Membrane Autopsy Research Articles

Characterization of membrane foulants in a pilot-scale tunnel construction wastewater treatment process

A pilot-scale combination of a microfiltration (MF) and a reverse osmosis (RO) membrane system was applied on-site to treat tunnel construction wastewater. The MF membrane system initially removed contaminants (turbidity of less than 0.3 NTU) in the form of particulate materials in the feed water, thereby allowing the combined MF–RO system to efficiently remove more than 99% of known organic and inorganic contaminants and qualify the reclaimed water for reuse. The MF membrane autopsy analysis using X-ray fluorescence (XRF) and inductively coupled plasma-mass spectrometry (ICP-MS) revealed that the dominant foulants were inorganic deposits involving Si, Al and Fe, comprising the main components of cement materials, as well as deposits involving heavy metals such as Mn, Cu and Zn in the form of particles. Thus, thick cake contaminants shown by field emission scanning electron microscope (FE-SEM) images might be induced via suspended solids consisting of cement and clay materials and metals.

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.

RO Membrane to Remove Sulfate: an Inland Brackish Water Desalination Pilot Study

The City of Fargo completed a Facility Plan of their Water Treatment Plant (WTP) in 2011 to address two main issues: increasing water demands and high sulfate concentrations within a raw water source (Sheyenne River) primarily due to Devils Lake flooding. Reverse Osmosis (RO) was recognized as the most appropriate technology for sulfate reduction, and recommended for use in the WTP expansion. An RO pilot study was performed to evaluate its feasibility for two operational scenarios. RO membranes experienced rapid fouling in the Polishing Scenario, which used RO to further treat filtered water from the existing WTP (pretreatment, lime softening, ozone, and granular filtration). RO membranes exhibited superior performance in the Parallel Scenario, which was a separate treatment process (coagulation/flocculation/sedimentation + microfiltration/ultrafiltration +RO) parallel to the existing WTP. RO membrane autopsies indicated that membrane fouling was organic and biological for the Polishing Scenario while organic and scaling for the Parallel Scenario. Optimization studies were performed in the Parallel Scenario to determine optimal coagulation conditions for pretreatment as well as flux, recovery, and membrane cleaning regimes for both the MF/UF and the RO. Uniquely, an RO membrane selection pilot was conducted for both scenarios to evaluate RO membranes from four different manufacturers. The slight difference surface chemistry among various RO membrane can cause substantial different performance. It was found that one RO membrane could not be cleaned adequately, although it has many successful applications elsewhere. This one year pilot study proved that RO technology is feasible to reduce sulfate concentrations to acceptable levels in the City’s finished water.

Membrane autopsy based bio-fouling investigation of distillery spent wash RO treatment plant

In this paper, a thorough investigation has been done to evaluate the effects of different pollutants on membrane performance by autopsy. Autopsy was performed on fresh and fouled reverse osmosis (RO) membrane elements from a distillery spent wash treatment plant by different analyses, such as field emission scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy and X-ray diffraction, to identify the cause of poor performance of an RO plant. Results obtained from the analysis of membranes indicate that a mixture of colloids and organic matters (polysaccharides and amines) along with the presence of multivalent ions (Ca, Mg, Fe and SO4) causes membrane fouling, which in turn affects membrane performance. Possible measures to improve treated effluent quality and mitigate fouling have been suggested for this particular case study.

Organic fouling behavior in direct contact membrane distillation

Organic fouling development in a direct contact membrane distillation system was investigated with synthetic model solutions of humic acid (HA), alginate acid (AA) and bovine serum albumin (BSA). A 40–50% flux decline was observed, with BSA and HA showing dominant fouling tendencies, while minimal fouling was observed with AA due to its hydrophilic nature. Based on the feed characterization analysis using liquid chromatography-organic carbon detector, the HA feed solution showed thermal disaggregation to low molecular weight-HA (LMW-HA) organics with increased feed temperature (50°C and 70°C). The HA fouled membrane autopsy analysis showed the penetration of organics through the membrane pores. In comparison, the BSA feed solution showed more significant deposits on the membrane surface (35.2% higher carbon mass compared to HA foulant) with less significant pore penetration. The mixed organic (MO) feed solution consisting of BSA, HA and AA altogether showed evidence of foulant to foulant interaction. The MO feed solution leads to a significant flux decline of 65% only at a later stage upon the disaggregation of LMW-HA organics that adhered on the membrane.

