Question

# Molar Ratio of struvite precipitation?

My question about the struvite precipitation (MgNH4PO4): Is the molar ratio of Mg:P the same as Mg: PO4, and N:P the same as NH4:PO4? Otherwise, Do I have to make any calculations when I convert from one form to another, like Mg:P to Mg: PO4? Thanks!

In case of struvite, the N and P refer exclusively to NH4 and PO4. So Mg:P == Mg:PO4 and N:P == NH4:PO4. The molar ratio refers to the mol-per-liter ratio of each component. For struvite precipitation, the molar ratio of all 3 components is simply 1:1:1.

It is the same because you are using molar.
Thank you very much for your response. Could you explain what you mean by the same molar?
Thank you very much for your time!
Samsul Islam
Dhaka University of Engineering & Technology
The molar ratio for struvite precipitation refers to the stoichiometric ratio of the reactants used in the chemical reaction that produces struvite (MgNH4PO4·6H2O). Struvite precipitation commonly occurs in wastewater treatment processes, where magnesium (Mg2+), ammonium (NH4+), and phosphate (PO43-) ions combine to form struvite crystals, which can help remove phosphorus from the wastewater.
The balanced chemical equation for struvite precipitation is as follows:
Mg2+ + NH4+ + PO43- + 6H2O → MgNH4PO4·6H2O
From the balanced equation, you can determine the molar ratio of the reactants. It is:
1 mol of Mg2+ : 1 mol of NH4+ : 1 mol of PO43- : 6 mol of H2O
This means that for the complete precipitation of struvite, you need one mole of each magnesium ion (Mg2+), ammonium ion (NH4+), and phosphate ion (PO43-) and six moles of water (H2O).
To achieve efficient struvite precipitation in practice, it is common to adjust the molar ratio of the reactants to ensure sufficient availability of all ions for the reaction. Generally, using a molar ratio that slightly exceeds the stoichiometric ratio can help improve precipitation efficiency and produce higher-quality struvite crystals. The specific molar ratio used in a struvite precipitation process may vary depending on the characteristics of the wastewater being treated and the desired outcome. It is essential to optimize the molar ratio to achieve the best results in a given wastewater treatment application.
Thank you very much for your answer. I have a question: how can I calculate the molar ratio of N:P and Mg:P from the following table below? Thanks!
In case of struvite, the N and P refer exclusively to NH4 and PO4. So Mg:P == Mg:PO4 and N:P == NH4:PO4. The molar ratio refers to the mol-per-liter ratio of each component. For struvite precipitation, the molar ratio of all 3 components is simply 1:1:1.

## Related Publications

Article
In this study, a novel two-stage aerobic granular sludge (AGS) system was developed to treat municipal wastewater. High removal efficiencies of phosphorus (91%) and nitrogen (81%) were obtained under a low influent carbon/nitrogen ratio of 5.4. The high nutrient removal was attributed to microbial segregation in the two sequencing batch reactors (S...
Article
Full-text available
The abatement of nutrient compounds from aqueous waste and wastewater is currently a priority issue. Indeed, the uncontrolled discharge of high levels of nutrients into water bodies causes serious deteriorations of environmental quality. On the other hand, the increasing request of nutrient compounds for agronomic utilizations makes it strictly nec...
Got a technical question?