Stephen Kroll

Amino-Functionalized Ceramic Capillary Membranes for Controlled Virus Retention

A straightforward chemical functionalization strategy using aminosilanes for high-flux yttria-stabilized zirconia capillary membranes is presented (macroporous, d50 = 144 nm, open porosity =49%, membrane flux ∼150 L/(m(2)hbar)). Three different aminosilanes with one, two or three amino groups per silane molecule, namely 3-aminopropyltriethoxysilane (APTES), N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AE-APTES) and N-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA), are used to generate the amino-functionalized membranes. With a higher number of amino groups per silane molecule increased loading capacities between 0.44 and 1.01 accessible amino groups/nm(2) membrane are achieved. Streaming potential measurements confirm that the zeta-potential of the membrane surface is converted from negative (non-functionalized) to positive (amino-functionalized). By operation in dead-end filtration mode using the model virus MS2 (diameter = 25 nm, IEP = 3.9) the virus retention capacity of the amino-functionalized membranes is significantly increased and log reduction values (LRVs) of up to 9.6 ± 0.3 (TPDA) are obtained whereas a LRV < 0.3 is provided by the non-functionalized membranes. Long-term dead-end filtration experiments for 1 week reveal a high stability of immobilized aminosilanes (TPDA), being robust against leaching. By iterative backflushing with desorption buffer MS2-loaded membranes are successfully regenerated being reusable for a new filtration cycle. The presented functionalization platform is highly promising for controlled virus retention.

Hierarchical Porous Zeolite Structures for Pressure Swing Adsorption Applications.

Porous adsorbents with hierarchical structured macropores ranging from 1 to 100 μm are prepared using a combination of freeze casting and additional sacrificial templating of polyurethane foams, with a zeolite 13X powder serving as adsorbent. The pore system of the prepared monoliths features micropores assigned to the zeolite 13X particle framework, interparticular pores of ∼1-2 μm, lamellar pores derived from freeze casting of ∼10 μm, and an interconnected pore network obtained from the sacrificial templates ranging from around 100 to 200 μm with a total porosity of 71%. Gas permeation measurements show an increase in intrinsic permeability by a factor of 14 for monoliths prepared with an additional sacrificial templated foam compared to monoliths solely providing freeze casting pores. Cyclic CO2 adsorption and desorption tests where pressure swings between 8 and 140 kPa reveal constant working capacities over multiple cycles. Furthermore, the monoliths feature a high volumetric working capacity of ∼1.34 mmol/cm(3) which is competitive to packed beds made of commercially available zeolite 13X beads (∼1.28 mmol/cm(3)). Combined with the faster CO2 uptake showing an adsorption of 50% within 5-8 s (beads ∼10 s), the monoliths show great potential for pressure swing adsorption applications, where high volumetric working capacities, fast uptakes, and low pressure drops are needed for a high system performance.

Silver nanoparticle-doped zirconia capillaries for enhanced bacterial filtration

Abstract Membrane clogging and biofilm formation are the most serious problems during water filtration. Silver nanoparticle (Agnano) coatings on filtration membranes can prevent bacterial adhesion and the initiation of biofilm formation. In this study, Agnano are immobilized via direct reduction on porous zirconia capillary membranes to generate a nanocomposite material combining the advantages of ceramics being chemically, thermally and mechanically stable with nanosilver, an efficient broadband bactericide for water decontamination. The filtration of bacterial suspensions of the fecal contaminant Escherichia coli reveals highly efficient bacterial retention capacities of the capillaries of 8 log reduction values, fulfilling the requirements on safe drinking water according to the U.S. Environmental Protection Agency. Maximum bacterial loading capacities of the capillary membranes are determined to be 3×109 bacterialcells/750mm2 capillary surface until back flushing is recommendable. The immobilized Agnano remain accessible and exhibit strong bactericidal properties by killing retained bacteria up to maximum bacterial loads of 6×108 bacterialcells/750mm2 capillary surface and the regenerated membranes regain filtration efficiencies of 95–100%. Silver release is moderate as only 0.8% of the initial silver loading is leached during a three-day filtration experiment leading to average silver contaminant levels of 100μg/L.

Development of a Novel Membrane Aerated Hollow-Fiber Microbioreactor

A new challenge in biotechnological processes is the development of flexible bioprocessing platforms, allowing strain selection, facilitating scale‐up and integrating separation steps. Miniaturization of such a cultivation system allows parallel use and the saving of resources but makes the supply of oxygen to the cells difficult. In this work we present a membrane aerated hollow‐fiber microbioreactor (HFMBR) which consists of an acrylic glass module equipped with two different types of membrane fibers. Fibers of polyethersulfone and polyvinyldifluoride were used for substrate and oxygen supply, respectively. Cultivation of E. coli as model organism and production of His‐tagged GFP were carried out in the extracapillary space of the membrane aerated HFMBR and compared with cultivations in shaking flask which are commonly used for screening experiments. The measurement of the oxygen transfer capacity and the online monitoring of the dissolved oxygen during the cultivation were performed using a fiber optic oxygen sensor. Online measurement of the optical density was also integrated to the bioreactor. Due to efficient oxygen transfer, a better cell growth than in the shaking flask experiments was achieved, while no negative influence on the GFP productivity was observed in the membrane aerated bioreactor. Thus the feasibility of a future integrated downstreaming could also be demonstrated.

