Forward Flush Research Articles

Stereoselective separation of omeprazole and 5-hydroxy-omeprazole using dried plasma spots and a heart-cutting 2D-LC approach for accurate CYP2C19 phenotyping

Omeprazole (OME) is a widely used gastric proton pump inhibitor, marketed as a racemic mixture comprising (S)- and (R)-enantiomers, with distinct pharmacokinetic profiles. OME is primarily metabolized by the cytochrome P450 enzymes 2C19 (CYP2C19) and 3A4 (CYP3A4). OME is a conventional probe for CYP2C19 phenotyping. Accurate measurement of these enantiomers and their metabolites is essential for pharmacokinetic studies. This article presents a sensitive and accurate two-dimensional liquid chromatography-mass spectrometry (LC-MS/MS) method for the simultaneous quantification of OME enantiomers and its hydroxylated metabolite (5-hydroxyomeprazole) in human plasma.The method involves an online extraction using an achiral Discovery HS C18 trapping column for purification (20 × 2.1 mm ID, 5μm particle size, Supelco) and subsequent forward flush elution onto a chlorinated phenylcarbamate cellulose-based chiral column (150x2mm ID, 3 μm particle size, Lux Cellulose-4, Phenomenex). The assay was fully validated and met international validation criteria for accuracy, precision, and stability and ensured high selectivity and sensitivity within a short runtime (<8 min). Application of this method to clinical samples demonstrated its utility in studying OME enantiomer pharmacokinetics, particularly its potential for phenotyping the activity of the CYP2C19 isoenzyme.This robust analytical approach offers a valuable tool for clinicians and researchers studying OME's pharmacokinetics, providing insights into its metabolism and potential implications for personalized medicine.

Modeling of spiral wound ultrafiltration membrane forward flushing during secondary wastewater upgrading for unrestricted irrigation

A two-stage membrane system comprising of an ultrafiltration (UF) stage followed by a reverse osmosis (RO) leg was employed for unrestricted irrigation. The UF stage served as a vital pretreatment step for the RO stage. To address the fouling phenomenon of the UF membrane, field experiments were meticulously conducted to thoroughly characterize the flow decline employing forward flushing. Forward flushing of the UF membrane was the preferred selected method although no other cleaning method was evaluated (besides once a week chemical cleaning). Optimal frequency of forward flushing and the associated costs per flush in the UF stage were carefully investigated.The spiral wound UF membranes was economically modeled to achieve most efficient filtration. Modeling considers a range of factors, including energy costs and clean water consumption per forward flush. General curves were obtained to describe the system's performance under diverse filtration conditions.Frequency of forward flushing, almost every 30 min, emerged as the recommended option. This approach proved to be effective in minimizing membrane fouling and sustaining filtration. Modeling of this strategy considered the costs associated with the frequent flushes, and it was found to be a justifiable investment given the considerable benefits in membrane performance and overall system efficiency.

Development of ball surface acoustic wave gas chromatograph for environmental monitoring in spacecraft and its application on the ground

For on-site analysis of surface materials on the Moon, planets, and small bodies and for the monitoring of air quality in crewed spacecraft, we have developed a portable gas chromatograph (GC) equipped with a ball surface acoustic wave (SAW) sensor. In this study, we fabricated a 10 cm cube GC that implements the forward flush method using two metal micro-electro-mechanical-system columns coated with different stationary phases in microchannels fabricated by wet etching and diffusion bonding of stainless-steel plates. Using this GC, we succeeded in analyzing 10 kinds of gas within 10 min. In addition, for the application of the ball SAW GC on the ground, we also developed a palm-sized GC with a single metal capillary column and used it in the analysis of the headspace gas of sake. We showed that the ratio of peak areas differed among odorants depending on the brand and brewing process of sake.

Low maintenance gravity-driven membrane filtration using hollow fibers: Effect of reducing space for biofilm growth and control strategies on permeate flux