Ten years of industrial and municipal membrane bioreactor (MBR) systems - lessons from the field.

The use of membrane bioreactors (MBRs) in activated sludge wastewater treatment has grown significantly in the last decade. While there is growing awareness and knowledge about the application of MBR technology in municipal wastewater treatment, not much information is available on the application of MBRs in industrial wastewater treatment. A comparative study of design data, operating conditions and the major challenges associated with MBR operations in 24 MBR plants treating both municipal and industrial wastewater, built by and/or operated by Praxair, Inc., is presented. Of the 24 MBR systems described, 12 of the plants used high purity oxygen (HPO). By enabling a wide range of food/microorganism ratios and loading conditions in the same system, HPO MBR systems can extend the options available to industrial plant operators to meet the challenges of wide fluctuations in organic loading and footprint limitations. While fouling in industrial MBR systems can be an issue, adequate flux and permeability values can be reliably maintained by the use of good maintenance strategies and effective process controls (pretreatment, cleaning and membrane autopsies).

Membrane scaling and flux decline during fertiliser-drawn forward osmosis desalination of brackish groundwater

Fertiliser-drawn forward osmosis (FDFO) desalination has been recently studied as one feasible application of forward osmosis (FO) for irrigation. In this study, the potential of membrane scaling in the FDFO process has been investigated during the desalination of brackish groundwater (BGW). While most fertilisers containing monovalent ions did not result in any scaling when used as an FO draw solution (DS), diammonium phosphate (DAP or (NH4)2HPO4) resulted in significant scaling, which contributed to severe flux decline. Membrane autopsy using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD) analysis indicated that the reverse diffusion of DAP from the DS to the feed solution was primarily responsible for scale formation during the FDFO process. Physical cleaning of the membrane with deionised water at varying crossflow velocities was employed to evaluate the reversibility of membrane scaling and the extent of flux recovery. For the membrane scaled using DAP as DS, 80–90% of the original flux was recovered when the crossflow velocity for physical cleaning was the same as the crossflow velocity during FDFO desalination. However, when a higher crossflow velocity or Reynolds number was used, the flux was recovered almost completely, irrespective of the DS concentration used. This study underscores the importance of selecting a suitable fertiliser for FDFO desalination of brackish groundwater to avoid membrane scaling and severe flux decline.

Inefficacy of osmotic backwash induced by sodium chloride salt solution in controlling SWRO membrane fouling

A study was conducted to evaluate the efficacy of osmotic backwash induced by high salt (NaCl) concentration solution on feed side of seawater reverse osmosis (SWRO) membranes, online and offline, in controlling membrane fouling and therefore minimizing/eliminating the need for chemical cleaning. SWRO membranes were deliberately fouled by feeding seawater from an open intake located on the Arabian Gulf Coast without dosing chemicals. The fouled membranes were subjected to offline cleaning with the salt solution of up to 25 % concentration. Despite the partial removal of foulants from the membrane surface, SWRO membrane performance could not be restored, indicating the ineffectiveness of osmotic backwash in aiding offline salt cleaning. Similarly, online osmotic backwash was found to be not only ineffective in removing foulants from membrane surfaces but actually increased the fouling rate, as indicated by faster fouling rates compared to other cases. Although the driving force required for the osmotic backwash existed, the generated back flow proved to be insufficient to detach foulants from membrane surfaces. During the study period, the average SWRO membrane flux was maintained between 19 and 23 LMH, whereas the average generated back flow flux by high salt concentration solution was only 11 LMH, which was not adequate to remove foulants from membrane surfaces. Moreover, it seems that the membrane configuration as well as inherent microstructure of SWRO membrane places certain constraints on the osmotic backwash process and renders osmotic backwash ineffective in tackling SWRO membrane fouling. Hence, chemical cleaning is essential to restore SWRO membrane performance whenever fouling occurs, and the use of highly concentrated salt solution does not have any significant benefit. Membrane autopsy revealed only an insignificant accumulation of biofouling layer despite the absence of disinfection. However, it was shown that culturable biofilm bacteria species isolated from membranes tolerated exposure to high salt concentrations at pH range of 7–8. In addition, the overall findings of the study indicate that SWRO membranes can be operated in Gulf seawater at a recovery of 30 % without using any chemicals, such as coagulant, disinfectant and antiscalant, for an acceptable period of time without performing membrane cleaning. This is highly likely, if media filters are used in the pretreatment and SWRO membranes are operated at normal flux and recovery ratio.

