Simplified analysis of contaminant rejection during ground- and surface water nanofiltration under the information collection rule

Demonstrating removal credits for contaminants of emerging concern in recycled water through a reverse osmosis barrier-A predictive framework

The performance of individual reverse osmosis (RO) systems varies significantly with different contaminants of emerging concern (CECs). As such, log reduction values (LRVs) of the concentration of these chemicals cannot be arbitrarily credited in water treatment and water recycling. This study looks to present an approach to the management of chemical risks by providing a systematic validation of RO barrier performance with respect to LRV credits for various classes of CECs. In this work, a one-off sampling campaign across five treatment barriers (strainer filtration, ultrafiltration, RO, ion exchange, chlorination) of a full-scale water recycling plant was conducted, followed by a systematic sampling campaign for a period of six weeks across just the RO barrier. The CECs screening methodology used GC-MS for quantification of 948 trace organic chemicals along with specific 44 per- and polyfluoroalkyl substances (PFAS) screening using LC-MS/MS to demonstrate the removal credits of the RO barrier to a wide spectrum of CECs. The work was used to validate an LRV barrier credit framework so as to predict the performance of a polyamide RO membrane for removal of a range of chemical classes, under typical operational conditions. Conductivity was validated as an efficient surrogate for membrane integrity and RO performance, along with specified operational conditions associated with permeate flux and recovery rate. A bioassay method (photobacterium test) showed good potential to be used as a quick measure to indicate the general toxicity of a sample caused by chemical contamination, because of its high detection sensitivity and time and cost efficiency.

Interdependence of Contributing Factors Governing Dead-End Fouling of Nanofiltration Membranes

Cake-enhanced concentration polarization (CECP) has been ascribed as the main cause of flux decline in dead-end filtration. An unfamiliar approach was used to investigate the role of CECP effects in the fouling of a nanofiltration membrane (NF-270) that poorly reject salts. Membrane–foulant affinity interaction energies were calculated from measured contact angles of foulants and membrane coupons based on the van der Waals/acid–base approach, and linked to resistance due to adsorption (R_a). In addition, other fouling mechanisms and resistance parameters were investigated using model organic and colloidal foulants. After selection, the foulants and membranes were characterized for various properties, and fouling experiments were conducted under controlled conditions. The fouled membranes were further characterized to gain more understanding of the fouling layer properties and flux decline mechanisms. Sodium alginate and latex greatly reduced membrane permeate flux as the flux declined by 86% and 59%, respectively, while there was minor flux decline when aluminum oxide was used as model foulant (<15% flux decline). More flux decline was noted when fouling was conducted with a combination of organic and colloidal foulants. Contrary to other studies, the addition of calcium did not seem to influence individual and combined fouling trends. Foulants adsorbed more on the membrane surface as the membrane–foulant affinity interactions became more attractive and pore blocking by the foulants was not important for these experiments. Hydraulic resistance due to cake formation (R_c) had a higher contributing effect on flux decline, while CECP effects were not substantial.

Development and application of relevance and reliability criteria for water treatment removal efficiencies of chemicals of emerging concern

With the growth in production and use of chemicals and the fact that many end up in the aquatic environment, there is an increasing need for advanced water treatment technologies that can remove chemicals of emerging concern (CECs) from water. The current lack of a homogenous approach for testing advanced water treatment technologies hampers the interpretation and evaluation of CEC removal efficiency data, and hinders informed decision making by stakeholders with regard to which treatment technology could satisfy their specific needs. Here a data evaluation framework is proposed to improve the use of current knowledge in the field of advanced water treatment technologies for drinking water and wastewater, consisting of a set of 9 relevance criteria and 51 reliability criteria. The two criteria sets underpin a thorough, unbiased and standardised method to select studies to evaluate and compare CEC removal efficiency of advanced water treatment technologies in a scientifically sound way. The relevance criteria set was applied to 244 papers on removal efficiency, of which only 20% fulfilled the criteria. The reliability criteria were applied to the remaining papers. In general these criteria were fulfilled with regards to information on the target compound, the water matrix and the treatment process conditions. However, there was a lack of information on data interpretation and statistics. In conclusion, a minority of the evaluated papers are suited for comparison across techniques, compounds and water matrixes. There is a clear need for more uniform reporting of water treatment studies for CEC removal. In the future this will benefit the selection of appropriate technologies.

