Abstract
Abstract Precipitation of phosphorus (P) as a struvite product from wastewater and local magnesium (Mg) sources is considered as a high economical prudent venture, as it has shown to bring down the cost of producing the product. However, there is a significant concentration of calcium (Ca) in these Mg and most wastewater sources. The presence of Ca in wastewater and Mg sources during struvite precipitation has been shown to negatively affect the quality of the struvite produced. The low struvite quality greatly impedes its use as a fertiliser given the economic value of the product as an alternative P fertiliser. This review paper provides an understanding of how the presence of Ca affects the purity, crystal size, and morphology of the struvite. Different methods that have been used to mitigate the effect of Ca on struvite quality have been reviewed. The factors that affect the recovery of P and the percentage recoveries of P by different Mg sources have also been reviewed. This paper serves as a basis for further research where the possibility of removing Ca from wastewater and Mg sources is explored. When Ca is removed before struvite precipitation is carried out, the quality of the product will be greatly improved.
Highlights
The presence of Ca2þ during struvite precipitation has been shown to negatively affect characteristics of the struvite produced (Le et al 2005, Li et al 2016; Liu & Wang 2019; Moragaspitiya et al 2019; Bayuseno & Schmahl 2020; Hutnik et al 2020)
This paper provides a review of the influence of Ca on struvite quality on purity, size, and morphology of the precipitate
It is not involved in any reaction, which competes for PO34À; when a certain mass of the precipitate is first dissolved in HCl and diluted with water, the purity of the struvite can be calculated by using the following equation:
Summary
The presence of Ca2þ during struvite precipitation has been shown to negatively affect characteristics of the struvite produced (Le et al 2005, Li et al 2016; Liu & Wang 2019; Moragaspitiya et al 2019; Bayuseno & Schmahl 2020; Hutnik et al 2020). Some natural Mg sources, which have shown potential to precipitate struvite, are wood ash (Sakthivel et al 2012; Huang et al 2017), brucite (Zhang et al 2009; Huang et al 2011; Hövelmann & Putnis 2016), dolomite (Roques et al 1991; Holmberg et al 2000; Chen et al 2017), and bittern, brine, or seawater (Li & Zhao 2002; Ye et al 2011; Lahav et al 2013; Liu et al 2013; Tran et al 2016; Huang et al 2017). This review paper discusses the impact of Ca on struvite quality in P recovery, and the methods used for reducing the impact to date has been reviewed to enable the use of an effective method in future studies
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