Advanced treatment of semiconductor wastewater by combined MBR–RO technology

The combination of membrane bioreactor and reverse osmosis (MBR–RO) is becoming an attractive technology for wastewater reclamation and reuse. In this work, the combined MBR–RO technology was applied to treat the semiconductor wastewater through a two-phase (I, II) operation. To demonstrate the feasibility of this technology, the operational performances of MBR and RO were investigated in Phase I. The good operational stability, high contaminant removal efficiency of the combined system, as well as qualified treated water for reuse were observed. To understand the possible fouling characteristics of RO membrane in a long-term operation, the antiscalant addition and chemical cleaning in RO process were abolished in Phase II. The membrane autopsy analysis showed that the dominant foulants on the RO membrane surface were loose inorganic deposits with plate-like morphology, while the biological and organic fouling were ignorable. The major component of the foulants was BaSO4, with small amounts of SrSO4 and deposits involving Ca, Si, Al, Mg, Fe and Zn. The foulants could be effectively removed by chemical cleaning of HCl–NaOH/EDTA. After the cleaning, the RO membrane permeability was recovered to the fresh one. This work provides a deep understanding of treating the semiconductor wastewater by MBR–RO technology for industrial application.

Results from 99 seawater RO membrane autopsies

This paper presents results from ninety-nine seawater reverse osmosis (SWRO) membrane autopsies carried out by the Genesys laboratory in Madrid from 2002 and outlines the technical issues surrounding fouling and scaling of sea water membranes. The authors discuss historical results of membrane autopsies and link recent trends and changes in plant design to potential fouling and scaling issues that may result in the future. Forty per cent of autopsies showed the presence of iron, 33% clay and 21% calcium and magnesium. The principle reason for membrane failure showed 27% was due to microbiological fouling, 19% were abraded, 18% oxidized, 12% of the samples showed metal oxide present as iron, manganese and aluminium. Scale formation from calcium carbonate, calcium sulfate and silica scale accounted for 8% of the membrane failures. Only 10% of the membranes were described as clean. There has been a trend over the last decade to increase recovery rates from 30% to 40–50%. This results in a greater concentration of cations and anions and likelihood of scale formation in last position elements. The presence of suspended solids and micro-organisms causes fouling in lead elements. To counter this there is a common practice of chlorinating, acidifying and coagulating the feed water. This is done principally with the commodity chemicals, sodium hypochlorite, sulfuric acid and iron chloride coagulant. The authors conclude from the results of ninety-nine SWRO membrane autopsies that the use of these commodity chemicals can be beneficial in the pre-treatment system but also can have some serious side effects for the membranes. Suggestions for alternative strategies are made.

Effect of dead cells on biofouling in the reverse osmosis process

Biofilm formation in membrane processes causes a flux decline, pressure drop increase, and other adverse effects. Understanding the mechanisms of fouling, control, and cleaning are important in order to resolve fouling problems. In this paper, the effect of cell viability on biofouling was studied via a feed water analysis and membrane autopsy. Pseudomonas aeruginosa PAO1 was used as the model bacteria. Biofouling tests were divided into two parts: live cells and dead cells (autoclaved cells). The feed water was periodically collected every 3 h to analyze the total direct counts (TDCs), heterotrophic plate counts (HPCs), and extracellular polymeric substances (EPS). A membrane autopsy was performed to characterize the fouled membrane through TDCs and EPS. When dead cells were inoculated into the feed water, low concentrations of TDCs and EPS were measured in both the feed water and fouled membrane. As a result, it was determined that initial flux decline by biofouling can be reduced if feedwater is disinfected before the reverse osmosis process.