Application of neural networks in membrane separation

Artificial neural networks (ANNs) as a powerful technique for solving complicated problems in membrane separation processes have been employed in a wide range of chemical engineering applications. ANNs can be used in the modeling of different processes more easily than other modeling methods. Besides that, the computing time in the design of a membrane separation plant is shorter compared to many mass transfer models. The membrane separation field requires an alternative model that can work alone or in parallel with theoretical or numerical types, which can be quicker and, many a time, much more reliable. They are helpful in cases when scientists do not thoroughly know the physical and chemical rules that govern systems. In ANN modeling, there is no requirement for a deep knowledge of the processes and mathematical equations that govern them. Neural networks are commonly used for the estimation of membrane performance characteristics such as the permeate flux and rejection over the entire range of the process variables, such as pressure, solute concentration, temperature, superficial flow velocity, etc. This review investigates the important aspects of ANNs such as methods of development and training, and modeling strategies in correlation with different types of applications [microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), electrodialysis (ED), etc.]. It also deals with particular types of ANNs that have been confirmed to be effective in practical applications and points out the advantages and disadvantages of using them. The combination of ANN with accurate model predictions and a mechanistic model with less accurate predictions that render physical and chemical laws can provide a thorough understanding of a process.

Water Reclamation Using a Ceramic Nanofiltration Membrane and Surface Flushing with Ozonated Water

A new membrane fouling control technique using ozonated water flushing was evaluated for direct nanofiltration (NF) of secondary wastewater effluent using a ceramic NF membrane. Experiments were conducted at a permeate flux of 44 L/m²h to evaluate the ozonated water flushing technique for fouling mitigation. Surface flushing with clean water did not effectively remove foulants from the NF membrane. In contrast, surface flushing with ozonated water (4 mg/L dissolved ozone) could effectively remove most foulants to restore the membrane permeability. This surface flushing technique using ozonated water was able to limit the progression of fouling to 35% in transmembrane pressure increase over five filtration cycles. Results from this study also heighten the need for further development of ceramic NF membrane to ensure adequate removal of pharmaceuticals and personal care products (PPCPs) for water recycling applications. The ceramic NF membrane used in this study showed approximately 40% TOC rejection, and the rejection of PPCPs was generally low and highly variable. It is expected that the fouling mitigation technique developed here is even more important for ceramic NF membranes with smaller pore size and thus better PPCP rejection.

Incorporation of Graphene-Related Carbon Nanosheets in Membrane Fabrication for Water Treatment: A Review

The minimization of the trade-off between the flux and the selectivity of membranes is a key area that researchers are continually working to optimise, particularly in the area of fabrication of novel membranes. Flux versus selectivity issues apply in many industrial applications of membranes, for example the unwanted diffusion of methanol in fuel cells, retention of valuable proteins in downstream processing of biopharmaceuticals, rejection of organic matter and micro-organisms in water treatment, or salt permeation in desalination. The incorporation of nanosheets within membrane structures can potentially lead to enhancements in such properties as the antifouling ability, hydrophilicy and permeability of membranes, with concomitant improvements in the flux/selectivity balance. Graphene nanosheets and derivatives such as graphene oxide and reduced graphene oxide have been investigated for this purpose, for example inclusion of nanosheets within the active layer of Reverse Osmosis or Nanofiltration membranes or the blending of nanosheets as fillers within Ultrafiltration membranes. This review summarizes the incorporation of graphene derivatives into polymeric membranes for water treatment with a focus on a number of industrial applications, including desalination and pharmaceutical removal, where enhancement of productivity and reduction in fouling characteristics have been afforded by appropriate incorporation of graphene derived nanosheets during membrane fabrication.

Membrane processes for removal of pharmaceutically active compounds (PhACs) from water and wastewaters

Pharmaceutically active compounds (PhACs), which find their way easily into the water sources, are emerging as a major concern for drinking water quality and aquatic species. Therefore, their removal from water sources is a priority from environmental point of view. During the past decade, different methods including membrane separation, adsorption systems and chemical transformation have been evaluated for removal of these compounds. This paper reviews different aspects of PhAC removal by using membrane separation processes, as they have been conventionally known to show high potential in the production of superior quality drinking and industrial water. In brief, osmosis membranes can efficiently remove almost all PhACs though its operational cost is relatively high and nanofiltration (NF) membranes are highly influenced by electrostatic and hydrophobic interaction. Moreover, the efficiency of membrane bioreactors (MBRs) is difficult to predict due to the complex interaction of compounds with microorganisms. To improve the performance and robustness of membrane technology, it is suggested to combine membranes with other systems, such as activated carbon and enzymatic degradation.

