Transmembrane Pressure Development Research Articles

Activating Biocake Communities Retards Jumps of Transmembrane Pressure in Membrane Bioreactors.

Sudden jump of transmembrane pressure (TMP) in membrane bioreactors (MBRs), associated with abrupt aggravation of membrane fouling, limits practical applications of MBRs and calls for effective mitigation strategies. While the TMP jump is generally related to the bacterial activity of biocakes, the mechanisms underlying the TMP jump remain unclear. Herein, we conducted various backwash protocols with different nutrient (e.g., nitrate and sodium acetate) loadings on fouled membranes in MBRs to reveal the critical role of bacterial activity of biocakes for the TMP jump. The filtration tests showed a lower TMP jump rate for the membrane backwashed with a nutrient solution (a mixture of 180 mg/L NaNO3 and 200 mg/L NaAc, averaged at 1.40 kPa/d) than that backwashed with tap water (averaged at 3.56 kPa/d), implying that TMP jump could be efficiently mitigated by providing sufficient nutrients to biocake bacteria. The characterization of biocakes showed that high-nutrient solution backwash considerably increased bacterial viability and activity, while considerably reducing biomolecule accumulation on membranes. The keystone taxa (e.g., g_Aeromonas and o_Chitinophagaceae) in the network of nutrient-enriched biocake communities were involved in nitrate reduction and biomolecule degradation. Ecological null model analyses revealed that the deterministic manner mainly shaped biocake communities with high-nutrient availability. Overall, this study highlights the significance of the bacterial activity of biocakes for TMP development and provides potential alternatives for controlling membrane fouling.

Enhanced total nitrogen removal and membrane fouling control by increasing biomass in MBR equipped with ceramic membrane

Simultaneous nitrification and denitrification (SND) is an efficient method to remove nitrogen in municipal wastewater treatment. However, low dissolved oxygen (DO) concentrations are generally required, leading to serious membrane fouling in membrane bioreactors (MBRs). This study aimed to clarify the synergistic effect of biomass and DO on nitrogen removal and membrane fouling. To achieve this goal, four submerged MBRs equipped with ceramic membranes were operated with different biomass (mixed liquor suspended solids (MLSS)) concentrations (3 000 mg/L, 5 000 mg/L, 7 500 mg/L, and 12 000 mg/L) under various DO concentrations (2.0 mg/L, 1.0 mg/L, and 0.5 mg/L). As a result, increasing biomass in the MBRs enhanced total nitrogen (TN) removal via SND, and excellent TN removal efficiencies of 60.7% and 75.8% were obtained using the MBR with an MLSS concentration of 12 000 mg/L and DO concentrations of 2.0 mg/L and 1.0 mg/L. However, a further decrease in DO deteriorated TN removal due to the inhibition of nitrification. Moreover, high MLSS concentrations were beneficial to membrane fouling control for ceramic membranes in MBRs. The lowest transmembrane pressure development rate was observed for the MBR with an MLSS concentration of 12 000 mg/L. High biomass offset the adverse effect of DO decrease on membrane fouling to some extent, and improved the stability of the reactor. Therefore, biomass might be an important parameter for membrane fouling reduction in ceramic MBRs. Overall, optimal biomass and DO concentrations for TN removal were identified, providing useful information for the successful operation of MBRs with efficient TN removal and membrane fouling control.

In-depth insight into improvement of simultaneous nitrification and denitrification/biofouling control by increasing sludge concentration in membrane reactor: performance, microbial assembly and metagenomic analysis

Currently, severe membrane fouling and inefficient nitrogen removal were two main issues that hindered the sustainable operation and further application of membrane bioreactor (MBR). This study aimed to simultaneously alleviate membrane fouling and improve nitrogen removal by applying high sludge concentration in MBR. Results showed that high sludge concentration (12000 mg/L) enhanced total nitrogen removal efficiency (78 %) and reduced transmembrane pressure development rate. Microbial community analysis revealed that high sludge concentration enriched functional bacteria associated with nitrogen removal, increased filamentous bacteria fraction in bio-cake and inhibited Thiothrix overgrowth in bulk sludge. From molecular level, the key genes involved in nitrogen metabolism, electron donor/adenosine triphosphate production and amino acid degradation were up-regulated under high sludge concentration. Overall, high sludge concentration improved microbial assembly and functional gene abundance, which not only enhanced nitrogen removal but also alleviated membrane fouling. This study provided an effective strategy for sustainable operation of MBR.

