Hollow Fiber Ultrafiltration System Research Articles

Noroviruses in raw sewage, secondary effluents and reclaimed water produced by sand-anthracite filters and membrane bioreactor/reverse osmosis system

The importance of noroviruses (NoVs) in the epidemiology of waterborne diseases has increased globally in the last decades. The present study aimed to monitor genogroup I and II noroviruses in different treatment stages of four wastewater treatment plants (WWTPs) in the metropolitan São Paulo. WWTPs consist of secondary (activated sludge) and tertiary treatments (coagulation, sand-anthracite filters, membrane bioreactor (MBR)/reverse osmosis (RO) and chlorination). Raw sewage (500mL) and treated effluents (1L) were concentrated by celite and reclaimed water (40L) by hollow-fiber ultrafiltration system. Quantitative (qPCR) and nested PCR with nucleotide sequencing were used for quantification and molecular characterization. NoVs were widely distributed in raw wastewater samples (83.3%–100% NoV GI and 91.6%–100% NoV GII) and viral loads varied from 3.8 to 6.66log10gcL−1 for NoV GI and 3.8 to 7.3log10gcL−1 for NoV GII. Mean virus removal efficiencies obtained for activated sludge processes ranged from 0.3 to 0.8 log10 for NoV GI and 0.4 to 1.4 log10 for NoV GII. NoVs were not detected in the reuse water produced by MBR/RO system, while sand-anthracite filters resulted in a NoV GI and GII decay of 1.1–1.6 log10 and 0.7–1.6 log10, respectively. A variety of genotypes (GI.2, GI.3a, GI.3b, GI.5, GII.1, GII.4 Sydney 2012, GII.5, GII.6, GII.17) was observed, with a predominance of GI.2 and GII.17 in the different genogroups. These results corroborate with recent data about the entry and dissemination of the emerging genotype GII.P17-GII.17 Kawasaki 2014 in the country, and may indicate a change in the epidemiological patterns of norovirus strains circulation in this region. This is the first large-scale study to evaluate burden and genotypes of noroviruses in WWTPs in Brazil, providing a rapid diagnosis of viruses circulating in the population.

Operation of passive membrane systems for drinking water treatment

The widespread adoption of submerged hollow fibre ultrafiltration (UF) for drinking water treatment is currently hindered by the complexity and cost of these membrane systems, especially in small/remote communities. Most of the complexity is associated with auxiliary fouling control measures, which include backwashing, air sparging and chemical cleaning. Recent studies have demonstrated that sustained operation without fouling control measures is possible, but little is known regarding the conditions under which extended operation can be sustained with minimal to no fouling control measures. The present study investigated the contribution of different auxiliary fouling control measures to the permeability that can be sustained, with the intent of minimizing the mechanical and operational complexity of submerged hollow fiber UF membrane systems while maximizing their throughput capacity.Sustained conditions could be achieved without backwashing, air sparging or chemical cleaning (i.e. passive operation), indicating that these fouling control measures can be eliminated, substantially simplifying the mechanical and operational complexity of submerged hollow fiber UF systems. The adoption of hydrostatic pressure (i.e. gravity) to provide the driving force for permeation further reduced the system complexity. Approximately 50% of the organic material in the raw water was removed during treatment. The sustained passive operation and effective removal of organic material was likely due to the microbial community that established itself on the membrane surface. The permeability that could be sustained was however only approximately 20% of that which can be maintained with fouling control measures. Retaining a small amount of air sparging (i.e. a few minutes daily) and incorporating a daily 1-h relaxation (i.e. permeate flux interruption) period prior to sparging more than doubled the permeability that could be sustained. Neither the approach used to interrupt the permeate flux nor that developed to draw air into the system for sparging using gravity add substantial mechanical or operational complexity to the system. The high throughput capacity that can be sustained by eliminating all but a couple of simple fouling control measures make passive membrane systems ideally suited to provide high quality water especially where access to financial resources, technical expertise and/or electrical power is limited.

