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gure 7 | Correlation between concentration of phytoplankton and raw water turbidity (RW), gravel filtered water (PFW) and slow sand filtered water (FW) during phase 2. Figure 7 depicts the correlations between turbidity and concentration of phytoplankton. The Pearson coefficients values below 1.0 NTU in rapid-filtered water fed by the same source used in this work.

Figure 7 gure 7 | Correlation between concentration of phytoplankton and raw water turbidity (RW), gravel filtered water (PFW) and slow sand filtered water (FW) during phase 2. Figure 7 depicts the correlations between turbidity and concentration of phytoplankton. The Pearson coefficients values below 1.0 NTU in rapid-filtered water fed by the same source used in this work.

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Figure 1 | Location of the dam in the city of Pacatuba, Ceara, Brazil
Figure 1 | Location of the dam in the city of Pacatuba, Ceara, Brazil
Figure 2 | Schematic pilot plant used in the research; there was no gravel filter (prefilter) in phase 1.
Figure 2 | Schematic pilot plant used in the research; there was no gravel filter (prefilter) in phase 1.
Table 1 | Averages values of flow and filtration rates used during the research phases pumped at a constant flow to the slow sand filter or gravel
Table 1 | Averages values of flow and filtration rates used during the research phases pumped at a constant flow to the slow sand filter or gravel
Figure 3 | Flowchart of the experimental investigation.
Figure 3 | Flowchart of the experimental investigation.
*For some days, there were no collections. only during the first 7 weeks. Table 2 | Parameters studied, methods used and frequency of collection of samples for quantification of the parameters monitored by multiplying the number of individuals counted for each species by their average number of cells per filament. This number was obtained by dividing the average length of the filaments by the cellular length. The average number of cells was calculated separately for the samples originat- ing from the raw water, the filtered water of the slow filter and the gravel filter.
*For some days, there were no collections. only during the first 7 weeks. Table 2 | Parameters studied, methods used and frequency of collection of samples for quantification of the parameters monitored by multiplying the number of individuals counted for each species by their average number of cells per filament. This number was obtained by dividing the average length of the filaments by the cellular length. The average number of cells was calculated separately for the samples originat- ing from the raw water, the filtered water of the slow filter and the gravel filter.
Figure 4 | Graphics box-plot of the values of turbidity of raw water during phases 1-3. Results of phases 1-3
Figure 4 | Graphics box-plot of the values of turbidity of raw water during phases 1-3. Results of phases 1-3
Figure 5 | Turbidity of raw water (RW) and filtered water (WF) and head loss during phase 1. Initially, the slow sand filter was operated without pre-filter and with a filtration rate average of 3.6 m day '. Due to the high concentration of phytoplankton present in the raw water (Ta ble 3), the filter bed was quickly clogged and the maximum head loss was reached in less than 24 h. Because of t his, t he operation of the slow sand filter was then restarted with a filtration rate of 1.8 m day‘, resulting in tur- bidi y red period of bidi drin uction greater than 75% after the maturation he filter (7 days). It then produced water with tur- y less than 2 NTU, which is within the acceptable king water standards for slow sand filtration in Brazil (Brasil 2004). Although the slow sand filter has shown good results (see Figure 5), the maximum head loss was however reached in only 15 days, even with a limited fil- tration rate (1.8 m day~?).
Figure 5 | Turbidity of raw water (RW) and filtered water (WF) and head loss during phase 1. Initially, the slow sand filter was operated without pre-filter and with a filtration rate average of 3.6 m day '. Due to the high concentration of phytoplankton present in the raw water (Ta ble 3), the filter bed was quickly clogged and the maximum head loss was reached in less than 24 h. Because of t his, t he operation of the slow sand filter was then restarted with a filtration rate of 1.8 m day‘, resulting in tur- bidi y red period of bidi drin uction greater than 75% after the maturation he filter (7 days). It then produced water with tur- y less than 2 NTU, which is within the acceptable king water standards for slow sand filtration in Brazil (Brasil 2004). Although the slow sand filter has shown good results (see Figure 5), the maximum head loss was however reached in only 15 days, even with a limited fil- tration rate (1.8 m day~?).
Table 4 | Descriptive statistics of the turbidity and phytoplankton values in Phase 2
Table 4 | Descriptive statistics of the turbidity and phytoplankton values in Phase 2
‘igure 6 | Graphics box-plot of log removal of (a) turbidity and (b) phytoplankton in the gravel filter (GF), in the slow sand filter (SSF) and in both filters (GF + SSF) in phase 2. RW: raw water; PFW: filtered water in gravel filter; FW: filtered water in slow sand filter; PF E: removal efficiency of the gravel filter; SF E: removal efficiency of the slow sand filte
‘igure 6 | Graphics box-plot of log removal of (a) turbidity and (b) phytoplankton in the gravel filter (GF), in the slow sand filter (SSF) and in both filters (GF + SSF) in phase 2. RW: raw water; PFW: filtered water in gravel filter; FW: filtered water in slow sand filter; PF E: removal efficiency of the gravel filter; SF E: removal efficiency of the slow sand filte
Table 5 | Descriptive statistics of the values of turbidity and phytoplankton in Phase 3. Acronyms in column 2 as for Table 4
Table 5 | Descriptive statistics of the values of turbidity and phytoplankton in Phase 3. Acronyms in column 2 as for Table 4
igure 8 | Total coliforms present in raw water (RW), gravel filtered water (PFW), slow sand filtered water (FW) and the removal by the gravel (PF E) and slow filter (SF E) during phase 2.
