Heated Aluminum Oxide Research Articles

Evaluation of various factors influencing dynamic membrane formation and performance using metal oxide adsorbent

A dynamic membrane (DM) comprises a layer of particles deposited onto a conventional membrane, which minimizes fouling of the primary membrane to enhance permeate fluxes. Because DMs are involved in adsorption, the size and material of the adsorbent significantly affect DM performance. However, the comprehensive effects of these factors on DMs remain unclear. Herein, the factors influencing DM morphology and performance were investigated by varying the size of two different DM adsorbent materials: heated aluminum oxide particles (HAOPs) and heated iron oxide particles (HIOPs), deposited on polymeric and ceramic (CE) membranes. The density of the dynamic layer increased as the adsorbent particle size decreased. All DMs exhibited approximately 30 % improved flux and higher humic acid (HA) removal efficiencies (HAOP-DM:90 %, HIOP-DM:82 %) than the virgin membranes. Adsorbent size significantly affected DM performance; a five-fold size reduction resulted in an approximately 25 % increase in HA removal. A membrane resistance model was employed to quantitatively analyze the DM performance. HIOP-DM exhibited 80 %–90 % reversible fouling, whereas HAOP-CE displayed 70 %–80 % irreversible fouling. Because reversible fouling was the dominant mechanism of HIOPs, the DMs were reused after chemical treatment. However, HAOP DMs required replacement, despite their high water flux retention and HA removal efficiency.

Synthesis of heated aluminum oxide particles impregnated with Prussian blue for cesium and natural organic matter adsorption: Experimental and machine learning modeling

Heated aluminum oxide particles impregnated with Prussian blue (HAOPs-PB) are synthesized for the first time using different molar ratios of aluminum sulfate and PB to improve the adsorption of cesium (133Cs+) and natural organic matter (NOM) from an aqueous solution. The Cs+ adsorption from various aqueous solutions, including surface, tap and deionized water by synthesized HAOPs-PB, is investigated. The influencing factors such as HAOPs-PB mixing ratio, pH and dosage are studied. In addition, pseudo 1st and 2nd order is tested for adsorption kinetics study. A machine learning model is developed using gene expression programming (GEP) to evaluate and optimize the adsorption process for Cs+ and NOM removal. Synthesized adsorbent showed maximum adsorption at a 1:1 M ratio of aluminum sulfate and PB in DI, tap, and surface water. The pseudo 2nd order kinetics model described the Cs + adsorption by HAOPs-PB more accurately that indicating physiochemical adsorption. Adsorption of Cs+ showed an increasing trend with higher HAOPs-PB concentration, while high pH also favored the adsorption. Maximum NOM adsorption is found at a higher HAOPs-PB dosage and a neutral pH value. Furthermore, the proposed GEP model shows outstanding performance for Cs+ adsorption modeling, whereas a modified-GEP model presents promising results for NOM adsorption prediction for testing dataset by learning the relationship between inputs and output with R2 values of 0.9348 and 0.889, respectively.

Molecular dynamics simulation of the competitive adsorption behavior of effluent organic matters by heated aluminum oxide particles (HAOPs)

Fouling mitigation of reverse osmosis membranes using various pre-treatment methods has received tremendous attention in the past years. The use of dynamic membranes particularly composed of heated aluminum oxide particles (HAOPs) appears to be a promising approach. Based off adsorption behaviors by individual foulants revealed by molecular dynamics (MD) simulations in an earlier study, this study targeted to understand the competitive adsorption of different constituents of effluent organic matters (EfOM) on HAOPs, which mimics the high local foulant concentration at the boundary layer. Quantitative analysis reveals that (i) EfOM constituents, except for low-molecular-weight neutrals, exhibit means to anchor onto HAOPs despite steric hindrance; (ii) adsorbed foulants exhibit significantly lower mobility and flexibility, indicating excellent adsorption capability of HAOPs before the dynamic membrane layer becoomes fully saturated with EfOM; and (iii) divalent ions and carboxylic group play critical roles in facilitating the adsorption of foulants. The MD results provide molecular-level mechanistic insights on the superior pre-treatment effectiveness by HAOPs.

