Jens-Ole Frier

Performance characteristics of fluidised bed biofilters in a novel laboratory-scale recirculation system for rainbow trout: nitrification rates, oxygen consumption and sludge collection

A laboratory-scale recirculating aquaculture system for fluidised bed biofilter evaluation was engineered. The design included all components found in typical full-scale commercial production systems. The system included two identical units each with oxygenation, UV treatment, cooling, biofiltration and a particulates separation device. Water from the two systems was mixed in a degassing unit. A 1 month test period after biofilter maturation revealed stable concentrations of total ammonia nitrogen (TAN), nitrite and nitrate within the system. Mean nitrification rate was 0.27 and 0.21 g TAN m−2 day−1. Oxygen consumption in the biofilters ranged between 56 and 64% due to nitrifying activity. Mass balances on nitrogen indicated that 48%, added via the feed, was converted to nitrate within the system, with 6% of the added nitrogen being found in the sludge. The remaining 43% was either used during fish growth, left the system, as organic nitrogenous compounds (or unidentified nitrogenous compounds), via the outlet, or was lost to the atmosphere. At least 61% of the nitrate produced was generated by the biofilters. The system proved to be an exceptional set-up for evaluation of the performance of fluidised bed biofilters, allowing both pre- and post-filter measurements of various water quality criteria.

Changes in patterns of persistent halogenated compounds through a pelagic food web in the Baltic Sea

The concentrations and patterns of persistent halogenated compounds (PHCs), including polychlorinated biphenyls (PCBs), DDT, hexachlorocyclohexanes (HCHs), hexachlorobenzene (HCB) and polybrominated diphenyl ethers (PBDEs) were examined in a pelagic food web from the southern Baltic Sea consisting of sediment, zooplankton, sprat, Atlantic salmon and anadromous brown trout. Lipid-normalized concentrations generally increased from low trophic levels to high trophic levels, with the exception of HCHs. Due to high concentrations of PBDEs in some zooplankton samples, biomagnification of BDE-47 was only observed for salmon/sprat and trout/sprat. Sprat collected individually and from salmon stomach had significantly different lipid-normalized concentrations and varied in their PHC pattern as well, possibly indicating a large natural variation within the Baltic Sea. The highest lipid-normalized concentrations were found in brown trout. Salmon and brown trout were similar in their PHC pattern suggesting similar food sources. Variation in PHC patterns among trophic levels was not smaller than that among geographically distinct locations, confirming the importance of comparable trophic levels for the assessment of PHC patterns, e.g. for tracing migratory fish.

The influence of dietary oxolinic acid on fluidised bed biofilter performance in a recirculation system / for rainbow trout Oncorhynchus mykiss

Abstract The effect of medicated feed, containing 2.35±0.01 mg oxolinic acid (OA) g−1, upon the performance of fluidised bed (FB) biofilters was examined over a 29-day period. Rainbow trout were used as stock animals in duplicate recirculation systems. OA was detectable within the systems throughout the period of study, with bulk water OA concentrations reaching 1.24 mg l−1 at their highest point. Sludge levels of OA were measured at 60 mg day−1 at peak. A mass balance for OA was undertaken on day 21 of the study. Seventy-two percent of the antibiotic could be recovered from the trout, sludge and water, with fish being of minimal significance at trial termination. The treated feed did not effect biofilter performance, either during the feeding period (7 days duration) or for 14 days post-feeding, with respect to nitrification rates. In separate studies, which employed a scale model of the recirculation system, maximum nitrification rates (MNR) were examined using media from each of the biofilters and four doses of OA (0.1–100 mg l−1). OA did not effect MNR, but water turbidity and bacterial count increased.

Modelling waste output from trout farms

The aim of waste modelling in aquaculture is to provide tools for simulating input, transformation, output and subsidiary degradation in recipients of organic compounds, nitrogen, and phosphorus. The direct purpose of this modelling is to make it possible for caretakers and water authorities to calculate waste discharge from existing and planned aquaculture activities. A special purpose is simulating outcome of waste water treatment and altered feeding programmes. Different submodels must be applied for P, N, and organics, as well as for the different phases of food and waste treatment. Altogether this calls for an array of co-operating submodels for a sufficient coverage of the options. In all the required fields there is some scientific background for numerical model approaches, and some submodels have been proposed. Because of its multidisciplinary character a synthesized approach is still lacking. Within trout farming this work attempts to establish the different submodels and outlines future possibilities for synthesizing the knowledge to a numerical model.

Organochlorine Fingerprinting to Determine Foraging Areas of Sea-Ranched Atlantic Salmon: A Case Study from Denmark

Abstract We used organochlorine fingerprinting to identify the principal marine foraging area in a sea-ranched population of Atlantic salmon Salmo salar from Denmark. The results of this study, the first to apply the method to teleosts, suggest that Atlantic salmon released as juveniles (age 1) in the River Gudenaa, Denmark, are utilizing the North Sea and not the Baltic Sea as their principal marine foraging area.