Changes In Transmembrane Pressure Research Articles

Influence of Solid Retention Time on Membrane Fouling and Biogas Recovery in Anerobic Membrane Bioreactor Treating Sugarcane Industry Wastewater in Sahelian Climate.

Sugarcane industries produce wastewater loaded with various pollutants. For reuse of treated wastewater and valorization of biogas in a Sahelian climatic context, the performance of an anaerobic membrane bioreactor was studied for two solid retention times (40 days and infinity). The pilot was fed with real wastewater from a sugarcane operation with an organic load ranging from 15 to 22 gCOD/L/d for 353 days. The temperature in the reactor was maintained at 35 °C. Acclimatization was the first stage during which suspended solids (SS) and volatile suspended solids (VSS) evolved from 9 to 13 g/L and from 5 to 10 g/L respectively, with a VSS/SS ratio of about 80%. While operating the pilot at a solid retention time (SRT) of 40 days, the chemical oxygen demand (COD) removal efficiency reached 85%, and the (VSS)/(TSS) ratio was 94% in the reactor. At infinity solid retention time, these values were 96% and 80%, respectively. The 40-day solid retention time resulted in a change in transmembrane pressure (TMP) from 0.0812 to 2.18 bar, with a maximum methane production of 0.21 L/gCOD removed. These values are lower than those observed at an infinite solid retention time, at which the maximum methane production of 0.29 L/gCOD was achieved, with a corresponding transmembrane pressure variation of up to 3.1 bar. At a shorter solid retention time, the fouling seemed to decrease with biogas production. However, we note interesting retention rates of over 95% for turbidity.

Effects of hollow fiber packing density and housing shape on the albumin filtration performance of CRRT filters

Continuous renal replacement therapy (CRRT) has become the most commonly used acute blood purification therapy for critically ill patients. As a key point of extracorporeal blood circulation, the CRRT filter plays a decisive role in therapeutic efficacy. However, few in vitro studies have been conducted on CRRT filters, particularly concerning the effects of design factors on filter effectiveness and safety profile; no comprehensive evaluation system has been established. Here, we designed nine CRRT filters with various combinations of hollow fiber packing density (PD) and housing shape (effective hollow fiber length (L) and inner housing diameter (D) ratio (L/D ratio)) and introduced a high-frequency sampling pressure monitor to accurately monitor small changes in transmembrane pressure (TMP) and ultrafiltration rate (UFR) over time. We also used concentration polarization mass transfer resistance (Rc), change in sieving coefficient (S) of albumin over time, and amount of albumin removed (Mfld) to investigate the effects of two design factors on albumin filtration performance and analyze the mechanism of protein filtration performance over time, thereby establishing a comprehensive in vitro evaluation system to explore the safety profile of CRRT filters. Our results showed that the nine CRRT filters designed with different combinations of PD (50%, 55%, and 60%) and L/D ratio (2.9, 5.3, and 9.3) were able to maintain stability in terms of hemodynamics and water permeability; the lowest Mfld was PD = 60% and L/D ratio = 9.3, which indicates that design factor optimization can effectively control albumin filtration, thereby improving the safety profile of CRRT filters.

Mitigation Mechanism of Membrane Fouling in MnFeOx Functionalized Ceramic Membrane Catalyzed Ozonation Process for Treating Natural Surface Water

