International Journal of Environmental Science and Technology
in the second and third stages. Fouling and scaling phenom- enon occurred more rapidly in these stages.
E ff ect of L S I factor against time
Figure 3 shows clearly LSI values of all stages of RO with- out acid plotting against time. In normal operation, when LSI factor was calculated, it resulted in high LSI values of all stages, particularly total reject where its LSI Value went up to 2.5. Due to the high LSI factor, RO membranes caused scaling and fouling rapidly and resulted in a rapid increase of RO pressures. Rapidly increased pressures and product flow drop needed chemical cleaning of RO membranes. Thus, RO membranes were cleaned repeatedly in order to normalize the pressure and product flow (Hoek et al. 2000).
Fig. 2 Effect of pressure curve of all stages against time for RO plant. The pressure increase is significant at each pressure stage. The salt concentration is higher at high pressure stage
Benchmar k ing of RO p l ant after acid treatment
Sulfuric acid started to dose in the feed line of RO. Table 2 clearly shows that after acid treatment product flow started to recover instead of dropped while pressures increment was normal during 2 months in Table 3. Therefore, scaling and fouling have been optimized as per regular operation. From Table 2, we can see that due to the acid treatment that has been applied to the raw water; the reject flow is constantly being reduced from 8.2 to 6.7 m 3 /h, while the product flow is increased from 18.4 to 19.9 m 3 /h. The pressure at each stage is also increased, as we can see from Table 3. The increase in pressure is due to the flow increase in the product flow. Tables 2 and 3 show that the acid treatment has improved the efficiency of the whole operation.
E ff ect of pressure of RO plant with time
Pressures of all stages with the passage of time did not increase abruptly as increased without acid addition, as shown in Fig. 4. Acid treatment is effective in such a way that pressure increment of first stage was 7.5% which was
Fig. 3 LSI factor on RO membrane with time before acid treatment. High LSI values are observed for every stage, including the total reject. LSI factor on RO membrane with time
Table 2 Effect of flow rates during 2 months with acid treatment
Date
1-Nov-19 10-Nov-19 20-Nov-19 30-Nov-19 9-Dec-19 19-Dec-19 29-Dec-19
Feed flow (m 3 /h) 26.6
26.6 18.6
26.6 18.9
26.6 19.2
26.6 19.5
26.6 19.7
26.6 19.9
Product (m 3 /h)
18.4
Reject flow (m 3 /h) 8.2
8
7.7
7.4
7.1
6.9
6.7
Table 3 Effect of pressures of all stages during 2 months with acid treatment Date
1-Nov-19 10-Nov-19 20-Nov-19 30-Nov-19 9-Dec-19 19-Dec-19 29-Dec-19
First-stage pressure Second-stage pressure Third-stage pressure Total reject pressure
Bar Bar Bar Bar
10.6
10.7
10.9
11 10
11.1 10.1
11.3 10.3
11.4 10.4
9.6 9.1 8.1
9.7 9.2 8.2
9.9 9.4 8.4
9.5 8.5
9.6 8.6
9.9 8.9
10
9
1 3
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