Dead-end Mode Research Articles

Poultry slaughterhouse wastewater treatment using a static granular bed reactor coupled with single stage nitrification-denitrification and ultrafiltration systems

This study evaluated the performance of a lab-scale poultry slaughterhouse wastewater (PSW) treatment system consisting of a static granular bed reactor (SGBR) coupled with single stage nitrification-denitrification (SND) bioreactor and ultrafiltration membrane module (ufMM) systems. The feasibility of treating PSW to a water quality standard compliant with industrial wastewater discharge standards was investigated. The SGBR was operated at hydraulic retention times (HRTs) ranging from 24 to 96 h and organic loading rates (OLRs) ranging from 0.73 to 12.49 g COD/L.day, for 138 days. The chemical oxygen demand (COD), total suspended solids (TSS), biological oxygen demand (BOD5) and fats, oils and grease (FOG) removal efficiencies achieved by the SGBR averaged 80%, 95%, 89% and 80%, respectively. The SND bioreactor achieved total nitrogen (TN) removal efficiencies of 33% and 79% for the SGBR effluent, when operated in down-flow mode without aeration and up-flow mode with aeration, respectively. The ufMMs, operated in dead-end filtration mode, were able to further reduce the COD and TSS by an average of 65% and 54%, respectively. The results for the PSW treatment system demonstrated the combined benefits of biological and physical treatment processes, with averaged COD, ortho-phosphate (PO43−-P), TSS and total dissolved solids (TDS) removal efficiencies of 91%, 51%, 97% and 52%, respectively, being achieved over 52 days. The final effluent was deemed suitable for discharge; although, the PO43- and NH4+-N requires further monitoring and the PSW treatment system design requires refinement.

Macrofiltration-A leap towards high efficiency microalgal harvesting: A case study using Scenedesmus acuminatus

In order to develop efficient membrane based harvesting techniques to accelerate microalgal commercialization, macrofiltration membranes of mixed cellulose with pore sizes of 0.45, 1.2, 3, 5, and 8 μm were evaluated for Scenedesmus acuminatus harvesting. The influences of pore size on the changes in membrane flux and flux recovery were investigated, followed by a SEM analysis of the fouled membranes. The performance of S. acuminatus harvesting using the 5 μm membrane was then compared with an ultrafiltration membrane, with both operating under a cross-flow mode. Macrofiltration operated with dead-end mode was further developed to achieve higher flux and higher solid content in the harvested biomass. The results showed that the 5 μm mixed cellulose membrane achieved the highest average flux due to its excellent anti-fouling performance. SEM images revealed that the presence of non-cellular and cellular foulants were responsible for the fouling of the smaller sized membranes, and membranes larger than 5 μm, respectively. Macrofiltration membrane harvesting was more efficient when a dead-end rather than a cross-flow operation was used. The average flux from a multiple-times filtration cycle reached 1845 ± 105 L·m−2·h−1 for the dead-end operated 5 μm macrofiltration membrane, which was 16-fold higher than that obtained using a cross-flow ultrafiltration membrane (107 ± 14 L·m−2·h−1). The solid content of macrofiltration-harvested biomass was 24%. This high flux and high solid content achieved through macrofiltration represents a great leap towards high-efficiency microalgal harvesting.

Characterization and quantification of structure and flow in multichannel polymer membranes by MRI

Polymeric multichannel hollow fiber membranes were developed to reduce fiber breakage and to increase the volume-to-membrane-surface ratio and consequently the efficiency of filtration processes. These membranes are commonly used in ultrafiltration and are operated in in-out dead-end mode. However, some of the filtration details are unknown. The filtration efficiency and flow in the multichannel membranes depend on filtration time and are expected to vary along spatial coordinates. In the current work, in-situ magnetic resonance imaging was used to answer these questions. Velocities were quantified in the feed channels to obtain a detailed understanding of the filtration process. Flow and deposits were measured in each of the seven channels during filtration of sodium alginate, which is a model substance for extracellular polymeric substances occurring in water treatment. Volume flow and flow profiles were calculated from phase contrast flow images. The flow in z-direction in the center channel was higher than in the surrounding channels. Flow profiles variate depending on the concentration of Ca2+, which changes the filtration mechanism of aqueous solutions of sodium alginate from concentration polarization to gel layer filtration.

Hydrophobic ceramic capillary membranes for versatile virus filtration

In this study, we present hydrophobic yttria-stabilized zirconia capillary membranes conditioned for virus filtration. These macroporous ceramic filters (d50 = 150 nm) efficiently extract viruses regardless of their surface charge with high throughput rates. For hydrophobic functionalization of the ceramic membranes we used two different silanes, n-hexyltriethoxysilane (HTS, C6-chain) and n-octyltriethoxysilane (OTS, C8-chain), in three different molarities. The virus retention of the membranes is tested in dead-end mode by intracapillary virus feeding using two small bacteriophages as model species: MS2 and PhiX174. Virus retention increases most strongly for hydrophobic capillaries functionalized with 0.05 M OTS, showing a virtually complete retention with log-reduction values (LRVs) of ~ 9 for both bacteriophages compared to the non-functionalized membrane with LRVs of 0.3 ± 0.1 for MS2 and 3.4 ± 0.2 for PhiX174. The functionalized membranes allow a high membrane flux of ~ 150 L/(m2hbar), with throughput rates up to ~ 400 L/(m2 h) while maintaining high filtration efficiency. Even under varying feed conditions using only mono- or divalent salt ions or pH values ranging from 3 to 9, retention capacities of the capillary membranes are high. Accordingly, such hydrophobic ceramic membranes offer a versatile alternative to conventional polymeric membranes for virus removal with greatly improved membrane flux.

Electro-Conductive Composite Gold-Polyethersulfone-Ultrafiltration-Membrane: Characterization of Membrane and Natural Organic Matter (NOM) Filtration Performance at Different In-Situ Applied Surface Potentials.

Next to the pore size distribution, surface charge is considered to be one main factor in the separation performance of ultrafiltration (UF) membranes. By applying an external surface potential onto an electro-conductive UF membrane, electrostatic induced rejection was investigated. This study introduces in a first part a relatively simple but yet not reported technology of membrane modification with direct current sputter deposition of ultrathin (15 nm) highly conductive gold layers. In a second part, characterization of the gold-coated UF flat sheet membrane with a molecular weight cut-off (MWCO) of 150 kDa is presented. Membrane parameters as contact angle (hydrophobicity), pure water permeability, MWCO, scanning electron microscopy imaging, zeta potential, surface conductivity and cyclic voltammetry of the virgin and the modified membrane are compared. Due to the coating, a high surface conductivity of 107 S m−1 was realized. Permeability of the modified membrane decreased by 40% but MWCO and contact angle remained almost unchanged. In a third part, cross-flow filtration experiments with negative charged Suwannee River Natural Organic Matter (SRNOM) are conducted at different cathodic and anodic applied potentials, different pH values (pH 4, 7, 10) and ionic strengths (0, 1, 10 mmol L−1). SRNOM rejection of not externally charged membrane was 28% in cross-flow and 5% in dead-end mode. Externally negative charged membrane (−1.5 V vs. Ag/AgCl) reached rejection of 64% which was close to the performance of commercial UF membrane with MWCO of 5 kDa. High ionic strengths or low pH of feed reduced the effect of electrostatic rejection.

Nanoparticle filtration through microporous ECTFE membrane in an alcoholic solution

