Phosphorus recovery by ion exchange in a solid carbonate: modeling of the process

Phosphorus (P) is a nutrient for plant growth but also a pollutant in water bodies causing eutrophication. The source of P is mainly human and animal wastewater and runoffs from different land uses. The objective of the present study is to evaluate P removal and recovery processes by ion exchange (IE) with solid carbonate (SC) in biodigestor-treated swine effluent (BTSE) using hydrogeochemical modeling. For this, BTSE compositions were obtained by literature review. A synthetized and characterized SC was used and the ion exchange site concentration ([SC-IE]) and the IE constants (K_ie) were obtained experimentally and applied to model P and major anion removal and recovery processes. P recovery was evaluated for different BTSE compositions and several concentrations of SC, dissolved P (HPO₄^2-), competing anions such as SO₄^2-, and CO₃^2-. The simulations suggest that a [SC-IE]:[HPO₄] of 1.4 molar ratio would allow the recovery of 90% of HPO₄ in BTSE, and at average alkalinity concentrations in BTSE, CO₃^2- would compete with HPO₄ for the SC-IE. The P recovery by the SC-IE process was compared with two other methods commonly used in P removal from BTSE: removal with aluminum sulfate and precipitation of struvite as a function of pH. The results suggest that SC-IE is the most efficient method in the pH range of BTSE. Besides, HPO₄^2- was readily recovered as inorganic P that may be reused in agriculture and industrial processes.