Bench-scale study of ultrafiltration membranes for evaluating membrane performance in surface water treatment

Currently, there is no standard bench-scale dead-end ultrafiltration (UF) testing system. The aim of the present study was to design and build a bench-scale hollow fiber UF system to assess the impact of operational parameters on membrane performance and fouling. A bench-scale hollow fiber UF system was built to operate at a constant flux (±2% of the set-point flux) and included automated backwash cycles. The development of the bench-scale system showed that it is very difficult to maintain a constant flux during the first minute of the filtration cycles, that digital flow meters are problematic, and that the volume of the backwash waste lines should be minimized. The system was evaluated with Ottawa River water, which has a relatively high hydrophobic natural organic matter content and is typical of Northern Canadian waters. The testing using different permeate fluxes, filtration cycle duration and backwash cycle duration showed that this system mimics the performance of larger systems and may be used to assess the impact of operating conditions on membrane fouling and alternative pretreatment options. Modeling the first, middle, and last filtration cycles of the six runs using single and dual blocking mechanisms yielded inconsistent results regarding the controlling fouling mechanisms.

Effect of inorganic colloidal water constituents on combined low-pressure membrane fouling with natural organic matter (NOM)

The impact of inorganic colloidal water constituents on fouling in low-pressure membrane systems was evaluated by carrying out ultrafiltration (UF) experiments using synthetic waters containing model foulants. Humic acid (HA), sodium alginate (SA), and bovine serum albumin (BSA) were chosen as model natural organic matter (NOM) foulants, and silicon dioxide and α-aluminum oxide were chosen as model inorganic colloidal foulants. The synthetic solutions were filtered using one lab-scale flat sheet UF system (i.e., unstirred filtration cell) and one pilot-scale hollow fiber UF system (i.e., custom made hollow fiber modules), both of which employed polyethersulfone (PES) membranes. Filtering the inorganic colloids by themselves did not result in any significant fouling, as evidenced by the negligible permeability decline and high hydraulic reversibility. However, when combined with NOM, severe permeability decline and hydraulic reversibility reduction were observed. Moreover, the permeability decline and reversibility loss of the combined inorganic colloids and NOM were more severe than the sum of the individual effects from organics and inorganic colloids, suggesting that combining the two acts to enhance fouling (i.e., synergistic fouling effects). Aluminum oxide tended to result in more severe synergistic fouling compared to silicon dioxide, suggesting that the inorganic colloid material character, especially its surface charge, affects the severity of combined fouling. Rejection of TOC and analysis of the fouled membranes by scanning electron microscopy indicated higher NOM adsorption by aluminum oxide colloids, which lead to a larger amount of foulants in the cake layer and a worse reversibility. Both the lab- and pilot-scale systems exhibited similar fouling behavior, thus indicating that the lab-scale system provides a meaningful representation of the pilot-scale system, even though the operating conditions are quite different. This study highlights the importance of interactions between foulants with respect to fouling in low-pressure membrane systems and showed conclusively that inorganic colloids play an important role in fouling of NOM. Moreover, present results underline the impact of colloidal surface charge on the resulting hydraulic and chemical fouling reversibility during ultrafiltration of natural waters containing NOM and inorganic colloids.

Experiences with a reinforced UF hollow-fiber water filtration system for pretreatment of desalinated water

There are several ultrafiltration (UF) systems on the market for pretreatment of desalinated water. Existing hollow-fiber UF systems usually focus on low TSS-loaded water sources (pressure-driven inside-out filtration) or higher loaded sources (submerged systems). This paper describes a newly developed product that bridges the feed water solids tolerance gap between these operational configurations, coupling the advantages of a reinforced hollow-fiber UF membrane with a pressure-driven, outside-in filtration process. Experiences and key findings from several pilot trials at different locations and diverse feed water compositions are summarized.