Molecular Dynamics Simulation of the Competitive Adsorption Behavior of Effluent Organic Matters by Heated Aluminum Oxide Particles (Haops)

Molecular Dynamics Simulation of the Competitive Adsorption Behavior of Effluent Organic Matters by Heated Aluminum Oxide Particles (Haops)

Synthesis of Heated Aluminum Oxide Particles Impregnated with Prussian Blue for Cesium and Natural Organic Matter Adsorption: Experimental and Machine Learning Modeling

Synthesis of Heated Aluminum Oxide Particles Impregnated with Prussian Blue for Cesium and Natural Organic Matter Adsorption: Experimental and Machine Learning Modeling

Natural organic matter removal by electrospun nanofiber membranes coated with heated aluminum oxide particles

The removal of natural organic matter (NOM) from water was studied using polyacrylonitrile (PAN) electrospun nanofibrous membrane (ENM) coated with HAOPs (heated aluminum oxide particles). The removal efficiencies of virgin PAN and HAOP-coated PAN were examined and the suitability of PAN as a support material for HAOPs was studied.The membranes were characterized with Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscope and energy dispersive X-ray spectrometer (SEM-EDS) as well as X-ray photoelectron spectroscopy (XPS). Several analytical techniques were applied to both the feed and the permeate to assess the effectiveness of NOM removal.In filtration of lake water, HAOPs efficiency in NOM removal was 56% measured by UV254 absorbance, but when it comes to virgin PAN membrane the removal efficiency was only 13%. In case of filtration of NOM's high molecular weight component, such as humic acid (HA), the rejection rate of HA was maintained above 97% of aromatic compounds of NOM, and above 43% of total organic carbon (TOC).Additionally, HA adsorption by HAOPs were fitted to isotherm models such as Langmuir and Freundlich models. The results showed that Langmuir model could fit the data better than Freundlich model. The kinetics of HA adsorption by HAOPs were also fitted to the pseudo-first order and pseudo-second order and for the initial HA concentration of 19.9 mg/L the pseudo-first order equation fitted the experimental data better with correlation coefficient of R2 = 0.8336.The results demonstrate that PAN ENM filtration has the potential to be employed as a pretreatment in water treatment and HAOP-coated PAN ENM can significantly enhance the removal of NOM.

Adsorption of Natural Organic Matter and Phosphorus from Surface Water Using Heated Aluminum Oxide (Predeposited) Dynamic Membrane Adsorber

The paper reports the removal of phosphorus and natural organic matter (NOM) from surface water by dynamic membrane (DM) adsorber. DM filter builds up as a layer of particles deposited via permeation through the membrane’s surface. This study reports the application of Heated Aluminium Oxide Particles (HAOPs) as a dynamic membrane adsorber. Filtration experiments were conducted with surface water and batch tests were carried out with synthetic water. The efficiency of phosphorus removal along with the efficiency of organics (represented as UV-254) removal was evaluated. Additionally, the impact of HAOPs surface loading on the changes of transmembrane pressure (TMP), the kinetics, isotherm modeling of the adsorption and the effect of the pH, the effect of ionic strength, the effect of coexisting organic matter on phosphorus removal efficiency were studied. In the case of phosphorus removal in batch adsorption experiments, its sorption kinetic and isotherm data were analyzed using pseudo-first- and pseudo-second-order models and Langmuir and Freundlich models, respectively. The results indicated that Langmuir adsorption isotherm fits the experimental data best (0.9894). The kinetics of phosphorus adsorption on HAOPs was best described by the pseudo-second-order model and the best removal was achieved at the pH 6–7 (96.65% on average). An increase in ionic strength did not impact the efficiency of phosphorus removal significantly. The outcome of this study highlights HAOPs efficiency in NOM removal up to 92% in filtration experiments. In the case of phosphorous, removal efficiency varied. For the highest HAOPs dose, the degree of phosphorus removal ranged up to 93 ± 5%. The same removal efficiency was observed for the lowest dose while for 17 g/m2 of HAOPs the fluctuations were larger and varied from 64.7% to 92%. The results demonstrate that HAOPs could potentially be applied in the removal of phosphorus from surface water, especially when there is a high concentration of phosphorus in the water. However, this process requires further research and optimization of its parameters.