Abstract Organic solvent filtration is an important industrial process. It is widely used in pharmaceutical manufacturing, chemical processing industry, semiconductor industry, auto assembly etc. Most of the particle filtration studies reported in open literature dealt with aqueous suspension medium. The current work has initiated a study of cross-flow solvent filtration behavior of microporous ethylene chlorotrifluoroethylene (ECTFE) membranes using 12 nm silica nanoparticles suspended in an aqueous solution containing 25% ethanol. In the constant pressure mode of operation of cross-flow microfiltration (MF), permeate samples were collected at different time intervals. The permeate particle size distribution (PSD) results for different experiments were identical. Particle agglomerates having less than 100 nm size can pass through the membrane; some fouling was observed. The governing fouling mechanisms for tests operated using 3.8 × 10−3 kg/m3 (3.8 ppm) at 6.9 × 103 Pag and 1.4 × 104 Pag were pore blocking. For tests conducted using 3.8 × 10−3 kg/m3 (3.8 ppm) at 27.6 × 103 Pag (4 psig) and 1.9 × 10−3 kg/m3 (1.9 ppm) at 6.9 × 103, 13.8 × 103 and 27.6 × 103 Pag (1, 2 and 4 psig), the mechanism was membrane resistance control. Less particles got embedded in membrane pores in experiments operated using suspensions with lower or higher particle concentrations with a higher transmembrane pressure. This is in good agreement with the values of the shear rate in the pore flow and scanning electron microscope images of the membrane after MF. In the dead-end mode of operation of solvent filtration using methanol, ethanol and 2-propanol, the permeate flux behavior follows Jmethanol > Jethanol > J2-propanol at all testing pressures. The values of permeance (kg/m2-s-Pa) determined from the slope of the linear plot of filtration flux vs. the applied pressure difference across the membrane, were 3.9 × 10−4, 2.3 × 10−4 and 3.0 × 10−5 for methanol, ethanol and 2-propanol, respectively. Further exploration was made on solvent sorption results reported earlier. The critical temperature of selected solvents shows a better correlation with solvent sorption rather than the solubility parameter.

Surface-nucleated heterogeneous growth of zeolitic imidazolate framework – A unique precursor towards catalytic ceramic membranes: Synthesis, characterization and organics degradation

A novel Co3O4 nanocatalyst functionalized Al2O3 ceramic membrane (CoFCM) with a honeycomb structure was prepared via an optimized surface-nucleated zeolitic imidazolate framework (ZIF-67) growth method. The Co3O4 hollow structure which was confirmed via chemical characterizations (XRD, FTIR, Raman and XPS), was formed on the membrane surface by one-step calcination of ZIF-67 membrane. The CoFCM was characterized by various techniques including the field emission scanning electron microscopy and atomic force microscopy. The results revealed the formation of well-defined Co3O4 layer on the porous Al2O3 ceramic membrane with the thickness of 1.5–2 µm. The growth mechanism of CoFCM was further proposed via XPS and the catalytic activity of CoFCM was investigated for the removal of sulfamethoxazole (SMX) with the addition of Oxone. The membrane performance was examined under a home-made dead-end mode. Results indicated that CoFCM has a rougher surface with an initial membrane resistance of 1.19 × 1011 m−1 and performs outstanding catalytic activity. The pure water permeability of CoFCM is 3024 L m−2 h−1 bar−1, which is comparable to that of the pristine ceramic membrane (<10% difference). The SMX removal efficiency achieved to >90% in 90 min with an Oxone addition of 0.1 g L−1. Meanwhile, the membrane showed excellent durability by retaining >95% of initial flux for at least 3 operational cycles with a low cobalt ion leaching via Oxone-assisted cleaning. Furthermore, the reaction mechanism of Oxone activation by CoFCM was proposed from the results of the electron paramagnetic resonance (EPR) and radical scavenger experiments.

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.

One pot preparation of polysulfone-amino functionalized SiO2 nanoparticle ultrafiltration membranes for water purification

Highly hydrophilic and fouling resistant polysulfone (PSF) membranes were prepared via one pot methodology by simultaneous phase inversion and nanoparticle formation. Membrane morphology, hydrophilicity, and surface charge behavior were thoroughly characterized by scanning electron microscopy, atomic force microscopy, contact angle, and zeta potential measurements. The SiO2-NH2 nanoparticle distribution in membrane matrix was also investigated by energy dispersive X-ray spectroscopy and transmission electron microscopy. The water purification performances, some of the membranes flux, rejection, and flux recovery, were evaluated by ultrafiltration of bovine serum albumin protein, Congo red, and methylene blue dyes under dead end mode. The fouling tendency of the membrane was evaluated by bovine serum albumin protein adsorption and ultrafiltration. The properties of the prepared membranes could be tuned by varying the SiO2-NH2 concentration. The nanocomposite membranes exhibited superior water permeation, rejection, and antifouling performance as compared to neat PSF membranes. Hydrophilicity was increased due to amino functionalized SiO2 particles, leading to up to 7-fold increase in water flux and more than 93% protein rejection efficiency with PSF-APTEOS-20 and -10 membranes, respectively. Overall, this work proves an easy and straightforward method for nanocomposite ultrafiltration membrane preparation with good separation and filtration efficiency.