The implementation of centralized drinking water treatment systems necessitates lower operational costs and improved biopolymer removal during ultrafiltration (UF), which can be afforded by gravity-driven membrane (GDM) filtration. However, prior to implementing GDM filtration in centralized systems, biofilm growth in compacted membrane configurations, such as inside-out hollow fiber (HF), and its impact on permeate flux need to be investigated. To this end, we operated modules with distinct limits on available space for biofilm growth: (1) outside-in 1.5 mm 7-capillary HF (non-limited), (2) inside-out 1.5 mm 7-capillary HF (limited), and (3) inside-out 0.9 mm 7-capillary HF (very limited). Here, we observed that the lower the space available for biofilm growth, the lower the permeate flux. To improve GDM performance with inside-out HF, we applied daily shear stress to the biofilm surface with forward flush (FF) or combined relaxation and forward flush (R+FF). We showed that applying shear stress to the biofilm surface was insufficient for controlling flux loss due to low available space for biofilm growth. At the experimental endpoint, we backwashed with a stepwise transmembrane pressure (TMP) increase or a single TMP on all inside-out HF modules, which removed the biofilm from its base. Afterwards, higher fluxes were yielded. We also showed that all modules exhibited a gradual increase in biopolymer removal followed by stabilization between 70 and 90%. Additionally, control of biofilm growth with surface shear stress did not affect biopolymer removal. In summary, the implementation of inside-out HF with GDM filtration is challenged by low available space for biofilm growth, but may be remedied with a regular backwash to remove biofilm from its base. We showed that a wider range of GDM applications are available; making GDM potentially compatible with implementation in centralized systems, if space limitation is taken into consideration for operation optimization.

Integration of oxalic acid chelation and Fenton process for synergistic relaxation-oxidation of persistent gel-like fouling of ceramic nanofiltration membranes

Ceramic nanofiltration (NF) is a newly-developed technology for water recycling, but is still limited to pilot-scale applications. Lacking efficient and eco-friendly strategies for cleaning ceramic NF membrane impedes its scaling-up in industries. Forward flush, backwash and acidic/caustic cleaning are not efficient enough. In this work, a novel oxalic acid-aided Fenton process was proposed for synergistic relaxation/oxidation of persistent Ca2+-mediated gel-like fouling of ceramic NF membrane. A reactive catalyst layer was online pre-coated on top of the membrane via a pressure-driven cross-flow pre-filtration of Fe3O4 hydrosols. The gel-like fouling was simulated by alginate in the presence of Ca2+ ions. Results show that the Fe3O4 loading could be readily tuned from 0.16 to 1.34 g m−2 by altering the permeate flux during the pre-coating. The membrane permeability loss due to the pre-coating was minimal (<10%). The combination of oxalic acid chelation and Fenton-based oxidation resulted in high flux recovery (85.07%) for the iron-oxide pre-coated membrane, whereas the single treatment by hydrogen peroxide (H2O2) or oxalic acid was inefficient. This synergistic effect was attributed to relaxation of the Ca2+-mediated gel layer via oxalic acid/Ca2+ chelation, which presumably facilitated H2O2 diffusion at the Fe3O4/foulant interface. The iron-oxide pre-coated membrane maintained stable initial normalized fluxes (83.33–90.15%) through the oxalic acid/H2O2 cleaning over five cycles, with no need of refreshing the iron-oxide pre-coat. Additionally, the leaching of iron from the iron-oxide pre-coat by oxalic acid was suppressed by the oxalic acid/H2O2 combination, owing to a reactive shielding by competitive sorption of H2O2 onto the Fe3O4 surface. Overall, the synergistic relaxation/oxidation method, demonstrated in this study, provides new insights into improving reactivity of Fenton-based processes on hybrid catalytic ceramic membranes for water treatment or fouling control.

Biofilm removal efficacy using direct electric current in cross-flow ultrafiltration processes for water treatment

Biofouling of membranes in water treatment is considered as one of the major practical problems. A novel and an efficient approach for cleaning biofilm grown on the membrane surface is proposed by applying a direct electric current (124 mA, 90 s) through platinum electrodes inside a cross-flow ultrafiltration channel. Depending on the electrochemical reactions occurring at the electrodes, either chlorine or hydrogen-producing configuration is realized by interchanging the current polarity. Baseline determination of the amount of chlorine generated and change in pH is assessed as a function of current intensity, linear cross-flow velocity, and duration of applied current. The efficiency of the proposed method is determined by investigating electrically treated biofilm through bacterial inactivation using Confocal Laser Scanning Microscopy (CLSM), bacterial cell structure changes through Scanning Electron Microscopy (SEM), and by estimating the amount of biomass removal through Optical Coherence Tomography (OCT). When a chlorine-producing electrode is placed at the inlet of the flow cell, 68% of bacterial inactivation is achieved without any modification of bacterial cell shape. Furthermore, a high and near-complete biomass removal is achieved (99%) after a subsequent forward flush of the electrically treated biofilm. However, placing a hydrogen-producing electrode at the inlet reveals a slightly lower bacterial inactivation (65%) and lower biomass removal (77%). Additional systematic experiments using individually sodium hydroxide (NaOH), sodium hypochlorite (NaOCl), or gas microbubbles enabled to elucidate the cause of biofilm removal, synergic effect of caustic agent NaOH and microbubbles.

