Abstract
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.
Highlights
The European Union’s circular economy strategy aims to increase the recycling and re-use of products and waste materials [1]
Fly ash contains mainly irregularly shaped particles and has no clear morphology. This is verified by FESEM; an image of untreated fly ash presented in Figure 2a,b illustrates the distribution of particle size
The change in temperature has no essential effect on the removal of ammonium using either fly ash sludge or commercial salts
Summary
The European Union’s circular economy strategy aims to increase the recycling and re-use of products and waste materials [1]. The use of industry waste material and side flows should be more effective. The first goal of the waste hierarchy is to prevent the formation of waste streams. If this is not possible, the step is to prepare waste for re-use, followed by recycling and other recovery (e.g., energy recovery). According to Sokka et al [3], re-use and symbiosis products manufactured from side flows or waste materials in the local industry carry a small environmental load
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