Granular ferric hydroxide adsorption as a pretreatment to achieve phosphorus reclamation and high water-recovery wastewater effluent desalination

High water-recovery reverse osmosis (RO) desalination of wastewater effluent is one promising solution to combat the global water scarcity. However, its implementation is often constrained by membrane scaling, with calcium phosphate scaling (Ca-P precipitates) being a primary challenge. This study explores the application of granulated ferric hydroxide (GFH) adsorption as a pretreatment to recover phosphorus (P), a key precursor to Ca-P precipitates related scaling, from P-rich wastewater effluent thereby facilitating subsequent effluent RO desalination at high water recovery ratios. The results highlight the GFH's strong affinity for phosphate and its partial adsorption of calcium, magnesium, and organic matter from the effluent, which are all advantageous in mitigating fouling and scaling. Optimized acid-base regeneration retained ∼ 85 % of P adsorption capacity after five cycles, indicating strong reusability. Moreover, the GFH treatment increased the water recovery ratio from 4 % to 75 % during subsequent RO desalination. Adjusting the GFH-treated effluent pH to 6.5 further improved the water recovery ratio to > 90 %. These results can be attributed to scaling mitigation, as confirmed by surface analyses and saturation index calculations. Overall, these findings highlight P adsorption as an effective and sustainable pretreatment approach for wastewater effluent RO desalination, enabling desalination at a high water recovery ratio while simultaneously achieving efficient P recovery.