can affect fish welfare. In the present study, PAA was applied in a pilot-scale carp (Cyprinus carpio) RAS (comprised of a fish culture tank of 1m3, a reservoir tank of 600L and a filter complex of 400L) every 3 or 4days for 5weeks, and the stress response of fish was monitored during every second PAA application by measuring cortisol in water. Results showed that the increase of water cortisol became less pronounced and the decrease of water cortisol occurred earlier after repeated applications of PAA, which indicates an adaptation of the stress response to PAA in the carp. Moreover, the mathematic model showed that the equal distribution of PAA in RAS was a slow progress, which depended on tanks size and flow rate. To avoid potential harm to the biofilter in RAS during PAA application, it's suggested that PAA should be applied only to the fish culture tank at a reduced flow rate. Statement of relevanceFish welfare becomes more and more important in aquaculture. However, there is a lack of knowledge if routine prophylaxis/disinfectant might affect fish welfare. In the present study, we tested how fish responded to repeated applications of peracetic acid (PAA) in a pilot-scale recirculating aquaculture system (RAS) via measurement of cortisol in water. The results showed that fishes reduced their stress during subsequent PAA application, indicating adaptation of fish to repeated prophylaxis/disinfection with PAA. Moreover, we established a model and measured the PAA concentration onsite to investigate the distribution of PAA in RAS. We found out that by simply adding PAA only to the fish culture tank with a reduced flow rate can avoid the potential harm on the biofilter. Findings from the current study provide insights that may prove of benefit to future treatment based studies.

Land-based growth of Atlantic salmon (Salmo salar) and consumers’ acceptance

Atlantic salmon (Salmo salar) is currently the highest valued species grown in Europe. The industry has been on the frontline of public concerns regarding sustainability which has increased the use of recirculating aquaculture systems (RAS). Salmon has changed from a luxury product to global commodity. Nevertheless, food products need to meet consumers demand for the industry to be successful. Descriptive sensory tests present a sophisticated tool for the comparison of product prototypes to understand consumer responses in relation to sensory attributes. Aquaculture is being promoted in the Basque region with the aim of creating a sustainable and complementary economic activity to the fishing and seafood sectors. Here, RAS and salmon have been prioritized as a potential technology and species respectively. Both salmon's growth and a hedonic evaluation of the final product's consumer acceptance and purchasing intention were studied. One thousand five hundred salmon individuals were grown for 497 days at two different thermal regimes in two pilot-scale RAS units using partial reuse water recirculation systems. Growth rates were significantly different for both temperature regimes during the second summer season; some compensatory growth patterns were observed that followed the timing of the natural thermal regime. No significant differences were observed at sensorial level between fillet samples from the present study and salmon from Denmark. Consumer's high level of acceptance and positive product purchasing intention reflect the possibility of locally marketing RAS grown salmon. This study refers to the first technical attempt at salmon in land-based aquaculture systems in northern Spain.