Changes In Transmembrane Pressure Research Articles

Fouling studies of capillary ultrafiltration membrane

Ultrafiltration (UF) membranes in capillary configuration are deployed in domestic water purification with respect to removal of contaminants. Fouling is an inherent phenomenon in UF process and has been reported to cause decline in flux, reduces membrane life, etc. So, it has to be thoroughly studied in order to optimise the logistics of process operation. Considering the concentration of contaminants in different parts of India, the fouling studies investigations were carried out in the range of 5–15 ppm of various constitutes such as Iron, Manganese, and the organic foulants – sodium alginate and humic acid. Out of various parameters affecting fouling like feed pressure, feed temperature, feed pH, the effort was directed towards studying the effect of various foulants (and at different loadings) on the membrane. Results obtained from experiments suggest that the fouling caused by the organics (sodium alginate and humic acid) is higher than that of inorganics (iron and manganese). Iron caused higher fouling than manganese. Sodium alginate caused higher fouling than humic acid. It is observed that humic acid caused more irreversible fouling than sodium alginate. Attempts have been made to develop a mathematical model to represent the fouling phenomena. The effect of fouling for different loadings of various foulants was seen in terms of change in transmembrane pressure (TMP), under conditions of constant permeate flow. TMP in the proposed model is expressed as the function of feed flow rate, intrinsic membrane porosity, permeability of the membrane, and the plugging constant. The values of plugging constant represent the interactions between the feed and the membrane and thus suggest the degree of fouling, both reversible and irreversible fouling, caused by different foulants and at different loadings. Irreversible pore constriction fraction is a measure of irreversible fouling and it has also been determined for different foulants and at different loadings.

Tracing biofouling to the structure of the microbial community and its metabolic products: A study of the three-stage MBR process

The biofouling characteristics of a sequential anoxic/aerobic-membrane bioreactor (A/O MBR) were analyzed during the three-stage process (fast-slow-fast transmembrane pressure (TMP) increasing). The results indicated: during the stage 1 (before day 1), the microbial communities in the activated sludge (AS), cake sludge (CS) and biofilm (BF) were similar to each other, and the adsorption of microbes and the metabolic products was the main factor that led to TMP increase; during the stage 2 (between day 1 and day 7), the cake layer begun to form and the TMP continued to rise gradually at a reduced rate compared to stage 1, at this point a characteristic microbial community colonized the CS with microorganisms such as Saprospiraceae and Comamonadaceae thriving on the membrane surface (BF) probably due to greater nutrient availability, and the predominance of these species in the microbial population led to the accumulation of biofouling metabolic products in the CS, which resulted in membrane fouling and the associated rise in TMP; during the final stage (after day 7), the biofilm had matured, and the activity of anaerobes stimulated cake compaction. The statistical analysis showed a correlation between the TMP changing rate and the carbonhydrates of soluble microbial products (SMPc) content in the CS. When the SMPc concentration rose slowly there was a low level of biofouling. However, when the SMPc accumulating rate was greater, it resulted in the more severe biofouling associated with the TMP jump. Furthermore, the correlation coefficient for the TMP increase and protein concentrations of extracellular polymeric substances (EPSp) in the CS was highly significant. The cluster analysis suggested that the AS microbial community remained stable during the three TMP change stages, while the CS and BF community were changed accompanied with the TMP change. The interaction between the microbial communities and the metabolic products lead to the significant correlation between them. The EPSp in conjunction with the SMPc were the main factors that accelerate the membrane fouling. The rapid rise of SMPc triggered a sudden increase in the TMP, while the accumulation of EPSp caused the sustained rise in TMP.

Microstructured spacers for submerged membrane filtration systems

We introduce a new type of membrane spacer design, based on the geometry of static mixers, for application in submerged membrane filtration. In particular we demonstrate the potential of the spacers to reduce air sparging and energy consumption. New operational modes are proposed and discussed critically.Critical flux measurements are performed with and without spacer at various process parameters such as spacer/channel height, air sparging rate and bubble size. The most relevant energy reducing parameters of submerged systems are determined with the Design of Experiments (DoE) methodology.Using the new spacers, the critical flux can be increased by 100%. Furthermore, fouling monitored by the trans-membrane pressure change can be significantly reduced by a factor of 7.5 when combined with elevated cross-flow velocities.

