J.S. (Hans) Vrouwenvelder
Delft University of Technology, Biotechnology, Faculty Member
This study evaluates with numerical simulations supported by experimental data the impact of biofouling on membrane performance in a cross-flow forward osmosis (FO) system. The two-dimensional numerical model couples liquid flow with... more
This study evaluates with numerical simulations supported by experimental data the impact of biofouling on membrane performance in a cross-flow forward osmosis (FO) system. The two-dimensional numerical model couples liquid flow with solute transport in the FO feed and draw channels , in the FO membrane support layer and in the biofilm developed on one or both sides of the membrane. The developed model was tested against experimental measurements at various osmotic pressure differences and in batch operation without and with the presence of biofilm on the membrane active layer. Numerical studies explored the effect of biofilm properties (thickness, hydraulic perme-ability and porosity), biofilm membrane surface coverage, and biofilm location on salt external concentration polarization and on the permeation flux. The numerical simulations revealed that (i) when biofouling occurs, external concentration polarization became important, (ii) the biofilm hydraulic permeability and membrane surface coverage have the highest impact on water flux, and (iii) the biofilm formed in the draw channel impacts the process performance more than when formed in the feed channel. The proposed mathematical model helps to understand the impact of biofouling in FO membrane systems and to develop possible strategies to reduce and control biofouling.
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Large seasonal variations in microbial drinking water quality can occur in distribution networks , but are often not taken into account when evaluating results from short-term water sampling campaigns. Temporal dynamics in bacterial... more
Large seasonal variations in microbial drinking water quality can occur in distribution networks , but are often not taken into account when evaluating results from short-term water sampling campaigns. Temporal dynamics in bacterial community characteristics were investigated during a two-year drinking water monitoring campaign in a full-scale distribution system operating without detectable disinfectant residual. A total of 368 water samples were collected on a biweekly basis at the water treatment plant (WTP) effluent and at one fixed location in the drinking water distribution network (NET). The samples were analysed for heterotrophic plate counts (HPC), Aeromonas plate counts, adenosine-tri-phosphate (ATP) concentrations, and flow cytometric (FCM) total and intact cell counts (TCC, ICC), water temperature, pH, conductivity, total organic carbon (TOC) and assimilable organic carbon (AOC). Multivariate analysis of the large dataset was performed to explore correla-tive trends between microbial and environmental parameters. The WTP effluent displayed considerable seasonal variations in TCC (from 90 × 10 3 cells mL-1 in winter time up to 455 × 10 3 cells mL-1 in summer time) and in bacterial ATP concentrations (<1–3.6 ng L-1), which were congruent with water temperature variations. These fluctuations were not detected with HPC and Aeromonas counts. The water in the network was predominantly influenced by the characteristics of the WTP effluent. The increase in ICC between the WTP effluent and the network sampling location was small (34 × 10 3 cells mL-1 on average) compared to seasonal fluctuations in ICC in the WTP effluent. Interestingly, the extent of bacterial growth in the NET was inversely correlated to AOC concentrations in the WTP effluent (Pearson's correlation factor r =-0.35), and positively correlated with water temperature (r = 0.49). Collecting a large dataset at high frequency over a two year period enabled the characterization of previously undocumented seasonal dynamics in the distribution network. Moreover, high-resolution FCM data enabled prediction of bacterial cell concentrations at specific water temperatures and time of year. The study highlights the need to systematically
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Forward osmosis (FO) is a novel membrane separation process that potentially can be used as an energy-saving alternative to conventional membrane processes. A hybrid sequential batch reactor (SBR)–FO process was explored. In this system,... more
Forward osmosis (FO) is a novel membrane separation process that potentially can be used as an energy-saving alternative to conventional membrane processes. A hybrid sequential batch reactor (SBR)–FO process was explored. In this system, a plate and frame FO cell including two flat-sheet FO membranes was submerged in a bioreactor treating synthetic domestic wastewater. The dissolved organic carbon (DOC) removal efficiency of the system was 98.55%. Total nitrogen removal was 62.4%, with nitrate, nitrite and ammonium removals of 58.4%, 96.2% and 88.4%, respectively. Phosphate removal was almost 100%. The 15-hour cycle average water flux of a virgin membrane with air scouring was 2.95 L/m 2 ·h −1. Air scouring can help to remove loose foulants from the membrane active layer, thus helping to recover up to 89.5% of the original flux. Chemical cleaning of the fouled active layer of the FO membrane was not as effective as air scouring. Natural organic matter (NOM) characterization methods (liquid chromatography–organic carbon detection (LC–OCD) and 3-D fluorescence excitation emission matrix (FEEM)) show that the FO membrane has a very good performance in rejecting
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Research Interests: Biofilms()
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Biological stability of drinking water refers to the concept of providing consumers with drinking water of same microbial quality at the tap as produced at the water treatment facility. However, uncontrolled growth of bacteria can occur... more
