Humic fractional deposition

Such low adhesion forces show that the membranes are well suited to many types of separation. The removal of humic acid was investigated as an example of a challenging separation. The blend membranes gave very good separation with little fouling. By quantification of the fraction of humic acids deposited during filtration it was possible to show that both planar (S5-20) and tubular (T5-20) versions of the membranes showed high critical flux values, whereas membranes... 

Figure 6.24 Fractional deposition of humic acids at different operating fluxes. The intercepts on the x-axis indicate the critical fluxes.

Schafer et al. [35] studied the role of concentration polarization and solution chemistry on the morphology of the humic acid fouling layer. Irreversible fouling occurred with all membranes at high calcium concentrations. Interestingly, it was found that the hydrophobic fraction of the humic acids was deposited preferentially on the membrane surface. This result is similar to the work of Ridgway et al. [31], who showed that the hydrophobic interaction between a bacterial cell surface and a membrane surface plays a key role in biofilm formation. The formation of two layers, one on top of the other, was also observed by Khatib et al. [36]. The formation of a Fe-Si gel layer directly on the membrane surface was mainly responsible for the fouhng. 

Biochemical compounds such as carbohydrates, proteins (amino acids), and lipids present in humic substance fractions (humic acid, fulvic acid, and humin) pose a problem in determining and characterizing humic substances in various environments, especially in freshly deposited lake sediments where relatively large amounts of those biochemicals are present. Common separation methods cannot separate true humic substances from non-humic substances. According to Riffaldi and Schnitzer (1972b), 6N HCl hydrolysis efficiently removes nonhumic substances from soil humic acid. However, the following questions remain unresolved ... 

The occurrence of HCP In HA fractions and Its absence In FL fractions suggests that the pollutant was strongly associated with organic matter and was probably deposited In the sediments In bound form. HCP may have been covalently bound to organic matter and released hydrolytically during base treatment. Laboratory studies support these observations Miller et al. (53) demonstrated that HCP covalently binds to rat tissue protein (In vitro) and Mathur and Morley (54) showed that a structurally similar compound, methoxychlor (2,2 -bls(jj-methoxyphenyl)l,l,l-trlchloroethane), strongly associated with a synthetic humic acid. 

Organic phosphorus associated with humic and fulvic acids represents >40% of the total soil phosphorus. The fulvic acid phosphorus constitutes a large fraction of the organic phosphorus in most soils and it is likely that this pool is derived from plant litter and recently deposited organic matter. 

Humus acids are a main component extracted by water from organic matter of rocks and deposits, first of all from soil and peat. The content of humic acids reaches in soils 10% by mass, in peats 25-50%, in coals up to 60%. The contents of fulvic acids - up to 15% in peats and 60% in coals. Relative contents of humic and fulvic acids in soils depend on their properties. In tundra and bleached forest soils dominate fulvic and in peats, chestnut and black-earth soils, humic acids. Frequently (but not always), with depth fraction of fulvic acids increases. 

Due to variations in the soil, such as humic constituents, sand fractions, clay minerals, peat minerals, wood rests, algal toxins, and deposits of shell lime, different reactions take place. The natural organic matter (NOM) in an aquifer is a complex mixture of substances, such as humic acids, fulvic acids, amino acids, carbohydrates, lipids, lignin, and waxes. 

---