정유량 막여과 파울링 모델을 이용한 막여과 정수 플랜트 공정 진단 기법

A process diagnosis method for membrane water treatment plant was developed using a constant flux membrane fouling model. This diagnosis method can be applied to a real-field membrane-based water treatment plant as an early alarming system for membrane fouling. The constant flux membrane fouling model was based on the simplest equation form to describe change in trans-membrane pressure (TMP) during the filtration cycle from a literature. The model was verified using a pilot-scale microfiltraton (MF) plant with two commercial MF membrane modules (72 m of membrane area). The predicted TMP data were produced using the model, where the modeling parameters were obtained by the least square method using the early plant data and modeling equations. The diagnosis was carried out by comparing the predicted TMP data (as baseline) and real plant data. As a result of the case study, the diagnsis method worked pretty well to predict the early points where fouling started to occur.

Factors affecting coagulation as a pretreatment to ultrafiltration membranes

Low pressure membranes can be effective in treating various types of water, but are subject to fouling. In this work, chemical coagulation was studied as a pretreatment to ultrafiltration (UF), with the goal of mitigating fouling while maintaining high permeate water quality. Alum and ferric chloride were evaluated, as well as two polyaluminum chloride (PACl) products of different basicities and compositions. A bench-scale hollow fiber UF unit was developed to study the treatment of raw and pretreated water from two southern Ontario drinking water sources. The four coagulants were compared at optimal dosages, as well as at lower dosages. The roles of mixing and pH conditions were also evaluated. Membrane fouling was evaluated by observing changes in trans-membrane pressure (TMP) over 3-day experiments. Under optimal dose conditions, all four coagulants were able to reduce the rate at which the membrane fouled to varying degrees for each water source. Total organic carbon (TOC) removal by the membrane was also enhanced with coagulation pretreatment as would be expected. Experiments conducted with low coagulant dosages displayed under-dosing and a subsequent increase in membrane fouling. Experiments conducted with modified raw water pH improved both membrane performance and TOC removal, while experiments with modified mixing intensities proved ineffective.

Evaluation of humic acid removal by a flat submerged membrane photoreactor

A flat submerged membrane combined with a TiO2/UV photocatalytic reactor (FSMPR) was employed in batch mode to remove humic acid (HA). HA removal efficiency was characterized by UV254 absorbance, UV-vis spectra, dissolved organic carbon (DOC) concentration, specific UV absorbance (SUVA), and trihalomethane formation potential (THMFP). The FSMPR process was effective in removing more than 86% of DOC and nearly 100% of UV254 absorbance, while the THMFPs of samples were reduced to < 19 μg/L after 150 min of treatment. In addition, changes in transmembrane pressure (TMP) with and without UV were evaluated; TiO2/UV was effective at controlling membrane fouling by HA. Analysis of the molecular weight (MW) distributions and three-dimensional excitation-emission matrix (EEM) fluorescence spectra of HAs revealed that the effectiveness in membrane fouling control is a result of changes in HA molecular characteristics. The TiO2/UV photocatalytic reactor caused the degradation of high MW, hydrophobic humic-like molecules to low MW, hydrophilic protein-like molecules, although this fraction was not completely removed during 150 min of treatment and was less responsible for membrane fouling.

전오존이 세라믹 막의 차압에 미치는 영향

Abstract : The performance of a domestic ceramic membrane with pore size of 0.1 µm was evaluated to produce drinking water. A pilot-scale ceramic membrane filtration plant with a capacity of 1 m 3 /d was operated at the filtration flux of 3.0 m 3 /m 2 ․d to investigate the effect of both backwash interval and pre-ozonation on TMP (trans-membrane pressure) increasing rate. The TMP increased with increasing the backwash interval. However, the application of pre-ozonation reduced the TMP increasing rate remarkably. When 1 mg/L of ozone was dosed with contact time of 5 min, TMP increasing rate at the backwash interval of 1 hr was reduced by 30%. This result indicated that pre-ozonation was very effective in reducing membrane fouling. There was almost no change in TMP increasing rate when the ozone contact time was maintained in the range of 5 to 15 min. Increasing ozone concentration up to 3 mg/L showed beneficial effect on TMP increasing rate. Key Words : Drinking Water, Ceramic Membrane, Trans Membrane Pressure (TMP), Pre-ozonation, Ozone Dose and Contact Time

Investigating the effect of colloids on the performance of a biofilm membrane reactor (BF-MBR) for treatment of municipal wastewater

Performance of membrane reactor in combination with moving-bed-biofilm reactor (BF-MBR) for treatment of municipal wastewater was investigated in relation to different organic loading rates; high and low rates. The membrane was operated with a constant flux of 50 LMH and 96% recovery. The fouling rate was evaluated as development of the trans-membrane pressure (TMP) during the operational time. Suspended solids (SS) concentrations, organic matter (COD/FCOD), particle size distributions (PSD), capillary suction time (CST) and time to filter (TTF) were measured daily and further related to TMP in order to determine major fouling factors. A higher fouling potential was observed for high-rate operating conditions. A fraction of organic matter below 1.2 im was mostly related to changes in TMP. Furthermore, a higher amount of particulate fraction below 0.1 im in membrane reactors during high-rate operating conditions presented a dominant contribution to membrane fouling and colloidal fouling.