Biological stability of drinking water refers to the concept of providing consumers with drinking water of same microbial quality at the tap as produced at the water treatment facility. However, uncontrolled growth of bacteria can occur during distribution in water mains and premise plumbing, and can lead to hygienic (e.g., development of opportunistic pathogens), aesthetic (e.g., deterioration of taste, odor, color) or operational (e.g., fouling or biocorrosion of pipes) problems. Drinking water contains diverse microorganisms competing for limited available nutrients for growth. Bacterial growth and interactions are regulated by factors, such as (i) type and concentration of available organic and inorganic nutrients, (ii) type and concentration of residual disinfectant, (iii) presence of predators, such as protozoa and invertebrates, (iv) environmental conditions, such as water temperature, and (v) spatial location of microorganisms (bulk water, sediment, or biofilm). Water treatment and distribution conditions in water mains and premise plumbing affect each of these factors and shape bacterial community characteristics (abundance, composition, viability) in distribution systems. Improved understanding of bacterial interactions in distribution systems and of environmental conditions impact is needed for better control of bacterial communities during drinking water production and distribution. This article reviews (i) existing knowledge on biological stability controlling factors and (ii) how these factors are affected by drinking water production and distribution conditions. In addition, (iii) the concept of biological stability is discussed in light of experience with well-established and new analytical methods, enabling high throughput analysis and in-depth characterization of bacterial communities in drinking water. We discussed, how knowledge gained from novel techniques will improve design and monitoring of water treatment and distribution systems in order to maintain good drinking water microbial quality up to consumer's tap. A new definition and methodological approach for biological stability is proposed.
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A systematic approach is presented for the assessment of (i) bacterial growth-controlling factors in drinking water and of (ii) the impact of distribution conditions on the extent of bacterial growth in full-scale distribution systems.... more
A systematic approach is presented for the assessment of (i) bacterial growth-controlling factors in drinking water and of (ii) the impact of distribution conditions on the extent of bacterial growth in full-scale distribution systems. The approach combines (i) quantification of changes in autochthonous bacterial cell concentrations in full-scale distribution systems with (ii) laboratory-scale batch bacterial growth-potential tests of drinking water samples under defined conditions. The growth-potential tests were done by direct-incubation of water samples, without modification of the original bacterial flora, and with flow cytometric quantification of bacterial growth. This method was shown to be reproducible (ca. 4% relative standard deviation) and sensitive (detection of bacterial growth down to 5 µg L À1 of added assimilable organic carbon). The principle of step-wise assessment of bacterial growth-controlling factors was demonstrated on bottled water, shown to be primarily carbon limited at 133 (±18) × 10 3 cells mL À1 and secondarily limited by inorganic nutrients at 5,500 (±1,700) × 10 3 cells mL À1. Analysis of the effluent of a Dutch full-scale drinking water treatment plant showed (1) bacterial growth inhibition as a result of end-point chlorination, (2) organic carbon limitation at 192 (±72) × 10 3 cells mL À1 and inorganic nutrient limitation at 375 (±31) × 10 3 cells mL À1. Significantly lower net bacterial growth was measured in the corresponding full-scale system (176 (±25) × 10 3 cells mL À1) than in the laboratory scale growth potential test of the same water (294 (±35) × 10 3 cells mL À1), highlighting the influence of distribution on bacterial growth. The systematic approach described herein provides quantitative information on the effect of drinking water properties and distribution system conditions on biological stability, which can assist water utilities in decision making on treatment or distribution system improvements to better control bacterial growth during water distribution.
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Micro-scale flow distribution in spacer-filled flow channels of spiral-wound membrane modules was determined with a particle image velocimetry system (PIV), aiming to elucidate the flow behaviour in spacer-filled flow channels.... more
Micro-scale flow distribution in spacer-filled flow channels of spiral-wound membrane modules was determined with a particle image velocimetry system (PIV), aiming to elucidate the flow behaviour in spacer-filled flow channels. Two-dimensional water velocity fields were measured in a flow cell (representing the feed spacer-filled flow channel of a spiral wound reverse osmosis membrane module without permeate production) at several planes throughout the channel height. At linear flow velocities (volumetric flow rate per cross-section of the flow channel considering the channel porosity, also described as crossflow velocities) used in practice (0.074 and 0.163 m$s À1) the recorded flow was laminar with only slight unsteadiness in the upper velocity limit. At higher linear flow velocity (0.3 m$s À1) the flow was observed to be unsteady and with recirculation zones. Measurements made at different locations in the flow cell exhibited very similar flow patterns within all feed spacer mesh elements, thus revealing the same hydrodynamic conditions along the length of the flow channel. Three-dimensional (3-D) computational fluid dynamics simulations were performed using the same geometries and flow parameters as the experiments, based on steady laminar flow assumption. The numerical results were in good agreement (0.85e0.95 BrayeCurtis similarity) with the measured flow fields at linear velocities of 0.074 and 0.163 m$s À1 , thus supporting the use of model-based studies in the optimization of feed spacer geometries and operational conditions of spiral wound membrane systems.
