| Summary: | Based on an understanding of how bacteria attach, grow and detach, new cleaning strategies, are urgently needed by many industries. In addition, a better understanding of microbial processes at surfaces offers opportunities for industrial developments, such as bioremediation, treatment of hazardous waste sites, bio-filtration and forming bio-barriers to protect soil and groundwater from contamination. This work aims to study and develop a model of the interaction energies that exist between a bacteria and mineral surfaces in the initial stages of bacterial adhesion and to compare this model to laboratory assessments of adhesion. The classical DLVO theory developed by Derjaguin-Landau-Verwey-Overbeek consists of two interaction energies (Lifshitz van der Waals and electrostatic double layer), which have been widely applied in colloidal interactions. The extended theory, XDLVO, developed by van Oss adds a consideration of acid base interactions and hydrophobicity effects and is currently the best favoured model for evaluating the behaviour of interactions between bacteria and surfaces in understanding bacterial adhesion either to encourage or to prevent biofilm formation. Introducing bacteria into groundwater containing minerals may lead to differences in attachment of the bacteria onto different mineral surfaces depending on their interaction potentials. The attachment process is governed by at least two types of interaction across the aqueous phase. These are the van der Waals (vdW) and Electrical Double Layer (EDL) interactions. This thesis focuses on both theoretically and experimentally determining these interactions as part of the attachment process. In order to determine the acid-base interaction energy, hydrophobicity (as the acid-base interaction energy is determined by the calculation from the value obtained from contact angle and surface tension values) of surfaces and contact angle measurements have been made by the asymmetric drop shape analysis technique and the thermodynamic approach has been used to calculate the surface tensions of bacteria and mineral surfaces. To determine the electric double layer (EDL) interaction potential, zeta potentials were measured by an electrokinetic technique (ZetaPALs). The streaming potential technique was also used with a cylindrical cell to measure zeta potentials of the mineral grains and bacteria suspension in contact with an aqueous phase. It was found that geometrical factor, surface charge and hydrophobicity effects play important roles in bacterial adhesion and these can be modelled as XDLVO theory interaction energies. A numerical van der Waals interaction energy for capsule shaped bacteria to flat mineral plate model is developed from Hamaker's Microscopic Approach and examined by the MapleSoft 14 computer programme. The van der Waals interaction energy from the capsule model is compared to the interaction energies between spherical shell bacteria and mineral surfaces at the early stage of the adhesion process. This numerical solution shows that the effect of different shaped bacteria and mineral surfaces on the interaction potential cannot be neglected even at small separation distances. Total interaction energy prediction using XDLVO found significant effects of environmental conditions including pH, ionic strength and mineral size and shape. The XDLVO model was found to most closely mirror the experimental results, which obtained from flow-cell attachment experiment under laminar flows where the bacterial adhesion was found well attached at pH between 5 to 6 in 0.1 M ionic strength.
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