Investigating the effect of colloids on the performance of a biofilm membrane reactor (BF-MBR) for treatment of municipal wastewater

Performance of membrane reactor in combination with moving-bed-biofilm reactor (BF-MBR) for treatment of municipal wastewater was investigated in relation to different organic loading rates; high and low rates. The membrane was operated with a constant flux of 50 LMH and 96% recovery. The fouling rate was evaluated as development of the trans-membrane pressure (TMP) during the operational time. Suspended solids (SS) concentrations, organic matter (COD/FCOD), particle size distributions (PSD), capillary suction time (CST) and time to filter (TTF) were measured daily and further related to TMP in order to determine major fouling factors. A higher fouling potential was observed for high-rate operating conditions. A fraction of organic matter below 1.2 ìm was mostly related to changes in TMP. Furthermore, a higher amount of particulate fraction below 0.1 ìm in membrane reactors during high-rate operating conditions presented a dominant contribution to membrane fouling and colloidal fouling.

Correlating TMP Increases with Microbial Characteristics in the Bio-Cake on the Membrane Surface in a Membrane Bioreactor

Subcritical flux operation is widely practiced in membrane bioreactors (MBRs) to avoid severe membrane fouling and, thus, to maintain sustainable permeability. Filtration at a constant subcritical flux, however, usually leads to a two-stage increase in the transmembrane pressure (TMP): initially slowly, then abruptly. We have investigated the mechanism of this two-stage TMP increase through analyses of the structure and microbial characteristics of the bio-cake formed on the membrane. The MBR was operated under various subcritical and supercritical flux conditions. Under subcritical conditions, we observed the typical two-stage TMP increase. When a constant flux augmented and reached the supercritical conditions, however, the dual TMP change gradually transformed into a steeper, one-stage TMP increase. The second stage TMP increase under the subcritical flux was closely related to the sudden increase in the concentration of extra-cellular polymeric substances (EPSs) at the bottom layer of the bio-cake; we attribute the one-stage TMP increase under the supercritical conditions to the accumulation of microbial flocs and the reduced porosity of the bio-cake under compression. We explain the variation of the EPS concentration in the bio-cake in terms of the spatial and temporal changes of the live-to-dead ratio along the depth of the bio-cake.

Biocompatible poly(N-vinyllactam)-based materials with environmentally-responsive permeability

Biocompatible polymer-based materials whose properties respond to environmental stimuli are of great value in biomedical and biotechnological applications (e.g., controlled release of drugs and sensitive reactants, bioseparations, spontaneous adjusting of flow of liquids including flow control in microfluidic devices). This study describes preparation and properties of biocompatible poly(N-vinyllactam)-based environment responsive composite membranes. The non-charged network N-vinyl lactam polymers form hydrogels that can exhibit swelling and de-swelling behaviour and, thus, regulate porosity of the membrane. The first part of the study has involved investigation of bulk polymerization reactivity of N-vinylcaprolactam (VCL)-based systems. VCL has been combined with up to 20 mol% of N-vinylpyrrolidone (N-vinylbutyrolactam). These synthetic processes have been investigated as thermal polymerizations (with and without a free-radical initiator) and photopolymerizations. Subsequently, the most reactive systems have been used to prepare composite materials by polymerization-modifying borosilicate microfibre membranes. The modified membranes have been characterized by the net mass gain, infrared spectra, and change in permeability in response to changes in ionic strength of the aqueous media. The permeability experiments have been carried out at constant fluxes and the resultant changes in trans-membrane pressure observed. Those membranes that are ionic-strength responsive could potentially be used for bio-separations and other types of biomedical and biotechnological applications.

