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Water treatment

The early filters were

The early filters were never completely successful because an adequate cleaning procedure was not available to the operators. Robert Thom in Scotland, and James Simpson in England were also pioneers in the development of filtration. Each learnt from previous failures, Thom with filters near Glasgow and Simpson with visits to the north of England and Scotland. Working with experimental plants, both discovered that the failures of filters were partially or completely due to surface clogging. Thom devised a self-cleaning filter, washed by reverse flow. Simpson’s method consisted in scraping off the thin dirty top layer, removing, washing, and restoring it at intervals. Both engineers used the method of arranging successively finer layers of filter media from the bottom to the top of the filter, as described in the British patent granted to Peacock in 1791. Thom’s filter, like Peacock’s, was cleaned by reverse-flow wash (Baker, 1981). In 1827, Thom built an up-flow slow sand filter (USSF) in Greenock. In 1838, he built similar filters for the near-by town of Paisley, treating water from an impounded gravity reservoir, thirty-four years after the first known filter for a municipal supply had been put into operation. Thom’s SSF at Paisley operated at a downward velocity of 0.23 mh -1 . Besides reverse flow, stirring the surface of the SSF with a rake and admitting a little water through the raw-water conduit was also considered to facilitate cleaning. According to Darcy (1856), quoted by Baker (1981), besides being washed by reverse flow, the Paisley filters were sometimes cleaned by removing one cm of surface sand and replacing it at infrequent intervals. Simpson’s experimental plant in London was made up of two settling reservoirs, working in parallel and followed by a filter (Fig. 2.2). Each reservoir was 9.8 m square at the top, 6.1 m at the bottom and 1.2 m deep; their low-water line was level with the high-water line of the filter. The filter was contained in a pond having 13.4-m square at the top, 7.9 m at the bottom and 1.8 m deep. The filter had a top surface of 92.9 m 2 and a depth of 1.2 m. The plant filtered 3.9 ls -1 (14 m 3 h -1 ), at a rate of 0.15 mh -1 . During tests, the filter was being scraped around once fortnight. Simpson considered this scraping procedure the best way of overcoming cleaning limitations he had observed in lateral and ascending filters during his study visits. Figure 2.2 Simpson’s London experimental slow sand filter, 1827-1828 (Adapted from Baker, 1981). 12

On January 14, 1829, Simpson’s one-acre (4,046.86 m 2 ) filter at Chelsea, known as the first English SSF, was put into operation. This type of SSF became the classical model of SSF. Thom’s design was used to a limited extent, but the elements of reverse-flow wash with the false bottom were to become principal features of the rapid filter developed in the United States of America (USA) during the 1880’s (Baker, 1981; Coffey and Reid, 1982). In 1856, Henry Darcy patented a filter in France, which included all of the elements of the American rapid filter, except one, coagulation. Darcy made an innovative combination of elements previously developed in England, France and Scotland (Baker, 1981; Coffey and Reid, 1982), with sound hydraulic considerations about flow through porous media, now known as Darcy's Law. This law states that the flow per unit of area of filtering bed is proportional to the hydraulic gradient in the porous media. In the 1880’s and early 1890’s, the rapid filter was developed in United States and coagulation, flocculation and sedimentation came to be regarded as important components of conventional rapid filtration (RF) water treatment plants (Baker, 1981; Coffey and Reid, 1982). RF made it easier to produce large volumes of water, but required chemical coagulation. However, whereas SSF was shown to reduce water borne disease, RF alone did not. Conventional RF treatment depend on chemical or physical disinfection to remove or inactivate efficiently microbial pathogens. This led to the wider use of chemical disinfectants during the 20 th century to reduce the sanitary risks associated with the treated water. Disinfectants have included heat, copper, silver, chlorine, ozone, ultraviolet radiation, and membranes. The most popular has been chlorine. Chlorine, as hypochlorite solution, started to be used at treatment plant level in Belgium in 1902, United States in 1904, Britain in 1911, and London in 1916. Chlorine as liquid (compressed in metal cylinders) was applied in the USA since 1913, and in Britain (London) since 1917 (Baker, 1981; Bryant and Fulton, 1992). Recent regulation concerning the control of disinfection by-products (Braghetta et al, 1997; EPA, 1998) have led to a better sequential application of the multiple stage treatment concept in which chlorination is logically the final treatment stage. Additionally there is a growing awareness that some pathogens (e.g. crystosporidia) are best removed by at an earlier stage, by filtration, as they are more resistant to chemical disinfection. The SSF technology has been successfully applied in the Northwest part of Europe since the 19 th century. In other regions the appropriate use and the impact of this technology has been rather limited. The growing application of RF and chemical disinfection in the 20 th century contributed significantly to the reduction of waterborne diseases and the improvement of productivity and quality of life in urban settlements which have had the opportunity to install and sustain these technologies. Whereas today a large number of different types of treatment exist for the purification of water, the selection of the most suitable option for a given community remains a major challenge, particularly if this concerns a low-income community with limited institutional capacity. This challenge requires a systematic approach, the selection and protection of the best available water resource, and the availability of relevant information on robust, efficient treatment technologies, to establish a solution that is economically sound and easy to operate, manage and maintain. 13

