Deposit Morphology and Surface Analysis

Mallevialle et al. (1989) described a range of surface analytical techniques that are available for foulant identification. Many techniques that are currently being used for organics characterisation (see Chapter 2) can potentially be used for membrane deposit characterisation. 

The determination of cake porosity and fractal dimension of membrane deposits is difficult. While filtration laws cart be applied, most assume a constant porosity. 

Veerapaneni and Wiesner (1997) studied the fractal dimension of a membrane deposit by re-suspending the cake and performing static light scattering. Control experiments showed that the structure did not 

XPS is a useful technique to determine the chemical state of a deposit. In theory, this technique is ideal to determine whether calcium is bridging namral organics and membrane, or if co-precipitation or complex deposition occurred. In practise, this has been attempted by jucker and Clark (1994), and binding energies where published. Unfortunately due to the unknown binding energies of the possible compounds a clear distinction is not yet possible (see also Chapter 2). 

Fouling with proteins has been measured with C marked proteins. Fouling was much higher for hydrophobic membranes like PA and PS, compared to CA. An inflection point in the adsorption isotherms indicated that two mechanisms of adsorption existed. A relationship between adsorption and hydraulic permeabilitj existed (Matthiasson (1983)). 

---