Coagulation of phosphorous and organic matter from marine,land-based recirculating aquaculture system effluents |
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| Affiliation: | 1. Technical University of Denmark, DTU Aqua, Section for Aquaculture, The North Sea Research Centre, P.O. Box 101, DK-9850 Hirtshals, Denmark;1. Sokoine University of Agriculture, Department of Animal, Aquaculture and Range Sciences, P.O Box, 3004, Morogoro, Tanzania;2. Mwalimu Julius K. Nyerere University of Agriculture and Technology, College of Fisheries and Aquatic Sciences, P.O Box 976, Musoma, Tanzania;3. Technical University of Denmark, DTU Aqua, Section for Aquaculture, The North Sea Research Centre, P.O. Box 101, DK-9850, Hirtshals, Denmark;4. Technical University of Denmark, Department of Environmental Engineering, DTU Environment, Bygningstorvet, Build. 115, DK-2800, Kgs. Lyngby, Denmark;1. Ecological Engineering Centre, Institute of Natural Resource Sciences, Zurich University of Applied Sciences, Grüentalstrasse 14, 8820 Wädenswil, Switzerland;2. Group of Plant Nutrition, Institute of Agricultural Sciences, ETH Zurich, Eschikon 33, 8315 Lindau, Switzerland;3. Landing Aquaculture, Hemelrijk 2A, 5281 PS Boxtel, the Netherlands;4. Environmental Genomics and Systems Biology Research Group, Institute of Natural Resource Sciences, Zurich University of Applied Sciences, Grüentalstrasse 14, 8820 Wädenswil, Switzerland;1. Technical University of Denmark, DTU Aqua, Section for Aquaculture, The North Sea Research Centre, P.O. Box 101, DK-9850 Hirtshals, Denmark;2. Aalborg University, Department of Biotechnology, Chemistry and Environmental Engineering, Sohngårdsholmsvej 49, DK-9000 Aalborg, Denmark |
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| Abstract: | Saline effluents from marine land-based aquaculture production can neither be disposed in common municipal wastewater treatment plants, nor disposed as landfill. Furthermore, stricter environmental regulations require the reduction of phosphorous and organic matter levels from marine environment discharges to minimize eutrophication. Chemical coagulation with FeCl3 and AlSO4 is commonly used for removing phosphorous and suspended solids in wastewater treatment. The capacity of these coagulants for creating particle aggregations depends on the characteristics and chemistry of the treated wastewater, such as the ionic strength or mixing conditions. Marine water has a higher ionic strength than fresh or brackish water, which may be beneficial when using chemical coagulants to treat the effluents from farms operated at high salinities. The following study compared the application of FeCl3 and AlSO4, to treat the two effluents discharged from a marine land-based recirculating aquaculture system (RAS) producing salmon (Salmo salar). The aim of the study was to determine; 1) in what effluent (sludge flow vs. exchange water overflow) at the end-of-pipe treatment the coagulant application is more efficient for the removal of PO43−-P, total suspended solids (TSS), total phosphorous (TP) and total chemical oxygen demand (TCOD); and 2) the optimal coagulant dose to apply and its associated chemical sludge production. The results show that more than 89 % removal of TCOD, TSS and TP is achieved when treating the sludge flow, arguably because the sludge flow contained the largest fraction of the target masses (P and organic matter) discharged from the system. Up to 80 % of TSS removal was achieved by simple sedimentation, and with the highest coagulant dose tested, up to 95 % of TSS could be removed from the effluent. To remove 90 % of PO43−-P, FeCl3 and AlSO4 need to be dosed at a molar ratio of 2.6:1 Fe:PO43−-P and 5.7:1 Al: PO43−-P, respectively. Dosing above 90 % removal efficiency did not significantly affect removal of PO43-P and TSS, but substantially increased the volume of chemical sludge produced. Finally, FeCl3 is proposed as a better overall alternative for P removal at the end-of-pipe treatment in marine land-based RAS. |
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| Keywords: | Aluminum sulfate Iron chloride Marine land-based RAS Organic matter Phosphorous |
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