  • Page 1 and 2: Development and Evaluation of Multi
  • Page 3 and 4: ACKNOWLEDGEMENTS To my supervisor,
  • Page 5 and 6: ABBREVIATIONS ABNT: Acuavalle: ACV:
  • Page 7 and 8: SOCs: Synthetic Organic Chemicals S
  • Page 9 and 10: u c V V f Vs uniformity coefficient
  • Page 11 and 12: TABLE OF CONTENTS 1. INTRODUCTION 1
  • Page 13 and 14: 4 MULTISTAGE FILTRATION EXPERIENCIE
  • Page 15 and 16: 1 INTRODUCTION Water is essential f
  • Page 17 and 18: Table 1.2 Access to WS&S in Colombi
  • Page 19 and 20: Table 1.5 Safe drinking water cover
  • Page 21 and 22: 1.2 Multiple Barriers Strategy and
  • Page 23 and 24: 2 OVERCOMING THE LIMITATIONS OF SLO
  • Page 25: adjustment, are among the technolog
  • Page 29 and 30: With increasing life expectancy, en
  • Page 31 and 32: Table 2.2 Treatments steps recommen
  • Page 33 and 34: In table 2.3, WHO guideline values
  • Page 35 and 36: 2.5 The Slow Sand Filtration Proces
  • Page 37 and 38: When the particles are very close t
  • Page 39 and 40: in which p 0 is the clean media por
  • Page 41 and 42: Yao et al (1971) related the remova
  • Page 43 and 44: compensate for the increase in the
  • Page 45 and 46: can be applied, but intermittent op
  • Page 47 and 48: Table 2.4 Comparison of design crit
  • Page 49 and 50: Although accepted as indirect indic
  • Page 51 and 52: 50% when the temperature falls from
  • Page 53 and 54: Figure 2.9 Flow diagram of the wate
  • Page 55 and 56: ut higher running costs, since more
  • Page 57 and 58: Headloss and flow control. Final he
  • Page 59 and 60: Figure 2.13 Influence of flow condi
  • Page 61 and 62: Operation and maintenance (O & M).
  • Page 63 and 64: in parallel (Galvis, 1983; Smet et
  • Page 65 and 66: cleaning simple, DyGF should behave
  • Page 67 and 68: case of Dortmund (Germany), the HGF
  • Page 69 and 70: Table 2.9 Data about three experien
  • Page 71 and 72: Some points of discussion about HGF
  • Page 73 and 74: and 600-800 NTU) and different filt
  • Page 75 and 76: the HGF units of Aesch (see table 2
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    in spite of the low removal efficie

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    order to overcome the water quality

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    full-scale units. In this research,

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    3 MULTISTAGE FILTRATION STUDIES WIT

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    in the case of UGFL. Initially, it

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    • Bigger and better-instrumented

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    l Figure 3.7 Plan view of Cinara's

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    The present research work was divid

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    Table 3.1. Design parameters, grave

