Advancing Sustainable Water Reuse Through Membrane Based Treatment Trains: A Comprehensive Evaluation of Productivity, Contaminant Removal, and Energy Efficiency of Ultrafiltration Nanofiltration and Reverse Osmosis

Abstract

Membrane technologies have emerged as an effective solution for sustainable water production for a wide variety of applications, including potable water reuse. Pressure-driven membrane processes, such as Ultrafiltration (F), Nanofiltration (NF) and reverse osmosis (RO) have proven their potential in water treatment and reuse, removing most organic contaminants. Water reuse has emerged as a non-traditional but rapidly growing solution to meet the increasing demand for clean water. Full advanced treatment (FAT) is a sequential treatment process that includes integrated membrane systems and an advanced oxidation process (AOP), that has become the primary treatment choice for potable water reuse globally. This work emphasizes the potential of each membrane filtration technology UF, NF and RO for improving productivity, reducing energy consumption, and enhancing contaminant removal in potable water reuse application.Data collected from continuously operated engineering-scale UF were pre-processed and analyzed for a cycle-by-cycle investigation on the net water production, water recovery, initial operating TMP, filtration cycle duration, and energy consumption. Operational parameters such as TMP backwash trigger, backwash duration, and CEB frequency were varied to study their impacts on the UF process. The results demonstrated the importance of the cycle-cycle approach which helped organize and examine the overall state of operating conditions of UF in long-term operations. Highest net water production was achieved with mid pressure TMP (103 kPa), while changing the backwash duration had minimal effect. Furthermore, CEB frequency was a key parameter to maximize water production and recovery. In potable water reuse applications, the wide-exclusive implementation of RO membrane is questionable, considering that NF could achieve similar organic and inorganic removal efficiencies. NF can be a more efficient implementation for organic pollutants removal due to the lower energy requirement compared with the RO membranes. In this study, NF was explored as a treatment process for potable water reuse applications. RO and NF (dense and loose) membranes were tested in bench and engineering-scales to quantify organic and inorganic solutes rejection and characterize organic compounds permeating. High TOC rejection was observed for dense and loose NF membranes, but loose NF poorly rejected divalent and monovalent ions. In general, the same rejection rates were observed by the dense NF compared to the RO for divalent ions, and slightly lower rejection rates for TOC and monovalent ions. Trace organics rejection was observed to be similar between the dense NF and RO membranes. Results demonstrated that dense NF membranes could be a sustainable alternative to RO. The need for enhanced permeability and selectivity, which have become key metrics in guiding membranes development. While the primary goal is to remove contaminants, and produce clean and safe water, targeted rejection is. The solute-solute selectivity is emerging due to the growing demand for sustainable and economical processes. The membrane permeability and selectivity alterations induced by chlorine exposure are well-established and extensively studied, especially for water permeability recovery. In this work, pristine and chlorine-exposed NF and RO membranes were used to provide details on the contaminants permeating through the membranes in terms of separation efficiency, and solute-solute selectivity. Bench-scale results demonstrated that chlorination increased the separation factor, and cation and anion separation factor was observed to be higher for NF than RO membranes. With progressive chlorination the separation factors for both membranes decreased leading to no solute-solute selectivity.