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galvis

Water treatment

Table 3.19. Descriptive

Table 3.19. Descriptive statistics for faecal coliforms (CFU/100ml) in CGF and SSF stages. Descriptive Raw Int. Line 1 Line 2 Line 3 Line 4 Lines 5 statistics water water UGFS SSF UGFL SSF MHGF SSF HGF SSF DGFS SSF Period I (CGF at 0.3 mh -1 ; SSF at 0.1 mh -1 ) Mean 41,184 24,758 65 0.1 369 0.8 929 2.3 182 0.7 147 0.8 S.D 31,215 31,500 91 0.3 388 1.6 725 3.3 135 1.4 161 1.6 Minimum 6,200 3,000 1 0.0 10 0.0 193 0.0 42 0.0 20 0.0 Maximum 117,000 158,000 390 1 1,800 7 4,000 13 660 7 780 6 Data (N) 31 31 31 31 31 31 31 31 31 31 31 31 Period II (CGF at 0.45 mh -1 ; SSF at 0.1 mh -1 ) Mean 31,800 8,843 45 0.1 452 2.7 513 2.0 90 0.2 38 0.3 S.D 20,944 8,668 52 0.3 760 5.6 429 2.8 125 0.5 33 0.5 Minimum 2,700 2,100 1 0.0 48 0.0 2 0.0 4 0.0 6 0.0 Maximum 94,000 50,000 250 1 5,600 35 2,220 18 820 2 172 2 Data (N) 53 53 53 53 53 53 53 53 53 53 53 53 Period III (CGF at 0.6 mh -1 ; SSF at 0.15 mh -1 ) Mean 97,779 16,823 64 0.5 637 1.7 735 1.1 124 0.2 62 0.2 S.D 74,498 22,374 48 0.7 545 3.0 574 1.3 163 0.4 32 0.5 Minimum 20,000 3,700 17 0.0 152 0.0 56 0.0 29 0.0 19 0.0 Maximum 300,000 121,000 206 2 2,900 12 2,833 4 940 1 142 2 Data (N) 30 30 30 30 30 30 30 30 30 30 30 30 Period IV (CGF at 0.75 mh -1 ; SSF at 0.15 mh -1 ) Mean 108,796 26,226 127 2.2 1,226 10.7 1,357 4.6 145 0.6 146 1.4 S.D 100,235 34,647 137 5.4 1,210 25.0 1,070 6.9 160 1.1 160 2.4 Minimum 12,091 2,000 7 0.0 203 0.0 48 0.0 20 0.0 7 0.0 Maximum 500,000 169,667 480 26 4,900 109 4,400 29 637 5 523 12 Data (N) 29 29 29 29 29 29 29 29 29 29 29 29 All integrated water flowing into CGF lines had maximum coliform values that were above those used to produce table 2.15. Therefore performance objectives were met because removal efficiencies reached in this study were higher than those indicated for CGF (90%) and SSF (95%) in table 2.15. During the 1 st period, for example, individual removal efficiencies in CGF were in the range 93.4 (for MHGF) to 99.4% (for UGFS), while in SSFs they were in the range 98.9% (for SSF2) to 99.7% (for SSF 1 , SSF 3 and SSF 4 ). CEHE (1999) reported mean faecal coliform removal efficiency of 82% in UGFS processing river water with an average of 1,075 CFU/100 ml. Eudovique (1992) reported an efficiency of 56% in UGFL having 78 CFU/100 ml in influent water. Pardón (1989) reported 77% in DGFS processing settled river water with 790 CFU/100 ml. Pardón (1989) also reported 84 % in HGF (filtration rate 0.3 to 0.5 mh -1 ) treating raw water with 400 to 60,200 faecal coliform per 100 ml and 12 °C as mean water temperature. These reported efficiencies are all lower than those found in the present study. A feasible explanation for the higher efficiencies found in this study with respect to those reported in the literature seems to be related to higher levels of faecal contamination reaching the CGF lines tested in Puerto Mallarino, together with favourable environmental conditions for biological activity. Water temperature during this study was 24 °C with SD of 1.2 °C. water with appropriate nutrient levels are expected to have better removal efficiencies for turbidity and microbiological contamination than those with low nutrient levels (e.g. Bellamy (1985) based on results with SSF). Low removal efficiency reported by Eudovique (1992) may be related to high filtration rates in UGFL (1.3 mh -1 ), besides other possible limiting factors. 110