Towards direct potable reuse with forward osmosis: Technical assessment of long-term process performance at the pilot scale

In this study we evaluated the performance of forward osmosis (FO) at the pilot scale to achieve simultaneous seawater desalination and wastewater reclamation. The investigation was performed with a commercial spiral wound FO membrane element for approximately 1300h of continuous operation, processing 900,000L of wastewater effluent and producing 10,000L of purified water through a hybrid FO-RO process. Water and solute fluxes were monitored during the study. Reversible and irreversible membrane fouling was observed; however, water flux was maintained at a relatively constant rate of 5.7±0.2Lm−2h−1 with MBR permeate feed and seawater draw solution. Subsequent increase of total suspended solids (TSS) concentration in the FO feed (secondary treated effluent with 5 to 16mgL−1 TSS) resulted in incremental flux decline; however, the membrane typically achieved stable water flux after the initial exposure to foulants. Additional analysis focused on bi-directional transport of inorganic species and a detailed evaluation of dissolved organic matter permeation through the membranes in the hybrid process. Evaluation of sample fluorescence revealed that the FO membrane and the hybrid process provide a strong barrier to protein-like fluorophores associated with wastewater effluent. Results also demonstrated the robust nature of dual barrier membrane systems to achieve greater than 99.9% removal of orthophosphate and dissolved organic carbon and more than 96% rejection of nitrate. Upon completion of the study a comprehensive membrane autopsy was performed on the FO and RO membranes. Organic fouling on the FO membrane was observed to have low adhesion to the membrane surface, but did result in some modification to membrane active layer properties.

Development of a high throughput cross-flow filtration system for detailed investigation of fouling processes

Fouling, more precisely biofouling, remains one of the main obstacles for a wider application of membrane technology. One of the most significant problems limiting membrane fouling control is the inadequate understanding of the basic mechanisms governing adsorption/deposition of foulants in and on membranes. A detailed knowledge with regard to fouling characteristics and development would be clearly advanced if a reliable and repeatable, non-invasive study tool would be available. For this purpose, a direct visual observation system, containing multiple separated cross-flow filtration units, coupled with either an optical or a confocal laser scanning microscope was developed. This approach allows the online, non-destructive monitoring of the fouling process while filtering and the high number of parallel filtrations makes it possible to either analyze different membranes, to apply statistical evaluations, run different feed solutions or to sample and perform membrane autopsies at different time points. This technique allows for the investigation of microbial ecology with respect to microbe–membrane attachment, site-specific associations of micro-organisms, deposition of foulants on the membrane surface and spatial organization of microbial communities on membrane surfaces through the use of fluorescent microscopy techniques. This manuscript illustrates the reproducibility of the developed research tool with respect to membrane flux decline and fouling characterization. Two membrane types, a polyvinylidene fluoride microfiltration (under filtering conditions) and a polyamide reverse osmosis membrane (in non-permeating mode), with respectively a bacterial foulant, Pseudomonas aeruginosa and tap water, were chosen as model systems.

The importance of laboratory water quality for studying initial bacterial adhesion during NF filtration processes

Biofouling of nanofiltration (NF) and reverse osmosis (RO) membranes for water treatment has been the subject of increased research effort in recent years. A prerequisite for undertaking fundamental experimental investigation on NF and RO processes is a procedure called compaction. This involves an initial phase of clean water permeation at high pressures until a stable permeate flux is reached. However water quality used during the compaction process may vary from one laboratory to another. The aim of this study was to investigate the impact of laboratory water quality during compaction of NF membranes. A second objective was to investigate if the water quality used during compaction influences initial bacterial adhesion.Experiments were undertaken with NF 270 membranes at 15 bar for permeate volumes of 0.5 L, 2 L, and 5 L using MilliQ, deionized or tap water. Membrane autopsies were performed at each permeation point for membrane surface characterisation by contact angle measurements, profilometry, and scanning electron microscopy. The biological content of compacted membranes was assessed by direct epi-fluorescence observation following nucleic acid staining. The compacted membranes were also employed as substrata for monitoring the initial adhesion of Ps. fluorescens under dynamic flow conditions for 30 min at 5 min intervals.Compared to MilliQ water, membrane compaction using deionized and tap water led to decreases in permeate flux, increase in surface hydrophobicity and led to significant build-up of a homogeneous fouling layer composed of both living and dead organisms (>106 cells cm−2). Subsequent measurements of bacterial adhesion resulted in cell loadings of 0.2 × 105, 1.0 × 105 cells cm−2 and 2.6 × 105 cells cm−2 for deionized, tap water and MilliQ water, respectively. These differences in initial cell adhesion rates demonstrate that choice of laboratory water can significantly impact the results of bacterial adhesion on NF membranes. Standardized protocols are therefore needed for the fundamental studies of bacterial adhesion and biofouling formation on NF and RO membrane. This can be implemented by first employing pure water during all membrane compaction procedures and for the modelled feed solutions used in the experiment.