Fouling control in ceramic nanofiltration membranes during municipal sewage treatment

Using ceramic nanofiltration membranes for treatment of municipal sewage is upcoming. However, the knowledge on fouling control methods for this application are very limited. The most commonly used fouling control method, chemical cleaning, has disadvantages. Chemical cleaning negatively impacts (i) the glass seal layer of tubular ceramic nanofiltration membranes and (ii) the environment, especially when using sodium hypochlorite for removal of organic fouling. Therefore, the use of chemical cleaning should be limited as much as possible. In this research, first, the well-known fouling control methods for polymeric micro- and ultrafiltration membranes, were studied on ceramic nanofiltration membranes: hydraulic backwash and forward flush. Second, a precoat method was combined with a chemical reaction to aid the detachment of the formed cake layer. In this method, a precoat layer was filtered atop of the membrane surface before the start of filtration. The precoat layer then acts as a barrier between the foulants and the membrane surface. After filtration, the precoat layer reacts with the cleaning reagent underneath the fouling layer to enable fast removal of fouling. Results showed that hydraulic backwash was not effective to be used for this type of membranes. Forward flush was able to maintain a higher flux but the relative production downtime was high. Reaction based precoat was most effective in maintaining a high flux and resulted in the highest net water production. Two reaction based precoat methods were tested of which the reaction of calcium carbonate with citric acid was more effective than a Fenton reaction.

Backwashing pressurized ultrafiltration using reverse osmosis brine in seawater desalination and its potential costs savings

This paper discusses the feasibility of using reverse osmosis concentrate to backwash ultrafiltration membranes in the seawater reverse osmosis desalination space. Brine is produced through DOW FILMTEC™ reverse osmosis elements and it backwashed every 90 min to DOW™ ultrafiltration membranes. A side-by-side validation is done for 15 d using two parallel ultrafiltration and reverse osmosis integrated systems. One line uses brine for backwashing, while the other uses conventional filtrated water. The optimization is proven to have the same cleaning efficiency than the conventional backwashing methods and no precipitation is observed in the fibers. An additional validation period that uses reverse osmosis brine during backwashes and only two backwash steps is also carried out successfully. These steps are the previously identified backwash top with air scour and forward flush. Fibers also show an excellent integrity after the whole experimental period. A model is built in order to analyze the backwash efficiency of the optimized conditions and the transmembrane pressure increases during the filtration cycle. The results show the same fouling tendency for the line operating with brine and the line operating with filtrated water. The efficiency of the ultrafiltration process is improved from 88 to 98% thanks to this optimization together with the previous researches. This represents filtrating 96 min extra per day and a reduction of 100% in the filtrated water used during backwashes. The chemical equivalent concentration is also optimized from 0.28 to 0.06 mg/L NaClO thanks to the adjustment of the chemically enhanced backwash frequency. This accounts for a 7.1% savings in the ultrafiltration step and for a 1.2% savings in the whole desalination process.

Optimizing seawater operating protocols for pressurized ultrafiltration based on advanced cleaning research

This paper is part of a global research project conducted by Dow Water & Process Solutions to optimize the efficiency of ultrafiltration processes. After an initial identification of the backwash as the key opportunity to increase the efficiency of the process, a study based on its optimization is developed. Main emphasis is given to the sequence and subsequent number of steps involved in the backwash. The ultimate goal is thus to increase the availability and recovery of the process while still attaining a high cleaning effect during the backwash. This optimization is done through the realization of various experiments using DOW™ Ultrafiltration SFP-2660 outside-in polyvinylidene difluoride (PVDF) membranes following an exhaustively planned factorial design of experiments. The factors being assessed are the steps normally performed during a backwash. These are the air scour (AS/D), the draining (D), the backwash top (BWT) with or without air scour, the backwash bottom (BWB) and the forward flush (FF). The responses analyzed are the calculated efficiency of the process and the experimentally obtained transmembrane pressure, which represents the fouling rate of the membrane. The results are analyzed through a formal statistical study of the analysis of the variance and are validated through 25 days of stable operation. The results show that the backwash can be simplified from an original sequence of five steps to only two steps, which are the backwash top with air scour and the forward flush without impairing the effectiveness of the cleanings. This leads to an increase in efficiency higher than 5%, which represents a decrease of 50% in the filtration inefficiency. This is achieved thanks to the reduction of the time invested for the cleanings and the decrease in the amount of water consumed.

