Process analysis and optimization of direct horizontal-flow roughing filtration

The objective of this study is to develop a pre-treatment technology for highly turbid river water, called direct horizontal-flow roughing filtration (DHRF), by combining the principles of direct filtration with a roughing filtration process. The first chapter discusses the background and importance of the study. Chapter 2 evaluates the feasibility of the combination of horizontal-flow and a direct filtration process, and assesses the influence of different process parameters on the performance of the combined process. Chapter 3 then develops a model to describe the flocculent particle removal in large grains in analogy to multiple-plate settler , and Chapter 4 determines the boundaries of different mechanisms occurring in the combined process. The mechanisms of coagulation are demarcated in terms of coagulant dose and pH, and the mechanisms related to particle removal in a gravel bed are demarcated in terms of grain size and filtration rate. Chapter 5 optimizes the process parameters of the combined process, while Chapter 6 assesses the influence of main raw water variables. A potentially appropriate roughing filter cleaning procedure is developed in Chapter 7; and design and operational guidelines are provided in Chapter 8. The study concludes that through this comparative analysis of horizontal-flow roughing filtration, DHRF, and the conventional process consisting of coagulation, flocculation and sedimentation, DHRF is an appropriate and cost-effective pre-treatment technology for towns and small cities in many developing countries.