Structural and chemical characterization of long-term reverse osmosis membrane fouling in a full scale desalination plant

The assessment of long-term fouling in reverse osmosis (RO) membranes was investigated through extensive membrane autopsy using different analytical techniques. The RO membranes were taken from a seawater desalination plant after 4years of operation. Chemical and structural characterization was performed using different analytical methods, including visual observation, optical microscopy (OM), scanning electron microscopy with energy dispersive X-ray (SEM-EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), inductively coupled plasma optical emission spectrometry (ICP-OES), atomic absorption spectroscopy (AAS) and ion chromatography (IC). The fouling layer consisted of particulate matter embedded in an apparently amorphous matrix, which was unevenly distributed over the membrane surface with the greatest accumulation in the valley areas. Inorganic and organic foulants were identified in the RO membranes. Inorganic foulants mainly consisted of hydrogen aluminosilicates and halite. The main organics substances identified were proteins, polysaccharides and humic compounds and were attributed to biofouling. Chemical analysis revealed that Si, Al, Cl, Ca, Na, Mg and K were the predominant elements contributing to membrane fouling. The reasons for the deposition of foulants on the RO membranes are the increase of membrane selectivity due to biofouling, the large size of cartridge filters and the high operating pressure.

Integrating bench- and full-scale nanofiltration testing for two surface waters

This study investigated the nanofiltration (NF) fouling behavior by two surface waters that serve as source waters for full-scale integrated membrane systems (IMS) of the Tatamagouche and Collins Park drinking water treatment plants (WTPs) in Nova Scotia, Canada. Bench-scale NF fouling experiments conducted under controlled laboratory conditions showed a flux decline of 25% with the Collins Park source water compared with a flux decline of 15% with the Tatamagouche source water over 96 hours of operation. The higher rate of flux decline observed was related to the water quality parameters observed in the Collins Park source water. Membrane autopsies were conducted on virgin and fouled membranes using different techniques to compare the fouling propensity of the two feed waters. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results showed considerable difference between the fouled membranes fed with two source waters. Analyses of full-scale NF fouling data from the two IMS plants reveal higher fouling in the Collins Park WTP. Full- and bench-scale NF fouling observations provide consistent results that together support ongoing membrane cleaning practices in the Collins Park WTP.

Reverse osmosis membranes oxidation by hypochlorite and chlorine dioxide: spectroscopic techniques vs. Fujiwara test

The aim of this work was the study of degradation of a commercial polyamide membrane by two commonly employed oxidants for disinfection in seawater desalination, hypochlorite, and chlorine dioxide. A conventional reverse osmosis (RO) membrane is a thin film composite membrane composed of three different layers, a polyester support web, a microporous polysulfone interlayer, and a thin cross-linked polyamide barrier layer on the top surface, which is the active layer of the RO membrane. The degree of membrane degradation in seawater was evaluated in terms of decline in membrane performance calculated from permeability and salt rejection. In order to establish a relationship between the hydraulic properties and spectroscopic data, infrared and X-ray photoemission techniques (ATR-FTIR and XPS) were employed. The obtained results were compared with the Fujiwara test which is usually performed in membrane autopsies to check the degradation of polyamides with halogens. The chemical degradation of the surface active layer was analyzed using infrared spectroscopy (ATR-FTIR) by monitoring the changes in the characteristic infrared bands of the polyamide. It is possible to calculate the transmittance bands ratio between peak at 1540 cm-1 (due to amide II) and peak at 1585 cm-1 (due to the polysulfone layer) in order to get the comparison of the degraded membranes with a virgin membrane. The amide II band was selected to evaluate the degradation process, because it is the first band that reduces its transmittance value when the degradation process begins. Once the ratio is obtained for the degraded membrane and considering the value obtained from the virgin membrane as the reference point, a new index is calculated named as degradation index. The higher the parameter is, the greater the chemical attacks the polyamide layer. X-ray spectroscopy (XPS) measures the elemental composition and the chemical state of the elements that exist in the surface of a solid. Evaluation of the binding energy is possible to determine if the halogens are attached to the polyamide structure. It was concluded in this work that both spectroscopic techniques ATR-FTIR and XPS could detect the membrane degradation process earlier than Fujiwara test.