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We demonstrate the use of Earth's field (EF) Nuclear Magnetic Resonance (NMR) to provide early non-destructive detection of active biofouling of a commercial spiral wound reverse osmosis (RO) membrane module. The RO membrane module was... more
We demonstrate the use of Earth's field (EF) Nuclear Magnetic Resonance (NMR) to provide early non-destructive detection of active biofouling of a commercial spiral wound reverse osmosis (RO) membrane module. The RO membrane module was actively biofouled to different extents, by the addition of biodegradable nutrients to the feed stream, as revealed by a subtle feed-channel pressure drop increase. Easily accessible EF NMR parameters (signal relaxation parameters T 1 , T 2 and the total NMR signal modified to be sensitive to stagnant fluid only) were measured and analysed in terms of their ability to detect the onset of biofouling. The EF NMR showed that fouling near the membrane module entrance significantly distorted the flow field through the whole membrane module. The total NMR signal is shown to be suitable for non-destructive early biofouling detection of spiral wound membrane modules, it was readily deployed at high (operational) flow rates, was particularly sensitive to flow field changes due to biofouling and could be deployed at any position along the membrane module axis. In addition to providing early fouling detection, the mobile EF NMR apparatus could also be used to (i) evaluate the production process of spiral wound membrane modules, and (ii) provide an in-situ determination of module cleaning process efficiency.
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Forward osmosis (FO) is an osmotically driven membrane process, where the membrane separates a draw solution (DS) with high salinity from a feed solution (FS) with low salinity. There can be a counter direction flow of salt (i.e., salt... more
Forward osmosis (FO) is an osmotically driven membrane process, where the membrane separates a draw solution (DS) with high salinity from a feed solution (FS) with low salinity. There can be a counter direction flow of salt (i.e., salt leakage) that may interact with the water flux through the FO membrane. For the first time reported, this study describes a new calcium carbonate scaling phenomenon in the seawater FO desalination process using ammonium bicarbonate as the DS. The scaling on the membrane surface at the feed side is caused by the interaction between an anion reversely diffused from the DS and a cation present in the FS, causing a significant decline of the water flux. The composition of the scaling layer is dominated by the solubility (represented as solubility product constant, K sp) of salt formed by the paired anion and cation. Membrane surface morphology plays a crucial role in the reversibility of the scaling. If the scaling occurs on the active layer of the FO membrane, hydraulic cleaning (increasing crossflow velocity) efficiency to restore the water flux is up to 82%. When scaling occurs on the support layer of the FO membrane, the hydraulic cleaning efficiency is strongly reduced, with only 36% of the water flux recovered. The present study reveals the risk of scaling induced by the interaction of feed solute and draw solute, which is different from the scaling caused by the supersaturation in reverse osmosis and other FO studies reported. The scaling investigated in this study can occur with a very low solute concentration at an early stage of the FO process. This finding provides an important implication for selection of draw solution and development of new membranes in the FO process.
Research Interests: Scaling()
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Due to the stringent limits for boron in drinking and irrigation water, water treatment facilities have to incur additional treatment to remove boron down to a safe concentration. Forward osmosis (FO) is a membrane technology that may... more
Due to the stringent limits for boron in drinking and irrigation water, water treatment facilities have to incur additional treatment to remove boron down to a safe concentration. Forward osmosis (FO) is a membrane technology that may reduce the energy required to remove boron present in seawater. In direct FO desalination hybrid systems, fresh water is recovered from seawater using a recoverable draw solution, FO membranes are expected to show high boron rejection. This study focuses on determining the boron rejection capabilities of a new generation thin-film composite (TFC) FO membrane compared to a first generation cellulose triacetate (CTA) FO membrane. The effects of water permeate flux, membrane structure, draw solute charge, and reverse solute flux on boron rejection were determined. For TFC and CTA FO membranes, experiments showed that when similar operating conditions are applied (e.g. membrane type and draw solute type) boron rejection decreases with increase in permeate flux. Reverse draw solute flux and membrane fouling have no significant impact on boron rejection. Compared to the first generation CTA FO membrane operated at the same conditions, the TFC FO membrane showed a 40% higher boron rejection capability and a 20% higher water flux. This demonstrates the potential for boron removal for new generation TFC FO membranes.
