Wim Doyen

The use of bacteria immobilized in tubular membrane reactors for heavy metal recovery and degradation of chlorinated aromatics

Abstract Microbial treatments of waste water can be done in membrane reactors. A membrane installed outside the reactor is used to separate bacteria from the treated effluent. A new membrane reactor concept is presented. The separation membrane is introduced in the reactor and not outside as in a normal one. The membrane plays the role of a separator of two streams and is used at the same time as the immobilizing support for the bacteria. The reactor keeps the bacteria active via a specific nutrient stream that is provided on one side of the membrane. The bacteria grow in and on the membrane where they form an active biofilm. The bacteria can treat the effluent on one side and can be kept active via the nutrient stream at the other side without contamination of the effluent by the nutrient. In this work, the performance of the BICMER (Bacteria Immobilized Composite MEmbrane Reactor) is demonstrated via treatments of effluents containing heavy metals or organic xenobiotics. For heavy metal removal Alcaligenes eutrophus CH34 bacteria were used. These bacteria induce a metal bioprecipitation process that results in the formation of crystalline metal carbonates, which are recovered on a separate column in the reactor. In this way metals can be recovered without disturbing the biofilm on the membrane. Metals such as Cd, Zn, Cu, Pb and Y can be reduced to less than 50 ppb. The metals Co, Ni, Pd and Ge are reduced to below 100 ppb. For organic xenobiotics Alcaligenes eutrophus AE1308 bacteria or other strains (depending on the xenobiotic to be degraded) were used. This strain degrades the xenobiotic 3-chlorobenzoate (Cba) and 2,4-dichlorophenoxyacetic acid to CO2, H2O and chloride). Concentrations of 3 mM Cba could be reduced to less than 0.1 mM. For other toxic organic compounds, different biodegrading strains need to be used.

A comparison between polysulfone, zirconia and organo-mineral membranes for use in ultrafiltration

Abstract In this paper, representative polymeric (a PSf/PVP membrane), ceramic (a ZrO 2 membrane) and organo-mineral (a ZrO 2 /PSf membrane) ultrafiltration membranes, all in the tubular configuration, are being compared for their basic membrane properties, and for the typical ultrafiltration application of protein recovery of cheese whey. These three different membranes with a quite similar pore size (the cut-off values for each of the three membranes were comprised between 25 000 and 50 000 Dalton) showed pure water permeability coefficients between 135 and 1250 l/h m 2 bar. The highest pure water flux was found for the organo-mineral membrane, the lowest for the polymeric membrane. By FESEM analysis of the top-surfaces (skin) of both the PSf/PVP and the ZrO 2 /PSf membrane a strong difference in surface-porosity was found. These results were claimed to partially explain the difference in pure water flux. From SEM pictures of the cross-section of the ZrO 2 /PSf membrane it could also be seen that the skin layer thickness is smaller, at these places where particles are present near the skin-surface, compared to the rest of the membrane as well as to the skin of the PSf/PVP membrane. These latter observations were also used to further explain the flux difference between the PSf/PVP and the ZrO 2 /PSf membrane. In application tests (ultrafiltration of a sweet Gouda cheese whey) these three rather different membranes surprisingly showed practically the same gel-layer controlled or plateau fluxes, the same flux stability, and flux/concentration factor behaviour. The protein retention in all the experiments was 99% or more. The permeability coefficient however for this sweet Gouda whey was identical for the PSf/PVP and the ZrO 2 membrane and equal to 50 l/h m 2 bar. On the contrary for the ZrO 2 /PSf organo-mineral membrane a nearly three fold higher permeability coefficient of 135 l/h m 2 bar was found. This property is partly attributed to the much higher surface porosity of the organo-mineral membrane as compared to the polymeric membrane. From this comparison one may conclude that for high fouling applications, the only positive effect upon using membranes with high permeability coefficients is a reduced transmembrane pressure for a given flux. However, for low fouling applications distinct gains in terms of flux can be expected upon using such membranes.

A new method of measuring and presenting the membrane fouling potential

The silt density index (SDI) and modified fouling index (MFI) characterisation methods are well known for the evaluation of membrane fouling potential of dispersed particulate matter (suspended solids, colloids) in a feed. The SDI and MFI methods, however, reduce the overall and very complex fouling phenomena into a one number value, on which the interpretation of the fouling potential of the feed is based. Considering such a one number characteristic, a significant amount of information from the fouling measurement (data) is lost. In this paper a concept is introduced in order to preserve such information and supplement the existing indexes. The proposed method measures, processes and presents data in a specific format. To illustrate the concept, some results are shown from measurements on three types of feed. Future systematic research will also include the measurement on some model feeds with, for example, well characterised dispersions for comparison purposes. However, based on the contents of this paper, a discussion on the method could be initiated.