Vibrational Spectroscopy as a Promising Toolbox for Analyzing Functionalized Ceramic Membranes

Ceramic materials find use in many fields including the life sciences and environmental engineering. For example, ceramic membranes have shown to be promising filters for water treatment and virus retention. The analysis of such materials, however, remains challenging. In the present study, the potential of three vibrational spectroscopic methods for characterizing functionalized ceramic membranes for water treatment is evaluated. For this purpose, Raman scattering, infrared (IR) absorption, and solvent infrared spectroscopy (SIRS) were employed. The data were analyzed with respect to spectral changes as well as using principal component analysis (PCA). The Raman spectra allow an unambiguous discrimination of the sample types. The IR spectra do not change systematically with functionalization state of the material. Solvent infrared spectroscopy allows a systematic distinction and enables studying the molecular interactions between the membrane surface and the solvent.

Adverse Effects of Immobilised Pseudoalteromonas on the Fish Pathogenic Vibrio anguillarum: An In Vitro Study

As a prerequisite for use in marine aquaculture, two immobilisation systems were developed by employing the probiotic bacterium Pseudoalteromonas sp. strain MLms_gA3. Their impact on the survivability of the fish pathogen Vibrio anguillarum was explored. Probiotic bacteria either grown as a biofilm on ceramic tiles or embedded in alginate beads were added to sterile artificial seawater that contained the fish pathogen. While immobilisation on ceramics followed a recently developed protocol, a medium allowing for alginate microencapsulation was newly developed. Anti-Vibrio activities were obtained with both immobilisation systems. The viable cell counts of V. anguillarum constantly decreased within the first two weeks of the treatments evidencing the potential of the immobilisation systems for providing probiotic-based protection against this pathogen.

ON THE PERFORMANCE OF POROUS SOUND ABSORBENT CERAMIC LINING IN A COMBUSTION CHAMBER TEST RIG

This paper discusses the potential of using porous ceramic lining as insulating material in combustion chambers with respect to their sound absorbent ability to suppress thermoacoustic instabilities. For this purpose a combustion chamber test rig was developed and different types of ceramic linings were tested. The examined range of power was between 40 and 250 kW and the air-propane equivalence ratio was between 1.2 and 2.0. The overall sound pressure level and frequency domain of a lean premixed swirl stabilized and piloted burner are presented. The resonance frequencies and sound pressure levels are obtained and compared for the different combustion chamber linings. The results show a significant decrease in overall sound pressure level by up to 23.5 dB for sound absorbent lining in comparison to the common sound reflecting combustion chamber lining. In summary, sound absorbent ceramic combustion chamber lining can contribute to improve the stability of lean premixed gas turbines.Copyright

Straightforward Processing Route for the Fabrication of Robust Hierarchical Zeolite Structures

Strong hierarchical porous zeolite structures are prepared by a sol–gel method using freeze gelation. Instead of conventional binders in powder form, such as bentonite or kaolin, it has been proven that using a freeze gelation method based on a colloidal silica sol is a more straightforward and easier-to-use-approach in fabricating highly mechanically stable zeolite monoliths. The resulting zeolite slurries possess superior rheological properties (not being pseudoplastic) and show low viscosities. This low viscosity of the slurry enables an increase in the solid content without compromising the extraordinary good flow behavior for casting applications. Additionally, in comparison to conventional powdery binders, zeolite samples prepared by using a colloidal silica sol exhibit a significantly higher mechanical strength. This mechanical strength can be further improved by either increasing the zeolite content or increasing the silica to zeolite ratio. Increasing the zeolite content leads to an increased volumetric adsorption capacity for CO2 as the test gas, resulting from the increased amount of zeolite particles per unit volume. In addition, a higher solid content of the zeolite monoliths leads to higher compression strengths, while showing the same elastic deformation and brittle failure characteristics. In turn, increasing the silica to zeolite ratio does not affect the volumetric adsorption capacity for CO2. Nevertheless, higher silica contents lead to a significant increase in the elastic deformation and absorbed work until failure. Therefore, the proposed processing route based on freeze gelation presents an easy and unique tool to tune the mechanical and gas adsorptive properties of hierarchically structured zeolite monoliths, according to the application requirements.