Natural Organic Matter Rejection Research Articles

Catalytic pre-coat on ceramic nanofiltration membranes for segregation and Fenton cleaning of high-resistance colloids in direct surface water treatment

Ceramic nanofiltration (NF) is a promising alternative for direct surface water treatment, but is hampered for full-scale applications by fouling and a lack of eco-friendly cleaning regimes. In this work, an innovative reactive pre-coat layer, consisting of an iron oxychloride catalyst, was constructed on top of commercial ceramic NF membranes, for segregating a large-sized colloid fraction in canal water and Fenton cleaning with a hydrogen peroxide (H2O2) solution. The large-sized colloids (3−30 μm) were identified as dominant substances fouling the TiO2 separation layer of the pristine membranes, leading to a fast increase in their filtration resistance, in contrast to the small-sized colloids (<0.04 μm) and natural organic matter (NOM). As a consequence, the catalyst pre-coat layer with a pore size of 0.1–0.5 μm was able to segregate the large-sized colloids from the TiO2 separation layer during direct filtration of the raw water. Moreover, filtration under an acceptable flux of around 23 L m−2 h−1 did not cause pore clogging in the catalyst pre-coat. In addition, Fenton oxidation initiated by the catalytic pre-coat efficiently restored the filtration resistance, whereas sole H2O2 flush of the pristine membrane was not effective. In the meantime, the TiO2 separation layer of the membrane exerted a high NOM rejection of approximately 90%, measured as dissolved organic carbon, while the catalyst pre-coat on the membrane remained active in Fenton cleaning, over five one-day cycles. The findings of this work may provide guidance on the structural and functional design of a catalytic pre-coat layer for a dual purpose of foulant segregation and oxidative removal, particularly in response to key fouling-causing substances, during membrane-based treatment of real water matrices.

Synergistic effect of GO/ZnO loading on the performance of cellulose acetate/chitosan blended reverse osmosis membranes for NOM rejection

Declining freshwater resources along with their pollution are threatening the life existence on earth. To meet the freshwater demand, one of the most appropriate and possible ways which has been adopted all over the world is to reuse wastewater by removing its impurities. Among many water pollutants, natural organic matter (NOM) is found to be responsible as major precursor for the formation of other pollutants. Removal of NOM from wastewater is being done by using membrane filtration systems incorporated with certain nanofillers to increase membranes efficiency and permeability. In this study, novel nanocomposite reverse osmosis (RO) membranes were prepared using cellulose acetate and chitosan in N,N-Dimethyl formamide. Graphene oxide (GO) nanosheets and zinc oxide (ZnO) in different concentration were loaded to modify the membranes for tuning their RO performance. The confirmation of the functional groups is demonstrated by Fourier transform infrared spectroscopy which revealed the specific peaks indicating the formation of the nano-composite membranes. The surface morphology was studied by scanning electronic microscopy which shows a gradual transformation of the membrane surface from voids-free to macro-voids filled surface up to threshold concentration of GO and ZnO. The thermal properties of GO based membranes were analyzed using thermogravimetric analysis and differential scanning calorimetry. The uniform interaction of the GO and ZnO with polymers induced the remarkable thermal properties of the synthesized membranes. Permeate flux and contact angle measurements were considered to estimate their water content (96%) capacity and NOM rejection (96%) using 0.1 ppm humic acid solution. The permeate flux, NOM rejection and the water content changed directly with GO and inversely with ZnO wt% in the membranes up to GO5 (GO:0.14: ZnO:0.03) whereas the contact angle exhibited the inverse relationship with GO and ZnO concentration in casting solution of the synthesized membranes. Hence it can be concluded that prepared RO membranes are suitable for NOM rejection and recommended for water treatment.

