Removal of aqueous nC60 fullerene from water by low pressure membrane filtration

The potential environmental and health risks of engineered nanoparticles such as buckminsterfullerene C60 in water require their removal during the production of drinking water. We present a study focusing on (i) the removal mechanism and (ii) the elucidation of the role of the membrane pore size during removal of nC60 fullerene nanoparticle suspensions in dead-end microfiltration and ultrafiltration mimicking separation in real industrial water treatment plants. Membranes were selected with pore sizes ranging from 18 nm to 500 nm to determine the significance of the nC60 to membrane pore size ratio and the adsorption affinity between nC60 and membrane material during filtration. Experiments were carried out with a dead-end bench-scale system operated at constant flux conditions including a hydraulic backwash cleaning procedure. nC60 nanoparticles can be efficiently removed by low pressure membrane technology with smaller and, unexpectedly, also by mostly similar or larger pores than the particle size, although the nC60 filtration behaviour appeared to be different. The nC60 size to membrane pore size ratio and the ratio of the cake-layer deposition resistance to the clean membrane resistance, both play an important role on the nC60 filtration behaviour and on the efficiency of the backwash procedure recovering the initial membrane filtration conditions. These results become specifically significant in the context of drinking water production, for which they provide relevant information for an accurate selection between membrane processes and operational parameters for the removal of nC60 in the drinking water treatment

Effect of multicomponent fouling during microfiltration of natural surface waters containing nC60 fullerene nanoparticles

To understand and mitigate the role of surface water composition and associated membrane fouling in the removal of nC(60) nanoparticles by low-pressure membranes, experiments were carried out with microfiltration membranes using natural feed waters, mimicking separation in real industrial water treatment plants. The effects of water composition, the presence of nanoparticles, and membrane fouling were investigated with a dead-end bench-scale system operated under constant flux conditions including a hydraulic backwash cleaning procedure. nC(60) nanoparticles can be efficiently removed by microfiltration and the removal efficiency is found to be independent of the water surface composition. However, the water composition controls the extent of fouling occurring during filtration. A synergistic effect on membrane fouling between nC(60) and surface water constituents such as natural organic matter (NOM) and its fractions is observed: the synergistic effect resulted in a transmembrane pressure (TMP) increase always higher than the sum of the TMP increase due to the filtration of nC(60) in ultrapure water and the TMP increase due to the surface water without nC(60)

Hollow fiber nanofiltration: From lab-scale research to full-scale applications

This review provides a comprehensive overview on the quickly developing field of polymeric hollow fiber (HF) nanofiltration (NF), including membrane (module) and process design, operational parameters, and full-scale applications. Six different methods are currently used to produce HF NF membranes: phase inversion, interfacial polymerization, grafting, coating, polyelectrolyte multilayers (PEM) and chemistry in a spinneret. While all methods have their strengths and weaknesses, several PEM based membranes stand out because of their high chemical stability. This combination of geometry and chemical stability can make HF NF a sustainable alternative to spiral wound NF. This is especially the case for applications with a high fouling load where, in contrast to spiral wound NF, HF NF typically does not require an intensive pre-treatment. In academic settings, experiments are typically done in small modules with single-component feeds. Several studies showed that it is important, but not always straightforward, to correlate these lab scale results to full scale performance. Indeed, process design parameters such as crossflow velocity and staging partly determine energy consumption and retention and need to be taken into account. Partly based on these insights and developments, in the last five years commercial HF NF modules have rapidly become available. At least 59 pilot-scale and 26 full-scale HF NF plants are currently in operation or under construction, mostly focusing on water treatment. A comparison between these plants shows that HF NF can be applied for a broad range of applications with excellent scalability, highlighting the growth potential for HF NF in the coming years

Insights into natural organic matter and its removal by ion exchange resins

Natural organic matter (NOM) is present in all surface and ground waters and originates from degradation and by-products of living organisms and plants. NOM can be separated by HPLC-Organic Carbon Detection into five fractions: biopolymers, humic substances, building blocks, low molecular weight acids and low molecular weight neutrals. Water quality is affected by the presence of NOM (fractions) and moreover it can cause several issues during water treatment processes. Therefore, its removal by a variety of technologies is widely studied. Anion exchange resins (AER) can effectively remove a major part of this NOM, but due to its complex nature, the process is still not completely understood and optimized. In this work, the removal of NOM by macroporous styrenic weak (WBA), strong (SBA) and combined weak/strong (W/SBA) base anion exchange resins is studied. The resins were used in two industrial relevant counter ion forms: the OH- or free base form for SBA and WBA resins respectively, using an NaOH conditioning solution as applied in water demineralisation units and a Cl- form using NaCl for SBA resins and HCl for the WBA and W/SBA resins, as seen in drinking water treatment and Dupont’s recently developed weak basic NOM scavenger resins respectively. The effect of this conditioning on the equilibrium pH and driving forces for NOM removal in batch mode experiments using synthetic water containing model compounds for the different NOM fractions was investigated. This study demonstrated that next to AER resin selection, the conditioning procedure is an important parameter to be considered in the design of NOM removal processes, especially when specific NOM fractions are targeted

