Design and modeling of novel low-pressure nanofiltration hollow fiber modules for water softening and desalination pretreatment

Omar Labban,Tzyy Haur Chong,John H Lienhard

doi:10.1016/j.desal.2018.04.002

Abstract

Given its high surface area to volume ratio and desirable mass transfer characteristics, the hollow fiber module configuration has been central to the development of RO and UF technologies over the past five decades. Recent studies have demonstrated the development of a novel class of low-pressure nanofiltration (NF) hollow fiber membranes with great promise for scale-up implementation. Further progress on large-scale deployment, however, has been restrained by the lack of an accurate predictive model, to guide module design and operation. Earlier models targeting hollow fiber modules are only suitable for RO or UF. In this work, we propose a new modeling approach suitable for NF based on the implementation of mass and momentum balances, coupled with a validated membrane transport model based on the extended Nernst-Planck equation to predict module performance at the system-level. Modeling results are validated with respect to synthetic seawater experiments reported in an earlier work. A preliminary module design is proposed, and parametric studies are employed to investigate the effect of varying key system parameters and elucidate the tradeoffs available during design. The model has significant implications for low-pressure nanofiltration, as well as hollow fiber NF module design and operation.

Highlights

Nanofiltration (NF), introduced in late 80’s, is a membrane process whose performance falls between ultrafiltration (UF) and reverse osmosis (RO); and as its name implies, has pore sizes on the order of 1 nm [1]
We develop a mathematical model to our knowledge the first to predict the performance of NF hollow fiber modules on the system-level, building from experiments run on a bench-scale setup
We demonstrated the successful implementation of a membrane transport model, introduced by Geraldes and Alves [12] based on the extended Nernst-Planck equation, to the newly developed LbL hollow fiber membranes [13]

Summary

Introduction

Nanofiltration (NF), introduced in late 80’s, is a membrane process whose performance falls between ultrafiltration (UF) and reverse osmosis (RO); and as its name implies, has pore sizes on the order of 1 nm (corresponding to a molecular weight cut-off, or MWCO, of 300 − 500 Da) [1]. With their unique selectivities and high permeabilities relative to RO, NF membranes presented a major milestone in membrane technology, have attracted considerable attention since their introduction, and have found numerous applications, spanning numerous fields from water and waste water treatment to biotechnological, pharmaceutical, and food industry applications [2]. More recent works from Roy et al [10, 11] explore the effect of temperature on NF pretreatment and scale prevention in thermal desalination

Methods

Results

Conclusion