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Water treatment

2.2 Health Risks

2.2 Health Risks Associated with Drinking Water The main health risk related to water supply systems that use surface water from unprotected catchment areas, stems from the discharge of untreated wastewater from human settlements, and industries. The contamination of a water source with human and animal excreta introduces a great variety of bacteria, viruses, protozoa and worms. The health risks associated with microbiological contamination are so important that their control is the priority. Poor water quality may be particularly harmful to children, old people or, members of the community with compromised immune systems. For these groups, the infectious doses are significantly lower than for the rest of the population (WHO, 1993). There are few chemical compounds that pose an acute health risk to the users, such as methaemoglobinaemia in infants due to high levels of nitrate, and situations where accidents occur in industry, mining activities or through the spraying of pesticides and herbicides. Even in such situations, risks may be small because the consumers often reject the contaminated water. Chemical pollution may, however, imply a chronic health risk associated with long periods of exposure. Its control is therefore important, but is a secondary concern in water supply systems that are subject to severe bacteriological contamination (WHO, 1993; Craun et al., 1994; Galal-Gorchev, 1996; WHO, 1997). Understanding that chlorine reacting with organic matter can cause oxidation by-products (OBPs) that may represent a chronic health risk (Rook, 1974), raised concerns about its application in controlling the transmission of cholera in Latin America (Salazar-Lindo et al., 1993). However, it has been established that the health risk associated with these byproducts is very small, compared with the risk related to inadequate disinfection. In reality, the chronic risks must not be ignored, but the acute risks of microbiological character are clearly much more important, especially in the case of systems drawing water from sources that are high in microbiological contamination. This is the situation in many countries with a poor sanitary situation and a low level of socio-economic development (Craun et al., 1994; Otterstetter and Zepeda, 1996; Galal-Gorchev, 1996). In the search for possible alternatives to chlorine, it is necessary to know if they produce OBPs, as well as factors such as whether they are equally effective, economically competitive, and easy to dose and supply. The selection of good quality water resources and the protection of the catchment area are of crucial importance to reduce both acute and chronic type of risks associated with drinking water (Geldreich and Craun, 1996; Okun, 1996). If required, proper treatment, including filtration, will reduce the required chlorine dose and the possible formation of by-products, thus making disinfection more efficient and secure (Lloyd et al, 1991). The incidence of water-borne diseases in USA has been eight times higher in communities using surface water sources without filtration, than in those using filtration (Craun et al., 1994). Consumers accept drinking water mainly through aesthetic considerations. Issues such as turbidity, colour, taste and odour can make them turn to other water sources, possibly more contaminated involving a high health risk. Thus these aesthetic aspects need to be taken into account in the development of water supply systems (WHO, 1993). 14

With increasing life expectancy, enhanced institutional capacities and improved economic conditions, water treatment has progressively combined technologies to reduce initially the acute health risks, often of microbiological nature, and later the chronic health risks, usually of physico-chemical origin. This is illustrated in figure 2.3, based on a previous work of Coffey and Reid (1982). Water Treatment Objectives and Priorities (Basic) (Advanced) Trace Levels of Organic Matter Chemicals and Toxicants Hardness Solids, Taste, and Odour Bacteria, Viruses, and Protozoa (Low) Socio-economic Level (Institutional Capacity) (High) Figure 2.3 Conceptual relation between socio-economic level and water treatment objectives. 2.3 Water Quality Guidelines and Standards Early criteria of water quality in the water industry were based on clarity, taste, odour, and the health of users. Later tests measured the amount of oxygen, nitrites, certain types of bacteria, and radioactive elements (Coffey and Reid, 1982). During the first half of the 20 th century the criteria in Europe and USA were directed primarily at prevention of transmission of enteric pathogens. In fact, Some 60 years ago, less than ten parameters served as guide for drinking water treatment. They assisted in the reduction of infant mortality rates to below 20 per 1,000 births, and the increase in life expectancy to values above 70 years in western industrialised countries (Wolman, 1981). Table 2.1 gives an overview of the USA standards on turbidity over the last four decades, showing that tighter standards have been established only very recently, with the advancement of knowledge and technology, and with better institutional, operational, and economical possibilities. Table 2.1 Overview of drinking water standards for turbidity in the United States (Sanks, 1987; Pontius, 1990) Period Maximum Permissible Turbidity (NTU) Prior to 1962 10.0 1962 to 1976 5.0 1976 to 1988 1.0 1989 to date for SSF 1 1.0 1989 to date for RF 1 0.5 1. SSF, slow sand filtration; RF, rapid filtration. The standards from 1989 indicate that the turbidity must be less than 5 NTU and meet the indicated turbidity limits in 95% of the samples taken The World Health Organisation published its second edition of the Guidelines for Drinking Water in three volumes (WHO, 1993; 1996; 1997). These Guidelines present an assessment of the health risks of waterborne pathogens and some 128 chemical contaminants. Guideline values 15

  • 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 and 26: adjustment, are among the technolog
  • Page 27: On January 14, 1829, Simpson’s on
  • 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
  • Page 77 and 78: 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

  • Page 280:

    Net present value (US$) of MSF and

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