Long-term tests were made to check flux decline during UF. Fig. 8 and Fig. 9 show the results. It is seen that (Jv/Jw) decreases along the UF process and its deviation is mostly more than 30%, indicating that the present process is affected by membrane fouling. In general, the fouling is a combination of initial pore blocking by polymeric chains and the acquisition of a fouling, second layer on the surface which modifies pore size distribution of the membrane [25] and [26]. As stated above from pH trends of UF flux, the initial pore blockage occurring at the start of UF can be ignored [14]. It was experimentally found that a gelatin-like, immobilized, compressible layer forms and deposits on the membrane surfaces. The thickness of the second layer is larger at higher pH (>5). Although it is not necessarily a ‘cake’, the built-up of polymers near the membrane interface can still be followed by the cake-filtration type of description [27].