Design of novel ultrafiltration systems based on robust polyphenylsulfone hollow fiber membranes for treatment of contaminated surface water

Abstract This work focuses on development of robust but economical hollow fiber ultrafiltration systems that could be operated with or without electric power to treat polluted surface water. A diverse experimental study was carried out to synthesize novel hollow fiber membranes based on polyphenylsulfone (PPSu) and polyvinylidenefluoride (PVDF) fibers for surface water treatment. A manual hollow fiber spinning machine incorporated with an inexpensive spinneret was designed to fabricate hollow fibers from dope compositions of 20 wt% PVDF in DMAc and 20 wt% PPSu in NMP by phase inversion technique. Isothermal ternary phase diagrams of PVDF or PPSu/solvent/non-solvent systems were established using three different solvents such as N,N- dimethylacetamide (DMAc), 1-methyl-2-pyrrolidinone (NMP) and N,N -dimethylformamide (DMF) with water being the non-solvent. The indigenous fibers had an approximate outer diameter of 1.5 mm and the wall thickness of 0.25 mm and were housed in inexpensive PVC and UPVC tubes using epoxy resin and nylon end connectors. PVDF hollow fibers (HF) exhibited 94.8% turbidity rejection, whereas PPSu fibers exhibited 91% rejection with 5 log E-Coliform reduction from surface water at a low hydraulic pressure of 1 bar with high flux values of 125 L m − 2 h − 1 and 73 L m − 2 h − 1 , respectively at a substantial water recovery of 80%. A water purification device capable of generating 25 L h − 1 purified water flow at an overhead tank pressure of 0.5 bar was designed and fabricated for households along with a hand pump operated submerged ultrafiltration (UF) system for treatment of surface water in flood prone regions. Detailed economic estimation of the indigenously designed water purification device for household purpose is presented which shows a low operating cost of 0.02 US $ per liter of purified water obtained.

Endospore recovery from large volumes using fieldable ultrafiltration for the diagnosis of drinking water treatment plants

Anaerobic sulfite-reducing and aerobic spore-forming bacteria are used as indicators to verify the reliability of water treatment plant efficiency. The objectives of this study aimed to highlight the more accurate endospore indicator for water treatment monitoring and to select an efficient filtration system in order to detect low amounts of endospores from large volumes. The performance of two different ultrafiltration modules was assessed with two filtration configurations (tangential and dead-end). The Hemoflow™ and the Dizzer® filters present recovery yields of 73% and 77% for 100-liter samples of drinking and sand filtered water, respectively. Both systems enabled detection of endospores at a concentration level of 100 spores in 100 liters, by analyzing the totality of the volume, whereas the standard method did not highlight the presence of spores, analyzing only 100 mL subsamples. In addition, experiments on a sand filtration pilot confirmed that the concentration calculation using the standard method is not reliable, due to extrapolation from the small volumes analyzed. This study highlights that the collection of large volumes using a fieldable dead-end hollow-fiber ultrafiltration system in association with the detection of anaerobic sulfite-reducing spore-forming bacteria is an effective way to monitor drinking water production.

Harvesting of Chlorella sp. using hollow fiber ultrafiltration

The suitability of the application of ultrafiltration (UF) to harvest Chlorella sp. from the culture medium was examined. We investigated the effects of two improved UF system, forward air-water flushing and backwash with permeate, on the concentration process. Backwash with permeate was selected as an optimization of the improved UF system, which was more effective for permeate flux recovery. Moreover, the hollow fiber UF system by adding periodical backwash with permeate was examined for Chlorella sp. harvesting. It was found that Chlorella sp. could be concentrated with high recovery in a lab-scale experiment. An overall algal biomass recovery of above 90% was achieved when the volume concentration factor was 10. For an original biomass of 1.3 ± 0.05 g/L, 1 min backwash followed by 20 min forward concentrating was more effective, which resulted in a recovery of 94% and a high average flux of 30.3 L/m(2)/h. In addition, the algal recovery was highly correlated to the volume concentration factor and the initial biomass. A high concentration factor or a high initial biomass resulted in a low biomass recovery.