Continuous Measurement of Multiple Gases Using Ball Surface Acoustic Wave Gas Chromatograph

Although portable gas chromatographs (GCs) have been developed for the monitoring of volatile organic compounds (VOCs) in working environments, they still need high power consumption for the heating column. Thus, we previously developed a portable surface acoustic wave (SAW) GC equipped with a ball SAW sensor and a micro-electromechanical-system column (ball SAW GC) and proved the usefulness of the forward flush (FF) method for realizing the fast analysis of multiple gases without a heater. However, its ability to measure ten kinds of VOCs at ppm order and automatic continuous measurement were not demonstrated. In this study, a ball SAW GC employing the FF method and equipped with a gas sampler for continuous injection was developed. Then, the performance of monitoring multiple gases in working environments was verified by measuring ten kinds of VOCs with maximum acceptable concentrations. Moreover, real-time monitoring of seven kinds of VOCs with a linear change in the response value to concentration changes was demonstrated.

A reversed-flow differential flow modulator for comprehensive two-dimensional gas chromatography

A simple and reliable differential flow modulator has been demonstrated which reverses the flow during the flush step. The modulator is constructed with commercially available capillary flow technology tees which simplifies the apparatus and permits wide range of column dimensions to be used because the modulator volume is adjustable. Using a reverse flush arrangement the tailing of the peak at the base (baseline rise between modulations) is reduced 10–20 fold as compared to forward flush modulation. This is most easily observed for peaks overloaded in the first dimension. Excellent reproducibility (<2% RSD) of area measurements has been demonstrated with a complex fragrance sample as well as the capacity to handle significant overloading without loss of resolution in the second dimension. Further demonstrating the flexibility of this modulator, separation of C1–6 alkanes and olefins are demonstrated with two porous layer open tubular columns.

Development of Multiple-Gas Analysis Method Using the Ball Surface Acoustic Wave Sensor

In the fields of energy exploitation, and for the safety and security of society, portable multiple-gas sensors are essential. Although the gas chromatograph (GC) is applicable to multiple-gas analysis, it is not portable. As a result, we have proposed the ball surface acoustic wave (SAW) GC using a ball SAW sensor, which realizes high sensitivity by the ultramultiple roundtrip propagation of a SAW and a separation column fabricated by micro-electro-mechanical-system technology. However, it takes too long for a portable GC such as the ball SAW GC to analyze mixed gases of high and low molecular weights at the same time. In this study, we developed the forward-flush (FF) method, involving two (or more) separation columns with a ball SAW sensor inserted after each column, to solve the above problem. Using the ball SAW GC with the FF method, we analyzed mixed gases of natural gas components and volatile organic compounds.

Distal filtration versus flow reversal: An ex vivo assessment of the choices for carotid embolic protection

Choices for embolic protection during carotid stent procedures include distal filtration (DF) and proximal occlusion with flow reversal (POFR). DF devices are widely used but have produced only modest improvements in clinical outcomes. There is less experience with POFR devices but single center reports suggest reduced emboli detected by transcranial Doppler (TCD). To determine if POFR offers a significant improvement in embolic protection, we tested five DF devices and two POFR devices with 8F and 10F sheath design in an ex vivo angioplasty system using human carotid plaques excised en bloc. Physiologic pressures and flows were used and the efficiency of plaque fragment removal by these devices compared. Thirty-three human carotid plaques removed en bloc were secured in tailored polytetrafluoroethylene (PTFE) grafts. The distal PTFE was either 6 mm or 5 mm inner diameter (ID). Saline was delivered through the excised carotid plaque as follows: a cleaning 50 mL flush was done prior to the angioplasty procedure and discarded; further flushes of forward flow were done with five pressurized "pulsations" of 10 mL each (50 mL), peak pressure 140 mm Hg. Balloon angioplasty was done with a 4 mm and then a 6 mm balloon. DF flushes were applied after each angioplasty and "postprocedure" after the device was removed. With POFR, 50 mL were collected through the sheath after balloon angioplasty by either back-pressure of 20 mm Hg, 40 mm Hg or 60 mm Hg, or by aspiration. Postangioplasty pressurized forward flush of 50 or 100 mL was done as described. Each flush was collected, centrifuged, and examined for plaque fragments. Fragments greater than 60 microns were sized and counted on a 100 micron grid. When DF devices were used in 6 mm lumen PTFE, the percent of fragments trapped was poor (13.7% to 27.8%). There were no statistically significant differences between the devices. The capture of fragments improved (22% vs 51.4%, P < .001) when devices appropriate for a 6 mm lumen were used in a 5 mm PTFE "ICA", functionally over-sizing the devices. POFR efficiency improved with increasing back-pressures and with repeated aspirations. Postprocedure, successive flushes of pressurized forward flow yielded additional plaque fragments and when the efficiency of POFR was assessed with forward flushing volumes similar to those used for DF, the efficiencies were similar, although larger fragments were more efficiently removed with POFR. In our model, both protection strategies were less than ideal. For POFR, high back pressures or multiple aspirations improve the efficiency of cerebral protection but additional fragments were released by pressurized flow even after aspiration of 150 mL of saline. DF devices create a pressure gradient and fragments apparently went around the device with pressurized flow in our PTFE lumen. Over-sizing of DF devices partially corrected this problem and increased over all DF efficiency to be comparable to POFR for smaller fragments but not for larger fragments.

