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Water treatment

UGFL 0.45 UGFS 0.45

UGFL 0.45 UGFS 0.45 (32;51;85) (44;85;410) 95 Percentile of faecal coliform in raw water data B B 6 < 110,000 B 5 < 60,000 B 4 < 20,000 B 3 < 10,000 Restrepo (7;25;55) Cañas G. (9;24;45) Shaloom Colombo (13;35;122) Retiro (13;38;110) UGFL 0.60 (30;45;66) UGFL 0.75 (28;52;320) Javeriana (22;57;300) UGFL 0.3 (47;72;125) UGFS 0.60 (38;81;250) UGFS 0.75 (35;83;320) UGFS 0.3 (74;196;500) B 2 < 5,000 (4;12;22) B 1 < 1,000 Ceylan (3;4;15) 95 Percentile of turbidity in raw water data A < 10 < 25 ≤ 40 ≤ 60 ≤ 75 ≤ 85 ≤ 200 A 1 A 2 A 3 A 4 A 5 A 6 A 7 (1) Pilot (Chapter 3) and full-scale (Chapter 4) MSF alternatives are distributed in this diagram according to their respective adjusted raw water 95 percentiles of turbidity and faecal coliform levels. All these MSF alternatives would fulfil the proposed treatment objectives with their adjusted raw water databases. (2) The following turbidity values are included between brackets close to the name of each MSF alternative (mean; P 95 ; and maximum values). A summary of statistics for turbidity, faecal coliform and colour values of adjusted databases are included in Annex 7. (3) This figure is used only to visualise raw water contamination levels and classifying MSF filtration alternatives according to the raw waters they could approx. process fulfilling proposed treatment objectives. This figure, in combination with tables 6.1 and 6.3, serves as a reference to estimate individual (each treatment stage) or cumulative (MSF alternative) removal efficiencies when dealing with similar raw water sources and environmental conditions to those found in the Andean Cauca Valley (Chapters 3 and 4). Figure 6.3. Distribution of MSF alternatives that would produce effluents fulfilling the proposed treatment objectives with their respective raw water sources. Individual and cumulative MSF removal efficiencies must be enough to fulfil treatment objectives (≤ 1,000 and 10 CFU/100 ml in the effluents of CGF and SSF stages respectively) processing raw water with maximum faecal coliform levels. Besides, MSF alternatives must produce ≤ 3 CFU/100 ml processing raw water with mean faecal coliform levels. Individual and cumulative MSF removal efficiencies should be enough to fulfil treatment objectives (≤ 15 PCU in the effluent of SSF stage) processing raw water with maximum colour levels. Considering the community acceptance of MSF effluents having mean colour values below 5 PCU (table 6.3) mean colour values included in figure 6.4 are such that MSF alternatives included in the example are able to produce final effluents with mean colour 201

values ≤ 5 PCU. However, effluent colour levels are understood as secondary treatment objectives and must not compromise the fulfilment of faecal coliform and turbidity treatment objectives. Nevertheless, final decisions about using surface water sources with high colour levels should be taken in agreement with the recipient communities. Identifying potential filtration stage alternatives. The MSF alternatives included in figure 6.3 are taken only as a reference because the selection example is developed by identifying and combining filtration stages rather than by taking any particular monitored (real) MSF alternative. The mean individual and cumulative turbidity, faecal coliform and colour removal efficiencies observed during the present study are taking also as a reference to estimate more general removal efficiencies for the Andean Cauca Valley of Colombia. Similar or lower removal values to those presented in tables 6.1 and 6.3 are assumed for each filtration stage depending on contamination levels, filter bed lengths and filtration velocities. Cost indicators (such as gravel bed lengths and number of units working in series) of the MSF alternatives included in figure 6.3 are also taken into account to make recommendations. For example, Retiro being able to process raw water type A 3 B 4 (figure and table 6.3) is cheaper to build and maintain than Restrepo being able to process raw water type A 2 B 4 . Retiro has UGFL (0.9 m gravel bed depth) operating at 0.5 mh -1 meanwhile Restrepo has HGF (7 m filter bed length) operating at 0.7 mh -1 . Of course Restrepo having a long HGF filter bed could be used to process more polluted water sources. However, after the results presented and discussed in Chapter 3, UGFL and UGFS are preferred to HGF alternatives for permanent solutions. Different combinations of filtration stages are identified to treat raw water types. In general, filter bed lengths increase with the contamination levels in raw water types while filtration rates decrease. Unsurprisingly, capital and running costs of MSF plants increase with increasing contamination levels in their raw water types. An example of different combinations of filtration stages, producing different MSF alternatives, is included in table 6.4 and figure 6.4. All these MSF alternatives fulfil proposed water treatment objectives. 6.4.1 Example of a selection guide for MSF alternatives Table and figure 6.4 summarise the iterative process followed to produce an example of a selection guide. A set of raw water types with different turbidity, faecal-coliform, and colour levels was adopted. Filtration stage alternatives and individual removal efficiencies were estimated based on results summarised in tables 6.1 and 6.3 and the literature review included in Chapter2. Filter bed length and filtration rates are indicated for each filtration stage. The characteristics of the filter media for the different filtration stages are in line with specifications and design criteria provided in table 3.1. 202