Significance of membrane type and feed stream in the ultrafiltration of sugarcane juice

This work examines the purification of sugarcane juice in a crossflow ultra filtration (UF) system. Experiments were conducted on-site at a sugar mill using fresh feed drawn from the appropriate stage in the sugar manufacturin g process. Different polymeric membranes with a nominal molecular weight cu toff rating in the 10-50 kD range were evaluated. The 20 kD polyethersulpho ne membrane was identified to be the most effective in terms of acceptable flux coupled with significant removal of nonsugar impurities. Subsequent tr ials were performed on four feed streams viz. mixed juice, raw juice, rotar y vacuum filtrate, and clarified juice. It was observed that with the excep tion of the clarified juice, the fine suspended particles (bagacillo) in al l the other streams formed a secondary filtration layer on the membrane sur face during the course of filtration. The permeate displayed a 1.5-3 unit r ise in juice purity, which is a remarkable improvement over the 0.5-1 unit rise obtained in the liming-sulphitation process. In addition, the UF perme ate was typically over three times as clear with a fivefold color reduction when compared to the clarified juice produced by the conventional process.