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galvis

Water treatment

The problems of

The problems of affordability and technical complexity associated with small to medium water treatment facilities are relevant for all high, medium and low income country economies. In some countries like England and the Netherlands, these problems have been reduced by encouraging large cities to extend the water service to smaller communities or, in areas with no large cities, by stimulating small communities to form regional water boards or regional water companies (NRC, 1997). In addition to water supply, these regional water boards or water companies have provided other water-related services. In contrast, the network for supplying drinking water in the United States of America (USA) is fragmented. In 1996, there were 54,728 community water systems (CWSs) in US serving 248 million people. They were distributed in 46,827 small systems (25-3,300) serving 25 million people; 4,332 medium (3,301-10,000) serving 25 million people; and 3,569 large (>10,001) serving 198 million people. While the small systems serve around 10% of the population covered by the US CWSs, they account for an inordinate percentage of the violations under the USA Safe Drinking Water Act, SDWA (Stout and Bik, 1998). The small communities face the greatest difficulty in supplying continuously water of adequate quality and quantity because they often lack the economies of scale needed to hire experienced operators and managers. In Canada and the US, special attention has been given to the development and promotion of treatment technologies for small to medium size communities in the last decade (Toft,. et al, 1989; EPA, 1998). In US the 1996 SDWA Amendments contain provisions related to WS systems serving

1.2 Multiple Barriers Strategy and Basic Water Treatment Concepts Applying different barriers is important to reduce the sanitary risks associated with drinking water due to microbial and physicochemical contaminants. This includes watershed management of land uses to protect surface and ground water; the selection and protection of the best available water sources; on site or off-site wastewater treatment and reuse; water treatment; adequate and well-maintained distribution system, and safe water practices by the consumers (Geldreich and Craun, 1996). Source water protection programmes are considered particularly relevant to small systems, where community participation is likely to be more effective (Stout and Bik, 1998). Because so many variables are associated with water contamination, it is not recommended to place the major burden of water quality enhancement on stream self-purification capacity or the water treatment processes. Therefore, water treatment is just one of the barriers to ensure that water produced from a given source complies with the national drinking water quality standards or the WHO guidelines. This is particularly important in the Andean region, where the majority of the WS systems rely on surface water sources. The level of treatment should be in harmony with aspects such as: the type of risk existing in the supply source and the institutional and socioeconomic conditions around a given community. Since infectious diseases, caused by pathogens are the most common health risk associated with drinking water, priority should be given to reduce this type of contaminants in water treatment (WHO, 1993; Gimbel, 1999), without ignoring the risks associated with chemical contaminants in the source water. “Whereas the research scientist can purify the most grossly polluted water on a laboratory or pilot scale, the full scale plants must be developed and designed to produce large quantities of safe water economically, and on continuos basis. Furthermore, the treatment plant must be operated and controlled by a technically trained, conscientious and skilled operator and such staff are at present scarce in most countries” (Lloyd et al, 1991). Due to the complexity of this issue, some basic concepts can be identified to making water treatment more methodical, reliable and efficient (Lloyd, 1974; Craun, 1988; Lloyd et al, 1991; Galvis, 1993; Galvis et al, 1994), as follows: • Multistage Water Treatment. This concept has a long history and has evolved gradually with the increased attention to water quality. According to the multistage water treatment concept, there should be more than one stage of treatment to produce water suitable for human consumption. Together these stages should progressively remove the raw water contaminants and consistently produce safe and wholesome final water. Ideally the safe state should be achieved before the terminal treatment stage so that failure of any one process should not result in significant risk of waterborne disease. As consequence the system should be robust and close to failsafe. • Integrated Water Treatment. In applying the multistage water treatment concept, it is important to understand that each unit process may not be equally effective at removing different types of pollutant. Integrated water treatment is therefore also an important concept, which requires that the strengths and weaknesses of each treatment stage, as well as the combination of the different treatment stages, in a plant be quantified and balanced, so that all contaminants are effectively removed at a feasible cost. In general, it is convenient to first separate the heaviest and larger material and gradually proceed by separating or inactivating the smaller material represented by particles that include colloidal solids and microbes. 7

  • 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: Table 1.5 Safe drinking water cover
  • Page 23 and 24: 2 OVERCOMING THE LIMITATIONS OF SLO
  • Page 25 and 26: adjustment, are among the technolog
  • Page 27 and 28: On January 14, 1829, Simpson’s on
  • 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
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    Some points of discussion about HGF

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    and 600-800 NTU) and different filt

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    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

  • Page 144 and 145:

    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

  • Page 220 and 221:

    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

  • Page 242 and 243:

    Mendenhall, W. and Sincich, T. (199

  • Page 244 and 245:

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

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

  • Page 248 and 249:

    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

  • Page 278 and 279:

    Construction quantities of DyGF com

  • Page 280:

    Net present value (US$) of MSF and

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