Effect of low frequencies and mixed wave of ultrasound and EDTA on flux recovery and cleaning of microfiltration membranes

The ability of low frequency ultrasound for cleaning fouled membrane has been proved. In this investigation, various frequencies and mixed wave ultrasound were used separately and together with two concentrations of EDTA as chelating agent in forward flush cleaning of MF membranes which was fouled by milk solution 1%. A statistical multifactor design was employed to obtain more precise results. The main factors involving several frequencies of 28, 45, 100 kHz and mixed wave ultrasound as well as two concentrations of 1 mMole and 3 mMole of EDTA and their interaction effects were evaluated on flux recovery, cleaned membrane resistance and cleaning efficiency. The results showed that mixed wave ultrasound individually and together with EDTA 1 mMole had higher cleaning efficiency than other treatments and there is a synergistic effect when ultrasound was used with EDTA as a cleaning factor. Also polynomial regression of flux as a function of time showed that only 5 min forward flushing under irradiation of effective frequency of ultrasound and a low concentration of EDTA are enough to approach the cleaning of fouled MF membranes.

Blocking of capillaries as fouling mechanism for dead-end ultrafiltration

In this paper plugging of capillaries in the potting is investigated. A lot of research has been done on fouling of the membrane surface (pore blocking, cake filtration) but research on other types of membrane fouling like plugging of capillaries is not so common. Experiments were performed with a lab-scale test installation under constant flux conditions with synthetic feed water containing ferric hydroxide flocks as a fouling component. The experiments showed that during operation capillaries became blocked by fouling plugs. The presence of blockages, especially in the potting at the concentrate side of the capillaries, could not be detected by measuring the clean water resistance. However such blockages did result in an increased forward flush pressure. A combination of the clean water resistance and the forward flush pressure is suitable for determining the fouling of a membrane and the effectiveness of a cleaning procedure. The part of the capillaries in the potting is not backwashed and therefore the hydraulic as well as the chemical cleaning is not efficient at this place.

Heterogeneous fouling in dead-end ultrafiltration

In the literature membrane fouling is defined as a homogenous fouling of the membrane surface. Pore blocking as well as cake formation increase the resistance of a membrane at each spot on the membrane to the same extent. This homogenous fouling is probably true for the first filtration cycle. But if the hydraulic cleaning of the membrane (backwash and/or forward flush) is not capable of removing all the fouling in the membrane module, we may expect a heterogeneous membrane surface and have to face different mechanisms in the next filtration cycles. In our research we found evidence for the existence of such heterogeneous fouling in dead-end ultrafiltration. Experiments are performed with small scale constant flux equipment with the possibility to perform an automated backwash and forward flush. Because of the small membrane surface only 8 liters per hour is filtered. With such a small volume experiments can be done with one batch of water or with synthetic water. Our results indicate that there are two different types of heterogeneous fouling: (1) Patches of fouling remaining on the membrane surface after a backwash causes a decrease of the available membrane surface. This fouling mechanism can be recognized by a disproportional increase of the build-up of the resistance during filtration. (2) Blocking of capillaries especially in the potting of the modules. This type of fouling is not necessarily affecting the transmembrane pressure. This type of fouling can be recognized by an increase of the forward flush pressure.

