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TABLE 2.5
2. MEMBRANE FOULANTS AND SALINE WATER PRETREATMENT TOC Content and Fractions of Various Seawater Sources
Seawater Source
Surface raw seawaterdPerth, Australia
Surface raw seawaterdAshkelon, Israel (May 2005)
Surface raw seawaterdAshkelon, Israel (Nov. 2005)
Surface raw seawaterdCarboneras, Spain
Well seawaterdGibraltar, Spain
Surface seawaterdGibraltar, Spain
Polysaccharides TOC (% of Total
(mg/L) TOC)
0.9 3
1.2 14
1.0 7
0.9 8
0.61
0.8 5
Humic Substances & Building Blocks
(% of Total TOC)
31
39
52
38
26
28
Low Molecular Weight Acids & Neutrals (% of Total TOC)
25
25
22
18
22
25
Other Low Molecular Weight Compounds
(% of Total TOC)
41
22
19
42
51
42
Analysis of various sources of seawater (Leparc et al., 2007; Schrotter et al., 2006) summa- rized in Table 2.5 indicates that TOC concentration of seawater may contain various fractions of organics depending on the origin of this water and the type of seawater intake. These frac- tions may also change depending on the season as well.
The analysis of Table 2.5 leads to the conclusion that low molecular weight organic com- pounds are typically the greatest fraction of the TOC in seawater (40%e50%). Most of these com- pounds, however, have limited fouling potential and therefore, the higher percentage of low molecular weight compounds in the water, the lower fouling potential this source water has.
A combination of high percentage of compounds from the “other low molecular weight” category, low TOC, and low polysaccharide content of the TOC is a clear indication for source water of low fouling potential. Based on this “rule of thumb,” the well seawater at the Gibraltar SWRO facility would have the lowest fouling potential from all sources listed in Table 2.5.
Comparison of the data from the Ashkelon seawater desalination plant in Israel indicates that the most easily biodegradable organics (polysaccharides) change seasonally and increase during the summer season along with the content of algal biomass in the Mediterranean Sea. This data also show that TOC concentration of seawater may not always correlate with the content of polysaccharides in this water. In this case, humic substances would be the main contributor of fouling to the SWRO membranes of the Ashkelon plant.