Effect of Membrane Pore Size on Membrane Fouling of Corundum Ceramic Membrane in MBR.

Ceramic membrane has emerged as a promising material to address the membrane fouling issue in membrane bioreactors (MBR). In order to optimize the structural property of ceramic membrane, four corundum ceramic membranes with the mean pore size of 0.50, 0.63, 0.80, and 1.02 μm were prepared, which were designated as C5, C7, C13, and C20, respectively. Long-term MBR experiments showed that the C7 membrane with medium pore size experienced the lowest trans-membrane pressure development rate. Both the decrease and increase of membrane pore size would lead to more severe membrane fouling in the MBR. It was also interesting that with the increase of membrane pore size, the relative proportion of cake layer resistance in total fouling resistance was gradually increased. The content of dissolved organic foulants (i.e., protein, polysaccharide and DOC) on the surface of C7 was quantified as the lowest among the different ceramic membranes. Microbial community analysis also revealed the C7 had a lower relative abundance of membrane fouling associated bacteria in its cake layer. The results clearly demonstrated that ceramic membrane fouling in MBR could be effectively alleviated through optimizing the membrane pore size, which was a key structural factor for preparation of ceramic membrane.

Effects of Viscosity on Submerged Membrane Microfiltration Systems.

Submerged microfiltration has a wide range of applications in water and wastewater treatment. Membrane fouling is a major problem, resulting in a severe decline in flux, high energy consumption and frequent membrane cleaning and replacement. The effect of viscosity was not previously studied under controlled conditions to relate it to the air scour. Hence, this study investigated the effect of viscosity on membrane fouling during the operation of submerged membrane microfiltration by adding predetermined amounts of glycerol to a kaolin clay suspension. The addition of glycerol increased the viscosity (from 0.001 to 0.003 Pa·s), resulting in a 3-fold higher transmembrane pressure (TMP) development. An increased airflow (air scour) rate by 3 fold (from 0.6 m3/m2/h to 1.8 m3/m2/h), reduced TMP development by 65%. Membrane fouling quickly developed during the initial stage of microfiltration operation. Therefore, special precautions to control fouling during the early stages of filtration could significantly enhance the operation of the microfilter. Higher airflow caused a reduction in average specific cake resistance, whereas higher viscosity increased this value.

Insight into the effect of in-situ galvanic micro-coagulation on membrane fouling mitigation treating surface water

Membrane fouling is an inevitable drawback of the membrane based long-term operations. In this study, we investigated a spontaneous galvanic process for membrane fouling mitigation, which termed as the in-situ galvanic micro-coagulation (GMC) process. Results demonstrated that the GMC contributed to a lower transmembrane pressure development in contrast with the control system (7.15 vs 14.11 KPa/LMH/cP for about 1200 h operation). Significantly, a reduced concentration of extracellular polymeric substances (EPS) in terms of polysaccharides and proteins was observed for the GMC system on both the membrane surface and membrane pores, in comparison with the control system i.e. (134.09 ± 7.37 vs 379.55 ± 9.64 μg/cm2 of polysaccharides and 27.48 ± 2.48 vs 35.87 ± 3.53 μg/cm2 of proteins) and (70.46 ± 1.93 vs 120.46 ± 3.21 μg/cm2 of polysaccharides and 17.96 ± 1.39 vs 20.52 ± 2.12 μg/cm2 of proteins) respectively. Additionally, higher accumulation of EPS on the membrane surface of control system results in higher roughness of biofilm, lower porosity, robust and thicker biopolymer microstructure as compared to the GMC system. This kind of morphology and biofilm structure formed on the membrane surface of control system directly contributed to the higher transmembrane pressure. Overall, this work shows a potentially feasible and promising approach for membrane fouling mitigation, especially for the decentralized system with relatively low permeate flux.

Abatement of the membrane biofouling: Performance of an in-situ integrated bioelectrochemical-ultrafiltration system

The practical applications of membrane-based water treatment techniques are constrained by the problem of membrane fouling. Various studies have revealed that interactions between extracellular polymeric substances (EPS) and the membrane surface determine the extent of irreversible fouling. Herein, we describe a novel bioelectrochemical system (BES) integrated with an ultrafiltration (UF) membrane in order to provide an enhanced antifouling property. It was found that the integrated BES membrane system had a superior performance compared to a conventional (control) UF system, as manifested by a much lower development of transmembrane pressure. The BES significantly reduced microbial viability in the membrane tank and the imposed electrode potential contributed to the degradation of biopolymers, which favored the alleviation of membrane fouling. Notably, the electron transfer between the acclimated microorganisms and the conductive membrane in the BES integrated system exhibited an increasing trend with the operation time, indicating a gradual increase in microbial electrical activity. Correspondingly, the accumulation of extracellular polymeric substances (EPS) on the membrane surface of the BES integrated system showed a substantial decrease compared to the control system, which could be attributed to a series of synergistic effects induced by the BES integration. The differences in the microbial diversity between the control and the BES integrated system revealed the microbial selectivity of the poised potential. Specifically, microbial strains with relatively high EPS production, like the genus of Zoogloea and Methyloversatilis, were reduced significantly in the BES integrated system, while the expression of the electroactive bacteria was promoted, which facilitated extracellular electron transfer (EET) and therefore the bioelectrochemical reactions. Overall, this study has presented a feasible and promising new approach for membrane fouling mitigation during the process of water treatment.

Impact of removal of natural organic matter from surface water by ion exchange: A case study of pilots in Belgium, United Kingdom and the Netherlands

Natural organic matter (NOM) fractions cause problems in drinking water treatment and supply. In the North Sea region, anionic ion exchange (IEX) in non-fixed bed configurations has been considered for NOM removal in drinking water treatment plants. This paper discusses several experiences of the impact of anion IEX on NOM removal and on NOM-related problems in water treatment locations of the North Sea region, considering the specific situation of the sites. The investigated parameters include the effect of anionic IEX on the removal of total NOM and specific NOM fractions, the amount of chemicals used for coagulation, the development of trans membrane pressure in microfiltration, the formation of assimilable organic carbon and the energy consumption during advanced oxidation, the removal of organics by activated carbon, and the formation of disinfection by-products. The pilot experiences at three treatment locations in Belgium, United Kingdom and the Netherlands show that anionic IEX (1) removed typically 40 to 60 percent of total NOM; (2) targeted mostly humic NOM fractions, and was not effective to remove biopolymers (3) contributed to lower coagulant doses and energy consumption in UV/advanced oxidation; (4) had limited influence on limiting the fouling of microfiltration membranes; (5) lowered the formation of disinfection by-products; and (6) it can improve biological stability.

Impact of adding aluminum hydroxyl chloride on membrane flux in an anaerobic membrane bioreactor

Coagulant addition and improved mixing conditions have been used in anaerobic membrane bioreactors (AnMBR) to improve membrane performance. Before coagulant was added, a flux of 8 L/m2 h was applicable and transmembrane pressure (TMP) increased from 1 kPa to 10 kPa in 5 days. However, after the coagulant was added, a flux as high as 50 L/m2 h was achieved with no noticeable increase in TMP during six hours of operation. Furthermore, at the same high flux, a long-term experiment showed that TMP increased to approximately 3 kPa in 20 days. Apparently, the applied coagulant significantly improved membrane performance. The reduction in the number of small particles was identified as the main cause for the high flux. However, the number of submicon particles increased in the long-term experiment. In addition, a model was developed that adequately described the TMP development in the short-term and long-term experiments. According to this model, the deterioration in specific cake resistance resulted in a sharp TMP increase in the long-term experiment. In addition, experiments showed that the effect of coagulant on sludge activity was minimal. This study demonstrated that the applied coagulant and reactor operation conditions (mixing properties) have potentials of interest for improving the membrane flux in AnMBR.

Differential ATR FTIR spectroscopy of membrane fouling: Contributions of the substrate/fouling films and correlations with transmembrane pressure

This study examined the formation of fouling films deposited on the surface of a polyethersulfone (PES) membrane during the filtration of alginate solutions with various ionic strengths. Membrane fouling was characterized by changes of the transmembrane pressure (TMP) and ex situ measured attenuated total reflectance (ATR) Fourier-transform IR (FTIR) spectra at varying stages of filtration runs. The ATR spectra that comprise the vibration bands characteristic of the PES substrate and the deposited film were processed taking into the gradual weakening of the PES substrate-specific bands, whose intensity was shown to depend on the wavenumber of IR radiation and the thickness of the deposited layer. Strongly linear correlations between ratios of first derivatives intensity and wavenumbers of the PES reference lines were established. Calculations of the PES bands’ attenuation coefficients allowed determining the apparent thickness and ATR FTIR vibrations of the fouling films per se. Strong correlations between TMP development and ATR-determined apparent thickness of the fouling layers were observed. The intensity of ATR absorbance at 3200 cm−1 was linearly correlated with TMP development for small TMP values before the point of rapidly developing failure of the hydraulic permeability of the system was reached.

Applying ultraviolet/persulfate (UV/PS) pre-oxidation for controlling ultrafiltration membrane fouling by natural organic matter (NOM) in surface water

Membrane fouling is a recognized obstacle for the application of ultrafiltration (UF) for drinking water treatment. In this study, ultraviolet/persulfate (UV/PS) oxidation was employed as a pretreatment to control membrane fouling caused by natural organic matter (NOM) in surface water. The effects of UV/PS pretreatment on amounts and characteristics of NOM were investigated in terms of dissolved organic carbon, fluorescent spectrum, molecular weight distribution and hydrophobicity. UF membrane fouling during filtration of raw and pre-oxidized water was compared with transmembrane pressure development, and the fouled membranes were further characterized using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results indicate that NOM was considerably degraded and partially mineralized (∼58%) by UV/PS pretreatment at a PS dose not exceeding 0.6 mM and a UV irradiation time within 120 min, which was attributed to the generation of sulfate and hydroxyl radicals. The fluorescent compounds in NOM were almost completely degraded (>98%) by the UV/PS pretreatment at a PS dose of 0.4 mM, except for tyrosine-like proteins (∼80%). Moreover, UV/PS pretreatment decreased the ratio of macromolecular compounds and increased the hydrophilic fractions, resulting in reduced NOM adhesion to the membrane. Hence, irreversible fouling by NOM was significantly retarded (∼75%) by the UV/PS pretreatment due to reduction in NOM, and more importantly by preferential degradation of fluorescent, macromolecular and hydrophobic compounds. Fouling control performance was considerably improved at increased PS doses and extended UV irradiation time.

Enhanced antimony(V) removal using synergistic effects of Fe hydrolytic flocs and ultrafiltration membrane with sludge discharge evaluation

The integration of adsorbents with ultrafiltration (UF) membranes is a promising method for alleviating membrane fouling and reducing land use. However, a number of problems have become apparent concerning the granular adsorbents used currently, such as high running cost, high chance of causing membrane surface damage, low in situ chemical cleaning efficiency, etc. Herein, to overcome these disadvantages, loose in situ hydrolyzed flocs were directly injected into the membrane tank, providing strong adsorption ability at low cost. To test the feasibility of this method, the heavy metal pollutant antimony (Sb (V)) in a water plant was chosen at a test case, which is similar to arsenic and difficult to remove. We found that Fe-based flocs integrated with an UF membrane showed a large potential advantage in removing Sb(V), even after running for 110 days. We demonstrated that the observed slow transmembrane pressure development could be ascribed to the loose floc cake layer formed, even though some extracellular polymeric substances were induced during operation. We also found that the floc cake layer was easily removed by washing with feed water or dissolved by in situ chemical cleaning under strongly acidic conditions, and many primary membrane pores were clearly observed. In addition, a relative long sludge discharge interval was feasible for this technology and the effluent quality was good, including the turbidity, chromaticity and iron concentration. Based on the excellent performance, these flocs integrated with UF membranes indeed show potential for application in water treatment.

Effect of intermittent ultrasound on controlling membrane fouling with coagulation pre-treatment: Significance of the nature of adsorbed organic matter

This study considers the potential advantages of applying intermittent ultrasound to the ultrafiltration (UF) process to control long term membrane fouling in the context of water treatment. By means of parallel, bench-scale tests using traditional coagulation pre-treatment prior to UF, and intermittent ultrasound during the operation (3min/10min every 3 days), the development of fouling material, and its nature (e.g. hydrophilic and hydrophobic), within the cake layer and membrane pores, have been evaluated in detail. In particular, the impact of intermittent ultrasound on bacteria growth and the production of extracellular polymeric substances (EPS) have been investigated. The results have shown that, compared to a control UF process, intermittent ultrasound reduces both reversible and irreversible fouling, with a 50% reduction in transmembrane pressure development over 60 days of operation. The intermittent ultrasound led to a much thinner cake layer which contained less EPS/biopolymers in the form of polysaccharides (g/g) and protein, as well as DNA concentrations. Material removed from the UF membrane by ultrasound was predominantly of high molecular weight (~100kDa) and hydrophilic in nature. Compared to the control membrane, pore deposits in the membrane receiving intermittent ultrasound contained much less high molecular weight, biopolymer-type substances, which was consistent with the reduced extent of irreversible fouling observed.

Application of pulsed UV-irradiation and pre-coagulation to control ultrafiltration membrane fouling in the treatment of micro-polluted surface water

A major cause of ultrafiltration (UF) membrane fouling is the accumulation of microorganisms and their associated soluble products. To mitigate fouling the application of pulsed short-wavelength ultraviolet (UVC) light (around 254 nm) within the membrane tank together with pre-coagulation was investigated. In mini-pilot-scale tests carried out in parallel with conventional pre-treatment (CUF), the impact of pulsed UV (CUF-UV) at different UV irradiances and fluxes on the increase of trans-membrane pressure (TMP) was evaluated and explained in terms of the quantity and nature of membrane deposits in the membrane cake layer and pores.The results indicated that at a flux of 20 L m−2 h−1, the pulsed UV (1 min within 31 min cycle) at 3.17 × 10−2 W/cm2 prevented any measureable increase in TMP over a period of 32 days, while there was a fourfold increase in TMP for the conventional pre-treatment. For the CUF-UV system the concentration of bacteria and soluble microbial products was much less than the conventional CUF system, and the cake layer was thinner and contained less biopolymers (proteins and polysaccharides). In addition, the pores of the CUF-UV membrane appeared to have less organic deposits, and particularly fractions with a high molecular weight (>10 kDa).At a lower UV irradiance (1.08 × 10−2 W/cm2), or higher flux (40 L m−2 h−1) with the same UV irradiance, there was a measurable increase in TMP, indicating some fouling of the CUF-UV membrane, but the rate of TMP development was significantly lower (∼50%) than the conventional CUF membrane system. Overall, the results show the potential advantages of applying intermittent (pulsed) UVC irradiation with coagulation to control UF membrane fouling.

Benefit of adding adsorbent in submerged membrane microfiltration treatment of wastewater

In this study, the effect of coupling ion-exchange resin (purolite) and powdered activated carbon (PAC) in a submerged membrane reactor was investigated in terms of (i) removal of different classes of organic matter and (ii) reduction of membrane fouling. The degree of fouling in a membrane hybrid system was modelled in terms of transmembrane pressure development and organic removal efficiency using a simple semi-empirical model. Among these three absorbents, PAC was the most effective with higher removal efficiency for DOC (almost 100% reduction of hydrophobic organic compounds). Excitation–emission matrix analysis and LC–OCD were employed for the detailed organic characterisation.

Pre-coagulation on the submerged membrane fouling in nano-scale: Effect of sedimentation process

Abstract Pre-coagulation and then flocculation with/without sedimentation before ultrafiltration (CSUF/CUF) was compared to explore the process for treating synthetic humic rich water and controlling membrane fouling. The sedimentation process caused larger flocs to be removed and zeta potential of the remaining flocs to be more negative. Also the fractal dimension of flocs became smaller after sedimentation process. All the data seemed to suggest that sedimentation process can improve the membrane fouling. On the contrary, the development of trans-membrane pressure (TMP) in CSUF surprisingly increased higher than that in CUF. The scanning electron microscope (SEM) images of cake layer on the surface of membrane showed that the size of nano-scale primary particles formed in coagulation process was heterogeneous. It also showed that the flocs formed by larger nano-scale primary particles were removed by sedimentation process, and the smaller nano-scale primary particles in CSUF maybe the crucial reason causing higher development of TMP. The density of cake layer on the CUF membrane surface with larger nano-scale particles was much lower than that by CSUF. Therefore, the characteristic of flocs, especially the size of nano-scale primary particles, may be the main factor inducing higher increase of TMP in CSUF, which should be explored in the future.

Application of Fe(II)/K2MnO4 as a pre-treatment for controlling UF membrane fouling in drinking water treatment

This paper describes some results of mini-pilot-scale tests concerning the performance of potassium manganate (K2MnO4) as a pre-treatment chemical prior to ultrafiltration. Manganate is an intermediate in the commercial preparation of permanganate and in aqueous reactions MnO42− can act as both an oxidant and a coagulant/adsorbent arising from the formation of insoluble MnO2. In addition, the combination of ferrous sulfate and manganate (Fe/Mn), offers a potentially cheaper and effective combination of pre-oxidant and coagulant compared to the chemicals used currently in water treatment (e.g. ozone, chlorine, ferric sulfate). In comparative tests with conventional ferric sulfate and using simulated raw water, the results showed that Fe/Mn pre-treatment substantially reduced membrane fouling in terms of the rate of trans-membrane pressure development (arising from both external and internal fouling). Fe/Mn pre-treatment was effective in reducing bacterial activity, changing the characteristics of organic matter and decreasing the production of extracellular polymeric substances (EPS) by bacteria. The external fouling in this process was determined by the EPS concentration, and the internal fouling mainly determined by the adsorption of lower MW organic matter to the membrane pores. Fe/Mn pre-treatment reduced the amounts of both types of fouling material within the cake layer and membrane pores in comparison to conventional pre-treatment with ferrous sulfate, most likely through the formation of solid-phase Fe(III) and MnO2 and by MnO42− oxidation, thereby leading to a substantial increase in membrane run time.

Modelling of particle deposition in a submerged membrane microfiltration system

In this study, microfiltration of a concentrated suspension of kaolin clay was performed in an aerated tank with submerged flat sheet membranes. Particle deposition was correlated with cake resistance based on experimental results. The effects of air flow rate and permeate flux on transmembrane pressure (TMP) and on membrane resistance were studied. The experimental results show that the filtration resistance due to cake formation plays a dominant role in the total filtration resistance. An increase in permeate flux caused higher TMP development due to an increased amount of particle deposition. Conversely, an increase in air flow rate reduced TMP by detaching deposited layers back into suspension. The particle deposition under different filtration flux and air flow rates was correlated to establish an empirical formula. Based on the experimental results, a general relationship between the cake resistance, permeate flux and particle deposition was derived as Rc=1.01×1012J·wc that suggests that the cake resistance is proportional to the multiplication of flux and cake deposition. Moreover, the effect of air flow on cake porosity was observed to be more significant at low permeate flux.

Performance of submerged membrane bioreactor (SMBR) with and without the addition of the different particle sizes of GAC as suspended medium

In this study the effect of different particle sizes of granular activated carbon (GAC) on the performance of a submerged membrane bioreactor (SMBR) was investigated. The sizes of GAC used were 150-300, 300-600 and 600-1200 μm. The SMBR was operated at a filtration flux of 20 L/m(2)h. The removal of dissolved organic carbon (DOC) and chemical oxygen demand (COD) with the addition of GAC was 95%. The concentration of biopolymers, humic, building block and low molecular weight neutral and acids in the SMBR effluent was reduced by 20%, 66-76%, 20-50%, 30-56%, respectively. It helped to reduce the sludge volume index (SVI) and transmembrane pressure (TMP) development by 30-40% and 58%, respectively. However, the removal of NH₄(+) and PO₄(3-) was relatively low of 35-45% and 34-43%, respectively. The SMBR effluent was rich in PO₄(3-) and was removed/recovered using hydrated ferric oxide (HFO). The removal of PO₄(3-) was almost 90%.

Membrane fouling by Fe-Humic cake layers in nano-scale: Effect of in-situ formed Fe(III) coagulant

The application of in-situ Fe(III) coagulant, formed by reacting Fe(II) and KMnO4 (Fe/Mn), before membrane ultrafiltration (Fe/Mn-CUF) has been compared with conventional dosing of an Fe(III) coagulant (Fe-CUF). The performance of the alternative coagulants has been evaluated in terms of membrane fouling using model waters containing humic acid. A lower development of trans-membrane pressure (TMP) suggested that in-situ formed Fe(III) caused a lower rate of fouling compared to the dosed Fe(III). The lower TMP development with in-situ formed Fe(III), compared to dosed Fe(III), was associated with smaller, fewer and less compact coagulant flocs and differences in the membrane cake layer; in both cases influent flocs were aggregates of nanometer-scale primary particles.Interestingly, TEM and SEM images showed that the size of nanometer-scale particles formed by in-situ Fe(III) was slightly larger than dosed Fe (III), and this contributed to a more porous cake layer. In addition, the Fe/Mn flocs formed a thinner cake layer than that formed by Fe flocs. Overall, the effect of decreasing the thickness and density of the cake layer and increasing the size of the nanometer-sized primary particles was significantly beneficial in reducing membrane fouling. Also NOM analysis by size exclusion chromatography (SEC) indicated that the in-situ Fe(III) coagulant achieved greater NOM removal than the dosed Fe(III), both in the UF influent and filtrate waters. In summary, the results have shown that in-situ Fe(III) is a superior pretreatment to conventional dosed Fe(III), in terms of significantly improving membrane performance (reduced fouling) with a little higher improvement in water quality.