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2.6 MICROBIAL FOULANTS 27 TABLE 2.6 Water Quality Parameters for Characterization of Organic Foulants
Source Water Quality Parameter
Total organic carbon (mg/L)
UV254 (cm1) SUVA
Pretreatment Issues and Considerations
If below 0.5 mg/Ldbiofouling is unlikely. Above 2 mg/L, then biofouling is very likely.
If below 0.5 cm1, the saline source water has low organic and biofouling potential.
If >4, then source water is dominated by aquatic humic matter and biofouling is unlikely.
If <2, source water is experiencing algal bloom and biofouling is likely.
2.5.2.2 UV254 Absorbance
The ultraviolet (UV) absorbance of seawater sample at 254 nanometers (nm) is an indirect measure for content of NOM. The UV254 absorbance of saline water sample is determined by filtering of the sample through a 0.45-mm filter and measuring of the absorbance of UV light of the filtrate with spectrophotometer. This measurement is based on the fact that specific molecular structures (chromophores) within the NOM molecules adsorb UV light.
Because the NOM composition may vary from one water source to another, UV254 absor- bance is not always easy to use for comparison of the fouling potential of different water sources. In addition, this parameter may not be reflective of the content of microbial foulants if the NOM contained in source water is not easily biodegradable.
Specific UV absorbance (SUVA) is defined as the UV absorbance divided by the concen- tration of dissolved organic carbon (DOC) in the source water. Edzwald and Haarhoff (2011) indicate that the SUVA can be used as an indirect indicator of occurrence of algal blooms in the source water. If SUVA is larger than 4, then NOM consists predominantly of aquatic humic matter and the source water is not exhibiting algal bloom conditions. If SUVA is between 2 and 4, then the source water NOM is a mix of AOM and aquatic humic matter, and the source water body from which the water originates is in an early stage of algal bloom. When SUVA is less than 2, then the NOM in the source water consists predom- inantly of AOM and the source water body is experiencing algal bloom.
2.5.3 Threshold Levels of Natural Organic Foulants
Table 2.6 presents threshold levels of key water quality parameters used for assessment of organic fouling potential of the saline source water.
2.6 MICROBIAL FOULANTS
2.6.1 Description
Microbial foulants are aquatic microorganisms and organic compounds excreted by them such as polysaccharides, proteins, and lipids, which are referenced as extracellular polymeric