Loose nanofiltration membranes for selective rejection of natural organic matter and mineral salts in drinking water treatment

Loose nanofiltration (LNF) is a promising technology for advanced treatment of drinking water, primarily owing to the potentially high rejection of natural organic matter (NOM) and high passage of mineral salts, particularly divalent cations, along with the low operating pressure. This study was devoted to relating the performance with the properties of LNF membranes, and obtaining the membrane properties most suitable for drinking water treatment. Cluster analysis indicated that the commercially available LNF membranes would behave quite differently, mainly depending on the molecular weight cut-off (MWCO). By using a treated natural water as the feed, a best-performing membrane had a mineral salts rejection lower than 30% and an NOM rejection higher than 70%, with the membrane water permeance at ∼17 L/m2/h/bar. The LNF membranes with high mineral salts/NOM selectivity should have an MWCO of around 1000 Da, sufficiently uniform pore sizes, and high surface negative charge density. The rejection characteristics for mineral ions by LNF membranes were similar with the relatively dense conventional NF membranes, but with a lower rejection difference among the ions, manifesting less strong co-ion and counter-ion competition effects. The LNF membranes with an MWCO of ∼1000 Da could satisfactorily remove (>80%) disinfection byproduct precursors, with small-sized protein-like and other substances remaining in the permeate water. This study helps to understand the rejection characteristics and mechanisms of LNF membranes, which will benefit the synthesis of high-performance LNF membranes for drinking water treatment and other applications.

Separation of natural organic matter and sodium chloride for salt recovery purposes in zero liquid discharge

The application of zero liquid discharge (ZLD) results in the generation of solid residual streams, which are often not fit for reuse. In this study, we assessed the separation of natural organic matter (NOM) and sodium chloride (NaCl) by nanofiltration (NF), electrodialysis (ED) and ion exchange (IEX) in reverse osmosis brine (RO-brine) and by the extraction of impurities from salt (SALEX) in the generated mixed solids of a full-scale ZLD water treatment plant.The NaCl recovery by NF, ED and IEX ranged 69-99% and the rejection of NOM ranged 18–19%, 43–65% and 53–76%, respectively. The recovery of NaCl by SALEX ranged 52–99%, while the rejection of NOM ranged 59–92%. The results show that NOM and NaCl can be separated both in RO-brine and mixed solids, opening opportunities for recovery of reusable salt from brines in ZLD.

Hybrid Hollow Fiber Nanofiltration-Calcite Contactor: A Novel Point-of-Entry Treatment for Removal of Dissolved Mn, Fe, NOM and Hardness from Domestic Groundwater Supplies.

Groundwater (GW) is one of the main potable water sources worldwide. However, the presence of undesirable compounds and particularly manganese (Mn) and iron (Fe) (mainly co-existing in GWs) are considered as objectionable components of potable water for both health and aesthetic issues. As such, individual dwellings supplied by domestic wells are especially threatened by these issues. Current domestic treatment technologies are complicated to operate and even dangerous if improperly maintained (e.g., catalytic filtration) or consume salts and produce spent brine which pollutes the environment (i.e., ion exchange resins). Therefore, it is of prime importance to design a simple and compact, yet robust, system for Mn and Fe control of the domestic GW sources, which can reliably guarantee the desired Mn limit in the finished water (g/L). In the course of this study, we demonstrated, for the first time, that a hybrid hollow fiber nanofiltration (HFNF)–calcite contactor process is a promising alternative for treating domestic GWs with elevated levels of Mn, Fe, natural organic matter (NOM) and hardness. The efficacy of the HFNF membranes in terms of removal of Mn, Fe, NOM and fouling was compared with commercially available NF270 and NF90 membranes. The results revealed that HFNF (100–200 Da) and NF90 maintained considerably high rejection of Mn, Fe and NOM due to their dominant sieving effect. In contrary, the rejections of the above-mentioned components were decreased in the presence of high hardness for the looser HFNF (200–300 Da) and NF270 membranes. No membrane fouling was detected and the permeate flux was stable when the hard GW was filtered with the HFNF membranes, regardless of their molecular weight cut-off and transmembrane pressure, while the permeability of the NF270 and NF90 membranes steadily decline during the filtration. Integrating a calcite contactor, as a post filtration step, to the HFNF process yielded further Mn, Fe and NOM removals from the HFNF permeate and adjustment of its hardness level. The best performance was achieved when a blend of Calcite–CorosexTM () was used as a post-treatment to the tight HFNF (100–200 Da).

