Field validation of multifunctional ion exchange process for reverse osmosis pretreatment and phosphate recovery during impaired water reuse

Conventional reverse osmosis (RO) pretreatment hardly achieves multifunctionality for simultaneous membrane scaling prevention and nutrient recovery during impaired water reuse. To address the challenge, we probed a multifunctional ion exchange pretreatment process achieving pH adjustment, calcium and organic compound removal, and phosphate recovery using real impaired surface water. Three types of ion exchangers were integrated in train including a polystyrene strong base anion exchanger (psSBA), a shallow-shell weak acid cation exchanger (SSWAC), and a hybrid anion exchanger (HAIX). The novelty is that SSWAC, which decreased aqueous pH from neutral to ∼ 5 and removed > 70 % calcium, was regenerated by recovered waste CO2 (> 80 % regeneration efficiency) to avoid strong acid regenerants and achieve CO2 utilization and sequestration. The front-positioned psSBA selectively pre-removed hydrophobic ionizable organic compound (HIOC) such as diclofenac at > 80 % removal to reduce HIOC interference on the latter-positioned HAIX. HAIX doped with ferric oxide nanoparticles (FeOnp) enabled selective phosphate removal from complex real impaired water. Over 70 % removal of phosphate and calcium by HAIX and SSWAC reduced calcium phosphate scaling risk and facilitated phosphate recovery as hydroxyapatite from spent regenerants that enriched with calcium and phosphate. We envision this study to facilitate resource recovery in water-nutrient-carbon nexus via engineered multifunctional ion exchange processes. © 2020 Elsevier Ltd