In order to efficiently remove NOMs in natural surface water and alleviate membrane pollution at the same time, a flat microfiltration ceramic membrane (CM) was modified with MnFeOX (Mn-Fe-CM), and a coagulation–precipitation–sand filtration pretreatment coupled with an in situ ozonation-ceramic membrane filtration system (Pretreatment/O3/Mn-Fe-CM) was constructed for this study. The results show that the removal rates of dissolved organic carbon (DOC), specific ultraviolet absorption (SUVA) and NH4+-N by the Pretreatment/O3/Mn-Fe-CM system were 51.1%, 67.9% and 65.71%, respectively. Macromolecular organic compounds such as aromatic proteins and soluble microbial products (SMPs) were also effectively removed. The working time of the membrane was about twice that in the Pretreatment/CM system without the in situ ozone oxidation, which was measured by the change in transmembrane pressure, proving that membrane fouling was significantly reduced. Finally, based on the SEM, AFM and other characterization results, it was concluded that the main mitigation mechanisms of membrane fouling in the Pretreatment/O3/Mn-Fe-CM system was as follows: (1) pretreatment could remove part of DOC and SUVA to reduce their subsequent entrapment on a membrane surface; (2) a certain amount of shear force generated by O3 aeration can reduce the adhesion of pollutants; (3) the loaded MnFeOX with a higher catalytic ability produced a smoother active layer on the surface of the ceramic membrane, which was conducive in reducing the contact among Mn-Fe-CM, O3 and pollutants, thus increasing the proportion of reversible pollution and further reducing the adhesion of pollutants; (4) Mn-Fe-CM catalyzed O3 to produce ·OH to degrade the pollutants adsorbed on the membrane surface into smaller molecular organic matter, which enabled them pass through the membrane pores, reducing their accumulation on the membrane surface.

CO2 as an Alternative to Traditional Antiscalants in Pressure-Driven Membrane Processes: An Experimental Study of Lab-Scale Operation and Cleaning Strategies.

Scaling, or inorganic fouling, is a major factor limiting the performance of membrane-based water treatment processes in long-term operation. Over the past few decades, extensive studies have been conducted to control the scale growth found in membrane processes and to develop sustainable and greener processes. This study details the role of CO2 in scale inhibition in membrane processes. The core concept of CO2 utilization is to reduce the influent pH and to minimize the risk of scale formation from magnesium or calcium salts. Three reverse osmosis (RO) units were operated with a control (U1), CO2 (U2), and a commercial antiscalant, MDC-220 (U3). The performances of all the units were compared in terms of change in transmembrane pressure (TMP). The overall efficiency trend was found as U1 > U3 > U2. The membrane surfaces were analyzed using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) for the morphological and elemental compositions, respectively. The surface analysis signified a significant increase in surface smoothness after scale deposition. The noticeable reduction in surface roughness can be described as a result of ionic deposition in the valley region. A sludge-like scale layer was found on the surface of the control membrane (U1) which could not be removed, even after an hour of chemical cleaning. After 20–30 min of cleaning, the U2 membrane was successfully restored to its original state. In brief, this study highlights the sustainable membrane process developed via CO2 utilization for scale inhibition, and the appropriate cleaning approaches.

Quorum quenching strategy for biofouling control in membrane photobioreactor

This study aims to reduce membrane fouling in membrane photobioreactor (MPBR) through the quorum quenching (QQ) strategy. For this purpose, the QQ beads (immobilized Rhodococcus sp. BH4) were added to the MPBR, and antifouling ability was evaluated in consideration of the changes in transmembrane pressure (TMP), extracellular polymeric substance (EPS), microbial community, and cake layer morphology on the membrane surface. The results showed that the TMP of control MPBR (MPBR-C) reached 818 mbar and 912 mbar on the operation hours of 35 and 170, while the TMP of experimental MPBR (MPBR-QQ) was only 448 mbar and 676 mbar, respectively. The QQ strategy effectively reduced the EPS content in MPBR. The microscopic observations indicated that the QQ diminished the cake layer formation and pore-blocking on the membrane surface. Comparisons of 16S and 18S gene communities revealed minor differences between bacterial and eukaryotic species in MPBRs at phylum and class levels.