Fabrication of graphene oxide incorporated polyethersulfone hybrid ultrafiltration membranes for humic acid removal

In this study, hybrid polyethersulfone membranes incorporated with graphene oxide were synthesized by a non-solvent induced phase separation approach. The influence of graphene oxide content on the membrane efficiency and fouling durability was elucidated, with emphasis on water flux, natural organic matter (NOM) rejection using humic acid as a model for NOM, and flux reduction due to fouling. The results revealed that the water flux increased with increasing GO content. It is worth noting that the MGO-5 membrane exhibits the highest Jw value (340 L m−2 h−1) among all the fabricated membrane, while the greatest JHA (193.78 L m−2 h−1) value was obtained for MGO-3 membrane. NOM rejection was improved significantly by the incorporation of GO. The best rejection value of HA solution using the membranes was observed for MGO-3 at pH 7. The presence of GO also improved the membrane reusability and antifouling capabilities, due to the enhancement of the hydrophilicity of the GO-membrane surface.

Performance of thin-film composite hollow fiber nanofiltration for the removal of dissolved Mn, Fe and NOM from domestic groundwater supplies

Groundwater (GW) is one of the most abundant water resources and around 1.5 billion people rely on GW as their main water supply. Manganese (Mn) and iron (Fe) are very common GW contaminants. Even though their presence is considered mainly as an organoleptic and operational nuisance, water with elevated Mn content may also lead to adverse health impacts. Amongst the most common treatment processes currently used to treat domestic GW supplies: catalytic filtration may lead to Mn leaching if improperly maintained; while ion exchange consumes a considerable amount of salt and produces a brine waste which pollutes the environment. Thus, it is proposed to design a simple, yet robust treatment system which can be implemented in small/remote communities or even domestic applications. To this end, the main objective of this investigation was to assess the potential application of novel outside-in sulfonated polyethersulfone thin-film composite hollow fiber nanofiltration (HFNF) membranes to remove dissolved Mn, Fe and natural organic matter (NOM) from domestic GW supplies. Of particular interest was the impact of GW matrix on performance of the HFNF membranes. Our experimental findings demonstrated that, in absence of hardness and the cumulative throughput of 1.9 L/m2, above 90% of Mn, Fe and NOM were retained by the examined HFNF membranes (MWCO ∼ 200 Da) regardless of their initial concentrations in the feed solution (250–1000 μ g/L). In contrast, increasing the hardness level reduced the removal of Mn and Fe ions. XPS analysis revealed that the surface properties of the HFNF membranes were altered when the membranes were exposed to calcium and magnesium salts. These observations were attributed to the propensity for Ca and Mg ions to bind to the sulfonic groups present on the surface of the HFNF membranes which, subsequently, weakens rejection by charge exclusion. On the other hand, in the absence of GW hardness, charge exclusion was mainly responsible for rejection of dissolved Mn and Fe. It was also found that GW hardness had no marked impact on the NOM rejection as the later was mostly removed by size exclusion.

Integrated oxidation membrane filtration process – NOM rejection and membrane fouling

The extent and mechanisms by which organic matter in a solution can be retained and foul a membrane largely depends on the molecular weight of the material being filtered and the molecular weight cut-off (MWCO) of the membrane. The present study investigated the effect of the MWCO of a membrane and the molecular weight distribution of natural organic matter (NOM) in a source water on the increase in resistance to the permeate flux over time. Of particular interest was the effect of oxidation, applied prior to membrane filtration, on the predominant fouling mechanism. Oxidation can change the molecular weight distribution of organic matter in raw water, and therefore the ability of a membrane to retain this organic matter.Oxidation, using both ozonation and UV/H2O2, could effectively reduce the extent of fouling for higher MWCO membranes. However, neither oxidation approaches could effectively reduce the extent of fouling for lower MWCO membranes, likely because oxidation could not effectively oxidize lower molecular weight organic matter. Althoug the data indicated that the extent of fouling is increasing with the amount of DOC retained by the membrane, no statistically significant correlation was observed between these parameters. The results suggest that oxidation did not affect the predominant fouling mechanism. However, it did affect the molecular weight distribution of the organic matter retained by the membranes, and as a result, the resistance offered by the foulant cake layer.

