Determining minimum ion exchange resin usage for NOM removal

For the design and analysis of an ion exchange (IEX) process, it is necessary to know the minimum IEX resin usage defined thermodynamically. Anion exchange resin sorption of dissolved natural organic matter (NOM) may follow an isotherm of either Type I or Type II, which are noticeably different at high surface coverage. The charge density of NOM, which monotonically increases with the pH, appears to play a critical role. Basic pH (high charge density) favors a Type I isotherm and acidic pH (low charge density) may change the isotherm to Type II. The Langmuir equation and the Wiegner-Jenny-Summers-Roberts (WJSR) equation can be used to quantify the Type I and Type II isotherms, respectively. Explicit relationships between minimum resin usage and desired level of removal are subsequently developed and the isotherm constants, along with the non-removable NOM fraction, are simultaneously estimated by an innovative least-squares regression (LSR) approach. The Langmuir isotherm-based model accurately describes the sorption removal of Type I isotherm, and the WJSR isotherm-based model accurately describes the sorption removal of Type II isotherm. At removals >30%, however, the two sorption models offer comparable minimum IEX resin usages. The sorption models and LSR methods developed herein are applicable to resin slurry contactors, including batch reactors, plug flow reactors, or continuous-flow stirred tank reactors.