Elevated levels of phosphate (P) in surface waters from anthropogenic activities contribute to eutrophication in aquatic environments, threatening ecosystems and the communities that rely on them. Simultaneously, phosphorus is an important resource that is currently non-renewably sourced from mining. This unbalanced P cycle motivates us to recover phosphorus from P-rich surface water bodies or wastewater. In this study, we demonstrated the ability of mineral-hydrogel composites seeded with calcium phosphate and calcium silicate-based mineral seeds to be applied for both the polishing of phosphate to low concentration levels (from 6.2 mg-P/L to ~0.1 mg-P/L) to prevent nutrient pollution and for phosphorus recovery from highly concentrated phosphate (&gt; 50 mg-P/L) containing wastewaters. We evaluated the P removal/recovery novel mineral-hydrogel composites composed of calcium alginate (Ca-Alg), calcium phosphate (CaP), and either wollastonite (Woll, a naturally occurring calcium silicate mineral), or calcium silicate hydrate (CSH). Through modulating the solubility of the calcium silicate-based mineral seed, the mineral-hydrogel composites were tuned for either P polishing or P recovery. Mineral-hydrogel composites with sparingly soluble Woll seeds were able to remove P from 6.2 mg-P/L to an average of 0.067 mg-P/L in a batch reactor system. On the other hand, highly soluble CSH mineral seed-containing composites can recover 70% of P from a P-rich solution with 50 mg-P/L with a final P-loading of 117.2 mg-P/g-dry Ca-Alg. Overall, by exploiting the synergy between CaP and calcium silicate-based seeds, we achieved highly effective management of P in wastewater at both high (&gt; 50 mg-P/L) and low P (6.2 mg-P/L) concentrations. Sparingly soluble Woll seeds enable effective P polishing, while highly soluble CSH mineral seeds promote high amounts of P recovery. This study demonstrated that CaP/calcium silicate-based mineral-hydrogel composites are a promising technology for P management in wastewater that will also enable a greener phosphorus cycle through P recovery.

Controlling calcium phosphate/calcium silicate chemistry in novel mineral-hydrogel composites to provide a robust platform for P removal and recovery

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ACS Fall 2022

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