High flux and high selectivity carbon nanotube composite membranes for natural organic matter removal

Abstract Multi-wall carbon nanotubes (MWCNTs)/polyaniline (PANI)/polyethersulfone (PES) membranes were fabricated by incorporation of in-situ polymerised MWCNTs/PANI complex for effective removal of natural organic matter (NOM) in water. The membrane showed high permeability (1400 L/m2/h (LMH)/bar), which is 30 times greater than the PES membrane. High NOM rejection rate (80%) was also observed for the composite membrane, which is 4 times higher than PES membrane. This superior performance is attributed to the synergetic effect of increased porosity, narrow pore size distribution and hydrophilicity, and positively charged of the membranes by the inclusion of MWCNTs/PANI complex. MWCNTs/PANI electron transfer complex successfully engineered chemical/physical properties of the membrane in order to have high NOM adsorption capacity and fast water flux. It is suggested that enhanced adsorption capacity is attributed to the electrostatic interaction between NOM and the membrane surface. Key factors contributing to the fast water flux and removal mechanism were covered in depth by characterization of physical and chemical properties of the membrane. The membrane demonstrated 100% water flux recovery and 65% total fouling ratio after cleaning with 0.1 M HCl/0.1 M NaOH solution for 1 h.

Natural organic matter fouling behaviors on superwetting nanofiltration membranes

Nanofiltration has been widely recognized as a promising technology for the removal of micro-molecular organic components from natural water. Natural organic matter (NOM), a very important precursor of disinfection by-products, is currently considered as the major cause of membrane fouling. It is necessary to develop a membrane with both high NOM rejection and anti-NOM fouling properties. In this study, both superhydrophilic and superhydrophobic nanofiltration membranes for NOM removal have been fabricated. The fouling behavior of NOM on superwetting nanofiltration membranes has been extensively investigated by using humic acid (HA) as the model foulant. The extended Derjaguin−Landau−Verwey−Overbeek approach and nanoindentor scratch tests suggested that the superhydrophilic membrane had the strongest repulsion force to HA due to the highest positive total interaction energy (ΔGTOT) value and the lowest critical load. Excitation emission matrix analyses of natural water also indicated that the superhydrophilic membrane showed resistance to fouling by hydrophobic substances and therefore high removal thereof. Conversely, the superhydrophobic membrane showed resistance to fouling by hydrophilic substances and therefore high removal capacity. Long-term operation suggested that the superhydrophilic membrane had high stability due to its anti-NOM fouling capacity. Based on the different anti-fouling properties of the studied superwetting membranes, a combination of superhydrophilic and superhydrophobic membranes was examined to further improve the removal of both hydrophobic and hydrophilic pollutants. With a combination of superhydrophilic and superhydrophobic membranes, the NOM rejection (RUV254) and DOC removal rates (RDOC) could be increased to 83.6% and 73.3%, respectively.

Application of amine-functionalized MCM-41 modified ultrafiltration membrane to remove chromium (VI) and copper (II)

A thin-film composite ultrafiltration (UF) membrane grafted with amine-functionalized MCM-41 was prepared and used for removing heavy metals from aqueous solution. The porous NH2-MCM-41 nano-particles formed a uniform hydrophilic and adsorptive layer on the thin-film which endowed the composite membrane with affinity to heavy metals and better anti-fouling performance. The adsorption capacity of Cr (VI) and Cu (II) on membrane were 2.8mg Cr/g and 3.7mg Cu/g, respectively, and their adsorption processes reached equilibrium around 5min. The continuous UF experiments demonstrated that the membrane can be used as an effective filter medium to purify the water containing trace heavy metals. The metals concentration in filtrates was maintained below initial concentration of 1mg/L (Cu) and 0.5mg/L (Cr) during the 7-hour filtration. The membrane’s adsorption capacity could be regenerated by being immersed in 0.5M HNO3. Besides, to examine its anti-fouling performance, the model NOM (natural organic matter) water was used as a feed solution. The composite membrane showed not only slower irreversible fouling evolution but also higher rejection of NOM compared with that without grafting NH2-MCM-41. The method reported in this study was efficient to enhance the rejection and anti-fouling performance of UF membrane, what’s more, endowed the membrane with affinity to heavy metals.