Organic matter removal from a membrane bioreactor effluent for reverse osmosis fouling mitigation by microgranular adsorptive filtration system

In this study, a prototype microgranular adsorptive filtration (μGAF) system was constructed employing a 7-bore ceramic membrane as the primary membrane and either heated aluminum oxide particles (HAOPs) or powdered activated carbon (PAC) as the pre-deposited dynamic membrane (DM). The system was used to pre-treat membrane bioreactor (MBR) effluent from a full-scale MBR-reverse osmosis (RO) water reclamation plant. The downstream RO performance and membrane fouling potential of the treated effluent were then assessed. The results indicated that: (i) although PAC removed more overall EfOM than HAOPs did, HAOPs were more effective in removing biopolymers such as polysaccharides and proteins, (ii) HAOPs virtually eliminated fouling of the primary ceramic membrane, whereas considerable fouling (much of it irreversible) occurred when the feed was pretreated with PAC, (iii) HAOPs removed more than 90% of the phosphorus and fluoride from the feed, but PAC removed negligible amounts of these contaminants, and (iv) HAOPs-treated effluent resulted in only a 43% decline in RO permeate water flux over 5 d of continuous filtration, as opposed to 62% flux decline for untreated or PAC-treated effluent. This study thus demonstrates the effectiveness of the HAOPs-based μGAF process as a pre-treatment for improving downstream RO recovery.

Adsorption of uranium from groundwater using heated aluminum oxide particles

The adsorption of uranium, U(VI) from groundwater was investigated using heated aluminum oxide particles (HAOPs) which were manufactured from aluminum sulfate. The effects of adsorbent dosage, pH, water temperature, contact time, and initial uranium concentrations on the removal of U(VI) were assessed in batch tests using groundwater containing CaUO2(CO3)32− and Ca2UO2(CO3)3(aq) as dominant species. The maximum adsorption density (qmax) value at pH 6.0 was relatively higher than those at higher pH because HAOPs with a negative surface charge readily bind with the cationic complexes (UO2(OH)+ and (UO2)3(OH)5+). U(VI) adsorption by HAOPs was higher at lower temperatures while the difference between 5 and 20 °C was not significant. The equilibrium adsorption capacity (qe) increased proportionally with increasing initial U(VI) concentration per specific amount of adsorbent. Anions such as sulfate and bicarbonate interfered with U(VI) adsorption at > 20 mM concentration. However, the U(VI) adsorption efficiency was not significantly changed by water temperature, pH and competing substances within the rages typically occurring in natural groundwater. The U(VI) adsorption by HAOPs rapidly reached saturation within 15 s, and was exothermic and spontaneous with chemical adsorption onto a single HAOP layer.

Effects of a Novel Adsorbent on Membrane Fouling by Natural Organic Matter in Drinking Water Treatment.

Irreversible fouling of water filtration membranes reduces filter longevity and results in higher costs associated with membrane maintenance and premature replacement. The search for effective pretreatment methods to remove foulants that tend to irreversibly foul membranes is ongoing. In this study, a novel adsorbent (Heated Aluminum Oxide Particles (HAOPs)) was deployed in a fully automated pilot system to remove natural organic matter (NOM) from the surface water source used at the UniVann water treatment plant (WTP) in Ullensaker County, Norway. The pilot plant treatment process consists of passing the water through a thin layer of HAOPs that has been deposited on a mesh support. The HAOPs layer acts as an active packed bed which removes NOM from the water. Fluxes around 120 L/m2/h (LMH) at transmembrane pressure (TMP) below 10.7 psi (0.7 bar) were achieved over production cycles excessing 12 h. Treatment achieved always >85% colour removal and effluent colour <5 mg Pt/L (the target of treatment), and always <0.01 NTU turbidity and non-detectable suspended solids in the permeate. The HAOPs mixture after saturated with NOM is easy to remove by disruption of the HAOPs by rinsing the mesh surface, and the sludge is easily dewatered to higher of dry solids content.

Mechanistic understanding of the adsorption of natural organic matter by heated aluminum oxide particles (HAOPs) via molecular dynamics simulation

Membrane fouling caused by natural organic matter (NOM) in water is a pressing problem. To address this, heated aluminum oxide particles (HAOPs) have been used as dynamic membranes pre-deposited onto the primary membrane to effectively remove NOM and thereby significantly diminish the fouling potential. An in-depth understanding of the mechanisms underlying the superior performance of HAOPs remains amiss, which motivated this study. Molecular dynamics (MD) simulations were conducted to systematically compare the performance of HAOPs, which have been reported to be particularly effective for high molecular weight (HMW) NOM, with the conventional powdered activated carbon (PAC) adsorbent. Six NOM constituents, three of which have HMW and three have low molecular weight (LMW), were studied. Results indicate that the mechanisms underlying the effective removal of HMW NOM by HAOPs include: (1) higher foulant-HAOPs interaction energy; (2) greater hydration of the HMW NOM, which thereby increases the affinity to the more hydrophilic HAOPs; (3) diminished mobility of the foulant once adsorbed, which deters desorption; and (4) higher peak intensities in the radial distribution functions for multiple functional groups on the HMW NOM foulants. These results are expected to be valuable towards the better design of such materials for mitigating membrane fouling.

