Messi Biology states that phosphorus is a key driver of water eutrophication. Excess phosphate in domestic sewage, aquaculture wastewater, and industrial wastewater can lead to ecological issues such as algal blooms, water hypoxia, and the depletion of aquatic life. Consequently, phosphorus removal has become an important step in water environment management. Among various phosphorus removal technologies, magnesium oxide (MgO) is increasingly utilized in water treatment due to its efficiency, stability, cost-effectiveness, and low risk of secondary pollution, offering an alternative approach for phosphorus control.
The mechanism of phosphorus removal using magnesium oxide involves the synergy of chemical precipitation and physical adsorption, providing dual pathways for phosphorus removal. Magnesium oxide is slightly soluble in water; once added to wastewater, it slowly hydrolyzes to form magnesium hydroxide, continuously releasing magnesium ions and hydroxide ions, which helps stabilize the pH within a favorable range of 8.5 to 9.5. In this alkaline environment, magnesium ions react with phosphate ions in the water to form sparingly soluble precipitates, such as magnesium phosphate and magnesium ammonium phosphate (struvite). These precipitates have low solubility products and can settle relatively quickly, facilitating the initial removal of phosphorus. Additionally, porous magnesium oxide features a high specific surface area with active sites, which can further adsorb residual trace phosphorus through electrostatic adsorption, ligand exchange, and surface complexation, helping the treated water meet discharge standards consistently.
Compared with conventional phosphorus removal processes, magnesium oxide offers several practical advantages. Traditional lime precipitation often leads to high pH levels, large volumes of sludge, and pipeline scaling. Metal salts, such as aluminum or iron salts, can be costly and carry a risk of residual metal ions, which may lead to secondary pollution. In contrast, magnesium oxide provides a milder alkalinity and a controlled reaction process without generating hazardous substances. The resulting sludge volume is approximately one-third of that produced by the lime method, showing favorable settling and dewatering performance, which helps reduce subsequent sludge disposal costs. Furthermore, raw materials for magnesium oxide are widely available—low-grade light-burned magnesium powder is often sufficient for engineering needs—making it a cost-effective alternative to traditional reagents. It can also concurrently remove certain heavy metals and fluorides from wastewater, offering multi-functional treatment benefits.
In engineering applications, magnesium oxide is relatively easy to operate and highly adaptable. It does not require complex equipment and can be directly added to aeration tanks, sedimentation tanks, or tertiary treatment units. The reaction proceeds at ambient temperature and pressure, making it suitable for various high-phosphorus wastewater scenarios, including municipal wastewater treatment plants, aquaculture facilities, food processing plants, and industrial parks. Practical application data indicates that phosphorus removal rates using magnesium oxide can reach over 95%, assisting facilities in meeting Class A discharge standards. Notably, the reaction product, magnesium ammonium phosphate (struvite), can be recovered and processed into slow-release fertilizer for agricultural use, supporting a circular economy model of “wastewater phosphorus removal and resource recovery” in line with green and low-carbon development concepts.
Currently, magnesium oxide-based phosphorus removal technology continues to evolve. Techniques such as porous modification, nanostructuring, and oxygen vacancy regulation are being researched to further enhance adsorption capacity and selectivity. Combining magnesium oxide with biological phosphorus removal processes creates a “biological + chemical” hybrid system, which maintains treatment efficiency while reducing chemical dosage. In scenarios such as decentralized rural wastewater treatment, urban black-odor water remediation, and emergency industrial wastewater treatment, magnesium oxide plays an important role due to its flexible dosing and rapid response.