Ultrathin graphene oxide membranes for the removal of humic acid

In this study, multiple layers of graphene oxide (GO) were coated on a commercially available polyethersulfone ultrafiltration membrane via simple vacuum filtration of a GO suspension. The effect of GO coating on the membrane performance and fouling resistance was examined, in terms of water flux, natural organic matter (NOM) rejection, and flux decline due to NOM fouling. The results showed that the water flux change of the permeate was minimal (less than ±10%), while NOM rejection was improved significantly by the GO coating (31%, 51%, and 67% for the GO-5nm, GO-10nm, and GO-30nm membranes, respectively). The GO-coated membranes also enhanced membrane recovery and antifouling capabilities, due mainly to increased hydrophilicity of the GO-membrane surface. These observations suggest that the GO-coated membrane, prepared by a facile filtration process in the laboratory, facilitates removal of NOM from water and minimizes the associated membrane fouling.

The removal of natural organic matter with LiCl–TiO2-doped PVDF membranes by integration of ultrafiltration with photocatalysis

Ultrafiltration has become one of the best alternatives replacing conventional drinking water treatment technologies because of increasing stringent regulations for drinking water quality. However, membrane fouling is an important factor which restricts its widespread application. In this study, the modified polyvinylidene fluoride (PVDF) membranes were prepared by adding different amounts of LiCl and TiO2 particles. The performances of PVDF–LiCl membranes and PVDF–LiCl–TiO2 membranes were investigated by discussing the rejection of natural organic matter (NOM) and flux decline in both dead-end and cross-flow filtration experiments. The effect of photocatalytic degradation on TiO2-doped PVDF membranes was also evaluated. Results from both this study and the previous one with the membrane prepared by adding organic addition agent PEG and TiO2 photocatalyst indicated that appropriate TiO2-doped modification on PVDF membrane could be an effective way for better NOM rejection and reduction of membrane fouling at the same time. TiO2-doped PVDF membrane also shows good self-cleaning ability. The fouled membrane can be cleaned with irradiation and the foulants' photocatalytic degradation is most effective in the first 30min.

Application of polysulfone/cyclodextrin mixed-matrix membranes in the removal of natural organic matter from water

The removal of natural organic matter (NOM) by polysulfone/β-cyclodextrin polyurethane (PSf/β-CDPU) mixed matrix membranes (MMMs) was investigated in order to establish the effect of the addition of β-cyclodextrin polyurethane (β-CDPU) in polysulfone (PSf) membrane on the rejection of NOM (humic acid) and the fouling resistance of MMMs. It was found that the effective pore sizes and molecular-weight-cut-off (MWCO) of hand-cast PSf membranes were improved by β-CDPU addition due to its large pore size and its conical structure being capable of allowing easy passage of water molecules. An increase in pure water flux was achieved with increase in β-CDPU concentration in the PSf MMMs. Furthermore, the pure water flux of the hand-cast PSf membrane improved from 12 to 137l/m2h when the applied pressure was increased from 0.62 to 2.41MPa. The highest NOM removal efficiency achieved was 69% based on TOC measurements whereas a 76% NOM removal efficiency was attained as calculated from UV254 analysis. Fourier transform infrared (FT-IR) spectroscopy analyses confirmed the absence of OH and CH groups on all membranes after NOM rejection. This accounted for the increase in contact angle obtained after rejection tests. It is suggested that solution–diffusion mechanism is responsible for NOM filtration/rejection process. In addition, scanning electron microscopy (SEM) micrographs (after NOM rejection tests) revealed that the addition of β-CDPU in PSf resulted in improved antifouling properties based on the agglomeration of NOM on the membrane surfaces.

