Geoffrey W. Stevens

Innovations in separations technology for the recycling and re-use of liquid waste streams

As the costs of wastewater disposal increase more emphasis is being placed upon the recovery and recycling of valuable chemicals contained within these streams. In this article, we review three separations technologies that facilitate such recycling. Solvent extraction is an established technique for recovery of heavy metals and other pollutants and is most useful in large and medium scale operations when solute concentrations are high. Membrane technology is a more recent development that can be used in conjunction with extraction solvents to extend the range of conditions under which such processes are viable. Finally, adsorption and ion-exchange processes provide the means for extracting valuable contaminants when the concentrations of such so lutes are low.

New murine model of spontaneous autologous tissue engineering, combining an arteriovenous pedicle with matrix materials

The authors previously described a model of tissue engineering in rats that involves the insertion of a vascular pedicle and matrix material into a semirigid closed chamber, which is buried subcutaneously. The purpose of this study was to develop a comparable model in mice, which could enable genetic mutants to be used to more extensively study the mechanisms of the angiogenesis, matrix production, and cellular migration and differentiation that occur in these models. A model that involves placing a split silicone tube around blood vessels in the mouse groin was developed and was demonstrated to successfully induce the formation of new vascularized tissue. Two vessel configurations, namely, a flow-through pedicle (n = 18 for three time points) and a ligated vascular pedicle (n = 18), were compared. The suitability of chambers constructed from either polycarbonate or silicone and the effects of incorporating either Matrigel equivalent (n = 18) or poly(dl-lactic-co-glycolic acid) (n = 18) on angiogenesis and tissue production were also tested. Empty chambers, chambers with vessels only, and chambers with matrix only served as control chambers. The results demonstrated that a flow-through type of vascular pedicle, rather than a ligated pedicle, was more reliable in terms of patency, angiogenesis, and tissue production, as were silicone chambers, compared with polycarbonate chambers. Marked angiogenesis occurred with both types of extracellular matrix scaffolds, and there was evidence that native cells could migrate into and survive within the added matrix, generating a vascularized three-dimensional construct. When Matrigel was used as the matrix, the chambers filled with adipose tissue, creating a highly vascularized fat flap. In some cases, new breast-like acini and duct tissue appeared within the fat. When poly(dl-lactic-co-glycolic acid) was used, the chambers filled with granulation and fibrous tissue but no fat or breast tissue was observed. No significant amount of tissue was generated in the control chambers. Operative times were short (25 minutes), and two chambers could be inserted into each mouse. In summary, the authors have developed an in vivo murine model for studying angiogenesis and tissue-engineering applications that is technically simple and quick to establish, has a high patency rate, and is well tolerated by the animals.

The Influence of Extracellular Matrix on the Generation of Vascularized, Engineered, Transplantable Tissue

Abstract: In a recently described model for tissue engineering, an arteriovenous loop comprising the femoral artery and vein with interposed vein graft is fabricated in the groin of an adult male rat, placed inside a polycarbonate chamber, and incubated subcutaneously. New vascularized granulation tissue will generate on this loop for up to 12 weeks. In the study described in this paper three different extracellular matrices were investigated for their ability to accelerate the amount of tissue generated compared with a no‐matrix control. Poly‐d,l‐lactic‐co‐glycolic acid (PLGA) produced the maximal weight of new tissue and vascularization and this peaked at two weeks, but regressed by four weeks. Matrigel was next best. It peaked at four weeks but by eight weeks it also had regressed. Fibrin (20 and 80 mg/ml), by contrast, did not integrate with the generating vascularized tissue and produced less weight and volume of tissue than controls without matrix. The limiting factors to growth appear to be the chamber size and the capacity of the neotissue to integrate with the matrix. Once the sides of the chamber are reached or tissue fails to integrate, encapsulation and regression follow. The intrinsic position of the blood supply within the neotissue has many advantages for tissue and organ engineering, such as ability to seed the construct with stem cells and microsurgically transfer new tissue to another site within the individual. In conclusion, this study has found that PLGA and Matrigel are the best matrices for the rapid growth of new vascularized tissue suitable for replantation or transplantation.

Separation of biological molecules using mesoporous molecular sieves

The selective separation and purification of biological molecules is important in a number of industries, especially those processing food or pharmaceuticals. However, the applications of molecular sieves for these separations have been limited by the available pore sizes (<1.5 nm). With the development of synthetic mesoporous molecular sieves the available pore size range has been extended, providing pores large enough to allow access for a number of biological molecules. These materials have unique properties desirable for adsorption including a highly regular structure, uniform pore sizes and a high surface area, thus offering potential for separations based on size exclusion and targeted surface chemistry. They can also be tailored to suit particular separations and are expected to have advantages over currently used adsorbents, such as bentonite and activated carbon. This work investigates the use of mesoporous molecular sieves for the separation of biological molecules. Adsorption experiments involving proteins (lysozyme and trypsin) and a vitamin (riboflavin), as model biological solutes, have been conducted to assess the potential of MCM-41 and MCM-48 as selective adsorbents. The results demonstrate the potential of these materials for use in size exclusion separations.

