University of Oulu

Kiani, S., Lehosmaa, K., Kløve, B., & Ronkanen, A.-K. (2022). Nitrogen removal of mine-influenced water in a hybrid bioreactor with floating hook-moss (Warnstorfia fluitans) in cold climate conditions. Ecological Engineering, 177, 106562.

Nitrogen removal of mine-influenced water in a hybrid bioreactor with floating hook-moss (Warnstorfia fluitans) in cold climate conditions

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Author: Kiani, Sepideh1; Lehosmaa, Kaisa2; Kløve, Bjørn1;
Organizations: 1Water, Energy and Environmental Engineering Research Unit, Faculty of Technology, P.O. Box 4300, FI-90014 University of Oulu, Finland
2Ecology and Genetics Research Unit, Faculty of Science, P.O. Box 3000, FI-90014 University of Oulu, Finland
3Freshwater Centre, Finnish Environment Institute SYKE, Paavo Havaksen tie 3, FI-90570 Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.8 MB)
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Language: English
Published: Elsevier, 2022
Publish Date: 2022-05-05


To remove nitrogen in cold conditions, we studied new nature-based treatment solutions using six pilot-scale reactors. The pilots were woodchip bioreactor (WBR), aquatic floating hook-moss (Warnstorfia fluitans) (MBR), and a combined woodchip and floating hook-moss hybrid unit (HBR) with an improved hydraulic design. The experiment was run in a climate room at temperatures of 10 °C and 5 °C and using mine water from two sites located in northern Finland. Unlike traditional horizontal flow woodchip bioreactors, in this study the hydraulic efficiency was improved from poor (λ = 0.06) in the woodchip bioreactor to satisfactory (λ = 0.51) in the hybrid unit by inserting two inner plates along the water flow and adding floating hook-moss. The hybrid bioreactor revealed the highest capability of nitrogen removal in all inorganic forms at T ≤ 10 °C with a mean HRT of 70.5 h. On average, 30–78 % of dissolved inorganic nitrogen was removed in the hybrid unit, which was 2 and 3 times more than in units consisting only of woodchip or floating hook-moss. The hybrid bioreactor revealed a maximum NO3-N removal rate of 1.0–5.2 g m⁻³ d⁻¹ and a 21.8–99.7 % removal efficiency for an average incoming NO3-N load of 40 g d⁻¹. The maximum NH⁺ ₄-N removal efficiency of 75.6 and 53 % took place in HBR and MBR, respectively, when the incoming NH⁺ ₄-N load was 23.6 ± 0.7 g d⁻¹ at 10 °C. Over the 154 days of the experiment, the hybrid unit removed a total of 2.95 kg DIN-N, which was 0.8 kg higher than the sum of the DIN-N mass removed in the individual woodchip (1.7 kg) and moss units (0.55 kg). The nitrogen content of the aquatic moss was higher in the hybrid unit compared to the moss unit, showing a higher contribution of N plant uptake. Overall, our results suggest that combining woodchips and aquatic moss in a hybrid unit with improved hydraulic efficiency using inner walls may enhance nitrogen removal in cold climate conditions.

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Series: Ecological engineering
ISSN: 0925-8574
ISSN-E: 1872-6992
ISSN-L: 0925-8574
Volume: 177
Article number: 106562
DOI: 10.1016/j.ecoleng.2022.106562
Type of Publication: A1 Journal article – refereed
Field of Science: 218 Environmental engineering
Funding: This study was funded by the Maa-ja vesitekniikan tuki ry. [grant no. 37413], K.H. Renlund Säätiö and Kaute-Säätiö, Kone Foundation [grant no. 201806416] and the European Regional Development Fund as part of the HuJa project, “Enhancing the treatment of metal containing storm waters and wastewaters by using natural materials (2015–2018)”.
Copyright information: © 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (