Irreversible Fouling Rate Research Articles

Cake porosity analysis using 1D-3D fractal dimensions in coagulation-microfiltration of NOM.

Fouling during coagulation-ceramic microfiltration of natural organic matter was investigated. Two process configurations (inline coagulation (IC) and tank coagulation (TC)) and two process conditions (types of coagulants-aluminum-based PAX and iron-based PIX-and G-values) were studied. The rate of irreversible fouling corresponding to the increase of initial transmembrane pressure after backwash of IC-PAX was lowest followed by TC-PAX and TC-PIX, while the performance of IC-PIX was found worst. The 1D and 2D fractal analysis revealed that flocs from IC were morphologically different from those of TC, leading to different filtration characteristics. The 3D fractal analysis revealed two groups of morphologically similar flocs: one led to successful filtration experiments, whereas the other led to unsuccessful ones. Cake porosity was found dependent on the floc morphology. Thus, such an approach was found complementary with fouling analysis by means of a membrane fouling model and minimization of fouling phenomenon was achieved by combining the two approaches.

Ultrafiltration Fouling: Impact of Backwash Frequency and Air Sparging

A bench-scale study was performed to optimize backwash frequency and air sparging conditions during ultrafiltration (UF) for drinking water treatment in order to minimize hydraulically irreversible fouling as well as operating and maintenance costs. Surface shear stress representing different air sparging conditions (continuous coarse bubble, intermittent coarse bubble, and large pulse bubble) was applied in combination with various backwash frequencies (0.5, 2, and 6 hours) during UF of two natural surface waters. Results indicated that air sparging during permeation with intermittent coarse or large pulse bubbles significantly reduced the rate of irreversible fouling. This allowed for longer permeation times (up to 6 hours) between backwashing, when compared to a baseline condition which assumed a 0.5 h-backwash frequency with no air sparging during permeation. As a result, operation and maintenance cost savings estimated at > $350,000/year for a 29 MLD membrane train could be realized. This study demonstrates that optimized air sparging could serve as a cost-effective UF fouling control strategy for drinking water production.

Performance of an AnMBR pilot plant treating high-strength lipid wastewater: Biological and filtration processes

The performance of an anaerobic membrane bioreactor (AnMBR) treating wastewater with high levels of oil and grease content from a snacks factory is studied and its effectiveness is demonstrated. The relation between the reversible and the irreversible fouling rate and the fouling propensity of the fatty matter were evaluated under a subcritical flux of 7.9 and 8.3 L/m2 h. Low Oil and Grease (O&G) concentrations of 500 mg/L produced an irreversible fouling rate of only 0.09 mbar/d, while the fouling rate was between 0.96 and 3.95 mbar/d for an average O&G concentration of 6 g/L. In spite of the significant increase in filtration resistance from 0.31 to 6.08 × 1012 m−1 after 40 days of continuous operation, the critical flux level hardly decreased from 11.1 to 9.7 L/(m2 h). With regard to the biological process, after a start-up period with an organic loading rate (OLR) of below 2 kg COD/(m3 d), the system was able to treat wastewater between 4.6 and 36 g O&G/L and the system remained stable for OLR at around 17 kg COD/(m3 d) for 2.8 d, without inhibitory signals. Acclimated sludge quickly reached maximum methane production and digested substrate with high oil and grease content, observing an increase in palmitic acid the first days and constant levels of propionic acid while fatty acids were in the medium.

Role of transparent exopolymer particles on membrane fouling in a full-scale ultrafiltration plant: Feed parameter analysis and membrane autopsy

Ultrafiltration (UF) is widely used for water purification, but membrane fouling remains an important issue. In this study, the role of transparent exopolymer particles (TEPs), recently put forward as possible major foulants, was investigated in the fouling process of a full-scale UF installation. Algae, TEPs and other parameters in the UF feed were monitored and correlated during an 8months long full-scale operation. Results revealed a complex fouling mechanism involving interactions mainly between algae, Fe (flocculant) and TEPs. Algae related parameters rather that TEP concentrations correlated stronger with irreversible fouling rates, suggesting that the overall role of TEPs in membrane fouling seems limited for this application. Finally, membrane autopsy showed the formation of a thick Fe-rich fouling layer on top of the fouled membranes, which could mostly be removed via cleaning-in-place. It remained partly irremovable in the form of some Fe-organic complexes.

Correlating ultrafiltration membrane fouling with membrane properties, water quality, and permeate flux

The effect of membrane properties, feed water quality, and permeate flux on ultrafiltration (UF) membrane fouling was systematically investigated. Fouling tests were carried out with three types of commercially available UF membrane and a variety of influents. The membrane fouling was assessed by the normalized fouling rate (F500). The results showed that the PVDF membrane with smaller contact angle was more resistant to membrane fouling than the PVC membrane. As for feed water parameters, significant correlations were observed between turbidity, total organic carbon, UV254, fluorescence intensity, and membrane fouling rates using Pearson Correlation Analysis. This was especially true for hydraulically irreversible fouling rate (Firr). Moreover, significant correlations between permeate fluxes and membrane fouling rates were observed. With these correlations, the critical flux and critical flux for irreversibility were calculated. It was found that the critical flux is strongly depended on feed water composition rather than membrane properties. Particulate matter, with a size of 0.45–1.2 μm in diameter, was proved to increase the critical flux and critical flux for irreversibility.

Determining flux behavior via a modified flux-step method for surface water treatment: pilot-scale ultrafiltration membrane operation

We present an alternative method for determining permeate flux behavior for membrane filtration of surface water. A modified flux-step method was developed and evaluated for two different submerged ultrafiltration membrane systems. Experimental results for a short-term pilot-scale system indicated that the modified method was able to determine the critical flux for irreversibility, improving on the conventional flux-step method. Using the modified method, the total membrane fouling rate and irreversible fouling rate can be used to simultaneously determine the threshold flux and critical flux for irreversibility. Based on the fluxes obtained in short-term tests, the long-term performance of the membrane system was also evaluated under operational conditions above the threshold flux and frequent variations in the turbidity of the surface water influent, combined with a cleaning regime. At a flux of 50L/m2·h for membrane A and 40L/m2·h for membrane B, the membrane fouling and fouling history were improved by cleaning through backwashing, draining of the membrane tank, and intermittent chemically enhanced backwash. Thus, by minimizing membrane fouling and transmembrane pressure increments based on the modified flux-step method, the membrane separation system cleaned using these methods achieved efficient surface water treatment under realistic operating conditions at high flux.

Poly(ether imide) membranes modified with charged surface‐modifying macromolecule—Its performance characteristics as ultrafiltration membranes

ABSTRACTModification of poly (ether imide) (PEI) ultrafiltration (UF) membranes was attempted by blending charged surface modifying macromolecule (cSMM). Compared to the pure PEI membrane, blending of PEI with cSMM resulted in blend membranes with enhanced UF characteristics such as lower hydraulic resistance (Rm) and higher pure water flux (PWF) coupled with higher water content (WC). Among the various modified membranes, blend membranes with 5 wt % cSMM concentration exhibited higher PWF (60.38 L m−2 h−1), WC (73.6%), protein permeate flux (27.12 L m−2 h−1) and lower flux decline rate (Rfd) (55.1%), Rm (5.21 kPa/L m−2 h−1), bovine serum albumin (BSA) rejection (87.1%). Meanwhile, the fouling resistant ability was studied by flux recovery ratio (FRR) after water and alkali cleaning, irreversible and reversible fouling rate. Higher FRR after water cleaning (95.07%), FRR after alkali cleaning (97.1%), reversible fouling rate (50.14%) and lower irreversible fouling rate (5%) exhibited by 5 wt % cSMM membranes showed its better antifouling ability compared to pure PEI and other blend membranes because of its higher hydrophilic nature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40320.

Fouling of low-pressure membranes during drinking water treatment: effect of NOM components and biofiltration pretreatment

Fouling is a major challenge for low-pressure membrane drinking water treatment systems. Previous research has demonstrated that under the right conditions, biofiltration is an effective method to reduce fouling of low-pressure polymeric membranes. This study provides additional insight into the effect of biofiltration as a pretreatment for fouling reduction by using river water with different raw water quality characteristics than has been examined in previous studies. Two parallel pilot-scale dual media (sand/anthracite) biological filters were operated continuously over a period of 14 months. Liquid chromatography–organic carbon detection analysis confirmed that the parallel biofilters performed similarly with both averaging on 21% biopolymer removal. Raw and treated water biopolymer concentrations were correlated, with increased absolute removals occurring at higher raw water concentrations. Ultrafiltration (UF) membrane fouling experiments showed substantial improvement in performance following biofiltration pretreatment by reducing hydraulically irreversible and reversible fouling rates by 14–68% and 8–55%, respectively. The results also reaffirm the importance of biopolymers at concentrations as low as ∼0.1 mg/L on irreversible and reversible UF membrane fouling and a minimal impact of humic substances.

Assessing the role of feed water constituents in irreversible membrane fouling of pilot-scale ultrafiltration drinking water treatment systems

Fluorescence excitation–emission matrix (EEM) approach together with principal component analysis (PCA) was used for assessing hydraulically irreversible fouling of three pilot-scale ultrafiltration (UF) systems containing full-scale and bench-scale hollow fiber membrane modules in drinking water treatment. These systems were operated for at least three months with extensive cycles of permeation, combination of back-pulsing and scouring and chemical cleaning. The principal component (PC) scores generated from the PCA of the fluorescence EEMs were found to be related to humic substances (HS), protein-like and colloidal/particulate matter content. PC scores of HS- and protein-like matter of the UF feed water, when considered separately, showed reasonably good correlations with the rate of hydraulically irreversible fouling for long-term UF operations. In contrast, comparatively weaker correlations for PC scores of colloidal/particulate matter and the rate of hydraulically irreversible fouling were obtained for all UF systems. Since, individual correlations could not fully explain the evolution of the rate of irreversible fouling, multi-linear regression models were developed to relate the combined effect of HS-like, protein-like and colloidal/particulate matter PC scores to the rate of hydraulically irreversible fouling for each specific UF system. These multi-linear regression models revealed significant individual and combined contribution of HS- and protein-like matter to the rate of hydraulically irreversible fouling, with protein-like matter generally showing the greatest contribution. The contribution of colloidal/particulate matter to the rate of hydraulically irreversible fouling was not as significant. The addition of polyaluminum chloride, as coagulant, to UF feed appeared to have a positive impact in reducing hydraulically irreversible fouling by these constituents. The proposed approach has applications in quantifying the individual and synergistic contribution of major natural water constituents to the rate of hydraulically irreversible membrane fouling and shows potential for controlling UF irreversible fouling in the production of drinking water.

Reproducibility and applicability of the flux step test for a hollow fibre membrane bioreactor

Results from flux step tests conducted on a pilot-scale hollow fibre immersed membrane bioreactor plant (HF iMBR) are reported. Trials combined a classic flux-step test, each step incorporating six backflush cycles, with an extended (15-h) test to evaluate trends in fouling. Both fouling rate, i.e. the rate of increase in transmembrane pressure (dTMP/dt) at a constant flux, and mean permeability were calculated and reproducibility assessed through the standard deviation. Applied nominal fluxes between 5 and 35Lm−2h−1 (LMH) were employed for the flux-step trials, and all experiments were (i) triplicated through simultaneous application across three central membrane elements in the seven-element membrane module, and (ii) repeated four times. Reproducibility was quantified as standard deviation (SD), and assessed with reference to both the mean permeability across the backflush cycle and the irreversible fouling rate across the three modules – the latter both for the short-term and long-term trials.Results indicated greatly reduced fouling (by 80–88% with respect to fouling rate) for the longer-term study compared with the flux-step data. Fouling rate SD values were slightly lower for the flux step data at 20–27% for the four highest flux steps compared with 30% for the longer trial conducted at 20LMH, based on quadruplicated data. Mean permeability data, on the other hand were much more reproducible, with SD values below 8%. It was concluded that significant variations in hydrodynamics can arise across a module comprising a number of elements, accounting for a 20–40% change in fouling rate. However, this cannot account for the differences recorded between the short-term and long-term fouling measurements, which are a facet of the flux step test conditions.

Powdered Activated Carbon-Microfiltration for Waste-Water Reuse

A range of activated carbon adsorbents have been assessed as pretreatment for microfiltration-based indirect potable reuse (IPR) pilot plant to evaluate the impact on combined membrane fouling and organics removal. Isotherm adsorption analysis showed wide variation between the different adsorbent materials with regards to organics removal and kinetics, and the removal for most of the reagents tested was found to be significantly influenced by temperature. The two commercial adsorbents with the highest removal rates and fastest kinetics were then each evaluated as pretreatment at pilot scale over a six hour period at two doses (5 and 25 mg/l) and operational fluxes (40 and 50 L m−2 h−1), based on a hollow fibre membrane module. One of the adsorbents provided a reduction in the irreversible fouling rate, and both were found to significantly improve the removal of organics.

MBR fouling control and permeate quality enhancement by polyaluminium chloride dosage: a case study

Scope of this study was to evaluate the effectiveness of a metal salt (polyaluminium chloride, PACl) dosage into a pilot-scale MBR (membrane bioreactor) in terms of fouling control and permeate quality enhancement, especially with reference to specific textile macro-pollutants (dyes and surfactants). The pilot plant was fed with a mixed domestic-textile wastewater (textile wastewater accounted for 65% of total flow and for 70% of total chemical oxygen demand, COD, load) and operated for 7.5 months without flux enhancers (step 1) and 3 months with the addition of PACl (step 2). The optimum dose was defined performing a jar-test campaign between step 1 and step 2 (12.5 mg gMLSS(-1) that corresponds to 0.4 g d(-1)). The addition of PACl resulted in a significant decrease of the filtration resistance due to cake layer formation (R(c), -65.4%) and of the irreversible fouling rate, evaluated as the average variation per unit time of the filtration resistance due to foulants adsorption on membrane pore wall (FR, -45.3%). As for permeate quality, removal rates related to total phosphorus and textile macro-parameters such as colour and anionic surfactants, increased by +64, +16 and +7%, respectively. No significant effect was observed on COD, non-ionic surfactants and nitrogen compounds removal.

Efficacy of relaxation, backflushing, chemical cleaning and clogging removal for an immersed hollow fibre membrane bioreactor

A pilot-scale hollow fibre immersed MBR, challenged with real municipal wastewater, was studied and operated under conditions identical to those prevailing at full-scale to assess the relative influence of backflushing, relaxation, chemical enhanced backflushing (CEB) and declogging on permeability decline and recovery. The influence of relaxation and backflushing was initially assessed using the conventional flux step method; results indicated reversible fouling to be similar for each method, whilst the irreversible fouling rate was significantly reduced by backflushing. For a given total backflush volume, fouling mitigation was found to be marginally better through employing higher backflush fluxes than longer backflush durations.The impact of the CEB on permeability recovery assessed at low and high fluxes indicated operation at more conservative fluxes to yield more sustained permeability. Under more aggressive operating conditions - fluxes of up to 35 L m−2 h−1 at specific aeration demand values of 0.25 Nm3/(m2 h) – long-term permeability decline took place which was not significantly ameliorated by chemical cleaning. On declogging the membrane through gentle agitation permeability recovery was significant, but was followed by a rapid permeability decline over the course of a few hours. Results suggested control of clogging to be of greater importance than that of fouling in sustaining permeability.

Decentralized Membrane Filtration System for Sustainable and Safe Drinking Water Supply in Low-Income Countries: Baseline Study

Decentralized membrane filtration systems (DMFS) have the potential to supply safe drinking water in low-income countries (LICs) where centralized municipal water treatment is practically infeasible. This study aimed at applying an integrated bench-scale and field-testing approach to assess the sustainability of a DMFS in producing safe drinking water in LICs. The state-of-the-art DMFS employed in this study was capable of removing bacteria, surrogate parasites, and viruses at log⁡ reductions above 7, 5, and 4, respectively, from evaluated waters (n=4). The technological sustainability of the DMFS was primarily affected by membrane fouling, and a linear correlation was found between the reversible/irreversible fouling rates of a miniature bench-scale system and those of the full-size DMFS caused by representative types of source waters. The total and irreversible fouling rates of the full-size DMFS were approximately 50% of those of the miniature system, regardless of the properties of the source waters. Similar quantitative relationships may be established between the fouling rates of the bench-scale system and those of other full-size DMFS. Overall, easy and cost-effective fouling control is warranted for sustainable application of DMFS in LICs, and bench-scale membrane testing serves as a potential screening tool for this purpose.