Fouling of nanofiltration membrane: Effects of NOM molecular weight and microcystins

Toxic cyanotoxins such as microcystins represent a human health risk in water bodies. Nanofiltration is an effective technology to remove these micro-contaminants from drinking water. However, long-term operational sustainability is necessary because of decreases in membrane fluxes over time and increasing operation costs. The rejection of natural organic matter (NOM) is a key issue regarding membrane fouling and flux decline, and is also of great importance in the water industry due to its relationship with public health. Therefore, this study aimed to analyse the effect of microcystins and NOM properties on membrane fouling and to understand the fouling mechanisms, using a series of experiments with different water types. Results showed that nanofiltration was capable of reducing low molecular weight NOM fractions from water and that these fractions were responsible for flux decline and membrane fouling. The adsorption of NOM onto the membrane surface was reduced in the presence of microcystins due to the hydrophobic character of microcystins, which are the first to be adsorbed on the membrane surface. Microcystins contributed to the rejection of smaller natural organic fractions by blocking the membrane pores and reducing NOM adsorption onto the membrane pores.

Flux patterns and membrane fouling propensity during desalination of seawater by forward osmosis

The membrane fouling propensity of natural seawater during forward osmosis was studied. Seawater from the Red Sea was used as the feed in a forward osmosis process while a 2 M sodium chloride solution was used as the draw solution. The process was conducted in a semi-batch mode under two crossflow velocities, 16.7 cm/s and 4.2 cm/s. For the first time reported, silica scaling was found to be the dominant inorganic fouling (scaling) on the surface of membrane active layer during seawater forward osmosis. Polymerization of dissolved silica was the major mechanism for the formation of silica scaling. After ten batches of seawater forward osmosis, the membrane surface was covered by a fouling layer of assorted polymerized silica clusters and natural organic matter, especially biopolymers. Moreover, the absorbed biopolymers also provided bacterial attachment sites. The accumulated organic fouling could be partially removed by water flushing while the polymerized silica was difficult to remove. The rate of flux decline was about 53% with a crossflow velocity of 16.7 cm/s while reaching more than 70% with a crossflow velocity of 4.2 cm/s. Both concentration polarization and fouling played roles in the decrease of flux. The salt rejection was stable at about 98% during seawater forward osmosis. In addition, an almost complete rejection of natural organic matter was attained. The results from this study are valuable for the design and development of a successful protocol for a pretreatment process before seawater forward osmosis and a cleaning method for fouled membranes.

Assessing the fouling mechanisms of high-pressure nanofiltration membrane using the modified Hermia model and the resistance-in-series model

The fouling phenomenon and associated fouling mechanisms of the cross-flow type nanofiltration membrane were investigated using the modified Hermia empirical model and the resistance-in-series model. The effects of pH on membrane permeate flux and the rejection of natural organic matter (NOM) were also studied. Natural water and the effluent of a rapid sand filter (SF) were used as the source waters. The results showed that when the raw water was treated, the highest flux decline occurred at pH 5 due to weak electrostatic repulsion between the charged membrane and NOM. Moreover, a two-step fouling process in flux decline before 7 h and after 7 h was observed during the treatment of the raw water. Ultimately, physically reversible rather than irreversible fouling was the main fouling mechanism. Standard blocking was not a fouling mechanism for either of the water samples treated at any pH level, indicating that the foulants were not adsorbed onto the inner walls of membrane pores. For raw water, intermediate blocking was the major fouling mechanism at all pH levels, whereas for the SF effluent, gel layer formation played the major role in membrane fouling at all pH levels.