Safety and Efficacy of Tandem Hemodialysis and Selective Plasma Exchange in Pretransplant Desensitization of ABO-Incompatible Kidney Transplantation

Introduction: In patients requiring both hemodialysis (HD) and apheresis, the 2 treatments can be performed simultaneously. At our hospital, selective plasma exchange (SePE) is often performed along with HD for removal of isoagglutinins before ABO-incompatible (ABOi) kidney transplantation. The 2 treatments can be completed within the HD schedule, which allows the treatment time to be shortened. This approach is also less stressful for patients because fewer punctures are required. In this study, we investigated the safety and efficacy of tandem HD and SePE. Methods: A total of 58 SePE sessions in 30 ABOi kidney transplant recipients were investigated. The SePE circuit was connected in parallel with the HD circuit, and tandem HD and SePE therapy was performed using filtration methods. The SePE sessions were divided into 2 groups: those with SePE monotherapy (group S, n = 20) and those with tandem therapy (group T, n = 38). Changes in transmembrane pressure (TMP), arterial pressure (AP), venous pressure (VP), and decrease in isoagglutinin titers over time were compared between the groups with adjustment for background data. Results: The internal pressures (AP and VP) were higher in group T, and there were significant differences in changes of TMP and AP over time between groups T and S. Membrane exchange was required in 1 case in group T due to coagulation. There was a more significant decrease of immunoglobulin G isoagglutinin titers in group T compared to group S. No case had antibody-mediated rejection after transplantation. Discussion/Conclusion: In HD/SePE tandem therapy, internal pressures were higher and TMP and AP tended to increase more compared to SePE monotherapy, but we were able to perform the 2 treatments without any functional problems. Tandem therapy was also effective in decreasing isoagglutinin titers, which suggests that this may be a beneficial treatment modality as apheresis before ABOi kidney transplantation.

Dialysis Filter Life, Anticoagulation, and Inflammation in COVID-19 and Acute Kidney Injury.

In recent studies, 5%–20% of hospitalized patients with coronavirus disease 2019 (COVID-19) developed AKI requiring RRT (CoV-AKI-RRT) (1,2) (L. Chan et al., unpublished observations). Hypercoagulability has been recognized as a salient feature of COVID-19 in the critically ill (3,4) and there have been anecdotal accounts of unexpectedly frequent dialysis filter clotting. However, there are limited data describing the magnitude of the problem. A recent report described clotting events in 28 of 29 patients with CoV-AKI-RRT and shorter filter lifespan compared with a historical control, but no details were provided regarding anticoagulation (4). Our objective was to examine the delivery of RRT and circuit interruptions in patients with CoV-AKI-RRT in comparison with those in the pre-COVID-19 era. With approval of the Institutional Review Board, waiver of informed consent, and in accordance with the Declaration of Helsinki, we conducted a retrospective single-center study, ancillary from our previously reported cohort (2). We identified hospitalized patients with COVID-19 (positive severe acute respiratory syndrome coronavirus 2 RNA PCR by nasopharyngeal swab) and AKI, who underwent RRT by sustained low-efficiency dialysis (SLED) for ≥8 hours in an intensive care unit between March and April of 2020 (study period: 4 weeks) by either prolonged intermittent or continuous RRT modality (5,6) using Fresenius 2008K/K2 (Bad Homburg, Germany) machines. At our hospital, continuous venovenous hemodiafiltration (CVVHDF) with PrismaFlex (Deerfield, IL) machines was restricted to the neurointensive care unit and was not expanded during the pandemic due to logistics. As pre-COVID-19 control, we included consecutive patients (reverse chronological order) with AKI without COVID-19 who underwent SLED in December of 2019. Electronic medical records were accessed and RRT flowsheets were manually reviewed to extract timing of initiation and interruption, blood flow rate (BFR), dialysate flow rate, and filter transmembrane pressure (TMP). Standard BFR was 200 …

In-line coagulation assessment for ultrafiltration fouling reduction to treat secondary effluent for water reuse.