Characterization and optimization of β-galactosidase immobilization process on a mixed-matrix membrane.

β-Galactosidase is an important enzyme catalyzing not only the hydrolysis of lactose to the monosaccharides glucose and galactose but also the transgalactosylation reaction to produce galacto-oligosaccharides (GOS). In this study, β-galactosidase was immobilized by adsorption on a mixed-matrix membrane containing zirconium dioxide. The maximum β-galactosidase adsorbed on these membranes was 1.6 g/m², however, maximal activity was achieved at an enzyme concentration of around 0.5 g/m². The tests conducted to investigate the optimal immobilization parameters suggested that higher immobilization can be achieved under extreme parameters (pH and temperature) but the activity was not retained at such extreme operational parameters. The investigations on immobilized enzymes indicated that no real shift occurred in its optimal temperature after immobilization though the activity in case of immobilized enzyme was better retained at lower temperature (5 °C). A shift of 0.5 unit was observed in optimal pH after immobilization (pH 6.5 to 7). Perhaps the most striking results are the kinetic parameters of the immobilized enzyme; while the Michaelis constant (K(m)) value increased almost eight times compared to the free enzyme, the maximum enzyme velocity (V(max)) remained almost constant.

Latest developments in ultrafiltration for large-scale drinking water applications☆

Abstract In view of the implementation of ultrafiltration for large-scale drinking water applications, the properties of the membranes, the types of modules and the mode of operation had to be reviewed. In this respect the surface porosity and adsorption characteristics of the membranes were improved, module sizes were adapted, and the semi-dead operational mode was pioneered. Thus treatment costs could be lowered to about DM 0.2–0.4/m 3 of treated permeate. This makes ultrafiltration a very promising unit operation for the next century. In this paper the most recent largescale applications of the players in this field will be discussed.

Reverse membrane bioreactor : Introduction to a new technology for biofuel production

The novel concept of reverse membrane bioreactors (rMBR) introduced in this review is a new membrane-assisted cell retention technique benefiting from the advantageous properties of both conventional MBRs and cell encapsulation techniques to tackle issues in bioconversion and fermentation of complex feeds. The rMBR applies high local cell density and membrane separation of cell/feed to the conventional immersed membrane bioreactor (iMBR) set up. Moreover, this new membrane configuration functions on basis of concentration-driven diffusion rather than pressure-driven convection previously used in conventional MBRs. These new features bring along the exceptional ability of rMBRs in aiding complex bioconversion and fermentation feeds containing high concentrations of inhibitory compounds, a variety of sugar sources and high suspended solid content. In the current review, the similarities and differences between the rMBR and conventional MBRs and cell encapsulation regarding advantages, disadvantages, principles and applications for biofuel production are presented and compared. Moreover, the potential of rMBRs in bioconversion of specific complex substrates of interest such as lignocellulosic hydrolysate is thoroughly studied.

Continuous Bioethanol Fermentation from Wheat Straw Hydrolysate with High Suspended Solid Content Using an Immersed Flat Sheet Membrane Bioreactor

Finding a technological approach that eases the production of lignocellulosic bioethanol has long been considered as a great industrial challenge. In the current study a membrane bioreactor (MBR) set-up using integrated permeate channel (IPC) membrane panels was used to simultaneously ferment pentose and hexose sugars to ethanol in continuous fermentation of high suspended solid wheat straw hydrolysate. The MBR was optimized to flawlessly operated at high SS concentrations of up to 20% without any significant changes in the permeate flux and transmembrane pressure. By the help of the retained high cell concentration, the yeast cells were capable of tolerating and detoxifying the inhibitory medium and succeeded to co-consume all glucose and up to 83% of xylose in a continuous fermentation mode leading to up to 83% of the theoretical ethanol yield.