Removal of divalent cations reduces fouling of ultrafiltration membranes

The effect of divalent ions on hydraulic irreversible fouling of ultrafiltration membranes was studied. Not only the effect of removing divalent ions by pretreatment of raw water with ion exchange is quantitatively studied, but also the effects of different types of backwash water are considered. By replacing divalent ions with sodium in cation exchange, the amount of hydraulic irreversible fouling (remaining fouling after backwashing) is reduced by at least 60%. When adding either calcium or magnesium to water treated with cation exchange, a linear relation is found between the ion concentration and the irreversible fouling rate. The effects of calcium and magnesium are identical when the concentrations are expressed in mol/L. Removing divalent ions from the backwash water does not affect irreversible fouling, but when using MilliQ water as backwash water, irreversible fouling can (almost) completely be prevented.

Influence of Dissolved Organic Carbon and Suspension Viscosity on Membrane Fouling in Submerged Membrane Bioreactor

This paper deals with the membrane fouling in membrane bioreactor (MBR). Based on the experimental data obtained in the MBR pilot plant study, the influence of F/M ratio on the irreversible and reversible fouling was discussed in the wide range of MLSS concentration. In the case of lower MLSS concentration (2,000–3,000 mg/L), irreversible fouling rate of membrane increased with increasing F/M ratio because of the accumulation of DOC in the mixed liquor. It seems that soluble microbial products with the similar size of the membrane pore will be most responsible for the irreversible fouling. In the case of higher MLSS concentration (8,000–12,000 mg/L), reversible fouling rate of membrane increased with increasing F/M ratio because of the increased suspension viscosity caused by the increased activated sludge size or volume even in the same MLSS concentration.

Impact of ultrafiltration operating conditions on membrane irreversible fouling

The main limitation of the ultrafiltration (UF) process identified in drinking water treatment is membrane fouling. Although adsorption of natural organic matter (NOM) is known to cause irreversible fouling, operating conditions also impact the degree of irreversible fouling. This study examined the impact of several operating parameters on fouling including flux, concentrate velocity in hollow fibers, backwash frequency, and transmembrane pressure. A hydrophilic cellulose derivative membrane and a hydrophobic acrylic polymer membrane were used to conduct these tests. Pilot testing showed that when short-term reversible fouling was limited during a filtration cycle by increasing the concentrate velocity, reducing the flux, and increasing the backwash frequency, the evolution of the membrane toward irreversible fouling could be controlled. It appeared that operating parameters should be adjusted to maintain the increase of transmembrane pressure below a certain limit, determined to be approximately 0.85 to 1.0 bar for the tested UF membrane, in order to minimize the rate of irreversible fouling. This threshold for transmembrane pressure was confirmed empirically by compiling data from over 36 pilot studies. Other testing results demonstrated that hydraulic backwash effectiveness decreased as the transmembrane pressure applied in the previous filtration cycle increased. Backwash efficiency in terms of membrane flux recovery after hydraulic backwash was reduced by 50% when the transmembrane pressure was increased from 0.4 bar to 1.4 bar.

Coagulation Pretreatment for Ultrafiltration of a Surface Water

Polysulfone ultrafiltration membranes were used to treat water from the Seine River—with and without coagulation pretreatment. Pretreatment with polyaluminum or ferric chloride coagulant reduced the rate of reversible fouling and increased the removal of dissolved organic carbon (DOC) but did not reduce the rate or extent of irreversible fouling of the membrane. Seine River water that had been treated by coagulation, filtration, and ozonation, i.e., tap water, also produced significant irreversible fouling. Most of the DOC in flocculated Seine River water and tap water consisted of polysaccharide materials of low molecular weight. Irreversible fouling may be due to the adsorption of these materials on membrane surfaces.