Low pressure membranes are attracting attention for their potential to improve secondary effluent quality, but membrane fouling can limit their widespread applicability. In this study, in-line coagulation as pre-treatment to ultrafiltration (UF) was investigated using a bench-scale hollow fiber membrane at a constant flux of 33 L/m2 h. Membrane fouling was monitored by observing change in trans-membrane pressure when the membrane was fed with secondary effluent and in-line coagulated secondary effluent over a 24-h period. The impact of four coagulants at different dosages on reversible and irreversible membrane fouling and permeate quality was studied. It was found that in-line coagulation improved UF performance to varying degrees depending on coagulant type and dosage. Generally, higher reduction of fouling was achieved by increasing coagulant dosage within the 0.5-5.0 mg/L range investigated. Ferric-based coagulants were better than aluminum-based coagulants with respect to improving membrane performance for the secondary effluent investigated, even at low dosages (0.5 mg/L). Further investigations are required to determine how in-line coagulation affects removal of organic compounds through UF membranes.

Evaluating the performance of an electro-membrane bioreactor in treatment of young leachate

Leachate generated from landfill, typically contains high amounts of different pollutions. Its composition may vary according to the origin and age of landfill. In this study, the performance of a laboratory-scale submerged electro-membrane bioreactor (SMEBR), an integrated process consisting of an electro-coagulation unit and a conventional submerged membrane bioreactor (SMBR) for treating young leachate was evaluated. SMEBR and SMBR as control reactor were operated simultaneously to compare. In SMEBR, perforated aluminum (Al) electrodes were used. SMEBR was operated under electrokinetic conditions at a current density of 24 mA/cm 2 for 50 days: at 180 s/day for 25 days (Stage I) and 360 s/day for 25 days (Stage II). Chemical oxygen demand (COD), ammonia nitrogen (NH 3 –N), color and metal removal performances were evaluated for both reactors. Also, the membrane fouling was examined by monitoring the change in transmembrane pressure over time. The concentration of dissolved oxygen (DO) was determined using the oxygen uptake rate in a period covering SMEBR operating conditions. Based on the results obtained, positive effects of electrical field SMEBR were clearly observed at Stage II. At the Stage II, the removal efficiency of COD was 6–15% higher in SMEBR compared to SMBR. The average NH 3 –N removal efficiencies in SMEBR and SMBR were 86 and 78%, respectively. Following the introduction of electrical current to SMEBR, DO concentrations were measured about 0.8 mg/L lower than SMBR; however, nitrification was not affected adversely. Additionally, chemical properties of SMEBR and SMBR membranes surfaces were characterized by using the Fourier-transform infrared spectroscopy.

Influence of a new method of applying adsorbents on membrane fouling in MBR systems

AbstractIn this study, adsorbent packed beds of granular zeolite and activated carbon (AC) were used to mitigate membrane fouling in the membrane bioreactor (MBR) systems. Specific oxygen uptake rate (SOUR), particle size distribution (PSD), transmembrane pressure (TMP), soluble microbial products (SMP), extracellular polymeric substances (EPS), Fourier‐transform infrared spectroscopy (FTIR) and excitation‐emission matrix (EEM) fluorescence spectroscopy were used to identify sludge and membrane cake layer characteristics. The changes in TMP demonstrated that using AC and ZE has resulted in a 38% and a 35% reduction in membrane fouling, respectively. Measuring EPS, SMP, proteins (PN) and polysaccharides (PS) in EPS and using FTIR and EEM revealed that AC and ZE have resulted in a decrease in SMP, EPS, PN and PS. The results showed that this method could reduce membrane fouling as much as the previous methods.

Control of indigenous quorum quenching bacteria on membrane biofouling in a short-period MBR

In this paper, the immobilized quorum quenching (QQ) bacteria – microbial bag was added to a short-period membrane bioreactor (MBR) and its antifouling ability and mechanism were studied by monitoring the changes in transmembrane pressure (TMP), along with the production of N-acyl-homoserine lactones (AHLs), extracellular polymeric substance (EPS) and soluble microbial products (SMP). The QQ bacteria showed efficient mitigation of TMP increase in different membrane fouling stages. In the control MBR group, the TMP reached 43 kPa on the 4th day, while in the experimental group, TMP of QQ-MBR was only 18 kPa at the same time. The detection result of EPS and SMP content of protein and polysaccharide in MBRs showed that QQ bacteria had significant inhibitory effects on EPS and SMP. Also, the QQ bacterial exhibited excellent AHLs degradation rate in MBR reaction tank.

Evaluation of circuit lifetime in continuous renal replacement therapy using two types of polysulfone membranes

BackgroundFor continuous venovenous hemofiltration (CVVH) to achieve an adequate therapeutic effect, prolonged stable administration and a long circuit lifetime are needed. The effects of hemofilters produced using various kinds of materials on circuit lifetime in CVVH have been examined, but no studies have investigated the effects of the length, diameter, or surface coating of hollow fibers. The aim of the present study was to evaluate the circuit lifetime in CVVH retrospectively using two types of polysulfone (PS) membranes.MethodsThe participants were patients with acute kidney injury who underwent CVVH from January to July 2017 at a university hospital. The patients were divided into two groups based on the PS membrane used: an SHG group using Hemofeel® SHG (Toray Medical) and an AEF group using Excelflo® AEF (Asahi Kasei Medical). The SHG hemofilter has a longer and thinner hollow fiber than the AEF hemofilter. The target CVVH duration was 48 h. Circuit lifetime was defined as the time until a CVVH malfunction was identified. A CVVH malfunction was defined as a problem in extracorporeal circulation or either a 100-mmHg increase in the inlet chamber pressure or a 50-mmHg decrease in the filtration chamber pressure from baseline. During CVVH, the transmembrane pressure (TMP) change rate from baseline (at 0.5 h after initiation) was monitored.ResultsThe SHG and AEF groups comprised eight and nine patients and underwent 10 and 14 sessions, respectively. No significant differences were seen between groups in patient characteristics or blood or filtration flow rate during CVVH. Although circuit lifetime tended to be longer in the SHG group, no significant differences in circuit lifetime were found between the two groups. The TMP change rate at 12 h after CVVH and thereafter was significantly higher in the AEF than that in the SHG group.ConclusionIn spite of using the same material, differences in the shape of the hollow fibers and surface treatment of the membrane affected the TMP change rate during CVVH in critically ill patients. To maximize circuit lifetimes, hemofilters should be chosen based on not only their materials but also their shape and membrane surface treatment.Trial registrationThe patients in this study were registered retrospectively. Registered 12 July 2018 (302-54).

Physical structure determines compression of membrane biofilms during Gravity Driven Membrane (GDM) ultrafiltration

Increasing transmembrane pressure (TMP) can compress and increase the hydraulic resistance of membrane biofilms. The purpose of the present study is to evaluate how compression of membrane biofilms occurs and how structural rearrangement can affect hydraulic resistance. Biofilms with heterogeneous and homogeneous physical structures were grown in membrane fouling simulators (MFS) in dead-end mode for 20 days with either (i) a nutrient enriched condition with a nutrient ratio of 100:30:10 (C: N: P), (ii) a phosphorus limitation (C: N: P ratio: 100:30:0), or (iii) river water (C: N: P ratio: ca. 100:10:1). The structural and hydraulic response of membrane biofilms to (a) changes in transmembrane pressures (0.06-0.1-0.5-0.1-0.06 bar) and (b) changes in permeate flux (10-15-20-15-10 L/m2/h) were investigated. Optical coherence tomography (OCT) was used to monitor biofilm structural response, and OCT images were processed to quantify changes in the mean biofilm thickness and relative roughness. Nutrient enriched and river water biofilms had heterogeneous physical structures with greater surface roughness (Ra' > 0.2) than homogeneous P limiting biofilms (Ra' < 0.2). Compression of biofilms with rough heterogeneous structures (Ra' > 0.2) was irreversible, indicated by irreversible decrease in surface roughness, partial relaxation in mean biofilm thickness and irreversible increase in hydraulic resistance. Compression of homogeneous biofilm (Ra' < 0.2) was on the other hand reversible, indicated by full relaxation of the biofilms structure and restoration of initial hydraulic resistance. Hydraulic response (i.e., change in the specific biofilm resistance) did not correspond with the change in physical structure of heterogeneous biofilms. The presented study provides a fundamental understanding of how biofilm physical structure can affect the biofilm's response to a change in TMP, with practical relevance for the operation of GDM filtration systems.