Research Interests: Biofilms()
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Forward osmosis (FO) presents a unique opportunity for integrated wastewater treatment and seawater desalination. This study assesses the efficiency of a submerged FO system to reduce the volume of wastewater that needs to be treated... more
Forward osmosis (FO) presents a unique opportunity for integrated wastewater treatment and seawater desalination. This study assesses the efficiency of a submerged FO system to reduce the volume of wastewater that needs to be treated while recovering high quality water that can be further treated for sustainable fresh water production. A semi-batch operation was employed with two membrane orientations in terms of active and support layers. A change of membrane orientation could improve the flux and slightly reduce the salt leakage from the draw solution to the feed solution. The formation of fouling on the membrane resulted in a decrease of the initial flux and average flux with both membrane orientations. The fouling layer on the membrane surface was determined to be caused by biopolymer-like substances. Osmotic backwash removed almost all organic foulants from the membrane surface, but did not improve the flux. There was a moderate to high retention of nutrients (N and P), varying from 56% to 99%, and almost a complete retention for trace metals regardless of membrane orientation. However the membrane showed a limited ability to retain low molecular weight acids and low molecular weight neutral compounds. This study identified a possible role of the FO process to integrate wastewater treatment and seawater desalination for a sustainable solution of the water-energy nexus for coastal cities.
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A two-dimensional mathematical model coupling fluid dynamics, salt and substrate transport and biofilm development in time was used to investigate the effects of cross-flow velocity and substrate availability on biofouling in reverse... more
A two-dimensional mathematical model coupling fluid dynamics, salt and substrate transport and biofilm development in time was used to investigate the effects of cross-flow velocity and substrate availability on biofouling in reverse osmosis (RO)/nanofiltration (NF) feed channels. Simulations performed in channels with or without spacer filaments describe how higher liquid velocities lead to less overall biomass amount in the channel by increasing the shear stress. In all studied cases at constant feed flow rate, biomass accumulation in the channel reached a steady state. Replicate simulation runs prove that the stochastic biomass attachment model does not affect the stationary biomass level achieved and has only a slight influence on the dynamics of biomass accumulation. Biofilm removal strategies based on velocity variations are evaluated. Numerical results indicate that sudden velocity increase could lead to biomass sloughing, followed however by biomass re-growth when returning to initial operating conditions. Simulations show particularities of substrate availability in membrane devices used for water treatment, e.g., the accumulation of rejected substrates at the membrane surface due to concentration polarization. Interestingly, with an increased biofilm thickness, the overall substrate consumption rate dominates over accumulation due to substrate concentration polarization, eventually leading to decreased substrate concentrations in the biofilm compared to bulk liquid.
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The impact of biofi lms on reverse osmosis (RO) membrane performance loss was studied using a two-dimensional mathematical model that couples fl uid dynamics, salt and substrate mass transport and biofi lm development. Decline in the... more
The impact of biofi lms on reverse osmosis (RO) membrane performance loss was studied using a two-dimensional mathematical model that couples fl uid dynamics, salt and substrate mass transport and biofi lm development. Decline in the permeate fl ux was simulated at different salt concentrations in the feed assuming: (i) the same feed pressure and (ii) pressures adjusted for constant initial fl ux. The pattern of biofi lm development in the spacer-fi lled membrane channel was similar for all cases. Numerical results indicated that the detrimental effect of a biofi lm is more pronounced for higher salinity of the feed, effect mainly due to the biofi lm-enhanced concentration polarization. When pressure is increased to compensate for the osmotic pressure created by higher salt in feed, the local fl ux under the biofi lm strongly deteriorates while a slight fl ux enhancement is observed in biofi lm-free areas. Parametric variation within commonly measured range of biofi lm permeability did not affect strongly the fl ux. Smaller effective diffusion coeffi cients of salt in the biofi lm slightly decreased the permeate fl ux.