Concentration polarization phenomenon during the nanofiltration of multi-ionic solutions: influence of the filtrated solution and operating conditions

One of the major difficulties for the prediction of separation performances in the case of multi-ionic mixtures nanofiltration lies in the description of the concentration polarization phenomenon. Usual models available in literature do not take account of the polarization phenomenon or only describe it cursorily. Very few studies dedicated to the understanding and the specific description of the concentration polarization phenomenon are available in literature and a 2-D multi-ionic model describing the layer heterogeneity along the membrane length has never been proposed yet. The model used in the present work, called Pore and Polarization Transport Model (PPTM), allows an accurate description of the concentration polarization layer occurring during the filtration of multi-ionic solutions by taking account of the radial electromigrative transport in the layer, the turbulence, as well as the axial heterogeneity. In this context, the present paper aims at proposing a numerical investigation of the influence of operating conditions on the behavior of the polarization layer occurring at the membrane vicinity. The input parameters governing the transport through the membrane have been assessed in a previous study in the same experimental conditions so that only the polarization layer is investigated here. The proposed model which was previously validated on experimental observed rejection curves is then used to understand how operating conditions, such as applied pressure, feed flow-rate, or divalent ion proportion, govern the polarization phenomenon. For this purpose, concentration and thickness axial profiles along the membrane length and radial profiles within the polarization layer are investigated for various conditions. Finally, the impact of the type of divalent ion and the number of ions is also studied on various mixtures.

Hydrodynamic modeling of NOM transport in UF: effects of charge density and ionic strength on effective size and sieving

The transport behavior of natural organic matter (NOM) across polyethersulfone (PES) UF membranes having a range of nominal molecularweight cutoffs (MWCOs) was investigated and described with a hydrodynamic transport model. Transport of whole NOM and NOM fractionated on an anion exchange resin (IRA 958) was measured to investigate the impact of NOM size and charge density. It was found that the dominant transport mechanism, characterized by the membrane Peclet number, depended on the membrane MWCO, and transitioned from diffusion to convection at a MWCO of about 10 kDa. Increasing ionic strength significantly decreased the effective solute radius and decreased the observed rejection of charged NOM fractions, whereas no significant change was seen for neutral fractions. Using an available theoretical model for partitioning of charged solutes, the effect of ionic strength on the electrical double layer thickness can account for the observed changes in effective solute radius. These results provide insight into the role of solute charge and electrostatic interactions in NOM transport behavior.

Influence of electrostatic interactions on the rejection with NF and assessment of the removal efficiency during NF/GAC treatment of pharmaceutically active compounds in surface water

The removal efficiency of several pharmaceutically active compounds from two different surface water types was investigated. Two different nanofiltration (NF) membranes (Trisep TS-80 and Desal HL) were first studied at low feed water recoveries (10%). In a second phase, the combination of an NF unit at higher feed water recovery (80%) with subsequent granular activated carbon (GAC) filtration of the permeate was investigated. Results indicate that removal of the selected pharmaceuticals with NF is mainly influenced by charge effects: negatively charged solutes are better removed, compared with uncharged solutes, which are, in turn, better removed compared with positively charged solutes. This latter trend is mainly due to charge attractions between the negatively charged membrane surface and positively charged solutes. Increasing feed concentrations of positively charged pharmaceuticals lead to increasing rejection values, due to membrane charge-shielding effects. The removal efficiency of pharmaceuticals with the combination NF/GAC is extremely high. This is mainly due to an increased adsorption capacity of the activated carbon since the largest part of the natural organic matter (NOM) is removed in the NF step. This NOM normally competes with pharmaceuticals for adsorption sites on the carbon.

Rejection of emerging organic micropollutants in nanofiltration-reverse osmosis membrane applications

The rejection of emerging trace organics by a variety of commercial reverse osmosis (RO), nanofiltration (NF), and ultra-low-pressure RO (ULPRO) membranes was investigated using TFC-HR, NF-90, NF-200, TFC-SR2, and XLE spiral membrane elements (Koch Membrane Systems, Wilmington, Massachusetts) to simulate operational conditions for drinking-water treatment and wastewater reclamation. In general, the presence of effluent organic matter (EfOM) improved the rejection of ionic organics by tight NF and RO membranes, as compared to a type-II water matrix (adjusted by ionic strength and hardness), likely as a result of a decreased negatively charged membrane surface. Rejection of ionic pharmaceutical residues and pesticides exceeded 95% by NF-90, XLE, and TFC-HR membranes and was above 89% for the NF-200 membrane. Hydrophobic nonionic compounds, such as bromoform and chloroform, exhibited a high initial rejection, as a result of both hydrophobic-hydrophobic solute-membrane interactions and steric exclusion, but rejection decreased significantly after 10 hours of operation because of partitioning of solutes through the membranes. This resulted in a partial removal of disinfection byproducts by the RO membrane TFC-HR. In a type-II water matrix, the effect of increasing feed water recoveries on rejection of hydrophilic ionic and nonionic compounds was compound-dependent and not consistent for different membranes. The presence of EfOM, however, could neutralize the effect of hydrodynamic operating condition on rejection performance. The ULPRO and tight NF membranes were operated at lower feed pressure, as compared to the TFC-HR, and provided a product water quality similar to a conventional RO membrane, regarding trace organics of interest.