Health Literacy in Familial Hypercholesterolemia: a Cross-national Study

In order to develop efficient membrane based harvesting techniques to accelerate microalgal commercialization, macrofiltration membranes of mixed cellulose with pore sizes of 0.45, 1.2, 3, 5, and 8 μm were evaluated for Scenedesmus acuminatus harvesting. The influences of pore size on the changes in membrane flux and flux recovery were investigated, followed by a SEM analysis of the fouled membranes. The performance of S. acuminatus harvesting using the 5 μm membrane was then compared with an ultrafiltration membrane, with both operating under a cross-flow mode. Macrofiltration operated with dead-end mode was further developed to achieve higher flux and higher solid content in the harvested biomass. The results showed that the 5 μm mixed cellulose membrane achieved the highest average flux due to its excellent anti-fouling performance. SEM images revealed that the presence of non-cellular and cellular foulants were responsible for the fouling of the smaller sized membranes, and membranes larger than 5 μm, respectively. Macrofiltration membrane harvesting was more efficient when a dead-end rather than a cross-flow operation was used. The average flux from a multiple-times filtration cycle reached 1845 ± 105 L·m−2·h−1 for the dead-end operated 5 μm macrofiltration membrane, which was 16-fold higher than that obtained using a cross-flow ultrafiltration membrane (107 ± 14 L·m−2·h−1). The solid content of macrofiltration-harvested biomass was 24%. This high flux and high solid content achieved through macrofiltration represents a great leap towards high-efficiency microalgal harvesting.

Impact of Gas Stoichiometry on the Result of Accelerated Stress Tests

Degradation issues remain among the main factors impeding the development of commercially viable fuel cell (FC) systems for transportation and stationary power applications. The necessity to keep costs and performances at reasonable levels led to the widespread use of carbon supported platinum (Pt) for electrodes and thin PFSA membranes as electrolyte. Both are quite fragile materials but currently without any convincing alternative. To better understand, and eventually limit degradation mechanisms, several kinds of accelerated stress tests (AST) have been developed targeting each material independently: namely open circuit voltage (OCV) for PFSA membranes, potentiostatic regimes for carbon, and potential cycling for Pt [1, 2]. Other accelerated stress tests corresponding to common fuel cell operation sequences were also proposed like constant current, start/stop, hydrogen starvation/dead-ended anode protocols [3,4], temperature, relative humidity or potential/load cycling, or even freeze/thaw protocols [5]. In this work, we focus on load cycling events, which are very close to the potential cycling performed during AST to study Pt and carbon degradation mechanisms. For obvious reasons, load cycling in actual fuel cell systems and potential cycling in AST are usually performed in overfed conditions [6]: i.e. the fuel cell is supplied with the gas flow rates corresponding to the highest current before the intensity increases. And in most of the cases, the gas flow rates are even permanently kept at the highest values during AST. To avoid supplying fuel and air in excess, most of fuel cell stacks are hybridized either with batteries or supercapacitors (SC) to improve the system dynamics (which in return increases its size and cost). Thanks to hybridization, the FC voltage can drop by a few hundreds of mV per cell during the time needed by the gas supply lines to adapt the flow rates, while batteries or SC keep the system power at the required value. However, the impact of such short reactant starvation events on FC performance and durability is not very well known. Therefore, we performed repeated current Heaviside steps as AST on PEM single cells; typical values were from 0.25 to 0.95 A/cm² (with corresponding FC voltages between 0.65 and 0.8 V). The gas flow rates were set either to the maximum current intensity (with air and H2 stoichiometries of 3 and 1.5 in open-anode or 1 in dead-end mode, respectively) or we let the gas lines adjust the flow rates when the current input changed, which took about half a second (during this time, the FC could fell to about 0.1 V). As shown on the Figure, the performance and electrochemical surface area repeatedly aged significantly slower in the second case, i.e. with short gas starvation events. To better understand this difference, similar experiments were performed in a segmented cell [7] with measurements of local currents, anode and cathode potentials. We observed that local cathode potentials were higher in overfed conditions while they dropped for a short time in the other case due to (most probably) oxygen depletion in the cathode compartment. Local negative currents were also observed sometimes when the load decreased, but since they were not associated to high local potentials, they did not worsen degradation. In the same way, since the FC dynamics were limited most probably by air supply, the anode (and thus cathode) local potentials remained low. These results suggest that FC voltage drops during transients due to short lacks of reactants can improve the durability of the catalyst layer, as well as optimize the system efficiency in terms of hydrogen consumption and air compressor power demand which can be a useful observation for the design of optimized hybridization strategies.

