University of Oulu

Elisangela Heiderscheidt, Axumawit Tesfamariam, Jani Pulkkinen, Jouni Vielma, Anna-kaisa Ronkanen, Solids management in freshwater-recirculating aquaculture systems: Effectivity of inorganic and organic coagulants and the impact of operating parameters, Science of The Total Environment, Volume 742, 2020, 140398, ISSN 0048-9697,

Solids management in freshwater-recirculating aquaculture systems : effectivity of inorganic and organic coagulants and the impact of operating parameters

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Author: Heiderscheidt, Elisangela1; Tesfamariam, Axumawit1; Pulkkinen, Jani2;
Organizations: 1Water Energy and Environmental Engineering Research Unit, Faculty of Technology, 90014 University of Oulu, Finland
2Natural Resources Institute Finland, Survontie 9A, 40500 Jyväskylä, Finland
Format: article
Version: accepted version
Access: open
Online Access: PDF Full Text (PDF, 0.7 MB)
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Language: English
Published: Elsevier, 2020
Publish Date: 2020-08-11


Coagulants are widely used for solids (uneaten food, faeces, etc.) management in recirculating aquaculture systems (RAS), but no recent research has been performed on the effectiveness of different coagulants in treatment of aquaculture sludge. This study examined the effectivity of selected inorganic (polyaluminium chloride, PAC) and organic products (polyamine- and starch-based) as coagulant agents for solids management in RAS. Reductions in residual concentrations of total phosphorus (tot-P), phosphate‑phosphorus (PO₄-P), suspended solids (SS) total nitrogen (tot-N), nitrate‑nitrogen (NO₃-N), ammonium‑nitrogen (NH₄-N), aluminium (Al) and chemical oxygen demand (COD) in reject water were determined. The effect of process parameters (coagulant type, dose, mixing and sedimentation time) on sludge treatment was also evaluated. The PAC products tested were most effective at concentrating pollutants (Tot-P, PO₄-P, SS, COD) in RAS sludge into the solid phase. The organic products tested, especially a high-molecular-weight polyamine product (pAmine1), achieved good performance and can be considered a valid alternative to inorganic salts. At optimum dose, PAC (dose ₃2 mg/L) and pAmine1 (dose 15 mg/L) removed, respectively, 99.₄% and 82.8% of turbidity, 98.2% and 65.₄% of PO₄-P and 97.7% and 7₃.6% of SS. The mixing time applied in flocculation and the time allowed for sedimentation had significant effects on coagulant performance, with the organic coagulants being most affected. Flocculation times of 5–15 min and sedimentation times of 15–60 min showed good results and can be used as a starting point in process optimisation with both inorganic and organic coagulants. The use of coagulants for treatment of RAS sludge enhances flock formation and improves particle settling characteristics, substantially decreasing nutrient, organics and solids concentration in reject water.

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Series: Science of the total environment
ISSN: 0048-9697
ISSN-E: 1879-1026
ISSN-L: 0048-9697
Volume: 742
Article number: 140398
DOI: 10.1016/j.scitotenv.2020.140398
Type of Publication: A1 Journal article – refereed
Field of Science: 218 Environmental engineering
Funding: This study was part of the project Aquaculture Innovation program funded by the European Maritime and Fisheries Fund. The authors would like to acknowledge the support received from the Natural Resources Institute Finland (Laukaa RAS fish farm, Finland) and personnel at the Water, Energy, and Environmental Engineering Research Unit at the University of Oulu, Oulu, Finland.
Copyright information: © 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license