Efficient phosphorus removal from MBR effluent with heated aluminum oxide particles (HAOPs)

Biological processes and chemical precipitation in combination with polishing by granular media or membrane filtration can remove 90–95% of the phosphorus (P) from wastewater. However, reducing the concentration to levels near those in high-quality receiving waters requires additional advanced treatment, typically including adsorption onto specialty media. These processes are often costly, they can be hard to control when the P loading varies, and their effectiveness can be compromised by the presence of competing adsorbates in the water. In this work, a novel process that might mitigate or overcome some of these challenges was explored. In the process, water is treated by passage through micron-sized adsorbent particles (Heated Aluminum Oxide Particles, HAOPs) packed in a layer that is < 1 mm thick, thus combining the attractive features of very small particles with those of flow through packed media.In laboratory tests using both synthetic feed and the effluent from an MBR at a full-scale wastewater treatment plant, the process removed P very efficiently until the HAOPs’ capacity was nearly exhausted, at which point rapid breakthrough of P occurred. The removal capacity was proportional to the thickness of the HAOPs layer and declined by only ∼20% when SO42−, Cl−, and NO3− were all added to the MBR effluent at concentrations of 30 mM (2880, 1065, and 1860 mg/L, respectively). Increasing the solution pH from 7.0 to 8.5 had a similar effect, and increasing the flux of water through the adsorbent layer from 200 to 600 LMH had an even smaller effect (∼10% reduction in removal capacity). In 18 days of continuous pilot-scale operation at the treatment plant, the process performed well, achieving 99.5% P removal steadily during the final seven days of testing, during which the P concentration in the feed ranged from 4 to 9 mg/L. The process also removed 52% of the organic matter in the MBR effluent, as represented by UV254. The sludge generated by the process was extremely easy to dewater and dry.

Using adsorbent mixtures to mitigate membrane fouling and remove NOM with microgranular adsorptive filtration

This study investigated the removal of natural organic matter (NOM) from water, and its effect on membrane fouling, by mixtures of heated aluminum oxide particles (HAOPs) and powdered activated carbon (PAC) in both batch and microgranular adsorptive filtration (µGAF) reactors. In batch reactors, increasing the portion of HAOPs in the adsorbent mixture led to a steady increase in membrane fouling. However, this trend was reversed when the water was pretreated with the same adsorbent mixtures in µGAF reactors. The opposing trends tracked the trend for removal of the biopolymer fraction of the NOM.The results are consistent with a hypothesis that the fouling was caused primarily by formation of a condensed, biopolymer-rich gel layer on the membrane surface. According to this hypothesis, when the feed was pretreated in batch reactors, some foulants were collected on each adsorbent, with PAC collecting more foulant than HAOPs did, but the accumulated material did not condense into a gel. However, when μGAF reactors were used instead of batch reactors for pretreatment, the tight packing of the adsorbent particles promoted the formation of a gel, leading to increased NOM removal in general and increased foulant removal in particular. The fact that fouling mitigation increased with increasing amounts of HAOPs and decreasing amounts of PAC in the μGAF adsorbent layer suggests that HAOPs are much more effective than PAC at promoting formation of the gel layer. Generalizing this result, it appears that pretreatment by mixtures of adsorbents in μGAF reactors could have significant advantages over conventional approaches in which a single adsorbent is applied in a well-mixed reactor.

