Robert F. Considine

Oocysts of Cryptosporidium parvum and model sand surfaces in aqueous solutions: an atomic force microscope (AFM) study.

Oocysts of C. parvum have been associated with several waterborne outbreaks of gastro-enteric disease. Currently, one of the main barriers to oocyst contamination of drinking waters is provided by sand-bed filtration. In this study an atomic force microscope (AFM) has been used to measure the force of interaction between oocysts of C. parvum and a model sand surface (silicate glass). The AFM force curves have been compared and contrasted with the corresponding electrical potentials obtained from electrophoretic measurements (zeta). It has been found that the surface of C. parvum oocysts possesses a hairy layer, most likely a result of surface proteins extending into solution. The hairy layer imposes a steric repulsion between the oocyst and sand surface, in addition to any electrostatic repulsion. The hairy layer collapsed to varying extents in the presence of dissolved calcium and dissolved organic carbon, indicating that the oocysts may be more readily adsorbed onto the model sand surface under these conditions. Conversely, as the two surfaces are pulled apart, the occasional attachment of oocyst surface proteins to the model sand surface can result in adhesion. The AFM results offer new insights into the oocyst surface of C. parvum, and the mechanism of interaction with model sand surfaces under conditions relevant to sand-bed filtration.

Interaction Forces Between Colloidal Silica in Aqueous Inorganic and Natural Organic Electrolyte Solutions

Atomic force microscopy (AFM) has been used to measure the force of interaction between pairs of silica colloids in aqueous inorganic and natural organic electrolyte solutions. In solutions containing a mixture of mono- and divalent inorganic ions, the force measurements on approach can be understood in terms of an electrical double-layer interaction, with decay lengths being comparable to the predicted Debye length. The force of interaction on separation in these mixed electrolyte solutions has been found to be entirely repulsive. Force measurements in a mixture of monovalent ions and natural organic matter (NOM), which is a common component of natural waters, are also reported. The decay length of the electrical double-layer interaction is observed to decrease upon addition of NOM. Force measurements on separation are characterized by pH-dependent adhesion, which has been interpreted in terms of specific surface adsorption and the intermolecular interaction of NOM. A comparison with particle micro-electrophoresis data for the silica colloids in the mixed electrolyte solutions has also been made.

Mapping the nano-scale interaction between bio-colloidal Giardia lamblia cysts and silica

Atomic force microscopy (AFM) has been used to measure the force of interaction between individual cysts of Giardia lamblia (bio-colloids) and an amorphous silica surface (hydrolysed silicon nitride AFM tip). The ζ-potentials of the cysts were calculated from microelectrophoresis data, and were compared with the information obtained from AFM force measurements. The dominant long-range force of interaction between cysts and the silica surfaces was steric in origin, with the magnitude of the steric force decreasing with decreasing pH. The decay length of the steric force decreased with an increase in the ionic strength and a decrease in pH. The cysts may be compressed by the pressures applied during the force measurements, with the surface compressibility reported herein as the interfacial spring constant. An increase in the interfacial spring constant occurred with a decrease in pH; indicative of the collapse of surface macromolecules. The information gained from the measurement of the interaction between G. lamblia and this model sand-like surface may assist optimisation of water treatment processes for the removal of cysts.

Informing Infrastructure Planning Processes For IUWM Projects

Water infrastructure planning has been practiced in much the same way for the centuries since the construction of the first water supply dams and sewers. This process has generally involved reactive, segmented and centralised infrastructure upgrades to meet specified service standards. In the last decade, increasing system stresses and new technologies are making traditional planning processes outdated. There is a growing acceptance of an Integrated Urban Water Management (IUWM) ideology within both industry and academia worldwide. The IUWM approach pushes for proactive long term integrated planning of all water services including environmental protection and liveability. However, there are large gaps in knowledge in regards to the best way to implement IUWM planning. The current study has set out to (1) analyse eight IUWM project planning case studies to determine issues affecting implementation of IUWM, and (2) develop conceptual models for IUWM infrastructure planning. Melbourne, Australia has been selected as the area of interest because Melbourne is recognised as a world leader in water management practices. The study has utilised a combination of primary data from interviews with 34 industry experts from 19 different organisations and confidential project planning documents, as well as secondary data from literature, government strategies and reports. Industry consultation, case study analysis and conceptual model development has uncovered an assortment of original findings which have not been considered in water-related academic literature previously. These newly identified issues pose a threat, and also a direction for growth as IUWM planning processes evolve into the future.

Direct force measurement between bio-colloidal Giardia lamblia cysts and colloidal silicate glass particles

Force-separation measurements between Giardia lamblia cysts and an inorganic oxide (silicate glass) have been obtained by using an atomic force microscope (AFM). The cysts are compressible on the scale of the loads applied during force measurement, with the surface compressibility expressed in terms of an interfacial spring constant (K(int)). The force of interaction prior to this Hookean region, on approach, is long-range and repulsive. The long-range force has been compared to models of the electrical double layer as well as an electrosteric layer. The comparison has led to the conclusion that the cyst surface can be described as a polyelectrolyte brush at intermediate separations (5-115 nm from linear compliance) with an electrical double layer often observed at larger separations. The dependence of the interaction force on surface retraction suggests that tethering between the cyst and siliceous surface can occur. The variation of the interaction with pH and upon variation with ionic strength has also been assessed. The information gained from the measurement of the interaction between G. lamblia and this model sandlike surface informs water treatment processes. Similar studies have been performed by us for the Cryptosporidium parvum (C. parvum) oocyst system to which this work is compared.