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Water treatment

100 Cumulative Frequency

100 Cumulative Frequency (%) 10 1 1 10 100 Turbidity (NTU) 100 Cumulative Frequency (%) 10 1 1 10 100 1000 Apparent Colour (CU) Raw Water UGFS DGFS SSF SSF Figure 3.4 Cumulative frequencies (%) distributions for turbidity and apparent colour in raw water and CGF and SSF effluents. Dry period, July-September 1986. 2000 Turbidity (NTU) 1600 1200 800 400 0 0 20 40 60 80 100 Time (Sec) DGFS 1 UGFS 1 Figure 3.5 Effluent turbidity changes during fast drainage of first modules of DGFS and UGFS. August 22 1986. 72

• Bigger and better-instrumented MSF pilot systems were considered to be necessary to improve operational conditions and to obtain more reliable data. • Vertical flow gravel filtration alternatives showed potential to reduce turbidity and to improve the possibilities of successfully applying SSF in a tropical Andean environment. • In spite of the limitations of apparent colour measurements, a surrogate parameter for natural organic matter (NOM), it seemed possible that CGF options could contribute to reduce the formation of oxidation by-products after terminal chemical disinfection. • Even during the dry period reported in the preliminary study, the observed removal efficiencies in all the gravel filtration alternatives were not enough to overcome the water quality limitations of SSF. Therefore, lower filtration rates, longer gravel beds, and smaller gravel sizes at the end of the filter beds were considered necessary to improve CGF removal efficiencies. • Dynamic gravel filtration (DyGF) should be included as a first CGF stage in other experimental pilot studies to improve the observed MSF performance. • Fast drainage showed a good potential for periodically cleaning the CGF units. A greater amount of turbidity (solids) was removed from the 1 st module of UGFS than from DGFS. Longer-term observations were considered necessary to more clearly define this potential. To continue these studies on MSF and to develop other Research and Development (R&D) activities with MSF and other water treatment technologies, Cinara gradually established a working station with the support of the Universidad del Valle (UV) and other national and international agencies. 3.1.3 The research and Technology Transfer Station at Puerto Mallarino Figure 3.6 Location in Cali of Cinara´s headquarters at the main campus of Universidad del Valle (1) and research station at Puerto Mallarino, EMCALI (2). Studies with pilot scale systems for the present research work were carried out at the Cinara institute's Research and Technology Transfer (R&TT) Station for drinking water. The station operates under an agreement between the Municipal Company for public services of Cali, EMCALI, and UV-Cinara. The station is located at the Northeast of Cali (figure 3.6) and was 73