Adsorption/Desorption of Magnesium to enhance Phosphorus Recovery in Wastewater

With a growing population and non-renewable reserves of phosphorous, there are concerns for future availability of this essential element. Currently, phosphorous is mined from phosphate rock deposits, but some estimates suggest that there will be a shortage of this resource by the end of the century. However, phosphorous can be recovered from sources such as wastewater and biosolids. Phosphorus recovery can decrease the risk of eutrophication, improve surface water health, and reduce the need for mining and refining P-bearing minerals. One approach is to precipitate the phosphorous from wastewater (e.g., urine) in minerals such as struvite (MgNH4PO4(s)). When the amount of Mg is increased, more phosphorus can be recovered. However, this uses more Mg than stoichiometrically required. In hopes of eliminating the loss of Mg, we are trying to recover and reuse the excess Mg added during precipitation. An iron oxide-based adsorption process was used to recover and reuse magnesium from the effluent of the struvite precipitation process. In doing so, we found that granular iron oxide (E33) has the potential to adsorb Mg from urine and struvite precipitation supernatant. We found that, as pH increases, the adsorption capacity of Mg increases. When phosphate is present in the synthetic urine solution, the adsorption of Mg is enhanced, and Mg enhances adsorption of phosphate to E33. Thus, supernatant phosphate can also be recovered in this process. Finally, Mg was successfully desorbed from the E33 at pH 4.5, which demonstrates the potential of this process for recovering and recycling Mg in struvite precipitation processes