After the present experience, faecal coliform removal efficiency of 90%, or even higher, seem possible particularly with CGF alternatives having long hydraulic retention times and processing highly polluted water sources. However a less demanding performance objective for faecal coliform removal than that included in table 2.15 should be considered dealing with less polluted water sources. During all tested periods mean colour values in CGF effluents were in the range of 15 (for UGFS and HGF during period III) to 40 PCU (for UGFL period I). The mean colour removal efficiencies in CGF lines were in the range of 28% (for UGFL period II) to 68% (for HGF period IV). The mean colour values in SSF effluents were in the range of 4 (for SSF 4 period IV) to 11 (for SSF 3 period II). The mean colour removal efficiencies in SSF units were in the range of 50 (for SSF 4 period III) to 84% (for SSF 2 period I). The higher removal efficiencies in this treatment stage are in those SSF units following the CGF lines with the higher colour effluent values. Depending on periods and CGF lines, SSF units had effluent colour levels ≤15 PCU during 83 (for SSF 2 , test period IV) to 100% of monitored time (table 3.21). Table 3.20. Descriptive statistics for colour (PCU) in CGF and SSF stages. Descriptive statistics Raw water Int. Line 1 Line 2 Line 3 Line 4 Lines 5 water UGFS SSF UGFL SSF MHGF SSF HGF SSF DGFS SSF Period I (CGF at 0.3 mh -1 ; SSF at 0.1 mh -1 ) Mean 81 72 22 6 40 5 35 6 24 6 30 6 S.D 61 54 16 5 33 4 23 5 17 5 21 6 Minimum 24 20 3 1 4 1 7 1 4 1 5 1 Maximum 250 240 64 22 150 17 102 18 71 19 90 26 Data (N) 34 34 34 34 34 34 34 34 34 34 34 34 Period II (CGF at 0.45 mh -1 ; SSF at 0.1 mh -1 ) Mean 54 46 21 7 33 10 29 11 22 9 24 10 S.D 29 23 12 4 18 8 17 6 10 5 12 6 Minimum 21 18 3 1 12 2 7 3 8 2 8 2 Maximum 190 155 75 19 125 42 125 31 66 28 75 30 Data (N) 51 51 51 51 51 51 51 51 51 51 51 51 Period III (CGF at 0.6 mh -1 ; SSF at 0.15 mh -1 ) Mean 35 30 14 6 21 7 18 8 14 7 16 7 S.D 12 11 7 3 9 3 8 3 6 4 6 3 Minimum 16 10 2 1 7 1 4 1 3 1 4 1 Maximum 72 55 33 10 46 15 38 13 31 17 31 13 Data (N) 30 30 30 30 30 30 30 30 30 30 30 30 Period IV (CGF at 0.75 mh -1 ; SSF at 0.15 mh -1 ) Mean 57 48 18 6 26 8 27 7 15 4 20 6 S.D 36 32 14 7 19 7 20 7 10 3 14 6 Minimum 16 12 3 1 5 1 4 1 2 1 3 1 Maximum 164 144 46 30 70 30 74 28 35 13 50 35 Data (N) 30 30 30 30 30 30 30 30 30 30 30 30 The capability of CGF to remove dissolved organic matter is gradually being recognised (Galvis et al, 1989; Galvis, 1993, Collins et al 1994). SSF units in this study presented mean colour removal efficiencies in the range 50 to 84% which is above the range of 30 to 42% often considered in literature reviews for mean colour removal values in SSF (e.g. Ellis, 1985; Lambert and Graham, 1995). The higher removal values found in this research could be due to better environment conditions contributing to a more active biomass, which is not facing periodic stress from strong seasonal changes as occurs in northern countries, where most of the information in this field has been produced. Other factors such as the 111