Modeling phosphate transport and removal in a compact bed filled with a mineral-based sorbent for domestic wastewater treatment

Phosphorus filter units containing mineral-based sorbents with a high phosphate (PO4) binding capacity have been shown to be appropriate for removing PO4 in the treatment of domestic wastewater in on-site facilities. However, a better understanding of their PO4 removal mechanisms, and reactions that could lead to the formation of PO4 compounds, is required to evaluate the potential utility of candidate sorbents. Models based on data obtained from laboratory-scale experiments with columns of selected materials can be valuable for acquiring such understanding. Thus, in this study the transport and removal of PO4 in experiments with a laboratory-scale column filled with a commercial silicate-based sorbent were modeled, using the hydro-geochemical transport code PHREEQC. The resulting models, that incorporated the dissolution of calcite, kinetic constrains for the dissolution of calcium oxide (CaO) and wollastonite (CaSiO3), and the precipitation of amorphous tricalcium phosphate, Ca3(PO4)2, successfully simulated the removal of PO4 observed in the experiments. Modeled calcium, modeled PO4 and mean (n=2) measured PO4 concentrations (a) and modeled and mean measured pH (b) in the filter effluent vs. bed volumes at a loading rate of 97±3Lm−2d−1. [Display omitted] •Removal of PO4 in filters for on-site wastewater treatment was modeled.•The hydro-geochemical transport code PHREEQC was used.•The models could successfully simulate PO4 removal measured in laboratory.•CaO, wollastonite and calcite were the phases dissolved from the material.•The only precipitated Ca–P compound suggested by the models was ATCP (Ca3(PO4)2).