Extracorporeal circuit pressure profiles during continuous venovenous haemofiltration

Continuous renal replacement therapy machines are capable of providing continuous pressure measurements at different points of the extracorporeal circuit. This study investigates the pattern of circuit pressure changes during high-volume continuous venovenous haemofiltration (CVVH) with regional anticoagulation with anticoagulant citrate dextrose in formula A. Extracorporeal circuit pressures during 91 treatments of CVVH were analysed. Distinct patterns of extracorporeal circuit pressures were observed: (a) the extracorporeal circuit pressures during a routine uncomplicated CVVH treatment remained close to initial values. The interquartile range (IQR) of pressures during the treatments were as follows: PA (arterial pressure) -3.5 to -10 mmHg, PV (venous pressure) 51 to 41.5 mmHg, PBE (prefilter pressure) 120.5 to 104 mmHg, PD2 (fluid outlet pressure) -23 to -70 mmHg, TMP (transmembrane pressure) 142.75 to 102.75 mmHg and PFD (pressure filter difference) 70 to 62 mmHg. (b) PD2 and TMP showed early separation from baseline values in CVVH treatment compromised by haemofilter clot. Haemofilter clotting problems were associated with median PD2 of -164 mmHg (IQR: -66.2 to -228.7), a fourfold increase from baseline. (c) PA and PV values changed abruptly in catheter-malfunction-related circuit disruption. Poorly functioning catheters tended to have a higher baseline PA (median: -33 versus -25.5) than in those without catheter problems; however, the difference was not statistically significant (p= 0.13). (d) A rise in PBE and PFD followed by changes in PD2 and TMP were noted in a treatment disrupted because of air detection chamber clotting. Distinct patterns of extracorporeal circuit pressures were present in patent and disrupted CVVH circuits. We suggest that the pattern of pressure profiles, not absolute values, may be more relevant in clinical practice.

Evaluation of biofouling phenomenon in suspended and attached growth membrane bioreactor systems

This article aims to examine fouling mechanism in attached and suspended growth membrane bioreactors (MBR) for three different biomass concentrations of 6, 10, and 15 g/L of MLSS. Laboratory scale experiments were conducted with two different sets of submerged MBRs: suspended (without media) and attached growth (with moving media) MBRs. The media used in the attached growth system was cylindrical polypropylene rings having outer and inner diameters of 4 mm and 3 mm, respectively, and a nominal density of 1.001 kg/m 3. Synthetic domestic wastewater was fed to the reactors at 2 h HRT and 500 mg/L COD. The biofouling phenomenon in the reactors was monitored by changes in transmembrane pressure (TMP) as a function of operating time. It was found in both reactors that the increase in fouling was associated with increasing MLSS concentration. However, the presence of moving media in the attached growth reactor could reduce the membrane fouling. The fouling mechanism that was proposed in the attached growth reactor was associated with the suspended and colloidal particles combination as a result of the movement of the media in the attached growth reactor. Thus, in biofouling along with EPS formation, particle size distribution plays a predominant role.

Permeate Flux Optimisation of a Pilot Microfiltration Plant for Cost-Effectiveness of Water Reclamation for Reuse

A pilot plant was constructed with eight elements of an Asahi microfiltration (MF) membrane—a total filtration surface area of 56 m2. Performance of the plant was examined in preparation of a secondary sewage effluent without coagulant for reverse osmosis membrane treatment. Production at different permeate flux was tested for evaluation of the changes in transmembrane pressure (TMP) and specific permeate flux (SPF) with time. Clean-in-place (CIP) was conducted when TMP reached a value about 2 atm after each test. For permeate flux of 48, 55, 61 and 66 L m−2h−1, the ceiling TMP was reached after filtration for approximately 420, 200, 225, and 195 h, respectively. The corresponding cumulative permeate volumes were 1130, 620, 765, 720 m3 before a CIP was necessary. The SPF decreased quickly with increases in permeate flux and the corresponding half-SPF times were 147, 89, 75 and 39 h for the respective flux studied. The membrane fouling tolerance was greater at a lower than at a higher flux. Analysis of the performance data suggests that run of the MF plant at higher permeate flux with more frequent and quick CIP might produce more water. The optimal filtration durations were found to be 12, 8, 7 and 3 days for permeate flux of 48, 55, 61 and 66 L m−2h−1, respectively. Prolonged filtration after the optimal interval without CIP may not maximise the economical benefit.

Preliminary Investigation of the Applicability of a Simulated Set‐up to Assess Membrane Fouling by Residence Time Distribution Studies

AbstractFouling of membrane systems represents significant cost in time, maintenance and quality in the food and dairy industry. While gross methods of fouling determination such as flux decline and changes in transmembrane pressure are adequate to determine the overall extent of fouling, finer tools are necessary to properly diagnose fouling and to properly assess the effectiveness of cleaning regimes. This study investigates the effect of simulated and actual fouling on the residence time distribution of a single pulse through a single membrane sheet. The differences in residence time distribution observed allow an assessment of the degree and spatial position of fouling material without any need to disrupt the operation of the membrane. This method can be used to assess the need for cleaning and maintenance as well as the effectiveness of cleaning regimes.