Insights Into Natural Organic Matter and Its Removal By Ion Exchange Resins

Natural organic matter (NOM) is present in all surface and ground waters and originates from degradation and by-products of living organisms and plants. NOM can be separated by HPLC-Organic Carbon Detection into five fractions: biopolymers, humic substances, building blocks, low molecular weight acids and low molecular weight neutrals. Water quality is affected by the presence of NOM (fractions) and moreover it can cause several issues during water treatment processes. Therefore, its removal by a variety of technologies is widely studied. Anion exchange resins (AER) can effectively remove a major part of this NOM, but due to its complex nature, the process is still not completely understood and optimized. In this work, the removal of NOM by macroporous styrenic weak (WBA), strong (SBA) and combined weak/strong (W/SBA) base anion exchange resins is studied. The resins were used in two industrial relevant counter ion forms: the OH- or free base form for SBA and WBA resins respectively, using an NaOH conditioning solution as applied in water demineralisation units and a Cl- form using NaCl for SBA resins and HCl for the WBA and W/SBA resins, as seen in drinking water treatment and Dupont’s recently developed weak basic NOM scavenger resins respectively. The effect of this conditioning on the equilibrium pH and driving forces for NOM removal in batch mode experiments using synthetic water containing model compounds for the different NOM fractions was investigated. This study demonstrated that next to AER resin selection, the conditioning procedure is an important parameter to be considered in the design of NOM removal processes, especially when specific NOM fractions are targeted

Can osmotic membrane bioreactor be a realistic solution for water reuse?

Abstract A growing emphasis on water recycling resulted in intense research activity, aiming to develop and validate reliable and high-quality water treatment processes at lowest cost. In parallel, significant advances in the field of osmotically driven processes have been obtained in the past decade. While the combination of membrane bioreactor (MBR) and reverse osmosis (RO) has become the preferred choice for water reuse, the osmotic membrane bioreactor (OMBR) has begun to be considered as a promising alternative. Based on the current state of knowledge, this paper critically asses the potential for OMBR to be implemented for water reuse application and highlights challenges to reach full scale operation. The initial vision of an energy-free osmotic gradient process is not realistic and its low fouling behaviour is still to be properly assessed. However, OMBR demonstrated unique features such as high rejection of contaminants and an absence of RO brine stream that can support its implementation, especially in the context of high end (potable, industrial) water reuse. However, to become a viable and effective technology for water reuse, significant research and development is still required. Tackling the salinity build-up, developing membranes and modules adapted to OMBR, evaluating long term performance and economics, validating removal of contaminants and developing design, maintenance and automatic control systems constitute critical topics to be considered in future research

A novel hybrid process of reverse electrodialysis and reverse osmosis for low energy seawater desalination and brine management

This paper introduces a novel concept for a hybrid desalination system that combines reverse electrodialysis (RED) and reverse osmosis (RO) processes. In this hybrid process the RED unit harvests the energy in the form of electricity from the salinity gradient between a highly concentrated solution (e.g., seawater or concentrated brine) and a low salinity solution (e.g., biologically treated secondary effluent or impaired water). The RED-treated high salinity solution has a lower salt concentration and serves as the feed solution for the RO unit to reduce the pump work. The concentrated RO brine provides the RED unit a better high salinity source for the energy recovery compared to seawater. In addition, the concentration of the discharged brine can be controlled by the RED unit for improving the water recovery and minimizing the impact on the environment. Different configurations of the hybrid RED–RO processes are presented for a comparative study on the basis of mathematical modeling. Specifically, various operating conditions for the RED unit are investigated for better adaptation to the hybrid system. The variations of the total specific energy consumption and the discharge brine concentration for various hybrid modes are simulated to verify the conceptual designs. The modeling results indicate that the RED–RO hybrid processes could substantially reduce the specific energy consumption and provide a better control of the discharge brine concentration in comparison to conventional seawater desalination RO processes

Hydrogel-coated feed spacers in two-phase flow cleaning in spiral wound membrane elements: A novel platform for eco-friendly biofouling mitigation

Biofouling is still a major challenge in the application of nanofiltration and reverse osmosis membranes. Here we present a platform approach for environmentally friendly biofouling control using a combination of a hydrogel-coated feed spacer and two-phase flow cleaning. Neutral (polyHEMA-co-PEG10MA), cationic (polyDMAEMA) and anionic (polySPMA) hydrogels have been successfully grafted onto polypropylene (PP) feed spacers via plasma-mediated UV-polymerization. These coatings maintained their chemical stability after 7 days incubation in neutral (pH 7), acidic (pH 5) and basic (pH 9) environments. Anti-biofouling properties of these coatings were evaluated by Escherichia coli attachment assay and nanofiltration experiments at a TMP of 600 kPag using tap water with additional nutrients as feed and by using optical coherence tomography. Especially the anionic polySPMA-coated PP feed spacer shows reduced attachment of E. coli and biofouling in the spacer-filled narrow channels resulting in delayed biofilm growth. Employing this highly hydrophilic coating during removal of biofouling by two-phase flow cleaning also showed enhanced cleaning efficiency, feed channel pressure drop and flux recoveries. The strong hydrophilic nature and the presence of negative charge on polySPMA are most probably responsible for the improved antifouling behavior. A combination of polySPMA-coated PP feed spacers and two-phase flow cleaning therefore is promising and an environmentally friendly approach to control biofouling in NF/RO systems employing spiral-wound membrane module