University of Oulu

Pesonen, J., Sauvola, E., Hu, T., & Tuomikoski, S. (2020). Use of side stream-based MgSO4 as a chemical precipitant in the simultaneous removal of nitrogen and phosphorus from wastewaters. Desalination and Water Treatment, 194, 389–395.

Use of side stream-based MgSO₄ as chemical precipitant in the simultaneous removal of nitrogen and phosphorus from wastewaters

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Author: Pesonen, Janne; Sauvola, Emilia1; Hu, Tao1;
Organizations: 1Research Unit of Sustainable Chemistry, University of Oulu, P.O. Box: 4300, FI-90014, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.2 MB)
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Language: English
Published: Desalination Publications, 2020
Publish Date: 2020-09-28


Wastewaters and agricultural sludges can contain high concentrations of phosphate and ammonium- or nitrate–nitrogen, which run off easily to waterways causing eutrophication in water bodies. However, it is possible to precipitate phosphate and ammonium as struvite and use it as recycled fertilizer. In this research, MgSO₄ solution obtained by treating fly ash (FA) or dolomite (DOL) with sulfuric acid was used as a precipitant for simultaneous phosphorus and nitrogen removal from synthetic (NH₄)₂HPO₄ solution. Precipitation experiments were performed at room temperature (20°C ± 2°C) using different molar ratios Mg:P:N (1.1–2:1–2:1–2) and precipitation times (4–24 h). The pH was adjusted to 9.0 and kept constant. In all cases, there were only minor changes in the removal of both ammonium and phosphate after 4 h of reaction time. Highest ammonium removal percentages after the 4 h test were 79.5% for MgSO₄ 1.3:1:1, DOL 1.1:1:1, and DOL 1.3:1:1. Highest ammonium removal percentages (75.5%) for FA based MgSO₄ solution were achieved using molar ratios Mg:P:N 2:1:1 and 1.1:2:2. Also, the highest phosphate removal percentages were achieved with these samples (97% for MgSO₄ 1.3:1:1, 93.3% for DOL 1.3:1:1, 89.8% for DOL 1.1:1:1, 84.5% for FA 2:1:1, and 82.5% for FA 1.1:2:2) Struvite was the only formed precipitation product in all cases as was confirmed by X-ray diffraction. Results indicate that fly ash and DOL based MgSO₄ solutions performed quite well compared to commercial MgSO₄ salt and they have great potential in the ammonium and phosphate precipitation.

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Series: Desalination and water treatment
ISSN: 1944-3994
ISSN-E: 1944-3986
ISSN-L: 1944-3994
Volume: 194
Pages: 389 - 395
DOI: 10.5004/dwt.2020.26037
Type of Publication: A1 Journal article – refereed
Field of Science: 218 Environmental engineering
215 Chemical engineering
116 Chemical sciences
Funding: This work was done under the auspices of the WaterPro project (ERDF project no: A74635, funded by Central Ostrobothnia Regional Council).
Copyright information: © 2020 Desalination Publications. The final authenticated version is available online at