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Abstract: Characterisation of membranes in order to determine how clean the membranes are is usually determined by (1) comparing the initial and final clean water flux (2) the product flux in the following run, (3) FTIR analysis, (4) streaming potential and (5) contact angles. However, these techniques do not provide information about where the remaining foulant resides. In this paper clean water flux results were combined with dye tests (Amido black) to reveal how clean the membranes really were after cleaning with both formulated and industrial cleaners. The dye tests not only identified the remains of protein foulant on the membrane after cleaning but also the presence of surfactant adsorbed to membranes and protein. Also, the dye tests showed for similar relative water fluxes (after fouling, cleaning and rinsing), for three different cleaners, the membranes were cleaned to vastly different degrees. In addition to this by combining the dye test results with the surface tension and pH of the cleaning solution, it was possible to determine the optimum pH and surface tension required for complete removal of protein deposits, without modifying the membrane too drastically. The role of sodium hydroxide (NaOH) and surfactant in the cleaner was investigated and it was found that for successful removal of proteins from membranes the cleaner needed to contain both NaOH and surfactant. [Copyright &y& Elsevier]

This paper investigates the utilisation of nanofiltration (NF), agitation (by pump or sonication), freezing and acetone extraction methods to purify paper machine o-water. The results were judged by regained pulp brightness and reduction of various components. In the NF experiments the brightness was almost totally regained. Also the reduction of most measured components like lignin and carbon were retained well by the membrane (PES). The metal ions (Si, Al, Mg, Na, K, Mn, Ca, Fe and Cu) were reduced in the permeate (retained by the membrane) to the level found in the clear filtrate. This indicated that the metal ions (Si, Al, Mg, Na, K, Mn, Ca, Fe and Cu) were not brightness-reducing components. The flux was rather low for a commercial application because the membrane was a low-flux membrane. The reduction of sugar, colour and lignin residuals was quite high (>80%), and it was considered that these were possibly brightness-reducing components. It was found that by treating the fines with acetone and then returning them to the original water, the colour was reduced to a high enough degree that approximately 50% of the brightness reduction was recovered. It was considered that coloured contaminants that were absorbed on the fines were removed or destroyed. The brightness recovery was >50% for both the TMP and PK4 o-water. The brightness recovery was greater using NF, but in that case so many substances were reduced in the permeate that it was difficult to determine which were the brightness-reducing substances. However, in the case of acetone washing, the only component that was reduced was the colour. For both o-water PK4 and TMP the colour was reduced by 50% and the brightness recovery was 50%, suggesting a direct correlation. Agitation of the water samples by the means of a pump and sonication showed no change in the water, which included no changes in the brightness. The same was also found for water samples that were frozen. These experiments also showed that temperature changes did not affect water composition. [Copyright &y& Elsevier]