The recovery of contaminated single-phase detergents used in dairy industries by means of NF is possible if the membranes and the operating conditions are correctly selected. The membrane used in this work (KOCH MPS-34, Koch Membrane Systems, USA) showed a very good performance, which was demonstrated after 1800 h operating continuously at industrial conditions and using real contaminated detergents as feed. Working at a great recovery ratio (75%), a high and stable permeate flux (45 L h 1 m 2) was ob- tained. No chemical cleaning was necessary during the experi- ments; only short rinsing steps were required when the permeate flux decreased (as a consequence of changes in the com- position of the contaminated detergent). The permeate obtained showed high pH, low surface tension and low amount of sus- pended solids, which are considered the most important parame- ters to obtain efficient cleaning rates. Membrane fouling was mainly caused by the precipitation of inorganic salts and the adsorption of organic matter on the membrane surface due to the concentration of the rejected species. However, the detergent components did not cause significant membrane fouling.
The efficiency of the NF permeate as a cleaner was checked at pilot plat scale using an UHT equipment fouled by different foods. The cleaning cycle consisted of two rinsing steps after and before the cleaning step, which was carried out with the recovered deter- gent. The methods used to check the degree of cleanliness of the UHT pilot plant (bioluminescence test and cell count) demon- strated the good performance of the permeate as a cleaner (RLU < 150 and CFU mL 1 < 10). Several tests were also performed to demonstrate the cleaning efficiency at real industrial conditions. The NF recovered contaminated single phase detergent was used to clean industrial ERCA yogurt filling machines. The low RLU (