Reverse-pressure back-flush in pilot scale, dead-end ultrafiltration of surface water

A simple protocol that makes use of the inertia of water to generate a rapid negative pressure differential across capillary ultrafiltration membranes is reported. This short-interval back-flush technique, preceded by cross-flow forward flush, was evaluated as an alternative to conventional back-flush to maintain membrane flux productivity in a pilot dead-end filtration application. Intermittent back-flush conditions are created when a reverse-pressure pulse, during which product is drawn in the reverse direction through the membrane wall, is introduced. The duration of the negative pressure-pulse peak is very short (1–2 s), after which it subsides and levels out in accordance with the net positive suction head of the centrifugal pump used to recirculate the feed. Reverse-pressure spikes of up to −90 kPa, which subside after only a few second to −40 kPa, were generated. The combined effect of reverse-pressure pulsation sequence of events is that of (i) a short back-flush (direct result of negative trans-membrane pressure conditions that are introduced) and (ii) flow destabilisation (sudden retardation and start-up of lumen-flow) during a forward flush that precedes the reverse-pressure pulse event. The reverse-pressure pulse technique was evaluated in a dead-end filtration pilot study producing potable water from a surface resource without the addition of chemicals. The membranes suffered no adverse effects and their flux performance was maintained reasonably well, even though the feed water turbidity reached values as high as 90 NTU during the exercise.

Optimization of membrane physical and chemical cleaning by a statistically designed approach

Membrane cleaning efficiency depends on many parameters such as hydrodynamic conditions, concentration and temperature of chemical cleaning solution, as well as sequence of cleaning. Various studies and industrial applications show that factorial design is an efficient method in optimization of operational parameters. In this study, a statistical factorial design was employed to identify more accurately the key factors as well as their interactions in both physical and chemical cleaning of ultrafiltration (UF) and reverse osmosis (RO) membranes in municipal wastewater reclamation. It was found that significant factors affecting physical cleaning of both UF and RO membranes are production interval between cleans, duration of backwash and pressure during forward flush. In chemical cleaning of both membranes, temperature and concentration of high pH cleaning solution and backwash after chemical cleaning play important roles. By using the optimized membrane cleaning methods, the cleaning efficiency was significantly improved, which can cause higher membrane filtration capacity and efficiency.

Fouling of ultrafiltration membranes in drinking water treatment of karstic spring waters

Three UF-systems were tested for the drinking water treatment of karstic spring water. The pilot plants were operated in Marmagen, which is located in North-Rhine Westfalia (Germany). One of the two tested capillary UF-systems (in-out mode) was backflushed with filtrate and with filtrate and hydrogen peroxide. The other one could be flushed with air and raw water (forward flush) before a backflush was performed. The third system was an immersed UF-system (out-in) where negative pressure on the filtrate side is applied. The capillary UF-systems were operated at high flux and long backflush intervals when turbidity was low. At high turbidities the permeability declined and could only be restored by chemical cleaning. For this particular water the immersed system showed also a permeability decline, which was less pronounced. The permeability recovered in normal operation, when the turbidity declined. Using SEM and EDX the fouling could be mainly attributed to small particles (well below 3 μm). Qualitative element analysis showed that silica is the main component of the formed cake layer.

Understanding membrane fouling in ultrafiltration of WWTP-effluent

The application of ultrafiltration to effluent of waste water treatment plants (WWTP-effluent) is getting increasing attention. However, many experiments show a rapid decrease in flux urging frequent and intensive cleaning. In order to understand the mechanisms of the occurring fouling process, various filtration and cleaning experiments were performed, giving information about the filterability of the feedwater (F) and the reversibility of the occurring fouling layer (R). Short-term fluxes are mainly determined by the filterability, while both the filterability and the reversibility greatly affect long-term fluxes. The objective of this research is to measure the filterability of WWTP-effluent and the reversibility of the occurring fouling layer in ultrafiltration of wwtp-effluent with and without pre-treatment. The results of the filtration experiments show a rapid decrease of flux resulting in a low value for the filterability, which also decreases during progressing filtration. The filterability is mainly related to the volume of treated water. Pre-treatment of the WWTP-effluent by in-line coagulation or by deep-bed filtration has little influence on the filterability. However, results on the reversibility show an improvement of the reversibility by pre-treatment. Both filterability of the WWTP-effluent and reversibility of the fouling layer are found to be independent of the applied flux. As to the applied cleaning methods, the back flush is far more effective than the forward flush even if combined with air. In all experiments the remaining fouling layer still has to be removed by an intensive chemical cleaning. This research indicates the very importance of reducing the formation of an irreversible, non-removable fouling layer.