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

This work examines the purification of sugarcane juice in a crossflow ultrafiltration (UF) system. Experiments were conducted on-site at a sugar mill using fresh feed drawn from the appropriate stage in the sugar manufacturing process. Different polymeric membranes with a nominal molecular weight cutoff rating in the 10-50 kD range were evaluated. The 20 kD polyethersulphone membrane was identified to be the most effective in terms of acceptable flux coupled with significant removal of nonsugar impurities. Subsequent trials were performed on four feed streams viz. mixed juice, raw juice, rotary vacuum filtrate, and clarified juice. It was observed that with the exception of the clarified juice, the fine suspended particles (bagacillo) in all the other streams formed a secondary filtration layer on the membrane surface during the course of filtration. The permeate displayed a 1.5-3 unit rise 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 permeate was typically over three times as clear with a fivefold color reduction when compared to the clarified juice produced by the conventional process.