igure 8 | Total coliforms present in raw water (RW), gravel filtered water (PFW), slow sand filtered water (FW) and the removal by the gravel (PF E) and slow filter (SF E) during phase 2.
igure 9 | Graphics box-plot of (a) log removal of turbidity and (b) phytoplankton (B) in the gravel filter (GF) and in the slow sand filter (SSF) and both filters (GF + SSF) in Phase 3.
igure 9 | Graphics box-plot of (a) log removal of turbidity and (b) phytoplankton (B) in the gravel filter (GF) and in the slow sand filter (SSF) and both filters (GF + SSF) in Phase 3.
Figure 10 | Graphics box-plot for Mann-Whitney comparison of log removal of turbidity of (a) gravel filtered water (PFW) and (b) slow sand filtered water (FW) between phases 2 and < had been reached in the gravel filter. This may be due to Confirming the previous statement, the slow sand filter was more efficient at removal of total coliform during Unlike the previous stage, in this phase the run filtration vas interrupted due to the maximum head loss available that aoe a as oy aes onan « sat "1 Confirming the previous statement, the slow sand filter Figures 10-12 show the box-plot graphs of Mann-Whitney test for comparison of log removal of turbidity, phytoplank- ton and total coliform from two of the three phases of research. For removal of turbidity, there was only a differ- ence in the performance of the slow sand filter between phases 2 and 3. In respect of the removal of phytoplankton, there was no difference between the phases for both filters since there were no p values less than 0.05. With regards to removal of total coliform, the slow sand filter performed differently in phases 2 and 3. Unlike the previous stage, in this phase the run filtration
Figure 10 | Graphics box-plot for Mann-Whitney comparison of log removal of turbidity of (a) gravel filtered water (PFW) and (b) slow sand filtered water (FW) between phases 2 and < had been reached in the gravel filter. This may be due to Confirming the previous statement, the slow sand filter was more efficient at removal of total coliform during Unlike the previous stage, in this phase the run filtration vas interrupted due to the maximum head loss available that aoe a as oy aes onan « sat "1 Confirming the previous statement, the slow sand filter Figures 10-12 show the box-plot graphs of Mann-Whitney test for comparison of log removal of turbidity, phytoplank- ton and total coliform from two of the three phases of research. For removal of turbidity, there was only a differ- ence in the performance of the slow sand filter between phases 2 and 3. In respect of the removal of phytoplankton, there was no difference between the phases for both filters since there were no p values less than 0.05. With regards to removal of total coliform, the slow sand filter performed differently in phases 2 and 3. Unlike the previous stage, in this phase the run filtration
Figure 11 | Graphics box-plot for Mann-Whitney test to compare the phytoplankton log removal in (a) the gravel filtered water (PFW) and (b) the slow sand filtered water (FW) between phases 2 and 3.
Figure 11 | Graphics box-plot for Mann-Whitney test to compare the phytoplankton log removal in (a) the gravel filtered water (PFW) and (b) the slow sand filtered water (FW) between phases 2 and 3.
Figure 12 | Graphics box-plot for Mann-Whitney test to compare the removal efficiency of total coliform in (a) the gravel filtered water and (b) slow sand filtered water between phases 2 and 3. phase 3 (Figure 12) than during phase 2. Removal greater than 99% was maintained throughout the operation period and 99.98% of removal was reached in the total coliforms count in two observations (i.e. a MPN of <1 individual in 100 mL).
Figure 12 | Graphics box-plot for Mann-Whitney test to compare the removal efficiency of total coliform in (a) the gravel filtered water and (b) slow sand filtered water between phases 2 and 3. phase 3 (Figure 12) than during phase 2. Removal greater than 99% was maintained throughout the operation period and 99.98% of removal was reached in the total coliforms count in two observations (i.e. a MPN of <1 individual in 100 mL).
“igure 13 | Total coliforms present in raw water (RW), gravel filtered water (PFW), slow sand filtered water (FW) and removal performed by the gravel filter (GF) and slow sand filter (SF) during phase 3. probably due to the increased filtration rate in phase 3.
“igure 13 | Total coliforms present in raw water (RW), gravel filtered water (PFW), slow sand filtered water (FW) and removal performed by the gravel filter (GF) and slow sand filter (SF) during phase 3. probably due to the increased filtration rate in phase 3.
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