Bacteriophage-based strategies for biofouling control in ultrafiltration: In situ biofouling mitigation, biocidal additives and biofilm cleanser

The ability of bacteriophages to infect and destroy specific bacteria makes them promising antimicrobial agents in industrial processes. In this study, potential strategies of bacteriophage-facilitated biofouling control during membrane ultrafiltration (UF) were investigated through use of the model T4 bacteriophage and the model host bacterium, Escherichia coli. In the dead-end filtration mode, phages were immobilized on the membrane surface to serve as biocidal agents and inhibit the propagation of bacteria in situ. After 6 h of filtration, a 36% flux reduction was observed for the T4-functionalized membrane in comparison to 71% for the non-functionalized membrane. Surface modification of the membrane using O2 plasma treatment resulted in increased numbers of bound phage and enhanced biofouling resistance of the membrane. Introducing the phage into the feed of a cross-flow filtration system effectively mitigated the water flux reduction of the membrane caused by bacterial growth. By modifying the concentration of phage additives, the growth of bacteria was delayed, inhibited, or eliminated. Phage treatment changed the structure of biofilms on the membrane surface and facilitated in situ biofilm cleaning. A 20% greater recovery in water flux was observed for the biofilm-contaminated membrane following phage-assisted cleaning when compared to the membrane cleaned via a physical washing process. Taken together, these results show that bacteriophage assisted anti-biofouling strategies have the potential to mitigate biofouling in membrane processes in an environmentally friendly manner.

Urea-assisted one-step synthesis of cobalt ferrite impregnated ceramic membrane for sulfamethoxazole degradation via peroxymonosulfate activation

In this study, a novel CoFe2O4 nanocatalyst impregnated Al2O3 ceramic membrane was prepared via a urea-assisted one-step combustion method. The catalytic membrane was characterized by field emission scanning electron microscopy (FESEM) with energy dispersive X-Ray analysis (EDX) and applied for the catalytic degradation of sulfamethoxazole (SMX) via peroxymonosulfate (PMS) activation under a dead-end membrane filtration mode for the first time. Results indicate that CoFe2O4 could be impregnated into the macropores throughout the whole Al2O3 ceramic membrane via this method and the CoFe2O4 loading amount could be controlled by the multiple impregnation cycles. The membrane filtration operation mode significantly enhances the accessibility of the catalytic active sites to PMS and SMX in microreactor environment and thus the CoFe2O4 impregnated membrane displays excellent catalytic activity for the SMX degradation. The pure water permeability flux can maintain at ∼3000 L m−2 h−1 bar−1 (LMHB) with the catalyst loading amount of 0.015 g/g Al2O3. In the membrane filtration system, the removal rate of SMX with the initial concentration of 10 mg L−1 can achieve to ∼98%, 70% and 40% with the residence time of 90, 36 and 18 s. The catalytic membrane shows a great tolerance at wide pH range (3–11), the existence of humic acid and anions. Meanwhile, the membrane shows self-cleaning property by retaining >90% of initial flux after 3 treatment cycles. Electron paramagnetic resonance (EPR) and radical quenching experiments indicate that both sulfate radical and hydroxyl radical are generated and sulfate radical is the dominant active species in the process.

