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Water treatment

nature of the organic

nature of the organic matter and the potential benefits of minor amounts of iron and manganese should also be considered (Collins et al, 1991; Spencer et al 1991). Table 3.21. Cumulative frequencies (%) in which performance objectives or drinking water quality guidelines are fulfilled in SSF effluents. CGF Effluents (%) SSF Effluents (%) CGF+SSF Turbidity Turbidity Faecal Coliforms Colour ≤ 5 ≤ 10 ≤ 15 ≤ 1 ≤ 5 ≤ 3 ≤ 25 ≤ 15 Period I CGF (0.3 mh -1 ) SSF (0.10 mh -1 ) UGFS+SSF 1 26 58 72 0 74 100 100 91 UGFL+SSF 2 5 27 40 5 86 94 100 97 MHGF+SSF 3 2 29 41 0 68 77 100 91 HGF+SSF 4 13 53 65 5 83 97 100 94 DGFS+SSF 5 10 45 57 7 69 94 100 94 Period II CGF (0.45 mh -1 ) SSF (0.10 mh -1 ) UGFS+SSF 1 40 79 88 29 95 100 100 94 UGFL+SSF 2 8 43 62 17 87 81 98 86 MHGF+SSF 3 14 57 75 19 91 87 100 88 HGF+SSF 4 25 80 89 22 95 100 100 92 DGFS+SSF 5 29 76 86 16 91 100 100 88 Period III CGF (0.60 mh -1 ) SSF (0.15 mh -1 ) UGFS+SSF 1 59 84 89 61 99 100 100 100 UGFL+SSF 2 27 65 74 51 99 87 100 100 MHGF+SSF 3 37 74 78 48 98 93 100 100 HGF+SSF 4 65 84 90 56 98 100 100 100 DGFS+SSF 5 51 82 88 47 99 100 100 100 Period IV CGF (0.75 mh -1 ) SSF (0.15 mh -1 ) UGFS+SSF 1 55 75 86 49 91 90 97 87 UGFL+SSF 2 39 61 68 46 85 62 90 83 MHGF+SSF 3 34 60 66 41 88 66 97 87 HGF+SSF 4 60 88 95 49 98 97 100 100 DGFS+SSF 5 47 70 83 42 89 93 100 97 3.2.4.2 Comparative analysis of different CGF alternatives. F-Test with ANOVA methodology was used to decide about the following (null) hypothesis (H 0 ): there are not significant statistical differences between the mean removal efficiencies of SS (or turbidity, faecal coliforms, or colour) in CGF filtration lines working with the same filtration rates. Tables 3.22 through 3.25 summarise comparative analyses made for SS, turbidity, faecal coliform, and colour removal efficiencies respectively. Based on filtration theory (sections 2.5.1-figure 2.5B and sections 2.8.2-figures 2.11 and 2.15) it was expected that HGF having similar gravel sizes but longer filter beds than UGFS and DGFS would show the highest mean SS removal efficiencies of all CGF lines. In other words, it was expected that MHGF had similar mean removal efficiencies compared with UGFS and DGFS. However, results in table 3.22 show that mean SS removal efficiencies are statistically alike (with 1% significance) in HGF, DGFS and UGFS during all tested periods. Consistently MHGF (with shorter filter bed length than HGF) shows lower efficiency than UGFS and DGFS. UGFL (having the shortest filter bed length of all CGF lines) shows the lowest mean removal efficiencies during all test periods but UGFL and MHGF had statistically similar mean removal efficiencies during periods II and III. 113

Tables 3.22 Comparative analyses of mean SS removal efficiencies in CGF lines. Suspended solids (mgl -1 ) in raw water (mean ± SD) CGF lines Descriptive statistics Removal efficiencies (%) Data Standard Mean (N) deviation (SD) Decision on Ho (a) Based on F-Test and ANOVA technique(α=1%) Hierarchical levels Based on Tukey Test (α=1%) 34 30 Period I (0.3 mh -1 ) HGF 3 96.57 2.9 HGF 3 (1) UGFS 3 95.67 3.0 UGFS 3 (1) 97 ± 135 DGFS 3 95.45 3.8 Ho is rejected DGFS 3 (1) MHGF 3 91.77 5.3 MHGF 3 (2) UGFL 92.38 4.2 UGFL (2) Period II (0.45 mh -1 ) HGF 3 92.48 5.9 HGF 3 (1) UGFS 3 91.63 6.8 UGFS 3 (1) 28 ± 44 DGFS 3 52 91.07 6.3 Ho is rejected DGFS 3 (1) MHGF 3 83.70 11.6 UGFL (2) UGFL 77.66 12.2 MHGF 3 (3) Period III (0.6 mh -1 ) HGF 3 91.47 7.6 HGF 3 (1) UGFS 3 90.67 7.6 UGFS 3 (1) 15 ± 11 DGFS 3 29 90.50 5.2 Ho is rejected DGFS 3 (2) MHGF 3 82.65 10.5 MHGF 3 (2) UGFL 76.39 10.1 UGFL (3) Period IV (0.75 mh -1 ) HGF 3 87.48 12.4 HGF 3 (1) UGFS 3 86.81 12.0 UGFS 3 (1) 20 ± 25 DGFS 3 83.91 10.7 Ho is rejected DGFS 3 (1) MHGF 3 71.76 16.7 MHGF 3 (2) UGFL 75.28 12.9 UGFL (2) (a) Ho: The mean SS removal efficiencies are statistically the same for all CGF alternatives. Table 3.23 Comparative analyses of mean turbidity removal efficiencies in CGF lines. Turbidity (NTU) in raw water (mean ± SD) (a) 74 ± 76 35 ± 34 29 ± 35 31 ± 40 MHGF Descriptive statistics Decision on Ho (a) CGF Hierarchical levels Removal efficiencies (%) Based on F-Test Based on Tukey lines Data Standard and ANOVA Mean Test (α=1%) (N) deviation (SD) technique (α=1%) Period I (0.3 mh -1 ) UGFS 3 80.34 9.1 UGFS 3 (1) HGF 3 77.53 10.2 HGF 3 (2) 65.10 14.0 MHGF 3 (4) DGFS 3 294 73.58 11.2 Ho is rejected DGFS 3 (3) UGFL 66.16 11.3 UGFL (4) 3 Period II (0.45 mh -1 ) UGFS 3 74.54 9.6 UGFS 3 (1) HGF 3 73.67 9.7 HGF 3 (1) DGFS 3 429 70.85 10.5 Ho is rejected DGFS 3 (2) MHGF 3 61.38 11.5 MHGF 3 (3) UGFL 52.63 11.7 UGFL (4) Period III (0.6 mh -1 ) UGFS 3 76.63 9.3 HGF 3 (1) HGF 3 76.07 10.6 UGFS 3 (1) DGFS 3 401 72.09 10.4 Ho is rejected DGFS 3 (2) MHGF 3 64.07 11.3 MHGF 3 (3) UGFL 57.65 12.1 UGFL (4) Period IV (0.75 mh -1 ) UGFS 3 76.14 6.2 HGF 3 (1) HGF 3 72.88 9.0 UGFS 3 (2) MHGF 3 55.16 17.3 MHGF 3 (5) DGFS 3 462 66.61 8.1 Ho is rejected DGFS 3 (3) UGFL 58.60 13.5 UGFL (4) Ho: The mean turbidity removal efficiencies are statistically the same for all CGF alternatives. 114