Current perspective and future research directions on defecation clarification for the manufacture of raw sugar

Abstract

Juice clarification is integral to the sugar-manufacturing process and determines the quality of clarified juice which is subsequently processed to produce sugar. Clarification performance is defined largely by turbidity of the clarified juice, but the presence of soluble impurities, colour and colour precursors, polysaccharides and proteins influence heat-transfer performance of evaporators and evaporating crystallizers, the crystallisation performance in evaporating crystallizers and the achievable yield and quality of sugar. The conventional defecation process is inadequate to remove these nonsucrose impurities, and the gradual worldwide transition to green-cane harvesting is introducing greater levels of impurities into the cane supply. As a result, the clarification station is now having to deal with not only the endogenous impurities (e.g. stalk impurities) but also the trash (leaves and tops) impurities. This paper reviews work that has been conducted over the years to remove these impurities and presents future research directions that should improve clarification performance. Examples of future research directions include development of multi-functional nanoparticles to significantly improve impurity removal; processing strategies to enhance precipitation of proteins and polysaccharides; and ballasting and adsorbent agents.