A gas management strategy for anode recirculation in a proton exchange membrane fuel cell

The anode configuration and gas management strategy are two of factors that affect the energy efficiency of a proton exchange membrane fuel cell. In order to improve the hydrogen utilization, unused hydrogen can be recirculated to the inlet using a pump. However, impurities diffusing from the cathode to the anode may cause the dilution of hydrogen in the anode. As a result, a gas management strategy is required for the anode recirculation configuration. In this preliminary study, a novel configuration for anode recirculation and a gas management strategy are proposed and verified by experiments. Two valves are installed in the recirculation line. The anode is operated in four modes (dead-end, recirculation, compression, and purge), and the real-time local current density (LCD) is monitored for gas management purposes. The results show that the LCD distribution is uniform during the recirculation mode and nonuniform during the dead-end and compression modes. With this configuration and gas management strategy, the cycle duration is increased by a factor of 6.5.

Correlation of surface concentration polarization with the surface electrochemistry of a permselective Membrane: An ex situ electrical impedance spectroscopy study

Abstract Surface concentration polarization induces fouling processes accompanied by changes in the resistance of a semipermeable membrane, but the connection between these two phenomena has not yet been evaluated. Here, we propose to connect them by introducing the concept of pH equivalent (pHeq), which is used to describe the electrical properties of a polarized membrane surface in terms of a pH value at which a membrane is conditioned. First, the resistance and capacitance of polyamide thin-film membranes conditioned at different pH were evaluated ex situ using electrical impedance spectroscopy (EIS), which decreases and increases in proportion with increasing pH when the pH exceeds the pKa of the ionization of carboxyl groups. Filtration of 0.1 mM Fe(III) chloride solution in dead-end mode was then conducted as a model reaction for the fouling process. The occurrence of concentration polarization in the early stage indeed led the capacitance and the resistance at the membrane/electrolyte interface to a pHeq similar to that of an alkaline-like environment, while no significant decline in flux or rejection was observed. In addition to being responsible for the formation of Fe(OH)3 in fouling, this high pHeq is also likely the bridge connecting the electrical characteristics of the membrane to macroscopic observations (flux and rejection) based on the electroviscous consideration.

Application of volume-retarded osmosis and low-pressure membrane hybrid process for water reclamation

A new concept of volume-retarded osmosis and low-pressure membrane (VRO-LPM) hybrid process was developed and evaluated for the first time in this study. Commercially available forward osmosis (FO) and ultrafiltration (UF) membranes were employed in a VRO-LPM hybrid process to overcome energy limitations of draw solution (DS) regeneration and production of permeate in the FO process. To evaluate its feasibility as a water reclamation process, and to optimize the operational conditions, cross-flow FO and dead-end mode UF processes were individually evaluated. For the FO process, a DS concentration of 0.15 g mL−1 of polysulfonate styrene (PSS) was determined to be optimal, having a high flux with a low reverse salt flux. The UF membrane with a molecular weight cut-off of 1 kDa was chosen for its high PSS rejection in the LPM process. As a single process, UF (LPM) exhibited a higher flux than FO, but this could be controlled by adjusting the effective membrane area of the FO and UF membranes in the VRO-LPM system. The VRO-LPM hybrid process only required a circulation pump for the FO process. This led to a decrease in the specific energy consumption of the VRO-LPM process for potable water production, that was similar to the single FO process. Therefore, the newly developed VRO-LPM hybrid process, with an appropriate DS selection, can be used as an energy efficient water production method, and can outperform conventional water reclamation processes.

The Effect of Concentration Factor on Membrane Fouling.

Bench-scale systems are often used to evaluate pretreatment methods and operational conditions that can be applied in full-scale ultrafiltration (UF) systems. However, the membrane packing density is substantially different in bench and full-scale systems. Differences in concentration factor (CF) at the solution–membrane interface as a result of packing density may impact the mass transfer and fouling rate and the applicability of bench-scale systems. The present study compared membrane resistance when considering raw water (CF = 1) and reject water (also commonly referred to as concentrate water) (CF > 1) as feed in UF systems operated in deposition (dead-end) mode. A positive relationship was observed between the concentration of the organic matter in the solution being filtered and resistance. Bench-scale trials conducted with CF = 1 water were more representative of full-scale operation than trials conducted with elevated CFs when considering membrane resistance and permeate quality. As such, the results of this study indicate that the use of the same feed water as used at full-scale (CF = 1) is appropriate to evaluate fouling in UF systems operated in deposition mode.