Role of natural organic matter (NOM), colloidal particles, and solution chemistry on ultrafiltration performance

Mechanistic studies on a charged ultrafiltration (UF) membrane fouled with natural organic matter (NOM) and colloidal particles are systematically investigated to understand the relative role of each NOM fraction and the presence of colloidal particulate to membrane fouling. Humic acid (HA), dextran, and kaolin were employed as surrogate model foulants representing the organic hydrophobic acid NOM, hydrophilic neutral NOM, and inorganic colloidal materials, respectively. The results obtained showed that the organic NOM of hydrophilic surrogate (dextran) plays a primary role in promoting membrane fouling, followed by hydrophobic acids and inorganic kaolin, but to a lesser extent than organic NOM compounds. Significant differences in the extent of fouling between dextran and HA have been observed despite filtering with identical membrane. Greater membrane fluxes and better DOC rejection shown by HA could be seen as evidence demonstrating the electrostatic interactions between HA and the negatively charged membrane surface, in addition to the steric hindrance mechanism, despite possessing relatively greater adsorptive interactions with the hydrophobic PSF membrane. These results suggest that NOM structural variations (aromatic versus aliphatic molecular structure), distribution (apparent molecular weight and size), and charge density are essential factors that determine the fouling potential of each NOM fraction. Feed solution containing all the NOM fractions (HA, dextran, and kaolin) fouled the membrane more readily than the individual organic and colloidal foulants, suggesting that an association of the latter two entities is responsible for the greater extent of membrane fouling. Furthermore, the electrokinetic effects of solution chemistry (ionic strength and Ca 2+) was employed to quantify the role of electrostatic interactions in providing principal effect that promotes better permeate flux and NOM rejection, particularly with the charged component such as HA. Moreover, observation of this study is beneficial in elucidating a clearer understanding on the influential factors and responsible mechanisms of UF fouling owing to single NOM solute and multiple NOM solute systems, with respect to membrane filterability and rejection efficiency.

The use of iron oxide-coated ceramic membranes in removing natural organic matter and phenol from waters

Ceramic tight-ultrafiltration (UF) membranes were coated with iron oxide layers to investigate the removals of phenol and/or natural organic matter (NOM) from waters. The effects of iron oxide coating on NOM rejections were dependent on NOM characteristics in waters. Iron oxide coating of the membrane increased NOM rejections in a water with high specific UV absorbance (SUVA) value, due to sorption of NOM, especially the UV 280 absorbing fractions, to the iron oxide surfaces. In the low-SUVA water, aluminum oxide and iron oxide membrane surfaces behaved similarly in terms of NOM rejection. There were no interactions among phenol and NOM fractions and their rejections by aluminum oxide or iron oxide surfaces of the ceramic membranes were not affected by each other. Pore size exclusion mechanism played minor role in the rejection of phenol; the major rejection mechanism was electrostatic repulsion, depending on water pH. Compared with the uncoated membrane, membrane coating did not change membrane permeability. Coated iron oxides were stable and iron leaking was not observed. Coating tight-UF ceramic membranes with iron oxide layers may improve NOM rejections during drinking water treatment, especially in waters with high SUVA values.

A green membrane functionalization method to decrease natural organic matter fouling

Cellulose acetate (CA) ultrafiltration membranes were functionalized using a green chemistry approach. In the functionalization, an enzyme, Porcine pancreatic crude type II lipase (PPL), was used to polycondensate poly ethylene glycol (PEG) to the surface of the CA membranes. Modification was verified using structural and morphological analyses. The unmodified and the modified membranes displayed similar initial flux values, flux decline curves and rejection efficiencies when dextran and bovine serum albumin (BSA) were used as feed solutions. This was likely due to the high degree of hydrophilicity and similar charge characteristics between the modified and unmodified membranes. However, when natural organic matter (NOM) was filtered through the membranes, it was determined that modification led to lower cake accumulation on the surface of the modified membrane, to lower flux declines during operation, while NOM rejection remained unchanged. Furthermore, after backwashing, the modified membrane regained nearly 97% of its initial flux value within 40 min of filtration, while the unmodified membrane recovered only 85%. This improvement is possibly due to the high flexibility of the PEG chains grafted. Therefore, the use of PPL to polycondensate PEG to a CA membrane was deemed a successful functionalization process to decrease NOM fouling.