Page 55 - ro membanes

38 2. MEMBRANE FOULANTS AND SALINE WATER PRETREATMENT TABLE 2.7 Water Quality Parameters for Characterization of Microbial Foulants
Source Water Quality Parameter
Total organic carbon (TOC), mg/L
TOC:TN:TP ratio
RO train differential pressure (DP) rate increase, bars/month
Chlorophyll a
TABLE 2.8
Total Algal Count, Cells/L
<10,000 10,000e20,000 20,000e40,000 40,000e60,000 >60,000
Algal Bloom Intensity
Non-algal bloom condition Low-intensity algal bloom Moderate algal bloom High-intensity algal bloom Severe algal bloom
Biofouling Potential of Saline Source Water
Minimal Low Medium High Very high
Pretreatment Issues and Considerations
If TOC < 0.5 mg/L the content of microbial foulants is low and the source seawater has minimal biofouling potential.
In a range of 0.5e2.0 mg/L the water has moderate fouling potential.
If TOC > 2.0 mg/L, the biofouling potential is high.
If the ratio is within 20% of 1:1:1 the water has low biofouling potential.
Any of the ratios exceeding 1.20:1 is an indication of source water with nutrient imbalance and elevated biofouling potential.
If DP increases with <0.1 bar/month, the source water has very low biofouling potential.
If DP increase is 0.1e0.4 bars/month, the water has moderate fouling potential. If the DP rate increase is more than 1.0 bar/month, the source water has high
fouling potential.
This parameter is indicative of algal bloom occurrence.
If water contains >0.5 mg/L source water may be in algal bloom condition. When heavy algal blooms occur, Chlorophyll a usually exceeds 4 mg/L.
Algal Count Thresholds Typically Used to Characterize Algal Bloom Severity and Biofouling Potential
bloom. As indicated in the previous section, Huang et al. (2013) have found statistically significant correlation between chlorophyll a and the fouling indicator of RO membranes.
It should be pointed out that elevated content of TOC does not necessarily mean that the source water intake is experiencing algal bloom. TOC is measure of all types of organic com- pounds contained in the source waterdoriginating from both living aquatic microorganisms and from NOM. For example, intake wells collecting source water from an alluvial aquifer yield saline source water with a high content of TOC, almost exclusively contributed by