Equilibrium-Based Temperature-Dependent Economic Analysis of the Recovery of Phosphorus from Different Wastewater Streams via Chemical Precipitation

Concerns over dwindling phosphorus (P) reserves and costs associated with wastewater remediation due to excessive nutrient content may be alleviated simultaneously via chemical precipitation of reusable P-containing solid phases. Many thermodynamic models have been developed to better understand the process of recovering valuable solids from industrial, farm, or municipal wastewater feedstocks. However, these models typically neglect temperature- and time-dependent formation of these recoverable solids. This work addresses these effects using a quasi-kinetic approach and a novel thermodynamic database that includes temperature-dependent expressions for equilibrium constants. The economic potential of the recovery of P from wastewater streams from different industrial sectors was also assessed on the basis of the cost of chemical inputs and sale of a valuable recovered P product, struvite (NH4MgPO4·6H2O). The results suggest that the formation of struvite is strongly favored at lower temperatures within the range of 5–35 °C, high N:P ratios, and lower Ca:Mg ratios. In addition, although the formation of struvite is generally favored at high pH values (∼8 to 10), costs associated with pH adjustments can be offset by other conditions, such as temperature and excess nitrogen and P. Finally, the processing of wastewater by cochineal insects was the most profitable of all of the streams analyzed.