Destructive and non-destructive methods for biofouling analysis investigated at the Adelaide Desalination Pilot Plant

In preparation for the operation of the 300 ML/day Adelaide Desalination Plant, a pilot plant was constructed to evaluate anticipated operational challenges, such as biofouling. Various methods for the control of biofouling have been proposed, however, in-situ early tools for detection of biofouling conditions in spiral wound reverse osmosis elements remain elusive. The current study investigated the use of novel methods for assessment of biofouling potential, using process stream samples obtained from the Adelaide Desalination Pilot Plant (ADPP). Non-destructive methods, including flow cytometry (FCM) and bacterial regrowth potential (BRP) analysis were used. X-ray photoelectron spectroscopy (XPS) and Time of Flight-Secondary Ion Mass Spectroscopy (ToF-SIMS) analyses were employed during destructive membrane autopsy to compliment the findings of the FCM & BRP. 16S rRNA analysis was undertaken on seawater samples and autopsied membrane elements to evaluate whether sampling of bulk process streams could provide early warning of potential RO membrane biofouling bacteria. BRP analysis allowed for calculation of whether had assimilable organic carbon (AOC) was consumed by biofilm on the membrane or being sloughing from the surface. XPS and ToF-SMIS analysis facilitated detection of polysaccharides and proteins adhered to the membrane surface. ToF-SIMS also allowed for the detection of foreign chemical contaminant (i.e. organosilicone). 16S rRNA analysis identified the bacteria species within the biofilm. It also allowed for non-destructive analysis of the biofilm microbial composition via swabbing of the RO element's exterior case. 16S rRNA analysis of biofilm on the exterior surface of an RO element correlated well with the microbial composition of internal membrane surface biofilm. This finding could assist utilities as a rapid, non-destructive assessment of potentially biofouling species. ► FCM can determine when the RO system is sloughing or producing bacteria. ► FCM confirmed bacterial contamination of the antiscalant solution. ► XPS has the potential to detect polysaccharides and proteins adhered to the membrane surface. ► ToF-SIMS indicated the presence of organosilicone fouling. ► 16S RNA identified bacteria species and biofilm composition via swabbing of the RO.

Analysis of local fouling in a pilot-scale submerged hollow-fiber membrane system for drinking water treatment by membrane autopsy

An analysis of local fouling in a pilot-scale submerged hollow-fiber membrane water treatment system for drinking water production is described in this paper. Membrane fouling was observed by using microscopic techniques with membrane specimen taken at different longitudinal and horizontal positions of a hollow-fiber membrane module. The resistance-in-series model was used to quantify local fouling resistances of membrane samples. Our results show that the recovery of the permeate flux of the hollow-fiber membrane located near the source of aeration was the highest after performing chemical cleaning. The irreversible fouling resistance was the largest for membrane samples taken near the open ends of the fibers, where the local pressure is expected to be highest. These axial features of irreversible fouling resistance were more pronounced at lower suspended solids concentration or higher set-point flux. However, the local aspect of reversible fouling was relatively less pronounced than the one of irreversible fouling. The results obtained from membrane autopsy were explained well by the local fouling phenomenon driven by the profile of local pressure along the fiber length and transient behavior of this profile during membrane operation. In addition, it was concluded that the individual membrane module experiencing more aeration would have a more localized pattern of membrane fouling, suggesting that the local fouling is more significant under relatively less demanding fouling conditions.

The relation between the RO fouling membrane and the feed water quality and the pretreatment in Djerba Island plant

The reverse osmosis system is exposed to many problems that affect its efficiency. The major problem is fouling membrane which is frequently related to the interaction between the quality of feed water and the pretreatment process. This paper treats two problems of RO plant in Djerba Island, the sulfuric water and the fouling membrane. For the first problem, the anaerobic process showed better performance than the aerobic process. Furthermore, the aerobic process of non-sulfuric water was affected after 6 years of operation with a fouling phenomenon at R.O membrane. This problem was correlated with the increase of the operating pressure, pressure drop and permeates conductivity. To identify causes of these problems, different investigations are carried out. Membrane autopsy, chemical analyses of feed water and follow-up of the operation parameters are performed. The membrane autopsy was achieved by SEM/EDS. The results show that the film is composed mostly with organic matter, silica, metallic matter and aluminum phosphate. This result is correlated with the phosphonate based antiscalant composition. Therefore, antiscalant selection and dosage appear to be critical for membrane fouling development.