Phosphate Removal from Water and Wastewater: A Novel Hybrid Exchanger Approach

This study presents the development and performance of a new phosphate-selective sorbent, referred to as hybrid anion exchanger or HEX. The study introduces a novel phosphate-selective sorbent, HEX, which combines the durability of polymeric anion exchange resins with the high sorption affinity of hydrated ferric oxide. The development and performance of HEX are supported by laboratory kinetic studies, revealing its selective phosphate removal capabilities in the presence of competing anions. The application of the film diffusion equation provides insights into the kinetic behavior. Moreover, column and field trials demonstrate consistent and effective phosphate removal with minimal leakage, showcasing the potential practical significance of HEX in mitigating water pollution caused by phosphate discharge. Phosphate discharged into surface waters can stimulate plant growth, resulting in eutrophication of rivers and lakes. Environmental problems may develop as P moves off-site into aquatic systems. Removal of P from wastewaters has long been a concern of municipalities, and technologies have been developed to lower P concentrations in wastewaters. HEX combines durability and mechanical strength of polymeric anion exchange resins with high sorption affinity of hydrated ferric oxide (HFO) toward phosphate. HEX is mechanically strong, durable and did not show any sign of fragmentation during repeated use lab and field trials. This superior feature makes it suitable for long term applications. Laboratory kinetic studies show that HEX selectively removes phosphate from the background of much higher concentrations of competing sulfate, chloride and bicarbonate anions due to the combined presence of Coulombic and Lewis acid base interactions. The kinetic data were analyzed using the film diffusion equation, and it was discovered that the exchange rate was controlled by the film diffusion process. Consistent results in the operating capacity of HEX resin with low phosphate leakage are also demonstrated by column and field studies.