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Water treatment

(GVs) are recommended

(GVs) are recommended for 95 of these contaminants, taking into account all sources of exposure (Galal-Gorchev, 1996). A GV "represents the concentration of a constituent that does not result in any significant risk to the health of the consumer over a lifetime" (WHO, 1993). The TDI, tolerable daily intake, is an estimate of a substance in drinking water (mg/kg or µg/kg of body weight) that can be ingested over a lifetime (70 years) without appreciable health risk. The TDI can be estimated (WHO, 1993) by dividing the no observed, or the lowest observed adverse effect level of a substance divided by an uncertainty factor (UF). The GVs in mgl -1 or µg/l is then derived by multiplying the TDI by bw, the body weight (60 kg for adults), and p, the fraction of the TDI allocated to drinking water, and dividing by C, the daily drinking water consumption (2 l for adults). In countries where relevant data are available, GVs should be tailored to local circumstances and conditions (Galal-Gorchev, 1996). Because of the large UF values generally involved in obtaining TDI estimates, short time periods of exposure exceeding GVs are unlikely to result in any deleterious effect on health (Galal-Gorchev, 1996). Pathogenic agents, unlike chemical pollutants, have a non-cumulative dose response; are discrete and not in solution, and are often clumped or adherent to solids, so that an infective dose cannot be predicted from their average concentration in water. Besides, the likelihood of infection depends upon the pathogen, as well as upon the immunity of the individual; and pathogens multiply in their host, and certain pathogenic bacteria are also able to multiply in food and beverages, thus perpetuating or even increasing the chances of infection (WHO, 1993). "Because of these properties there is no tolerable lower limit for pathogens, and water intended for human consumption, for preparing food and drink, or for personal hygiene should thus contain no agents pathogenic to humans" (WHO, 1993). To produce safe water from the bacteriological point of view, WHO (1993) recommends the absence of the indicators E. coli or thermotolerant (faecal) coliform bacteria in any single sample of 100 ml. This takes into account that they are the most numerous and specific bacterial indicator of faecal pollution, in spite of some limitations of specificity and regrowth, particularly of the thermotolerant (faecal) coliform bacteria in tropical environments. GVs are not set for viruses and protozoa due to the lack of appropriate surrogates for these types of pathogens, as well as to the technical and economical limitations to detect them in large volumes of water. The criteria for the degree of treatment recommended by WHO (1993) to produce drinking water from surface sources with a negligible risk of containing viruses are summarised in table 2.2. Although pre-disinfection is recommended in this table, other treatment stages such as storage or coarse filtration should be preferred to reduce the required doses of chemical disinfectants and risks associated with oxidation by-products. WHO (1993) considers that “ the attainment of the bacteriological criteria [absence of E. coli or thermotolerant coliform bacteria] and the application of treatment for virological reduction [table 2.2] should, except in extraordinary cases of extreme contamination by parasites, ensure that the water has a negligible risk of transmitting parasitic diseases”. However, the guidelines published by WHO (1993) do not include information on performance of the treatment steps to facilitate process selection and combination to fulfil water treatment objectives with different levels of contamination in the water sources. 16

Table 2.2 Treatments steps recommended by WHO to produce water with negligible virus risk from surface water sources (WHO, 1993). Type of surface water source Recommended treatment • Protected, impounded upland water; essentially free • Disinfection 1 of faecal contamination • Protected, impounded water; or upland river; faecal • Filtration 2 and disinfection contamination • Unprotected lowland rivers; faecal contamination • Pre-disinfection or storage, filtration, disinfection • Unprotected watershed; Heavy faecal contamination • Pre-disinfection or storage, filtration, additional treatment 3 , and disinfection • Unprotected watershed; gross faecal contamination • Not recommended for drinking water supply 1. Before terminal disinfection median turbidity < 1 NTU and < 5 NTU in single samples. Residual of free chlorine > 0.5 mgl -1 after at least 30 minutes of contact time at pH < 8.0, or an equivalent disinfection process for > 99.99% of enterovirus inactivation. 2. SSF or RF preceded by coagulation-flocculation, or an equivalent filtration process for > 90% enterovirus reduction. 3. Additional treatment may consist of slow sand filtration, ozonation with granular activated carbon adsorption, or any other process demonstrated to achieve > 99 % enterovirus reduction. The first application of water quality standards at the federal level in the USA was based on the Safe Drinking Water Act (SDWA) of 1974. This regulation became effective in 1977, covering microbial, organic, and inorganic pollutants. Concern for the DBPs and the new synthetic organic chemicals (SOCs) led the USA Congress to enact the 1986 amendments to the SDWA, resulting in the development of new regulations between 1986 and 1991. This meant an increase in the number of contaminants regulated from four in 1925, to more than 100 by the end of the century (EPA, 1989; Okun, 1996). In 1989, under the SDWA, the Surface Water Treatment Rule (SWTR) and the Total Coliform Rule (TCR) were published. Combined, these two rules were intended to control pathogens in general. Under the SWTR a treatment technique was established requiring a reduction in source water concentration of Giardia of 99.9% (3 logs) and a reduction of viruses of 99.99% (4 logs). These treatment efficiencies are assumed if systems use specified technologies, which meet established design, operating, and performance criteria. Systems using surface water - or water that is under the direct influence of surface water - must filter water unless they meet source water quality criteria and watershed control provision, summarised as follows, based on Pontius, (1990). • The level of faecal contamination must be less than 20 CFU/100 ml in 90% of the samples. • The turbidity has to be below 5 NTU. Sometimes higher values are accepted, provided they occur less than twice per year. • The disinfection has to be conducted in such a way that it inactivates 99.9% of the cysts of Giardia lamblia and 99.99% of viruses. This is controlled by prescribing minimum residual chlorine levels and contact times before the water reaches the first consumers at the peak consumption hour. • A sustained control programme for the catchment area needs to be developed. • Sanitary inspections are needed every year with participation of the health authorities. • Outbreaks of water-borne diseases should be eliminated. • Compliance with the procedures concerning indicators for faecal contamination is required. • Compliance with the procedures related to the maximum level of trihalomethanes. The SWTR was oriented to protect public health against the exposure to Giardia lamblia, viruses, Legionella, and heterotrophic bacteria, as well as many other pathogenic organisms. The SWTR requires disinfection considering that all surface water sources may be subject to faecal contamination, and because current microbial water quality indicators, such as E. coli, are not adequate surrogates of pathogens more resistant to disinfection than are the 17

  • 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 and 28: On January 14, 1829, Simpson’s on
  • Page 29: With increasing life expectancy, en
  • 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
  • Page 79 and 80: order to overcome the water quality
  • Page 81 and 82:

    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

  • Page 184 and 185:

    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

  • Page 216 and 217:

    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

  • Page 234 and 235:

    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

  • Page 246 and 247:

    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

  • Page 252 and 253:

    Annex 2: Design of Manifolds Manifo

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

  • Page 256 and 257:

    R 1 = (total orifice area / lateral

  • Page 258 and 259:

    0.30 0.25 0.20 0.15 0.10 0.05 0.00

  • Page 260 and 261:

    Table A.4-2 General notation for th

  • Page 262 and 263:

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

  • Page 264 and 265:

    Annex 5: Residence times in coarse

  • Page 266 and 267:

    Table A5-1 Percentage of incoming w

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    Annex 6 Number and Type of Valves N

  • Page 270:

    Table A7-1. Descriptive statistics

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    Tables A7-3 Removal efficiencies of

  • Page 276 and 277:

    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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