Assessment of the removal and inactivation of influenza viruses H5N1 and H1N1 by drinking water treatment

Since 2003, there has been significant concern about the possibility of an outbreak of avian influenza virus subtype H5N1. Moreover, in the last few months, a pandemic of a novel swine-origin influenza A virus, namely A(H1N1), has already caused hundreds of thousands of human cases of illness and thousands of deaths. As those viruses could possibly contaminate water resources through wild birds excreta or through sewage, the aim of our work was to find out whether the treatment processes in use in the drinking water industry are suitable for eradicating them. The effectiveness of physical treatments (coagulation–flocculation–settling, membrane ultrafiltration and ultraviolet) was assessed on H5N1, and that of disinfectants (monochloramine, chlorine dioxide, chlorine, and ozone) was established for both the H5N1 and H1N1 viruses. Natural water samples were spiked with human H5N1/H1N1 viruses. For the coagulation–settling experiments, raw surface water was treated in jar-test pilots with 3 different coagulating agents (aluminum sulfate, ferric chloride, aluminum polychorosulfate). Membrane performance was quantified using a hollow-fiber ultrafiltration system. Ultraviolet irradiation experiments were conducted with a collimated beam that made it possible to assess the effectiveness of various UV doses (25–60 mJ/cm 2). In the case of ozone, 0.5 mg/L and 1 mg/L residual concentrations were tested with a contact time of 10 min. Finally, for chlorine, chlorine dioxide and monochloramine treatments, several residual oxidant target levels were tested (from 0.3 to 3 mg/L) with contact times of 5–120 min. The infectivity of the H5N1 and H1N1 viruses in water samples was quantified in cell culture using a microtiter endpoint titration. The impact of coagulation–settling on the H5N1 subtype was quite low and variable. In contrast, ultrafiltration achieved more than a 3-log reduction (and more than a 4-log removal in most cases), and UV treatment was readily effective on its inactivation (more than a 5-log inactivation with a UV dose of 25 mJ/cm 2). Of the chemical disinfection treatments, ozone, chlorine and chlorine dioxide were all very effective in inactivating H5N1 and H1N1, whereas monochloramine treatment required higher doses and longer contact times to achieve significant reductions. Our findings suggest that the water treatment strategies that are currently used for surface water treatment are entirely suitable for removing and/or inactivating influenza A viruses. Appropriate preventive actions can be defined for single disinfection treatment plants.

CFD modeling of a transient hollow fiber ultrafiltration system for protein concentration

A transient model based on the finite element method (CFD Comsol) to simulate numerically the flow (momentum equation) and the concentration (diffusion–convection equation) in an ultrafiltration unit is presented. The CFD model was developed by solving the 2D Navier–Stokes equation and the mass conservation equation for transient conditions. A resistance model was used to link the retained protein concentration, the feed and permeate velocity and the pressure at the membrane surface. The ultrafiltration unit consists of a hollow fiber module, a feed tank and a feed pump. In the hollow fiber module, the variable transmembrane pressure, a variable viscosity of the retentate and a polarization layer and a time variable cake occurring on the membrane are considered. Under laminar flow regime, the model allows for the predictions of the velocity fields, the pressure and the concentration along the membrane fiber. The model predictions for the transient permeate flux and the pressure profile in the fiber are compared to experimental data during the concentration of soy protein extracts in a hollow fiber module where total retention of the soy protein is achieved. The comparison shows that the proposed model fits well with the experiments and shows the interest to take into account the variation of resistance and the concentration dependant viscosity flux. The model shows that the transmembrane pressure is an important element on the polarization concentration profile and that a constant transmembrane pressure yields erroneous conclusion on the concentration polarization. The model alleviates some limitations on the polarization modeling avoiding the need to estimate the polarization thickness in the computation of the polarization resistance. The flexibility of the current model is only limited by the ability of the user to accurately define the variations of the properties of the system for industrial applications.

Validation of hollow fiber ultrafiltration and real-time PCR using bacteriophage PP7 as surrogate for the quantification of viruses from water samples