Dynamic interactions between microbubbles in water

The interaction between moving bubbles, vapor voids in liquid, can arguably represent the simplest dynamical system in continuum mechanics as only a liquid and its vapor phase are involved. Surprisingly, and perhaps because of the ephemeral nature of bubbles, there has been no direct measurement of the time-dependent force between colliding bubbles which probes the effects of surface deformations and hydrodynamic flow on length scales down to nanometers. Using ultrasonically generated microbubbles (∼100 μm size) that have been accurately positioned in an atomic force microscope, we have made direct measurements of the force between two bubbles in water under controlled collision conditions that are similar to Brownian particles in solution. The experimental results together with detailed modeling reveal the nature of hydrodynamic boundary conditions at the air/water interface, the importance of the coupling of hydrodynamic flow, attractive van der Waals–Lifshitz forces, and bubble deformation in determining the conditions and mechanisms that lead to bubble coalescence. The observed behavior differs from intuitions gained from previous studies conducted using rigid particles. These direct force measurements reveal no specific ion effects at high ionic strengths or any special role of thermal fluctuations in film thickness in triggering the onset of bubble coalescence.

Ammonia Removal from Wastewaters Using Natural Australian Zeolite. I. Characterization of the Zeolite

This study considered the potential of a natural Australian zeolite, clinoptilolite, to remove ammonium from water. Ammonium-exchange capacity and rates of adsorption are critical to the assessment of the feasibility of the zeolite for application to continuous wastewater treatment. A laboratory study was undertaken, using pure solutions, to investigate the equilibria and kinetic characteristics of ammonium exchange in the zeolite. Binary equilibrium experiments provided information on the adsorption characteristics of the zeolite in terms of ammonia capacity at varying solution concentrations. These experiments also revealed that the highest ammonium removal efficiency was achieved when the zeolites exchange sites were converted to the sodium form. Multicomponent equilibrium experiments were carried out to determine the effects of competing cations on the ammonium-exchange capacity of the zeolite. The laboratory study indicated the zeolites selectivity for ammonium ions over other cations typically pre...

Ammonia Removal from Wastewaters Using Natural Australian Zeolite. II. Pilot-Scale Study Using Continuous Packed Column Process

A pilot-scale process was designed and operated to investigate the continuous removal of ammonia from sewage using natural zeolite from Australia. The process consisted of a fixed-bed ion-exchange system operated in the downflow mode. Evaluation of the pilot process was initially undertaken for ammonia removal from tap water spiked with ammonium chloride to provide performance data in the absence of competing cations. The performance of the pilot process was then assessed using sewage as feed. Breakthrough curves were constructed for a range of treatment flow rates. Existing models for packed bed performance were shown to be able to predict the breakthrough behavior of the process. The results of a study are presented that show that Australian natural zeolite, clinoptilolite, may be successfully employed in a fixed-bed ion-exchange process to achieve high ammonia removal efficiencies from aqueous solutions at rates commensurate with sand filtration. The rate of uptake of ammonium by the zeolite is sufficient to support a continuous high rate process.

Application of ultrasound in membrane separation processes : a review

Membrane fouling is one of the major problems encountered during the application of membrane filtration. While power ultrasound has been used as a cleaning mechanism for many decades it has only recently been applied to membrane systems. This review provides an overview of the application of ultrasound in membrane filtration processes on both flux enhancement and membrane cleaning. The ultrasonic cleaning mechanisms, influence of operating parameters and effects of ultrasound on membrane and feed solutions have been examined. Most reports indicate that ultrasound increases membrane permeation by either reducing the depth of the foulant cake layer or by increasing turbulence in the concentration polarisation layer. There is ongoing debate as to whether these effects arise from acoustic cavitation or microstreaming. The main experimental parameters that alter the efficiency of ultrasonic treatment such as external pressure, power density, cross-flow velocity, frequency, temperature and feed properties have also been reviewed. There is a discrepancy in the literature regarding the integrity of membranes following sonication. Hence larger scale trials of ultrasonic application to different membrane modules over a number of years of operation are required to confirm that these impacts do not reduce the total membrane life. Furthermore, work is required to confirm the ultimate effect Corresponding author: Muthupandian Ashokkumar, School of Chemistry, University of Melbourne, Parkville, Victoria 3010, Australia. Tel.: +61 3 8344 7090; Fax: +61 3 93475180, Email address: masho(5)unimelb.edu.au.

Review of solvent based carbon-dioxide capture technologies

Currently, a large proportion of global fossil fuel emissions originate from large point sources such as power generation or industrial processes. This trend is expected to continue until the year 2030 and beyond. Carbon capture and storage (CCS), a straightforward and effective carbon reduction approach, will play a significant role in reducing emissions from these sources into the future if atmospheric carbon dioxide (CO2) emissions are to be stabilized and global warming limited below a threshold of 2 °C. This review provides an update on the status of large scale integrated CCS technologies using solvent absorption for CO2 capture and provides an insight into the development of new solvents, including advanced amine solvents, amino acid salts, carbonate systems, aqueous ammonia, immiscible liquids and ionic liquids. These proposed new solvents aim to reduce the overall cost CO2 capture by improving the CO2 absorption rate, CO2 capture capacity, thereby reducing equipment size and decreasing the energy required for solvent regeneration.

Dynamic forces between bubbles and surfaces and hydrodynamic boundary conditions.

A bubble attached to the end of an atomic force microscope cantilever and driven toward or away from a flat mica surface across an aqueous film is used to characterize the dynamic force that arises from hydrodynamic drainage and electrical double layer interactions across the nanometer thick intervening aqueous film. The hydrodynamic response of the air/water interface can range from a classical fully immobile, no-slip surface in the presence of added surfactants to a partially mobile interface in an electrolyte solution without added surfactants. A model that includes the convection and diffusion of trace surface contaminants can account for the observed behavior presented. This model predicts quantitatively different interfacial dynamics to the Navier slip model that can also be used to fit dynamic force data with a post hoc choice of a slip length.