Fluorescence enabled direct visual observation for diagnosis of ultrafiltration membrane fouling by bi‐disperse submicron particle suspensions

AbstractWhilst direct observation (DO) methodologies can describe back‐transport of supra‐micron particles, present technologies are unable to discriminate submicron particles, which are primarily responsible for membrane fouling. In this study, we therefore introduce a fluorescence enabled direct visual observation (RLF‐DVO) methodology to permit visual characterisation of submicron particle transport during cross‐flow filtration. Particle discrimination was achievable for particle diameters exceeding 0.25 µm; however, this was dependent upon particle concentration and the cross‐flow velocity employed. Nevertheless, this is considerably below the detection limit of current techniques (around 3 µm). During filtration of a binary dispersion comprised of submicron particles, deposition was observed before a change in transmembrane pressure was detected, which underpins the important role of DO for fouling diagnosis. Based on observations made during this study, recommendations are proposed that will further improve resolution. Importantly, this study demonstrates RLF‐DVO can provide real‐time description of submicron particle transport during cross‐flow filtration.

Development of a high-rate submerged anaerobic membrane bioreactor

ABSTRACTTypically, anaerobic membrane bioreactors are operated at an organic loading rate (OLR) less than 10 kg chemical oxygen demand (COD)/m3 d. This paper discusses the development and performance of a high-rate submerged anaerobic membrane bioreactor (SAnMBR) for a high-strength synthetic industrial wastewater treatment. An OLR as high as 41 kg COD/m3 d was achieved with excellent COD removal efficiency (>99%). The membrane was operated at constant fluxes (9.4–9.9 ± 0.5 L/m2 h) and the change in trans-membrane pressure (TMP) was monitored to characterize the membrane performance. The results showed a low TMP (<5 kPa) under steady-state operation with only biogas sparging and relaxation as control strategy for over 300 days, implying no significant fouling was developed. Inorganic fouling was the dominant fouling mechanism occurred at the end of the study. The results suggest that the newly developed SAnMBR configuration can treat high-strength wastewater at lower capital expenditure while still providing superior effluent quality for water reuse or system closure.

Influence of microbial floatation on membrane fouling due to particles and organic matters in submerged microfiltration

AbstractThis study investigated the effect of microbubble floatation on the fouling of microfiltration membranes. Synthetic feed solutions containing either kaolin or alginic acid were used for the membrane filtration tests. A dissolve air flotation system using a pump-type microbubble generator was adopted as a pretreatment for microfiltration system. A multi-array submerged membrane filtration system was used to monitor the changes in transmembrane pressure with time under various operating conditions. Turbidity removal efficiency, particle counts, and fouling rate for the microfiltration membrane were measured after the microfiltration floatation. The effect of coagulant dose on the treated water quality and membrane performance was also investigated. Results showed that microbubble floatation without coagulant was effective to reduce membrane fouling by kaolin but it was not very effective to control fouling by alginate. With the aid of coagulant, microbubble flotation could control fouling by alginat...

Transport membrane condenser for water and heat recovery from gaseous streams: Performance evaluation

Using a tubular ceramic membrane as the transport membrane condenser for simultaneous water and heat recovery from gaseous streams is experimentally investigated in the current study. The effects of several important operational parameters (e.g. gas flow rate, coolant flow rate, transmembrane pressure and inlet gas temperature) on the process performance in terms of mass and heat transfer across the membrane are systematically studied. It is found that mass and heat transfer rates can be enhanced by increasing the gas flow rate, coolant water flow rate and the temperature of the inlet gas stream. To improve the water and heat recovery, a low gas flow rate but a high coolant flow rate should be maintained. Increasing the transmembrane pressure difference decreases the mass and heat transfer mainly due to the reduced inlet gas humidity, enthalpy and flow rate. However, water and heat recovery does not change significantly with the change in transmembrane pressure. 20–60% water recovery and 33–85% heat recovery are achievable when using cold water as the coolant. The mass transfer mechanism in membrane condensation is complex and needs further exploration. These findings offer significant implications in using transport membrane condensers for water and heat recovery from gas streams with high moisture.

