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Water treatment

Table 4.3 Sampling

Table 4.3 Sampling points and frequencies at MSF plants. These frequencies were applied in the period October 1990-July 1992. Sampling for basic water quality parameters continued but frequencies were gradually reduced until Dec. 1998. Parameter Raw water DyGF Stage CGF Stage SSF Stage Turbidity (NTU) (2) 2w 2w 2w 2w Colour (PCU) (2) 2w 2w 2w 2w Faecal coliforms (CFU/100 ml) (2) 2w 2w 2w 2w Temperature ( o C) (2) f - - - pH (Units) (2) f - f f Total Iron and manganese (mgl -1 ) m - m m Suspend solids (mgl -1 ) w w w w Filterability (ml (3min) -1 ) (3) m m m m Dissolved oxygen (mgl -1 ) (2) f f f f Total alkalinity (mgl -1 Ca CO 3 ) m - m m Total hardness (mgl -1 Ca CO 3 ) m - m m Head loss (cm) (2) - 2w 2w 2w Flow (ls -1 ) (2) 2w 2w 2w 2w 1 w= weekly; f= fortnightly; m= monthly 2. The sampling frequency for these parameters was reduced to once a month during the period August 1992 – December 1995. Afterwards sampling became sporadic. 3. Only during 1991 4.4.1.6 Data management An information system, similar to that described for MSF pilot system, was designed for MSF plants. Data were analysed to obtain descriptive statistics. Comparative analyses were not performed due to the differences in source water quality, design and operating conditions of MSF plants. 4.4.2 Results and specific discussion 4.4.2.1. Raw water The mean raw temperature feeding MSF plants in the coffee region (Ceylan, Restrepo, and Marina) was in the range 18 to 21ºC, meanwhile it was 22 to 23ºC in the case of MSF plants located around Cali (Retiro, Cañasgordas, Elvira, Colombo, Shaloom, and Javeriana). Mean raw water temperature at Puerto Mallarino (Cauca River) was 24ºC during similar monitoring period. Descriptive statistics for raw water turbidity, colour, suspended solids, and faecal coliform levels are included in tables 4.4, 4.5, and 4.6. Figure 4.12 shows cumulative frequency distributions for turbidity and faecal coliform levels in surface water sources feeding MSF plants. These highland raw water sources show low to moderate levels of turbidity and a wide range of microbiological contamination, due the human pollution activities and discharge of untreated sewage. Raw water turbidity and faecal coliform levels in all water sources for MSF plants were lower than those observed in the Cauca River at Puerto Mallarino. 158

Table 4.4 Descriptive statistics for turbidity, colour, suspended solids and faecal coliform levels in multistage filtration (MSF) plants with upflow gravel filtration in layers (UGFL) as first or second coarse gravel filtration (CGF) stage. October 1990 to December 1998 Descriptives PARCELACION EL RETIRO COLOMBO-BRITANICO CLUB SHALOOM LA RIVERA Statistics Raw DyGF Raw Raw Raw UGFL SSF DyGF UGFL SSF DyGF UGFL SSF Water (*) Water Water Water Reservoir UGFL SSF Turbidity (NTU) Mean 14.8 7.2 4.2 0.9 14.6 6.4 4.5 0.6 3.8 3.0 1.9 0.8 5.9 3.9 1.7 0.6 SD 17.2 7.4 3.8 1.1 16.1 7.5 7.2 0.5 3.7 3.1 1.4 0.6 5.7 5.2 3.0 0.6 Minimum 3.0 1.0 1.0 0.2 2.0 1.4 0.7 0.2 0.5 0.4 0.3 0.2 1.5 1.0 0.3 0.2 Maximum 120 47 25 12 122 62 80 6.0 22 18 8.3 2.9 30 51 32 4.3 No. (Data) 203 197 204 209 286 258 261 372 70 66 69 70 49 125 126 127 Colour (PCU) Mean 24 20 16 5 25 19 16 4 15 12 10 6 15 14 8 3 SD 19 16 10 4 17 15 14 3 9 8 7 4 9 6 3 2 Minimum 2 2 2 2 3 2 2 2 4 3 2 2 3 2 2 2 Maximum 188 158 51 30 122 107 114 15 42 34 31 19 54 28 19 19 No. (Data) 199 189 102 202 291 252 257 373 65 65 64 65 49 125 126 127 Suspended Solids (mgl -1 ) Mean 20.3 4.5 1.3 0.1 22.3 3.2 1.4 0.1 1.9 0.9 0.2 0.1 4.4 2.1 0.3 0.2 SD 41.4 6.4 2.2 0.1 46.9 5.0 3.1 0.1 2.8 1.6 0.3 0.0 7.4 1.6 0.3 0.1 Minimum 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Maximum 316 40 14 0.8 392 45 35 0.6 11 7.0 1.0 0.1 42 5.9 1.1 0.8 No. (Data) 154 152 155 159 194 193 196 197 31 30 31 31 36 43 44 43 Faecal Coliforms (CFU/100ml) Mean 6,416 2,152 301 1,4 51,916 10,063 2,008 0.9 2,895 1,680 214 4.3 3,600 1,174 69 0.5 SD 17,582 9,930 337 5,0 73,140 19,170 4,664 4.5 3,341 2,305 226 8.5 4,583 3,755 100 2.6 Minimum 140 120 2 0 800 210 24 0 20 8 0 0 110 0 0 0 Maximum 162,000 105,500 2,040 53 677,000 193,000 48,400 82 14,200 10,900 1,120 56 23,100 36,000 730 28 No. (Data) 247 113 215 322 283 180 253 370 69 40 69 70 49 121 124 125 (*) Dynamic Gravel Filter. October/1991 to December/1998 159 159