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The aquaculture industry is growing fast but facing two major challenges: a shortage of suitable locations for growth and the need to reduce environmental impacts. One solution for both these challenges is inland production through recirculating aquaculture systems (RAS). The RAS technique is rather new, and several practical issues need to be solved. In this study, an experimental platform, consisting of ten individual RAS units, was built for small-scale testing of different RAS designs and operation methods, and two preliminary experiments were conducted. In the first experiment, the capability of different chemical additions (sodium nitrite, ammonium chloride and/or cane sugar) to fasten the startup of the nitrification bioreactor was tested. In addition, the suitability and reliability of an online water measurement system in monitoring nitrification process with was evaluated. We demonstrated that when using a combination of sodium nitrite and ammonium chloride in a concentration of 5 mg l −1 , nitrification started one week before than when using only ammonium chloride or a clean start with rainbow trout ( Oncorhynchus mykiss ). In the second experiment, the effect of different relative water renewal rates (RWR) on water quality, rainbow trout growth and feed conversion ratio (FCR) were examined at 16 °C. Based on the results, FCR increased when RWR went below 478 l kg −1 , and the specific growth rate decreased when RWR went below 514 l kg −1 . Furthermore, when RWR decreased, nitrate, nitrite and organic material accumulated in the circulating water. In conclusion, we showed using experimental RAS platform that online water quality monitoring is a useful tool in following the effect of different management practices. Furthermore, we demonstrated that chemical substrate additions provide the fastest biofilter startup, and that water management is still in the key role in defining the fish production in RAS. [ABSTRACT FROM AUTHOR]

Thermophilic aeration of cattle slurry and food industrial by-products was studied with the aim to improve hygienic qualities of the slurry so that it could be used as a safe fertiliser for berries to be eaten raw. We also wanted to study if the process would be energetically favourable in an arctic climate.Cattle slurry alone or with whey and/or jam waste was treated. The tests were done in a well heat-insulated reactor with a 10 m3 volume. Temperature increases up to over 70 °C could be recorded in 19 days even though some processes were carried out in wintertime when the ambient air temperature was less than 0 °C. The heat energy formed was higher than the electrical energy needed to carry out the aeration. The hygienic qualities of the aerated product were good with only minor nitrogen losses. The end product could be useful as a fertiliser and soil improving compound to increase the organic matter content of agricultural soil. Cattle slurry alone was well suited as the raw material if attaining a high temperature was the main goal. A part of slurry could be replaced with food-industrial side products. Whey waste suited better for co-composting than jam waste but the mixture of whey, jam waste, and slurry was optimal for composting. [Copyright &y& Elsevier]

• Organic material accumulated in the two-moving-bed systems. • Nitrite concentrations increased in the two-fixed-bed systems. • Different bioreactor designs did not affect fish health or growth. The effect of bioreactor design on nitrification efficiency has been well studied, but less is known about the overall impacts on water quality. Besides nitrification, submerged fixed bed bioreactors (FBBR) trap fine solid particles, whereas moving bed bioreactors (MBBR) grind solids, possibly increasing solids and particle accumulation in the system. In this experiment, the effects of different combinations of fixed bed and moving bed bioreactors on water quality, solids removal, particle size distribution, fish health based on histopathological changes and nitrification efficiency were studied in laboratory scale recirculating aquaculture systems (RAS) with rainbow trout (Oncorhynchus mykiss). Three set-ups with triplicate tanks were used: 1. two consecutive fixed bed bioreactors (FF); 2. a fixed bed bioreactor followed by a moving bed bioreactor (FM) and 3. two consecutive moving bed bioreactors (MM). Fish performance was not influenced by the design of the bioreactor, specific growth rate (SGR) being between 1.59 and 1.64% d−1 and feed conversion ratio (FCR) between 0.95 and 0.98. Water nitrite concentration was higher in the FF systems compared to FM and MM systems, whereas the average total ammonia nitrogen concentration (TAN) was not influenced by the treatments. Nitrification rate, which was measured in the laboratory, followed the water nitrite levels, indicating highest total ammonium oxidation rates in the MM systems. UV254 absorbance and total organic carbon (TOC) concentrations were higher in the groups with moving bed systems, indicating accumulation of organic substances in the circulating water. The total volume of particles was higher in the MM systems as compared to the FF systems. The total solids balance was similar in all the bioreactor groups, since the removal of solids by the FBBR backwash was compensated by the drum filter in the FM and MM systems. In general, no significant histopathological difference in gill, kidney, heart and liver tissue were observed between the RAS treatment groups and the flow-through treatment. [ABSTRACT FROM AUTHOR]