Novel anti-fouling Fe2O3/TiO2 nanowire membranes for humic acid removal from water

Membrane fouling is one of the major obstacles inhibiting the wide application of membrane technologies for water treatment. Membranes with surface modification of titanium dioxide (TiO2) nanoparticles or TiO2 nanowire membranes (Ti–NWM) have demonstrated reduced membrane fouling due to the photocatalytic capability of TiO2 in degrading foulants on the membrane surface. However, the wide band gap of TiO2 makes it only absorb ultraviolet light, which limits its applications under solar irradiation. In this study, a novel membrane made of interwoven iron oxide (Fe2O3) nanowires and TiO2 nanowires (FeTi–NWM) has demonstrated superior anti-fouling capability in removing humic acid (HA) from water. Results showed that under simulated solar irradiation the FeTi–NWM achieved nearly complete HA removal during a 2h short-term test at an initial HA concentration of 200mg/L, compared with 89% HA removal by Ti–NWM. During a 12h long-term test, the FeTi–NWM maintained 98% HA removal, while the Ti–NWM showed only 55% removal at the end. Without solar irradiation, the FeTi–NWM was severely contaminated and by contrast, a clean surface was maintained under solar irradiation after the 12h test and the transmembrane pressure change was minimal. The improved HA removal by FeTi–NWM compared with Ti–NWM and its excellent anti-fouling capability under solar irradiation can be attributed to (1) the enhanced HA absorption by Fe2O3 nanowires and (2) the formed Fe2O3/TiO2 heterojunctions that increase photo-induced charge transfer and improve visible light activity.

Microfiltration of skim milk and modified skim milk using a 0.1-µm ceramic uniform transmembrane pressure system at temperatures of 50, 55, 60, and 65°C

Increasing the temperature of microfiltration (MF) to >50°C may allow for operation at higher fluxes and reduce the bacterial growth during MF. However, there is a concern that operating at higher temperatures could cause calcium phosphate precipitation that would lead to membrane fouling. Our objective was to determine the effect of operating a 0.1-µm ceramic uniform transmembrane pressure MF unit at temperatures of 50, 55, 60, and 65°C on membrane fouling and serum protein (SP) removal from skim milk with and without removal of low-molecular-weight soluble milk components by ultrafiltration (UF) before MF at a flux of 54kg/m2 per hour. For each replicate, 1,000kg of pasteurized skim milk was split into 2 batches. One batch was ultrafiltered (with diafiltration) to remove an average of 89±2% of the lactose and a percentage of the soluble calcium and phosphorus. The retentate from UF was diluted back to the protein concentration of skim milk, creating the diluted UF retentate (DUR). On subsequent days, both the DUR and skim milk were run on the MF unit with the flux maintained at 54kg/m2 per hour and a concentration factor of 3× and the system run in recycle mode. The temperature of MF was increased in 5°C steps from 50 to 65°C, with a 1-h stabilization period after each increase. During the run, transmembrane pressure was monitored and permeate and retentate samples were taken and analyzed to determine if any changes in SP, calcium, or phosphorus passage through the membrane occurred. Increasing temperature of MF from 50 to 65°C at a flux of 54kg/m2 per hour did not produce a large increase in membrane fouling when using either skim milk or a DUR as the MF feed type as measured by changes in transmembrane pressure. Increasing the temperature to 65°C only caused a slight reduction in calcium concentration in the permeate (11±3%) that was similar between the 2MF feed types. Increasing processing temperature reduced the percentage of SP removal by the process, but the increased temperature also caused a decrease in casein contamination in the permeate with no evidence of membrane fouling.

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.