Attempts to reduce effluent loadings from salmon farms by varying feeding frequencies and mechanical effluent treatment
Bergheim, A.; Forsberg, O.I. (1993). Attempts to reduce effluent loadings from salmon farms by varying feeding frequencies and mechanical effluent treatment, in: Barnabé, G. et al. Production, environment and quality: Proceedings of the International Conference Bordeaux Aquaculture '92, Bordeaux, France, March 25-27, 1992. EAS Special Publication, 18: pp. 115-124
In: Barnabé, G.; Kestemont, P. (Ed.) (1993). Production, environment and quality: Proceedings of the International Conference Bordeaux Aquaculture '92, Bordeaux, France, March 25-27, 1992. Special Publication European Aquaculture Society, 18. European Aquaculture Society: Gent. 587 pp., more
In: Special Publication European Aquaculture Society. European Aquaculture Society: Bredene. ISSN 0774-0689, more
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Document type: Conference paper
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| Authors | | Top |
- Bergheim, A.
- Forsberg, O.I.
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| Abstract |
Variation of feeding frequency in tanks stocked with adult Atlantic salmon was found to have no influence on effluent loadings, growth rates or feed conversion ratios (FCR). For both periodical and continuous feeding frequencies (2-4 and 170-250 feedings a day) the range of values found were as follows: effluent loadings expressed as g.kg-1 fish/24h were 0.5-1.4g suspended dry matter (SDM), 0.01-0.05 g total phosphorus (TP), 0.15-0.30g total nitrogen (TN) and 0.1-0.2g total ammonia nitrogen (TAN), and feed conversion ratio (FCR) was 1.0-1.2kg dry feed.kg-1 fish gain. To remove sludge, a UNIK Rotary Filter unit with two rotating microsieves with mesh sizes of 350/150µm and 60µm was installed at the tank outlets.The unit removed on average 68% of SDM, 63% of TP and 20% of TN. About 35% of dissolved phosphate (PO4-P) was removed through the unit. The treatment efficiency was high considering the low effluent concentrations (2-5mg SDM.l-1). The UNIK unit with a standard backwashing system normally produces a sludge water quantity of 0.5-2% of the total passing flow. This leads to a daily sludge water volume of 10-30m3 with a concentration of 50-500mg SDM.l-1. To dewater the sludge water a two step system with sieving (mesh size: 60µm) and sedimentation (outflow rate: 0.2m³.h-1) was tested. This system routinely produced a settled sludge quantity of 1-1.5 l.kg-1 feed supplied. Compared to concentration levels before dewatering, total dry matter (TDM) was increased 100-200 times to 50-100 g TDM.l-1 sludge. The average treatment efficiency of the dewatering process was 70-80% for SDM and TP, and 60-65% for TN and total organic carbon (TOC). |
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