The recovery of backwash water from sand filters by ultrafiltration

Abstract Groundwater is still one of the main sources for the production of drinking water. In the preparation of drinking water, the groundwater is first aerated and then filtered through a sand filter in order to remove Fe, Mn, NH4 and methane. After saturation, these sand filters have to be backwashed periodically. In the past, the backwash water was discharged in the sewage either directly or after sedimentation. However, the first pilot trials with ultrafiltration showed already in 1995 that this technique was very promising for the recovery of backwash water. As a result, the first full-scale ultrafiltration installation was built at the drinking water company NRE (Nutsbedrijf Regio Eindhoven, now WOB) in Eindhoven, Holland, in 1997. A Belgian drinking water company started in the beginning of 1998, in collaboration with Vito, with pilot testing on this subject. Long-term experiments were carried out at four different locations, with different water qualities. At one location the backwash water coming directly from the sand filters (bulk fraction) was filtered; at the other locations the supernatant, which is formed after sedimentation in a settler, was used as feed for the UF pilot. As a result of the sedimentation process, the Fe content is lower in the supernatant than in the bulk fraction. The experiments were done with two different membranes: X-Flow and Stork. Both membranes are operating in dead-end mode with a standard backwash procedure in a very reliable and stable way. Special attention was given to the optimization of the chemical cleaning procedure and the permeate quality in respect of colony forming units (CFU). At the last location, a set of short-term experiments was carried out in order to get more insight in the fouling behaviour of the backwash water. Therefore, different operation modes were compared (low-high fluxes, short-long filtration time), keeping the dirt load either constant or variable. These results will also be discussed in this paper.

Methodology for accelerated pre-selection of UF type of membranes for large scale applications☆

This paper describes two assessment methods for UF type of membranes for large-scale applications. The combination of those two methods results in quite clear and unambiguous answers to the question what membranes are of interest for long-term testing. With the first method, called dead-end filtration method, information is generated on the suitability of the membrane and on the combination of the membrane material, the module hydraulics and assembly. With this method the evolution of TMP is monitored upon filtration cycles of 20 minutes with raw water at a flux rate of 120 l/h.m 2 , alternated with backwash cycles with permeate of 40 seconds at 1.2 bar negative TMP. The second method, called cross-flow filtration method, gives exclusively information on the suitability of the membrane material. This is being done by the measurement of the absolute value of the so-called plateau fluxes in cross-flow mode at 0.2 m/s linear velocity. For this purpose raw water concentrates are being used. Three open UF type of membranes, all three in hollow fibre configuration were assessed with these two methods. It was shown that the PSf based membrane (Koch PM100) reached already after 4 filtration cycles a TMP of 1 bar and showed the lowest plateau flux (25 l/h.m 2 ). This indicated that the membrane suffered from interaction with the raw water. Moreover, it is possible that something was wrong with the hydraulics of this membrane. The two other membranes were PES/PVP based. These membranes showed much less TMP increase over time. The first membrane of this type was X-Flow UFC, the second Stork Friesland Superfil 015-010. It was no problem to operate the first membrane for 18 hours without addition of chemicals for cleaning. The second membrane reached the maximum allowed TMP of 1 bar after 16 hours of operation at the end of the filtration cycle. Moreover, for both membranes a higher plateau flux value (35 l/h.m 2 ) was found. Both observations indicate that this type of membrane material is much more interesting than PSf. It was also shown that the X-Flow membrane gives the lowest absolute TMP values, which is attributed to its higher pure water permeability (740 l/h.m 2 .bar) as compared to the Stork Friesland membrane (pure water permeability of 350 l/h.m 2 .bar) and the Koch membrane (pure water permeability of 290 l/h.m 2 .bar). A last observation was a TMP increase of only 0.1 bar per cycle for the X-Flow membrane, as compared to 0.2 bar for the two others. This observation is in agreement with earlier made FESEM pictures of the inner surfaces. This means that the X-Flow membrane rather acts as a depth filter, whereas the two other membranes act as a surface filter.

Characterization and analysis of the adsorption immobilization mechanism of β-galactosidase on metal oxide powders

Immobilization of the enzymes plays a vital role in enhancing their applicability in a wide range of applications, thus ensuring the use of sustainable enzymatic processes over the conventional chemical processes on an industrial scale. This study provides the background information for the selection and screening of inorganic metal oxide (MO) powders for their use as fillers in mixed matrix membranes for enzyme immobilization as the future aim. A total of 13 MOs, ranging in size from 0.01 μm to 3 times higher than ZrO2 (used as a reference MO in this study). Upon heat treatment at 900 °C, up to 15%, 52% and 42% decline was observed in the amount of immobilized enzyme in case of alumina metal oxides (MOs), ZrO2 and TiO2, respectively. The results suggested that both isoelectric point and surface area of the MO influence the immobilization. The most important observation in this study was that the bonding of the enzyme to the MO surface seems to be mediated by the bonding/interaction of the buffer to the enzyme.