Factors affecting the rejection of organic solutes during NF/RO treatment--a literature review

The incomplete rejection of certain pesticides, disinfection by-products, endocrine disrupting compounds, and pharmaceutically active compounds has been reported during full- and pilot-scale high-pressure membrane applications. Since the removal of these compounds in water and wastewater treatment applications is of great importance where a high product water quality is desired, an understanding of the factors affecting the permeation of solutes in high-pressure membrane systems is needed. In this paper, findings of a comprehensive literature review are reported, targeting membrane rejection mechanisms and factors affecting rejection. The following key solute parameters were identified to primarily affect solute rejection: molecular weight (MW), molecular size (length and width), acid disassociation constant (pKa), hydrophobicity/hydrophilicity (log Kow), and diffusion coefficient (Dp). Key membrane properties affecting rejection that were identified include molecular weight cut-off, pore size, surface charge (measured as zeta potential), hydrophobicity/hydrophilicity (measured as contact angle), and surface morphology (measured as roughness). In addition, feed water composition, such as pH, ionic strength, hardness, and the presence of organic matter, was also identified as having an influence on solute rejection. From the knowledge gained during the literature review, a rejection diagram was proposed, which qualitatively allows prediction of solute rejection if certain solute and membrane properties are known.

Recovery of clindamycin from fermentation wastewater with nanofiltration membranes

Experiments were carried out on clindamycin's separation and recovery from clindamycin fermentation wastewater with nanofiltration (NF) membranes. Four types of flat-sheet NF membranes, DLNF-1, NTR-7250, XCNF-1 and MPF-44, were tested under different dynamic operating conditions. It was found that the operating pressure and solute concentration had great influence on membrane performance while flow rates (or velocities) had little influence on membrane performance. Experiments on SO4(2-) rejection were conducted with such four flat-sheet NF membranes because SO4(2-) had bad influence on microbes in biochemical process following the NF process. The results indicated that DLNF-1 and MPF-44 membranes had higher SO4(2-) rejection among four membranes. Two spiral membranes, MPS-44 (1.4 m2) and DLNF2-30 (0.24 m2), were adopted in a concentrating process for clindamycin's separation and recovery from clindamycin fermentation wastewater under laboratory conditions. After being operated for 60h, clindamycin wastewater was concentrated from 266 to 26L, and the clindamycin was concentrated from 220 to 1940 mg/L, which met the demand of reuse. This research may widen the application of NF membranes in disposal of pharmaceutical wastewater.

Removal of pollutants from surface water and groundwater by nanofiltration: overview of possible applications in the drinking water industry

During the last decade, nanofiltration (NF) made a breakthrough in drinking water production for the removal of pollutants. The combination of new standards for drinking water quality and the steady improvement of the nanofiltration process have led to new insights, possible applications and new projects on lab-scale, pilot scale and industrial scale. This paper offers an overview of the applications in the drinking water industry that have already been realised or that are suggested on the basis of lab-scale research. Applications can be found in the treatment of surface water as well as groundwater. The possibility of using NF for the removal of hardness, natural organic material (NOM), micropollutants such as pesticides and VOCs, viruses and bacteria, salinity, nitrates, and arsenic will be discussed. Some of these applications have proven to be reliable and can be considered as known techniques; other applications are still studied on laboratory scale. Modelling is difficult due to effects of fouling and interaction between different components. The current insight in the separation mechanisms will be briefly discussed.

Disinfection byproduct relationships and speciation in chlorinated nanofiltered waters

The formation and speciation of disinfection byproducts (DBPs) resulting from chlorination of nanofilter permeates obtained from various source water locations and membrane types are examined. Specific ultraviolet absorbance and bromide utilization are shown to decrease following nanofiltration. Both dissolved organic carbon (DOC) concentration and ultraviolet absorbance at 254 nm were found to correlate strongly with trihalomethane (THM), haloacetic acid (HAA), and total organic halide (TOX) concentrations in chlorinated nanofilter permeates, suggesting that they can be employed as surrogates for DBPs in nanofiltered waters. Because smooth curves were obtained for individual THM and HAA species as well as bromine and chlorine incorporation into THMs and HAAs as a function of Br-/DOC molar ratio, it is likely that mole fractions of these DBPs are more strongly influenced by chlorination conditions, Br-, and DOC concentrations than NOM source and membrane type. Mole fractions of mono-, di-, and trihalogenated HAAs were found to be independent of Br-/DOC. Even at a very low Br-/DOC of 2.9microM/mM, the mixed bromochloro- and tribromoacetic acids constituted 20% of total HAAs on a molar basis. This increased to approximately 50% as Br-/DOC increased to approximately 25microM/mM or more, proving that a large fraction of HAAs may not be covered under existing federal regulations. Total THM and HAA9 concentrations decreased in permeate waters with increasing Br-/DOC suggesting that nanofilter permeates are limited with respect to DBP precursors.