Chemical & Biomolecualr Engineering

A nea technique to determ.ine rapidly diffusion coefficients in liquids i.k described. Diffusion experiments are carried out in closed capillaries constructed from scintillation material. The rate of diffusion of radioactive tracers is detected in the capillaries using a standard liquid scintillation analyzer. Solution of the Fickian diffusion equation using Laplace trans-

Although poly(R-hydroxy esters), especially the PLGA family of lactic acid/glycolic acid copolymers, have many properties which make them promising materials for tissue engineering, the inherent chemistry of surfaces made from these particular polymers is problematic. In vivo, they promote a strong foreign-body response as a result of nonspecific adsorption and denaturation of serum proteins, which generally results in the formation of a nonfunctional fibrous capsule. Surface modification post-production of the scaffolds is an often-utilized approach to solving this problem, conceptually allowing the formation of a scaffold with mechanical properties defined by the bulk material and molecular-level interactions defined by the modified surface properties. A promising concept is the so-called "blank slate": essentially a surface that is rendered resistant to nonspecific protein adsorption but can be readily activated to covalently bind bio-functional molecules such as extracellular matrix proteins, growth factors or polysaccharides. This study focuses on the use of the quartz crystal microbalance (QCM) to follow the layer-by-layer (LbL) electrostatic deposition of high molecular weight hyaluronic acid and chitosan onto PLGA surfaces rendered positively charged by aminolysis, to form a robust, protein-resistant coating. We further show that this surface may be further functionalized via the covalent attachment of collagen IV, which may then be used as a template for the self-assembly of basement membrane components from dilute Matrigel. The response of NIH-3T3 fibroblasts to these surfaces was also followed and shown to closely parallel the results observed in the QCM.

MCM-41 is a synthetic, mesoporous silicate material, which currently has limited use as an industrial catalyst. This material is considered to have good potential for adsorption/separation applications due to its regular hexagonal structure, uniform pore distribution, large surface area and large pore volume. In order to enhance the adsorption of metal ions on MCM-41, a metal ion chelating agent, acetylacetone is added and the capacity of the adsorbent for three divalent metal cations in aqueous solutions; Cu(II), Ni(II) and Co(II) determined. Adsorption isotherms for these metal ions are presented, along with adsorption selectivity with respect to pH. Metal ion adsorption results are compared with published data for solvent extraction systems utilising pure acetylacetone and acetylacetone in benzene. It was found that the MCM-41/acetylacetone system produced equal or better metals removal in comparison to solvent extraction methods for some of the metal species tested. Further, the pH of maximum adsorption is shifted in the MCM-41 system compared with the solvent extraction case, thus presenting the possibility of processing under different conditions.

Sludge reduction and dewatering is an important aspect of water and waste water treatment. This is especially true in the case of Australia's Antarctic contaminated site remediation program, where the reduction in volume of wastes to be returned to Australia can lead to significant transport and handling cost savings. The dewatering characterisation of water treatment sludges from an Antarctic contaminated site was conducted using a theory of suspension dewatering developed by Buscall, Landman and White. This theory uses fundamental material properties of compressibility and permeability to determine the diffusivity of a suspension. Diffusivity is a useful property that can be used to directly compare the dewaterability of various sludges. In this investigation, several water treatment sludges were collected and characterised in the field to determine the impact of temperature and additives on compressibility, permeability and diffusivity. The Antarctic sludges were found to be less compressible and less permeable than materials such as mineral suspensions and alum water treatment sludges. Compressibility was found to decrease with the addition of powdered coagulation aids such as bentonite and chitosan.

The stability of silicate MCM-41 in aqueous solutions for up to 12 days has been dramatically improved by silylation with hexamethyldisilazane (HMDS). Mesoporous molecular sieves including MCM-41 show promise for application as selective media for separations of large molecules such as proteins, which are important in the food and pharmaceutical industries. However, many such applications involve aqueous solutions in which MCM-41 has limited stability. Thus, hexamethyldisilazane has been used to create a hydrophobic surface coating on both flat silica and MCM-41 in order to improve their stability in aqueous solutions. This coating was shown to persist on the flat surfaces after aging in water for up to 7 days, using contact angle measurements and atomic force microscopy, unlike a coating applied using trichloromethylsilane which was removed by water. The HMDS-coated MCM-41 showed much greater structural stability than uncoated MCM-41 in both water and an aqueous potassium phosphate buffer solution of pH 6 for extended periods.

Water collection and treatment is often required for effective cold regions contaminated site clean-up, where large volumes of meltwater runoff might otherwise become contaminated during remediation activities and disperse pollutants into the surrounding environment. Waste reduction is particularly important for remediation activities in remote cold regions, as the handling, transport and eventual disposal of material is very costly and logistically difficult. A mobile water treatment system has been constructed for deployment to remote cold regions contaminated sites for use during clean-up activities. This paper describes coagulation and dewatering experiments and modelling techniques that were used to optimise the water treatment process and reduce sludge volumes. Coagulation was assessed by laboratory experiments to determine the impact of a number of operating parameters. Sludge dewaterability was characterised using a recent theory of suspension consolidation. The parameters of greatest importance for water treatment were pH, flowrate and the ratio of coagulant to suspended solids. Sludge dewatering experiments and modelling found transient batch settling and freeze-thaw to be the most effective sludge reduction techniques for Antarctic applications. D

In this investigation different sorbent materials (MYCELX coated sand, granular activated carbon (GAC) and surfactantmodifed zeolite (SMZ)) were tested for their suitability for capture of sparingly soluble hydrocarbons in soil water. These materials were assessed for their potential use in permeable reactive barriers in cold regions. Batch sorption tests at 20°C and 4°C were performed along with a number of surface characterization techniques, including thermogravimetric analysis, nitrogen adsorption and Fourier transform infrared analysis (FTIR). ionic strength and pH tests were also conducted to determine their impact on hydrocarbon sorption.

... Kathy A. Northcott a , Corresponding Author Contact Information , E-mail The Corresponding Author , Ian Snape b , Michael A. Connor a and Geoffrey W ... the size of the continent because it tends to occur on rare coastal ice-free areas where biodiversity is high and animals breed. ...

Water collection and treatment is often required for effective cold regions contaminated site clean-up. Large volumes of meltwater runoff can become contaminated during remediation activities and disperse pollutants into the surrounding environment. Of particular importance for Antarctic contaminated sites is the impact of contaminant metals from polluted sites into nearby marine environments and the sensitivity of these environments. A mobile water treatment system was constructed for deployment to remote cold regions contaminated sites for use during clean-up activities. The water treatment system is designed to remove contaminants associated with particles and colloids via coagulation and settling and dissolved metals via ion exchange. This paper gives an overview of laboratory tests necessary to ensure the safe operation of the water treatment plant during the remediation of an abandoned waste disposal site in the Thala Valley near Casey station Antarctica. The results show that through a detailed understanding of the mechanisms this technology can be used to treat water to meet the required guidelines for sensitive environments.

A field trial for removal of dissolved metal contaminants in water from an abandoned waste disposal site, using ion-exchange columns of an iminodiacetic acid chelating ion-exchange (IDA) resin, was conducted at Casey Station, Antarctica. An on-site monitoring technique, employing 3M Empore chelating disks for preconcentration for analysis by atomic absorption spectrometry (AAS), was also trialled for measurement of dissolved metal concentration in the treated water. The field trial indicated that the ionexchange columns of Amberlite IRC748 were suitable for the application, with concentrations of contaminant metals in treated waters successfully reduced. The observed order of selectivity for contaminant metals was markedly different to that observed in previous laboratory tests; the presence of organic ligands and colloidal iron in the natural waters on-site interfered with the retention of Cu and Fe, reducing selectivity for these metals. The on-site monitoring technique was considered capable of producing results of sufficient accuracy and reproducibility to identify that the ion-exchange columns were effectively reducing metal contaminant concentrations, and to identify breakthrough of the ion-exchange columns. Concentrations of Cd, Ni and Zn corresponded well with the dissolved metal fraction measured by ICP-MS, although Pb analysis was less precise. However, interference from organic ligands and colloids probably caused underestimation in the measurement of these metals. The on-site monitoring technique was useful for providing rapid feedback during clean-up at this remote site. However, the interferences would require careful evaluation in order to relate the measurements to water quality standards or objectives.

Dairy ultrafiltration permeate (UFP) has been filtered using polyamide nanofiltration (NF) membranes in order to separate potentially valuable calcium and lactose from unwanted monovalent salts. An investigation into both the fouling and separation behaviour has been carried out to gather useful information for the optimal selection of operating conditions that maximise efficiency and yield. Supersaturated calcium phosphate in the feed resulted in severe flux decline during filtration at high temperatures and pH due to salt precipitation. Investigation into the ion separation behaviour using sub-saturated model solutions containing KCl and CaCl 2 showed that the addition of the trivalent anions citrate and phosphate changed the pH dependent separation of K þ and Ca 2þ . For the multicomponent system, maximum calcium rejection and minimum potassium rejection occurred at high pH, whereas the opposite was true for calcium in the simpler systems. A possible explanation for this separation behaviour has been proposed which incorporates the membrane charge, represented by the zeta potential, and the speciation of calcium with these anions.