Study of an Innovative Versatile Flow Design Suitable for Fuel Cells

Flow field plays an important role in the performances of the fuel cells, especially in large area fuel cells. In the present work, an innovative, versatile flow field, capable of combining in different conventional modes is reported and evaluated in a polymer electrolyte fuel cell (PEFC) with an active area of 150 cm2. The proposed design is capable of offering serpentine, interdigitated, counterflow, dead-end, and serpentine-interdigitated hybrid mode. Moreover, it is possible to switch over from one flow mode to another mode of flow during operation at any point of time. The flow design consists of the multichannel parallel serpentine flow (SP) field and a pair of an inlet and outlet manifolds instead of conventional single inlet and outlet manifold. Flow distribution was successfully altered without affecting the performances, and it was observed a combination of serpentine and interdigitated on the cathode side offered steady performance for more than 20 min when it was operated at a current density of 700 mA cm−2.

Optimization of hybrid coagulation-ultrafiltration process for potable water treatment using response surface methodology

Abstract In order to optimize the operating conditions for a combined polyaluminum chloride (PACl) coagulation/flocculation and ultrafiltration process for treating potable water, the main, second order and interaction effects of PACl dose and flocculation retention time (FRT) on permeate turbidity, UV254 and membrane permeability were investigated using a 100 kDa hollow fiber membrane operated in the dead-end mode. A multilevel factorial design was used to determine the relevant ranges of the two factors for optimization. A 22 central composite design (CCD) was then used to develop mathematical correlation models for the optimum operating conditions. The main effect of PACl dose was the most significant factor on all the responses. For permeability, both the main effect of FRT and FRT–PACl dose interactions were found to be insignificant. The optimum PACl dose and FRT for the feed water were 20 mg/L and 14 min, respectively. Corresponding permeate turbidity, UV254 and permeability were 0.15 ± 0.01 NTU, 0.003 ± 0.001 cm−1 and 62.0 ± 9.52 Lm−2 h−1 bar−1, respectively. Experimental validation runs confirmed the reliability of the predicted optimal conditions thus implying that CCD models can be used to predict/optimize the quality and quantity of permeate from hybrid coagulation–ultrafiltration systems for potable water treatment.

Effect of membrane property and feed water organic matter quality on long-term performance of the gravity-driven membrane filtration process.

This study investigated the influence of membrane property and feed water organic matter quality on the permeate flux and water quality during gravity-driven membrane (GDM) filtration. GDM filtration was continuously carried out over 500days at hydrostatic pressure of 65mbar in dead-end mode without any back-flushing or membrane cleaning. Three ultrafiltration (UF) membranes (PES-100kDa, PVDF-120kDa, and PVDF-100kDa) and one microfiltration (MF) membrane (PTFE-0.3μm) were tested for treating lake water with varied organic matter qualities due to algal growth. The fluxes of the four membranes rapidly decreased to ~8L/(m2×h) within a week of GDM filtration. The flux variations were quite similar for the four membranes during the entire GDM filtration, indicating that membrane property has a little effect on the flux. The flux strongly depends on the feed water organic matter quality. The average flux in treating low organics containing water (7-60days) was ~5L/(m2×h) and decreased to ~2L/(m2×h) in treating high organics containing water (60-300days). The accumulation of algal-derived biopolymers was mainly responsible for the flux decline by forming biofilms with high permeation resistance. The average flux in 300-500days increased to ~3.5L/(m2×h) when the feed water contained lower levels of biopolymers and higher levels of easily biodegradable organics, which created open and heterogeneous biofilms with lower permeation resistance. Removal efficiency for Escherichia coli was more than 5 log, while the removal efficiency for total bacterial cells was 1 log-2 log for the four membranes, indicating some bacterial regrowth after the filtration. Removal efficiency for the MS2 phage was 2.4 log and 1.5 log for the fouled PES-UF and PTFE-MF membranes.