A quantitative real-time TaqMan ® PCR system for Pseudomonas aeruginosa bacteriophage PP7 was designed to detect PP7 as surrogate in performance tests of 2 hollow fiber ultrafiltration systems in series. Fifty-six storm water samples from 21 sites representing agricultural, urban and highway locations in California were collected. The optimized procedure gave recoveries of spiked PP7 of 64±4.8% (mean±SEM). The PP7 assay was validated over 5 orders of magnitude with an assay limit of detection of 5 gene copies per reaction volume. Sample-dependent variables like enzymatic inhibition during PCR analysis, filtration recovery and extraction efficiency were quantified and incorporated to calculate a specific sample limit of detection ( S LOD) for the spiked surrogate PP7. S LOD values were highly variable among samples; they were independent of physicochemical parameters including conductivity, turbidity, total suspended solids and pH but strongly correlated with the dilution factor required to relieve enzymatic inhibition during PCR analysis. To determine actual gene copies of PP7, a dilution approach was developed that involves assaying several dilutions within a range where inhibitors do not affect the efficiency of amplification and linear regression to determine the theoretical C t value when there is no inhibition. For the detection of viral pathogens, an internal standard like PP7 can be used to calculate filtration recoveries when quantifying pathogens and to determine whether filtration or inhibitor concentration affect nucleic acid extraction efficiency. Additionally, by defining S LOD values per sample and pathogenic organism analyzed, it should be possible to critically investigate the absence of detects for a particular pathogen and determine probabilities of risk associated with a specific sample limit of detection.

Simplified CFD approach of a hollow fiber ultrafiltration system

Abstract Pressure driven membrane filtration processes have emerged as cost effective and confirmed technologies. Ultrafiltration is used to produce drinking water. Hollow fiber membranes are used in industrial processes but there is still a need of predicting pressure drops for design and optimization purposes: to control the production of water, to anticipate problems such as the clogging of the hollow fibers and/or the module position and to consider energy consumption. This prediction could also enhance current models that calculate pressure drop using the Hagen–Poiseuille law. In this work, the flow characteristics controlling the performance of a hollow fiber membrane module are investigated numerically. The aim of this study is to determine the pressure drop in a module depending on the operating conditions and membrane characteristics: a simplified model equation is proposed. We use a commercial CFD package (FLUENT). Numerical simulation can provide a better understanding of module performance, especially for permeable wall and/or complex multi-component systems. CFD can be used to better apprehend fluid flows in complex geometries and to test the influence of process parameters. The results are compared to experimental data obtained with an industrial pilot plant: a good agreement with our relation is obtained.

Comparison of 2 ultrafiltration systems for the concentration of seeded viruses from environmental waters

The use of ultrafiltration as a concentration method to recover viruses from environmental waters was investigated. Two ultrafiltration systems (hollow fiber and tangential flow) in a large- (100 L) and small-scale (2 L) configuration were able to recover greater than 50% of multiple viruses (bacteriophage PP7 and T1 and poliovirus type 2) from varying water turbidities (10-157 nephelometric turbidity units (NTU)) simultaneously. Mean recoveries (n = 3) in ground and surface water by the large-scale hollow fiber ultrafiltration system (100 L) were comparable to recoveries observed in the small-scale system (2 L). Recovery of seeded viruses in highly turbid waters from small-scale tangential flow (2 L) (screen and open channel) and hollow fiber ultrafilters (2 L) (small pilot) were greater than 70%. Clogging occurred in the hollow fiber pencil module and when particulate concentrations exceeded 1.6 g/L and 5.5 g/L (dry mass) in the screen and open channel filters, respectively. The small pilot module was able to filter all concentrates without clogging. The small pilot hollow fiber ultrafilter was used to test recovery of seeded viruses from surface waters from different geographical regions in 10-L volumes. Recoveries >70% were observed from all locations.

Hollow-fiber ultrafiltration of Cryptosporidium parvum oocysts from a wide variety of 10-L surface water samples.

An optimized hollow-fiber ultrafiltration system (50 000 MWCO) was developed to concentrate Cryptosporidium oocysts from 10-L samples of environmental water. Seeded experiments were conducted using a number of surface-water samples from the southwestern U.S.A. and source water from four water districts with histories of poor oocyst recovery. Ultrafiltration produced a mean recovery of 47.9% from 19 water samples (55.3% from 39 individual tests). We also compared oocyst recoveries using the hollow-fiber ultrafiltration system with those using the Envirochek filter. In limited comparison tests, the hollow-fiber ultrafiltration system produced recoveries similar to those of the Envirochek filter (hollow fiber, 74.1% (SD = 2.8); Envirochek, 71.9% (SD = 5.2)) in low-turbidity (3.9 NTU) samples and performed better than the Envirochek filter in high-turbidity (159.0 NTU) samples (hollow fiber, 27.5%; Envirochek, 0.4%). These results indicate that hollow-fiber ultrafiltration can efficiently recover oocysts from a wide variety of surface waters and may be a cost-effective alternative for concentrating Cryptosporidium from water, given the reusable nature of the filter.

