University of Oulu

Myllymäki, P.; Pesonen, J.; Romar, H.; Hu, T.; Tynjälä, P.; Lassi, U. The Use of Ca- and Mg-Rich Fly Ash as a Chemical Precipitant in the Simultaneous Removal of Nitrogen and Phosphorus—Recycling and Reuse. Recycling 2019, 4, 14.

The use of Ca- and Mg-rich fly ash as a chemical precipitant in the simultaneous removal of nitrogen and phosphorus : recycling and reuse

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Author: Myllymäki, Pekka1; Pesonen, Janne1; Romar, Henrik1;
Organizations: 1Research Unit of Sustainable Chemistry, University of Oulu, P.O. Box 8000, FI-90014 Oulu, Finland
2Unit of Applied Chemistry, Kokkola University Consortium Chydenius, University of Jyvaskyla,P.O. Box 567, FI-67101 Kokkola, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.7 MB)
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Language: English
Published: Multidisciplinary Digital Publishing Institute, 2019
Publish Date: 2019-10-04


The European Union’s circular economy strategy aims to increase the recycling and re-use of products and waste materials. According to the strategy, the use of industry waste material should be more effective. A chemical precipitation method to simultaneously remove phosphorus and nitrogen from synthetic (NH4)2HPO4 solution and the liquid phase of anaerobic digestate using fly ash as a precipitant was tested. Fly ash is a waste material formed in the power plant process. It mainly contains calcium oxide (CaO) and magnesium oxide (MgO). Saturated precipitant solution was prepared from fly ash, which was added in small proportions to (NH4)2HPO4 solution during the experiment. Fly ash’s effectiveness as a precipitant was compared with that of commercial CaO and MgO salts, and it can be observed that fly ash removed as much ammonium and phosphate as commercial salts. Fly ash sufficiently removed ammonium nitrogen and phosphate from the liquid phase of anaerobic digestate, which led to the formation of ammonium magnesium hydrogen phosphate hydrate, struvite (NH4MgPO4·6H2O), and calcium hydroxide phosphate, monetite, CaPO3(OH). In this study, we have shown for the first time that fly ash can be used to manufacture recycled, slow-release fertilizers from anaerobic digestate.

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Series: Recycling
ISSN: 2313-4321
ISSN-E: 2313-4321
ISSN-L: 2313-4321
Volume: 4
Issue: 2
Article number: 14
DOI: 10.3390/recycling4020014
Type of Publication: A1 Journal article – refereed
Field of Science: 218 Environmental engineering
116 Chemical sciences
Copyright information: © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (