A thesis submitted in partial fulfilment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1990

Chemical interactions among the suspended particles and filter media grains play an important role in filtration process in deciding the filter efficiency. Successful attachment and removal are prompted by interparticle forces caused by electrostatic forces among them. These forces depend on the zeta potential (ZP) of the particles and filter medium. A lab-scale study carried out to study the effect of ionic strength on performance of a deep bed filter indicated that the filter efficiency was minimum at low ionic strength values where ZP of particles in suspension was negative. Increase of ionic strength yielded increase in filter efficiency . The variation of filter efficiency at initial stage and during the filter run was related to particle -filter grain and particle-particle attachment coefficients (a and a respectively). p The experimental study conducted to relate the polymer dose and the deep bed filter efficiency indicated that there is a clear optimum of polymer dose with respect to filter efficiency . Maximum a a and almost ' p zero ZP were obtained at this polymer dose. The effect of ionic strength on membrane filtration was studied experimentally. This study clearly showed that the ionic strength which corresponds to near zero negative zeta potential of suspension resulted in maximum flux. The quantitative approach illustrated in this study for the effect of ionic strength and polymer dose in deep bed filtration and membrane filtration will give a fillip for incorporation of chemical effects in design consideration.