The recirculating aquaculture system (RAS) is an ever-developing technology for producing fish with a low environmental impact. However, off-flavors can be a major problem in RAS fish production. Off-flavor compounds are of microbial origin and are accumulated in fish flesh. They typically cause a musty and earthy taste and odor, which consumers find unacceptable. Here we hypothesized that oxidizing compounds such as ozone (O 3), hydrogen peroxide (H 2 O 2), and their combinations, referred to as advanced oxidation processes (AOP)s, can remove or decrease these compounds in water and prevent their accumulation in fish. In this study, four different oxidative treatments (O 3 low (0.4 mg O 3 L−1), O 3 high (0.8 mg O 3 L−1), H 2 O 2 (0.15 µl L−1), AOP (0.4 mg O 3 L−1 & H 2 O 2 0.10 µl L−1), and controls were applied to 10 experimental RASs for four months. The results showed that the treatments can reduce dissolved organic carbon (DOC) and the off-flavor compounds (geosmin, GSM and 2-methyl isoborneol, MIB) in circulating water, but they were not able to prevent the accumulated off-flavors in fish flesh below the sensory threshold. There was no significant difference in off-flavor removal between the treatments, which indicates that O 3 treatment was ineffective in these conditions. However, H 2 O 2 could still reduce the off-flavor concentrations in water. • Treatments were able to reduce off-flavors in water. • Larger ozone doses were manageable and did not cause immediate harm to fish. • Ozone treatment were ineffective in managing the off-flavors in fish. • Hydrogen peroxide and advanced oxidation showed future potential. [ABSTRACT FROM AUTHOR]

Abstract: The disappearance of malachite green (MG) residues was determined in fry of rainbow trout (Oncorhynchus mykiss) after six repeated treatments of the eggs at the hatching stage with MG oxalate at exposure levels of 1, 3 and 6mg l−1 for 30min. Fry samples were taken from newly hatched fry (0days post-hatch, d.p.h.) and at regular time intervals at 16, 31, 43, 57 and 96d.p.h. The residues of MG and its major metabolite, leucomalachite green (LMG), were found to accumulate in the fry after MG treatments of eggs, with the highest residue levels being determined in the newly hatched fry. After exposures of 3mg l−1 MG, mean concentrations of 1170±106µg kg−1 and 276±38.6µg kg−1 (n =3) were found in fry for LMG and MG, respectively. However, the disappearance of residues occurred rapidly in the fry, such that by 43d.p.h. only low levels of LMG could be determined. To confirm the elimination of residues, determinations were made also in fry muscle at 96d.p.h. but no residues were detected. The residues of MG in fry were determined by liquid chromatography-tandem mass spectrometric (LC-MS/MS) analysis with a limit of detection (LOD) of 0.5µg kg−1 and a limit of quantification (LOQ) of 1.0µg kg−1. The accumulation as well as the elimination of residues correlated well with the level of exposure. During the study, the fry increased their weight, such that at the end of the study, their mean body weight was about 150 times greater than the mean body weight of the newly hatched fry. As the disappearance of residues occurred in conjunction with the growth of fry, the present results indicate that no residues of MG will remain in the fish intended for human consumption, if MG treatment takes place at the hatching stage under controlled conditions. [Copyright &y& Elsevier]

Abstract: Effects of soybean meal (SBM) based diet on growth performance, histology of the intestinal epithelium and on the gut microbiota of juvenile rainbow trout (Oncorhynchus mykiss) were investigated on two trials lasting for 8 weeks (Trial I) and 18 weeks (Trial II). The microbiological characterization was done both with conventional plating techniques, biochemical profiling and length heterogeneity analysis of PCR amplified 16S rDNA (LH-PCR). Typical histological changes were found after 18 weeks of SBM feeding (Trial II). Mean height of simple foldings were significantly higher within the group fed with fish meal (FM) based diet. These changes were not, however, reflected in the appearance, behavior and weight gain of the fish, although the feed conversion rate (FCR) was higher, compared to fish fed with the traditional FM feed. In both SBM and FM groups the counts of cultivable intestinal bacteria dropped within the first 4 weeks of feeding (Trial I). Subsequently, the bacterial numbers increased in the FM group, but not in the SBM group by the 8th week of the trial. The LH-PCR data suggested also that diet-related qualitative changes in the microbiota had occurred (Trial II). The main identified bacteria were mainly representatives of the genera Aeromonas, Sphingomonas and Chryseomonas, and among the lactic acid bacteria, Lactococcus and Lactobacillus. Future research will be directed to the identification and eventual elimination the SBM-associated factors involved in the inflammatory responses and unfavorable FCR, in particular by modifying the intestinal microbiota. [Copyright &y& Elsevier]

