This ‘hydraulic’ resistance is frequently referred to as a pure material parameter that is solely determined by the geometric properties of the substances that form the fouling layer. This additional pressure loss significantly influences the total energetic efficiency of the filtration process and is attributed to molecular friction in the stationary fouling layer. The deposition of water constituents on the membrane surface in solid or gel-like form (fouling) usually has the effect that a fluid passing the membrane at a constant rate experiences a higher pressure drop than in an equivalent case without fouling. Results further indicate that commonly applied models like the Kozeny–Carman equation are lacking a size-dependent parameter that causes a disproportionate decrease of colloidal fouling layer resistance with decreasing foulant particle size. The extent of this effect is identical irrespective of whether the ionic strength is increased or decreased. A minor reversible ionic strength effect could also be demonstrated. This time-dependent effect is largely irreversible and therefore most likely due to persistent changes in fouling layer structure. ionic strength prevailing during layer build-up or filtration sequence of different particle sizes). First results show that the hydraulic resistance of a fully developed colloidal layer is not exclusively determined by the physicochemical properties of its constituents but seems to be strongly dependent on the specific way of its formation (e.g.
A new measuring approach using a dead-end filtration test-cell allows exactly this, irrespective of any simultaneously occurring concentration polarization phenomena. The synchrony of several resistance mechanisms like hydraulic, osmotic, and electro-kinetic as well as numerous coupling effects complicate the analysis of their individual contributions to the fouling extent. Colloidal fouling is one of the main reasons for the reduced efficiency of membrane-based water desalination processes.
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