Evaluation and optimization of a reusable hollow fiber ultrafilter as a first step in concentrating cryptosporidium parvum oocysts from water

Experiments with a small-scale hollow fiber ultrafiltration system (50,000 MWCO) was used to characterize the filtration process and identify conditions that optimize the recovery of Cryptosporidium parvum oocysts from 2 L samples of water. Seeded experiments were conducted using deionized water as well as four environmental water sources (tap, ground, Arkansas river, and Rio Grande river; 0–30.9 NTU). Optimal and consistent recovery of spiked oocysts was observed (68–81%), when the membrane was sanitized with a 10% sodium dodecyl sulfate (SDS) solution and then blocked with 5% fetal bovine serum (FBS).

Intermittent crossflushing of hollow fiber ultrafiltration systems

The successful operation of dead-end ultrafiltration systems depends on the effectiveness of cleaning (hydraulic and/or chemical cleaning). In this study, backwashing conditions such as pressure and duration were studied in order to maximize the net flux per cycle. Monitoring the backwash flux and turbidity of the backwash water showed that the efficiency of backwashing was more dependent on backwashing time than pressure. The effectiveness of backwashing was significantly improved by the use of crossflushing. In general, 99.9±1% flux restoration could be achieved when backwashing was preceded by crossflushing while 94.5±1% could be achieved by backwashing alone. Crossflushing was more effective when the crossflush velocity in the fiber was in the turbulent regime (v ≅ 1.6 m/s). Crossflushing and pressure pulsing can be employed to increase the efficiency of dead-end, hollow fiber ultrafiltration systems because the frequency of backwashing and chemical cleaning, permeate consumption and system down time are reduced.

Concentration of Seeded and Naturally Occurring Enteroviruses from Waters of Varying Quality by Hollow Fiber Ultrafiltration

A semi-automated hollow fiber ultrafiltration system was used to concentrate viruses from tap water, river water and treated and untreated wastewater. Samples were dehydrated by filtration through an asymmetric polysulfone hollow fiber module with a molecular weight cut-off of 10,000 D. Retained solute was recovered from the filter by backwashing with water, buffer and other solutions. One hundred liters of tap water seeded with poliovirus type 2 Sabin were processed in 161 ± 22 minutes (average flux 1.2 ± 0.1 × 10−3 cm/sec). Retained virus was recovered from the filter by backwashing with 150 ml of 0.05 M glycine, pH 10.0, which was further reduced to about 10 ml by the organic flocculation technique. Average recovery of 60 plaque-forming units (PFU) of poliovirus from 100 1 of tapwater was 148 ± 10%. Hudson River water (100 1 with an average turbidity of 3.2 NTU) was processed in 218 ± 34 minutes (average flux 0.8 ± 0.2 × 10−3 cm/sec). Recovery of 114 PFU of poliovirus seeded into 99 1 of river water was 35%. No natural virus was recovered from unseeded river water. Naturally occurring viruses, tentatively identified as echovirus type 14, coxsackie virus type A9 and coxsackie virus types B2-B5, were isolated from concentrates qf treated and untreated wastewater (average fluxes 0.58 × 10−3 and 0.46 × 10−3 cm/sec, respectively).

Hollow Fiber Ultrafiltration of Cottage Cheese Whey: Performance Study

The operation of hollow fiber ultrafiltration systems is discussed. Critical factors of fiber diameter, transmembrane pressure, pH, temperature, diafiltration, and cleanability are discussed for XM50 and PM10 hollow fiber ultrafiltration membranes in cottage cheese whey processing. While each membrane has its own particular characteristics, advantages and disadvantages, the 45 mil XM50 fiber, with 26.5 ft2 of membrane area (43 in long fibers) is considered to be the optimal fiber for most cheese whey applications.