Membrane bioreactor fouling in sub-critical filtration conditions: a local critical flux concept

This study shows the changes in transmembrane pressure in a membrane bioreactor (MBR) operating at a constant flux and in well-defined biological conditions. Despite the initial choice of filtration conditions at sub-critical flux, gradual fouling is seen to develop in membrane material which, after long periods of experimentation without intermediary membrane regeneration, proves to be hydraulically irreversible. Thus a single parameter model was set up, whose value could be derived from monitoring the changes in transmembrane pressure. It works on the hypothesis that the open surface is reduced due to a successive blocking of membrane pores. The development of this model has shown that, despite operating conditions held at constant flux, an increase occurs in the rate of circulation in the pores which remain open, which may reach critical local filtration conditions, resulting in the formation of deposits which are reversible but induce an abrupt change in transmembrane pressure.

Experimental studies in the dead-end ultrafiltration of dextran: analysis of concentration polarization

Considerable theoretical and experimental work has been published to explain the cause of flux decline in the ultrafiltration (UF) of dextran. However, an experimental determination of resistance contributions due to polarization to the overall filtration resistance has not been addressed. Also, the effects of feed concentration and applied pressure on membrane concentration and boundary layer thickness and unsteady-state flux response to a step change in trans-membrane pressure have not been reported. This work reports experimental results of the ultrafiltration of dextran with a fully retentive membrane along with a procedure to determine the contributions of various resistances to filtration. It was observed that the ultrafiltration of dextran was osmotically limited in our work. The contribution of polarization resistance was found to be dependent on applied pressures and initial bulk feed concentrations whereas the boundary layer thickness of polarization was affected by feed concentration alone.

Transmembrane pressure profiles during constant flux microfiltration of bovine serum albumin

Many microfiltration systems are now run at constant filtrate flux to achieve improved performance; however, large increases in transmembrane pressure are often required to maintain the flux at a constant value due to membrane fouling. We have developed a new mathematical model to describe the change in transmembrane pressure during constant flux microfiltration. Fouling is assumed to occur first by pore blockage, with a cake then forming over the blocked areas of the membrane. This combined pore blockage-cake filtration model is in good agreement with experimental data obtained during the constant flux filtration of bovine serum albumin through track-etched microfiltration membranes. The total volume of the feed solution that can be filtered through the membrane before the transmembrane pressure exceeds some critical value increases with decreasing flux due to the reduction in the rate of cake growth at low flux. Model simulations were used to provide important insights into the design and operation of constant flux microfiltration processes.

A statistical method for quantifying the different fouling effects of three combined water sources on an ultrafiltration membrane

A simple statistical model has been developed to explain the fouling of an ultrafiltration (UF) membrane treating three mixed feedwater matrices. A tubular UF membrane operating under dead-end conditions, based at the Millennium Dome Water Recycling Plant, was used for this study. The feedwaters comprised surface water, greywater and groundwater, all having distinct quality differences. The analysis utilises the least-squares fit regression technique. Fouling, as manifested in the diurnal change in trans-membrane pressure (TMP), is related numerically to the volumes of the feedwaters, the mean TMP and the cross product of mean TMP with water volume. It was found that the impact of the recovered greywater on TMP was not statistically significant only due to the low daily volumes of this matrix generated, compared with those of the other sources. The model that best described the data was chosen on the basis of highest R 2 and lowest residual mean square, and demonstrated the surface water to be more fouling than the ground water by a factor, which is a function of the mean TMP.

Unsteady state flux response: a method to determine the nature of the solute and gel layer in membrane filtration

The unsteady-state permeate flux response to a step change in transmembrane pressure is shown to result in unique flux–pressure profiles for the three types of solutes common in membrane ultrafiltration (UF): (a) solutes which exert an osmotic pressure but do not form a ‘gel’; (b) solutes which do not exert an osmotic pressure but form a ‘gel’ and (c) solutes which exert an osmotic pressure and also form a ‘gel’. It is also shown that for stirred cell UF, changes in the bulk feed solution properties (concentration, volume) are negligible on the time scale needed to attain a stable permeate flux. Unsteady-state permeate flux measurements could therefore be made at short filtration times so that the results would not be masked by changes in bulk properties.