2.1. Ultrafiltration pilot plant
UF laboratory plant was equipped with a Rayflow flat sheet module from ORELIS (France) which allows to work with two
membranes of 100 cm2 each one, working in series and operating by cross-flow filtration mode. The tank for the feed and cleaning solution has a capacity of 15 l.
2.2. Membranes
The UF membranes tested in this study were from MicrodynNadir. One of them was a polyethersulfone (PES) membrane with a molecular weight cut-off of 5 kDa (membrane UP005) and the other one was a hydrophilic polyethersulfone (PESH) membrane with a molecular weight cut-off of 30 kDa (membrane UH030). The membranes can be used at operating conditions of pH and temperature in the range of 0–14 and until 95 C respectively.
2.3. Fouling solution
Bovine serum albumin (BSA, purity >98%, Sigma–Aldrich,Germany) solution was employed as organic foulant. Solutions
with a concentration of 1% w/w and pH 7.5 were prepared for the fouling step. According to the manufacturer, the molecular weight of the BSA is about 66 kDa. Mixing of the stock solution was performed for a period of 24 h in a glass beaker with magnetic stirring to guarantee the complete BSA dissolution and then the stock solution was stored at 4 C.
2.4. Contact angle measurements
The contacts angle of the UH030 and UP005 membranes (virgin,fouled and cleaned) were measured on Dataphysics OCA instrument . To measure the contact angle of each membrane a surface of 1500 mm2 in pieces of 60 mm of length and 25 mm of width was analyzed. The contact angle was determined by measuring the average contact angle (right and left) of 10 extra pure water drops on the membrane surface (10 different locations for each membrane). The time for the water droplet to reach the equilibrium with the membrane surface is important because if there is mobility of the polymer chains, the functional groups in contact with the drop of water can change and interfere with the results. In this case, the time was about 10–20 s until the equilibrium was confirmed.