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    Figure 3.9. Piezometer distribution

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    were used to collect samples for DO

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    were poured into a funnel using fil

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    H 0 : H a : Treatment levels workin

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    3.2 Results and Specific Discussion

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    3.2.2 Dynamic gravel filtration (Dy

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    Mean faecal coliform removal effici

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    Table 3.10 Comparative analysis of

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    DyGF-A had flow reductions in the r

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    The experimental data used to produ

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    Previous observations were further

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    ates (figure 3.17 B). However, at t

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    Longer “initial-ripening” perio

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    Table 3.17. Descriptive statistics

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    100 Filtration rate = 0.3 mh -1 100

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    After the present experience, faeca

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    nature of the organic matter and th

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    Table 3.24 Comparative analyses of

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    3.2.4.3. Filtration run lengths and

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    deep bed filter (data not included

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    and operational considerations Pard

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    than in sand samples from other SSF

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    Step dose tracer tests were made at

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    for HGFS and from 3 to 5 for HGF. T

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    Constant and declining filtration r

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    The efficiency levels summarised be

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    Surface area of CGF and SSF units.

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    community based organisations and l

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    systems. All these systems were fed

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    Parts of the suburban settlements o

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    Figure 4.2. Layout of Retiro MSF pl

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    Traditionally, in the WS&S of Colom

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    Photo 4.10. Partial cleaning activi

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    Figure 4.3 Location of full-scale M

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    4.4.1.3 Main characteristics of mul

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    Figure 4.4 Layout of Restrepo MSF p

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    Figure 4.6 Layout of Javeriana MSF

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    Figure 4.9 Layout of Cañasgordas M

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    Figure 4.11. Layout of Ceylan MSF p

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    Table 4.4 Descriptive statistics fo

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    Water sources in the coffee region

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    Filterability results seem to under

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    Table 4.8 Mean removal efficiencies

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    The length of this ripening period

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    in Peru (Pardon, 1989) and Colombia

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    Photo 4.24 Drainage facilities in u

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    the Cauca Valley. This is not the c

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    Pardon (1989) reports similar evide

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    5. COST OF MULTI-STAGE FILTRATION P

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    ecame formally established as WS en

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    Models for assessing construction q

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    MSF system can then be calculated o

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    5.7 Cost Model for the Cali Area an

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    Table 5.8. Annual labour costs due

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    5.8 General Discussion The followin

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    systems. The differences between MS

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    guideline for colour is < 15 PCU (W

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    Table 6.1. Individual (at each trea

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    Table 6.3. Individual (at each trea

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    As shown in tables 6.1 and 6.3, col

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    UGFL 0.45 UGFS 0.45 (32;51;85) (44;

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    Table 6.4. An example of identifica

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    MSF technology showed great flexibi

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    In harmony with the new development

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    epresents the risk the community ha

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    The selection of MSF alternatives i

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    scouring and transporting away prev

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    REFERENCES ABNT, (1989) NB-592 Proj

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    Craun, G.F., Bull, R.J., Clark, R.M

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    Drinking Water Disinfection, ed. by

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    Huisman, L. (1989) Plain Sedimentat

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    Mendenhall, W. and Sincich, T. (199

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    Ridley, J.E. (1967) Experience in t

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    Visscher, J.T. and Galvis, G. (1992

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    ANNEXES Annex 1: Accessories for Mu

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    aw water. The red colour is used fo

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    Annex 2: Design of Manifolds Manifo

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    + q 2 Q1 (1.2 qn + qn) (2.2 qn) = =

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    R 1 = (total orifice area / lateral

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    0.30 0.25 0.20 0.15 0.10 0.05 0.00

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    Table A.4-2 General notation for th

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    Box A4-3. Sum of Square Error (SSE)

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    Annex 5: Residence times in coarse

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    Table A5-1 Percentage of incoming w

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    Annex 6 Number and Type of Valves N

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    Table A7-1. Descriptive statistics

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    Tables A7-3 Removal efficiencies of

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    Tables A7-5 Removal efficiencies of

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    Construction quantities of DyGF com

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    Net present value (US$) of MSF and