Presence of Fe-Al binary oxide adsorbent cake layer in ceramic membrane filtration and their impact for removal of HA and BSA

To enhance the removal of natural organic matter (NOM) in ceramic (Ce) membrane filtration, an iron-aluminum binary oxide (FAO) was applied to the ceramic membrane surface as the adsorbent cake layer, and it was compared with heated aluminum oxide (HAO) for the evaluation of the control of NOM. Both the HAO and FAO adsorbent cake layers efficiently removed the NOM regardless of NOM's hydrophobic/hydrophilic characteristics, and the dissolved organic carbon (DOC) removal in NOM for FAO was 1–1.12 times greater than that for HAO, which means FAO was more efficient in the removal of DOC in NOM. FAO (0.03 μm), which is smaller in size than HAO (0.4 μm), had greater flux reduction than HAO. The flux reduction increased as the filtration proceeded because most of the organic foulants (colloid/particles and soluble NOM) were captured by the adsorbent cake layer, which caused fouling between the membrane surface and the adsorbent cake layer. However, no chemically irreversible fouling was observed on the Ce membrane at the end of the FAO adsorbent cake layer filtration. This means that a stable adsorbent cake layer by FAO formed on the Ce membrane, and that the reduced pure water flux of the Ce membrane, resulting from the NOM fouling, can easily be recovered through physicochemical cleaning.

Effect of heated aluminum oxide particles dynamic membranes on polymeric and ceramic microfiltration membrane

Effect of heated aluminum oxide particles dynamic membranes on polymeric and ceramic microfiltration membrane

Mitigation of NOM fouling of ultrafiltration membranes by pre-deposited heated aluminum oxide particles with different crystallinity

A major cause of ultrafiltration (UF) membrane fouling in surface water treatment is natural organic matter (NOM). Some studies have reported that heated aluminum oxide particles (HAOPs), prepared by boiling a suspension containing precipitates of the common coagulant alum, can remove substantial amounts of NOM and reduce fouling when they were pre-deposited on UF membranes. However, the influence of the size and structure of the HAOPs in mitigating NOM membrane fouling has not been fully explored so far. This work has investigated the change in microstructure of the HAOPs during the heating process and the subsequent effect on the performance of the membrane process, and especially on the mitigation of fouling. As the heating time increased, the structure of the HAOPs transformed gradually from an amorphous nature to a semi-crystal, and then to a microcrystalline phase. It was found that this micro-crystallization process played a key role in affecting the structural properties of the nano-scale particles and the membrane filtration performance. During the crystalline transition, a change of particle size distribution occurred and the average particle size was found to decrease gradually owing to a dehydration reaction. The smaller particle size of the HAOPs provides a denser pre-filtration layer for NOM separation, and their more rigid structure reduces layer compression and hydraulic resistance during operation. Optimization of the pre-heating condition and surface loading can effectively enhance the performance of the HAOPs layer in reducing NOM fouling in the UF membrane system.

Evaluation of natural organic matter adsorption on Fe-Al binary oxide: Comparison with single metal oxides

The adsorption characteristics of three types of standard natural organic matter (NOM) on iron-aluminum (Fe-Al) binary oxide (FAO) and heated aluminum oxide (HAO) under natural surface water condition were investigated using various adsorption isotherms and kinetic models. FAO was synthesized by Fe oxide and Al oxide, mixed using the sol-gel hydrothermal method, and aluminum sulfate was used to make HAO. The amount of adsorbed NOM was increased to 79.6 mg g−1 for humic acid (HA), 101.1 mg g−1 for sodium alginate (SA) in the FAO, but the maximum adsorption capacity of bovine serum albumin (BSA) (461.3 mg g−1) was identified on the HAO. The adsorption of HA, BSA, and SA dramatically increased (>70%) on FAO in 5 min and HA was significantly removed (90%) among the three NOM. Mutual interaction among the adsorbed NOM (BSA) occurred on the HAO surface during adsorption due to formation of monolayer by protein molecules at neutral pH. The pseudo second order clearly represented the adsorption kinetics for both adsorbents. The equilibrium isotherm data of FAO was better exhibited by the Langmuir isotherm model than by the Freundlich isotherm, but HAO was a slightly non-linear Langmuir type. Also, the free energy, enthalpy, and entropy of adsorption were determined from the thermodynamic experiments. Adsorption on FAO was spontaneous and an exothermic process. Fluorescence excitation-emission matrix (FEEM) spectra were used to elucidate the variation in organic components. The results obtained suggests that the significant changes in the surface property of the adsorbent (large surface area, increased crystalline intensity, and fine particle size) were effectively determined by the Fe-synthesized Al oxide mixed using the sol-gel hydrothermal method. The results also suggest that the changes enhanced the adsorption capacity, whereby three NOM were notably removed on FAO regardless of NOM characteristics (hydrophobic and hydrophilic).