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A two-dimensional (2-d) mathematical model describing the effect of biofilm development on the performance of a spiral-wound reverse osmosis (RO) membrane device was developed. The micro-scale model combines hydrodynamics and mass... more
A two-dimensional (2-d) mathematical model describing the effect of biofilm development on the performance of a spiral-wound reverse osmosis (RO) membrane device was developed. The micro-scale model combines hydrodynamics and mass transport of solutes (salt and substrate) with biomass attachment, biofilm growth and detachment due to mechanical stress induced by liquid flow in the feed channel. The model explains several experimental observations when operating at constant pressure: loss of permeate flux with increased salt passage in time and achievement of a quasi-steady state flux and biomass amount. The model also shows how the local balance between biofilm growth and detachment leads to irregular biofilm distribution in the feed channel and suggests places where most biomass accumulation is expected. Numerical simulations were performed in configurations without spacer or with different spacer geometries (submerged, cavity and zigzag). Three mechanisms were identified by which biofilms on RO membranes contribute to performance loss: (i) biofilm-enhanced concentration polarization; (ii) increased hydraulic resistance to trans-membrane flow; and (iii) increased feed channel pressure drop. For seawater and brackish water desalination, biofilm-enhanced concentration polarization appears to affect most the local flux. This modeling approach, combining computational fluid dynamics (CFD) with biofilm models allows a systematic study of biofouling in membrane systems. Moreover the approach is useful for improving feed spacer design and to evaluate operational conditions for minimum biofouling of reverse osmosis and nanofiltration (NF) membrane devices.
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Reverse osmosis (RO) is an important membrane separation process, widely used for desalination applications. RO is part of a rapidly growing market as the demand for clean fresh water around the world continues to expand. A major... more
Reverse osmosis (RO) is an important membrane separation process, widely used for desalination applications. RO is part of a rapidly growing market as the demand for clean fresh water around the world continues to expand. A major industrial challenge for RO operations is control of fouling of the membrane modules. Fouling decreases production capacity and water quality and increases operating costs. Biofilm growth in the membrane modules, commonly referred to as biofouling, is in practice arguably the major fouling type. Different cleaning strategies are employed to remove such foulants and evaluation of cleaning effectiveness is often difficult, with operators relying on indirect measurements of fouling such as the pressure drop across the membrane module. The present study aims to evaluate chemical cleaning of biofouled RO membranes using magnetic resonance imaging (MRI). Membrane fouling simulators (MFS) were fouled in the laboratory, then subsequently cleaned using combinations of sodium dodecyl sulphate (SDS) and sodium hydroxide (NaOH) and observed using MRI. Both MRI structural and velocity images showed marked changes in biofilm distribution. A small volume of accumulated biomass had a large impact on the effective surface area for water production, the value of which was more accurately calculated using the velocity images. The extracted effective membrane surface area correlated well with the feed channel pressure drop. Additionally with this in situ MRI technique, the effect of fouling extent and time on cleaning effectiveness (biomass removal and effective surface area) were investigated. Cleanings at an early stage of biofouling was more efficient in removing biomass than cleaning performed at a later stage.
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Studies with a new tool — the Membrane Fouling Simulator (MFS) — illustrate that the MFS can be used to quantify and characterize fouling. Using the MFS, fouling can be monitored by (1) operational parameters like pressure drop, (2)... more
Studies with a new tool — the Membrane Fouling Simulator (MFS) — illustrate that the MFS can be used to quantify and characterize fouling. Using the MFS, fouling can be monitored by (1) operational parameters like pressure drop, (2) non-destructive (visual, microscopic) observations using the sight glass and (3) analysis of coupons sampled from the membrane sheet in the MFS. The small scale of the MFS makes it easy to handle and requires small amounts of water and chemicals, enhancing the possibility to test several MFS units in parallel. A comparison study of the MFS and spiral-wound membrane modules showed the same fouling. The MFS is representative for spiral membrane elements, indicating that the MFS is suitable to study and monitor biofouling.
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Operational problems in membrane installations used in water treatment can be caused by a variety of fouling types. Therefore, a systematic approach based on the application of an autopsy of membrane elements followed by analysis has been... more
Operational problems in membrane installations used in water treatment can be caused by a variety of fouling types. Therefore, a systematic approach based on the application of an autopsy of membrane elements followed by analysis has been developed, which enables an integral diagnosis of the type and extent of fouling. Analysis includes both biological parameters for biomass quantification (ATP) and biomass characterisation and chemical parameters for determining the presence of inorganic compounds (ICP-MS). Advantages of this approach include: first, complete and conclusive information about the nature and extent of fouling of the membrane filtration plant; and secondly, rapid diagnosis (within 8 hours) of biofouling. In addition to membrane element analysis, also a suite of monitoring tools (AOC test, biofilm monitor, oxygen consumption monitor and scaleguard) is available for elucidation and control of the processes responsible for the fouling problems. These tools can also be used to test chemicals for their effect on (bio)fouling. Research is continuing to substantiate relationships between test parameters and the extent of operational problems.
Research Interests: Fouling()
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