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galvis

Water treatment

Table 6.1. Individual

Table 6.1. Individual (at each treatment stage) and cumulative (up to the end of SSF stage) mean removal efficiencies of basic water quality parameters in MSF pilot system at Puerto Mallarino. Stage Filtration Influent mean values Individual mean efficiencies Rates (mh -1 ) Period Turbidity (NTU) Colour (PCU) Faecal Coliforms (CFU/100 ml) Turbidity (%) Colour (%) Faecal Coliforms (log. units) DyGF stage (0.9 – 1.4) I 109 81 41,184 32 11 0.2 DyGF (1.4 – 2.5) II 59 54 31,800 41 15 0.6 (1.4 – 2.5) III 51 35 97,779 43 14 0.8 (1.9 – 2.8) IV 52 57 108,796 40 16 0.6 CGF stage 0.3 I 74 72 24,758 84 69 2.6 UGFS 0.45 II 35 46 8,843 77 54 2.3 0.6 III 29 30 16,823 77 53 2.4 0.75 IV 31 48 26,226 75 63 2.3 0.3 I 74 72 24,758 70 44 1.8 UGFL 0.45 II 35 46 8,843 54 28 1.3 0.6 III 29 30 16,823 55 30 1.4 0.75 IV 31 48 26,226 61 46 1.3 SSF stage 0.1 I 12 22 65 64 73 2.8 SSF 1 0.1 II 8.1 21 45 75 67 2.7 0.55 III 6.6 14 64 82 57 2.1 0.15 IV 7.8 18 127 74 67 1.8 0.1 I 22 40 369 85 88 3.1 SSF 2 0.1 II 16 33 452 79 70 2.2 0.15 III 13 21 637 89 67 2.6 0.15 IV 12 26 1,226 77 69 2.0 Treatment lines Period Effluent mean values Cumulative mean efficiencies I 4.3 6 0.1 96 93 5.6 DyGF + UGFS + SSF1 II 2.0 7 0.1 97 87 5.5 III 1.2 6 0.5 98 83 5.3 IV 2.0 6 2.2 96 89 4.7 I 3.2 5 0.8 97 94 5.1 DyGF + UGFL + SSF2 II 3.3 10 2.7 94 81 4.1 III 1.4 7 1.7 97 80 4.8 IV 2.8 8 10.7 95 86 4.0 UGFS comprises three filtration steps. The contributions of each step to the overall removal efficiencies of this CGF stage are included in table 6.2. This table also includes the removal efficiencies of UGFL for comparative purposes. Most of the influent SS to the UGFS line were removed in the 1 st filtration step. During period III, for example, the 1 st , 2 nd , and 3 rd steps removed on average 72, 11, and 11% of influent SS respectively. This result is in harmony with the higher headlosses found in the 1 st step in comparison with the other two steps (Section 3.2.4.3 and table 3.27). In contrast, the 3 rd filtration step shows higher faecal coliform removal efficiencies (log units) than the other two steps. It seems to be that the step by step filtration approach in this treatment line (UGFS) probably provided a better environment for polishing micro-organisms at the end of this CGF filtration alternative than in UGFL. 195

Table 6.2. Individual (at each filtration step) and cumulative (at the end of the filtration stage) removal efficiencies of upflow CGF stages of MSF pilot system at Puerto Mallarino. Test period Water after DyGF (1) 1 2 3 Mean values CGF stages UGFS UGFL CGF units Individual (2) Individual UGFL Cumulative & 1 2 3 cumulative Removal efficiencies Turbidity (NTU) Turbidity removal (%) I 35 20 14 8 16 43 30 43 77 54 II 29 18 12 6 13 38 33 50 79 55 Faecal coliforms (CFU/100ml) Faecal coliforms removal (log. units) I 8,843 2,279 425 45 452 0.6 0.7 1.0 2.3 1.3 II 6,570 1,184 421 61 400 0.7 0.5 0.8 2.0 1.2 Colour (PCU) Colour removal (%) I 46 39 31 21 33 15 21 32 54 28 II 32 26 22 16 22 18 15 27 50 31 (1) Integrated water after DyGF stage (2) Individual contributions of each treatment unit to the cumulative removal efficiencies of the CGF stage The results in table 6.3 also show how the different full-scale MSF plants adapted to the type of raw water and the faecal coliform levels in it. In Shaloom the DyGF and CGF stages contributed 1.2 of the overall 2.8 log-units reduction, and in Colombo, which receives more contaminated water, the combination of DyGF and CGF stages contributed 1.8 of the overall 4.7 log-units reduction. However, the SSF stage in Colombo seems to be overloaded and a better application of the integrated water treatment concept would indicate a more robust CGF stage to reduce the risk of any failure in SSF which could compromise the role of terminal disinfection as a safety barrier. In spite of the high mean removal efficiencies showed by all MSF alternatives included in this study, they showed differences in fulfilling proposed treatment objectives, depending on factors such as turbidity removal efficiencies, filtration rates, initial costs, and O&M requirements. These factors will be considered in the process of developing selection guide examples. Turbidity removal efficiencies. As presented in Chapter 4, full-scale MSF alternatives processing surface water sources with mean turbidity values in the range of 4 to 24 NTU did not have limitations in fulfilling the proposed treatment objective for this parameter. In contrast, as shown in Chapter 3, pilot scale MSF alternatives processing Cauca River water, showed some limitations in producing water with turbidities consistently ≤ 5 NTU, particularly during the 1 st test period. In spite of the low filtration rate used during this period (0.3 mh -1 ) all CGF alternatives failed to produce mean turbidity values < 10 NTU before the SSF stage. The high mean raw water turbidity value (109 NTU) together with the lengthy initial ripening period observed in CGF stage could have contributed to the poor performance observed during period I. 196

Dec2015