a study on the performance of limestone roughing filter - ePrints@USM

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2.8 Roughing Filter Theory Roughing filtration is more of an art than a science. Numerous researchers have tried to describe the filtration mechanisms in mathematical models applying either the phenomenological or the trajectory approach. In the first approach important variables, such as filtration rate, filter size, depth and porosity are used to describe filter efficiency. In the second approach it focuses more on transport mechanism of the particles (Wegelin, 1996). While the contaminated water passes through the filter, microbes and other particles are removed. Although the removal mechanisms are not well understood, they are believed to be a combination of biological, physical and chemical mechanisms. Specific mechanisms may include biological action, attachment of microbes to filter media by electrochemical force and physical straining (WHO, 2004). 2.8.1 Flow Rate and Head Loss Control Flow rate is an important factor affecting removal in roughing filter. In particular, sedimentation and biological mechanisms depend on the filtration rates (Cleary, 2005). Lower filtration rates allow less turbulent conditions in the filter media interstices and facilitate gravitational sedimentation, reduces fluid shear on the deposited particles, and increase the hydraulic retention time in biologically active regions of the filter. The main objective of roughing filter is to reduce the amount of solid matter from the raw water. Filters are usually operated at the filtration rate of up to 1.5 m 3 /m 2 /h and size of filter material ranged between 4 mm and 20 mm. Head loss in a roughing filter is usually small. Head loss can be recorded as water level difference between the 13
inlet and outlet water level (Wegelin, 1996). The head loss in a filter can be calculated as; h C V 2 D = 1.07L 4 (2.1) ψgdf Where h L C D Re μ d = head loss (m) = filter depth (m) = (24/Re) + (3/√Re) + 0.34 (the drag coefficient) = Vd/μ (dimensionless Reynolds Number) = kinematics viscosity of fluid (m 2 /s) = particle diameter (m) Ψ = dimensionless shape or sphericity factor (
Page 1 and 2: A STUDY ON THE PERFORMANCE OF LIMES
Page 3 and 4: ACKNOWLEDGEMENTS This research was
Page 5 and 6: TABLE OF CONTENTS ACKNOWLEDGEMENTS
Page 7 and 8: 3.5.6 Measurement of Dissolved Oxyg
Page 9 and 10: Appendix E- Effluent Concentration
Page 11 and 12: 4.13 One-way ANOVA Results for the
Page 13 and 14: 4.7 Boxplot of Suspended Solids for
Page 15 and 16: A.1 Sieve Analysis for Small Size M
Page 17 and 18: D.33 Probability Plot of Untreated
Page 19 and 20: E.4 Effluent Concentration with Fil
Page 21 and 22: LIST OF SYMBOLS AND ABBREVIATIONS T
Page 23 and 24: mV SSA C z λ E V f μ x 2 s σ s I
Page 25 and 26: Secara amnya, penuras kasar adalah
Page 27 and 28: efficiency than smaller filter medi
Page 29 and 30: The slow sand filters constructed i
Page 31 and 32: CHAPTER 2 LITERATURE REVIEW 2.0 Imp
Page 33 and 34: Water treatment plants have success
Page 35 and 36: that can deplete oxygen in receivin
Page 37 and 38: eductions of coliform organisms wit
Page 39: 2.7 Roughing Filter for Wastewater
Page 43 and 44: Figure 2.4: Sedimentations on Filte
Page 45 and 46: Figure 2.5: Interception on Filter
Page 47 and 48: smaller interstices between smaller
Page 49 and 50: discuss in detail, the reason might
Page 51: 2.10 Removal Capabilities of Roughi

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