[Display omitted] • The highest nitrate removal rate was 11.6 g N m−3 d-1 in the woodchip bioreactor. • 79 % of the phosphate was removed in the woodchip bioreactor. • The highest organic carbon removal was observed in the constructed wetland. • Organic matter leaching caused oxygen depletion in the wetland and sand filter. Recirculating aquaculture systems (RAS) discharge management limits the development of the aquaculture sector, because RAS do not automatically result in low nutrient emissions. Research has helped develop discharge management systems such as wetlands and woodchip bioreactors that have been adopted by Danish commercial model trout farms. To further develop the Danish concept, we have modelled and built a novel "zero-discharge" recirculating aquaculture system with an annual capacity of approximately 14 tonnes. The aim of this paper is to describe the entire concept and present the results from the start-up phase of the whole system. The concept includes the treatment of RAS effluent (overflow and sludge supernatant) using a hybrid solution of a woodchip bioreactor, constructed vertical wetland, and sand infiltration. Using this three-step process, the nitrate, phosphorus, and organic matter effluent are decreased to acceptable levels to reuse the water in the RAS process reducing the need for new raw water. In the first nine months of operation, a water treatment field was used as an end-of-pipe treatment to ensure the water was safe to recirculate for fish. During the winter, the water temperature dropped to 2.7 degrees in the sand filter, but the frost did not reach the water levels in any of the treatment processes. It therefore appears that a hybrid solution can operate sufficiently even in winter conditions. In the first year of operation, a woodchip bioreactor can remove 97 % of the nitrate, although the slow start-up of the RAS caused the bioreactor to be N-limited. On average, 79 % and 92 % of the inflow phosphate concentration was removed in the woodchip bioreactor and the entire hybrid treatment field respectively. The wetland and sand filter removed organic matter sufficiently (35 %), but because of the longer than designed actual water residence, it leached from the bioreactor more than was expected. Further experimentation is needed to identify the financial applicability and performance during higher feeding rates. [ABSTRACT FROM AUTHOR]

Aquaculture needs practical solutions for nutrient removal to achieve sustainable fish production. Passive denitrifying bioreactors may provide an ecological, low-cost and low-maintenance approach for wastewater nitrogen removal. However, innovative organic materials are needed to enhance nitrate removal from the low carbon effluents in intensive recirculating aquaculture systems (RAS). In this study, we tested three additional carbon sources, including biochar, dried Sphagnum sp. moss and industrial potato residues, to enhance the performance of woodchip bioreactors treating the low carbon RAS wastewater. We assessed nitrate (NO 3 −) removal and microbial community composition during a one-year in situ column test with real aquaculture wastewater. We found no significant differences in the NO 3 − removal rates between the woodchip-only bioreactor and bioreactors with a zone of biochar or Sphagnum sp. moss (maximum removal rate 31–33 g NO 3 −-N m−3 d−1), but potato residues increased NO 3 − removal rate to 38 g NO 3 −-N m−3 d−1, with stable annual reduction efficiency of 93%. The readily available carbon released from potato residues increased NO 3 −-N removal capacity of the bioreactor even at higher inflow concentrations (>52 mg L−1). The microbial community and its predicted functional potential in the potato residue bioreactor differed markedly from those of the other bioreactors. Adding potato residues to woodchip material enabled smaller bioreactor size to be used for NO 3 − removal. This study introduced industrial potato by-product as an alternative carbon source for the woodchip denitrification process, and the encouraging results may pave the way toward growth of blue bioeconomy using the RAS. • Woodchip bioreactors removed 31–38 g NO 3 −-N m−3 d−1 from intensive aquaculture effluent. • Additional potato residues to woodchip material increased 13% of nitrate removal rate. • The potato residue bioreactor hosted a distinctly different microbial community. [ABSTRACT FROM AUTHOR]