Evaluation of effectiveness of natural organic compounds removal from water in hybrid processes

Abstract Natural organic matter (Natural Organic Matter – NOM) represents a mixture of diverse chemical structure and different properties. The humic substances constitute an important component of NOM, and they are responsible for water color and taste, also they can contribute to the formation of disinfection by-products (DBP). Therefore, removal of NOM is considered to be one of the important technological operations during water treatment. The present study evaluate the effectiveness of NOM removal from water by one of the hybrid process and the results showed that the use of this process allows to improve the efficiency of water purification and also reduces the intensity of blocking membranes. Batch adsorption tests of heated aluminum oxide particles (HAOPs) showed that the NOM removal efficiency has been between 86 to 77% at a dose 5 and 10 mg·dm−3, respectively for both tested natural water.

Effect of water chemistry and operational conditions on μGAF process performance

Microgranular adsorptive filtration (μGAF) is a water treatment technique in which adsorption and granular media filtration operate simultaneously as water passes through a thin layer of adsorbent pre-deposited on a woven mesh or membrane. Our previous work showed that when heated aluminum oxide particles (HAOPs) are the adsorbent in such systems, substantial natural organic matter (NOM) removal and fouling reduction can be achieved. The present study investigated the effects of feed water chemistry and operational conditions on μGAF performance. Parameters investigated include the pH, ionic strength, and concentration of divalent cations in the feed, the flux through the adsorbent layer, and the pressure drop across both the adsorbent layer and the membrane. In the range from pH 3 to 9, lower pH promoted removal of NOM in general, and transparent exopolymer particles (TEP) in particular, by HAOPs. These enhanced removals led to increased fouling of the HAOPs layer and reduced fouling of a downstream membrane. Higher ionic strength exacerbated fouling of the bare membrane but had little effect on the ability of HAOPs to collect foulants from the feed. Increased concentrations of divalent cations reduced membrane fouling slightly, possibly due to the agglomeration of polysaccharides caused by divalent cations. Increasing the flux through the HAOPs layer had essentially the same effect as lowering the pH of the feed – it enhanced removal of NOM and TEP by, and increased fouling of, the HAOPs layer, thereby reducing fouling of the downstream membrane.The HAOPs layer was incompressible, even when some NOM had accumulated on or in it, suggesting that NOM molecules adsorb on the HAOPs throughout the layer and do not form a continuous gel layer on top of the HAOPs layer. Particulate and colloidal matter were inferred to be the dominant foulants in μGAF units, whereas soluble NOM (including soluble TEP) was the key foulant in the downstream membrane units.

HAOPs pretreatment to reduce membrane fouling: Foulant identification, removal, and interactions

Fouling of an ultrafiltration membrane by raw lake water, the same water after passage through a layer of heated aluminum oxide particles (HAOPs), and the fractionated natural organic matter (NOM) (based on hydrophobicity) of each of those waters was investigated. When each fraction of the raw water was fed to the membrane at the same DOC concentration, the hydrophobic (HPO) fraction was the least well retained by the membrane, but it caused the most fouling, whereas the hydrophilic (HPI) fraction was the most efficiently retained fraction and caused the least fouling. Furthermore, whenever the feed contained mixtures of different fractions, fouling was worse than would be predicted by a simple mixing model, indicating that interactions among the fractions are important factors in the fouling process.Treatment of the raw water by HAOPs substantially removed fulvics from all five feed solutions (raw water, the HPO, TPI [transphilic], and HPI fractions, and the reconstituted water) and humics from all except the HPI fraction (which contained very little humic material in the first place). In contrast, HAOPs treatment removed aromatic proteins only from the HPI fraction. HAOPs also selectively removed higher-MW NOM. The treatment significantly mitigated membrane fouling by all the fractions to a greater extent than would be expected based on DOC removal.The fouling of membranes fed either raw water or HAOPs-pretreated water was largely reversed by alkaline cleaning. The NOM that was released by the cleaning step was enriched in aromatic proteins and non-fluorescent fractions, but it contained much less humic and fulvic matter and overall fluorescence than raw water. The results suggest that a non-fluorescent HPO fraction of the NOM accumulated on the membrane and is responsible for substantial fouling, and that interactions among different fractions are important contributors to fouling.