Flocculant Assessment Using a Portable Batch

The reproducibility of settling tests performed on a simple, portable laboratory settling kit has been evaluated statistically and found to be acceptable. A range of partially hydrolysed polyacrylamide flocculants, having differing degrees of hydrolysis, was tested and the optimum degree of hydrolysis for Mount Edgecombe juices was found to lie between 45 and 50 %. Introduction The clarification step in raw sugar manufacture is designed to remove insoluble suspended impurities from the mixed juice. This suspended matter comprises primarily field soil, organic debris, denatured proteins and precipitated calcium phosp h a t e ~ . ~ ~ The range of particle sizes extends from those visible to the naked eye right down to those in the colloidal region. The smaller particles settle out extremely slowly and in fact may be kept in suspension by convection currents or Brownian motion. The stability of these colloidal suspensions and their tendency to coagulate is to a large extent dependent upon the surface charge characteristics of the colloidal particles. The suspended matter in cane juice is predominantly of negative charge and it has been found that flocculation can be induced by a class of compounds known as anionic polyelectrolytes. Over the past 10-15 years the use of partially hydrolysed polyacrylamides has gained wide acceptance in the sugar industry.l9 2 * 3 9 A considerable amount of research has been done on the structure and mechanism of this floc f o r m a t i ~ n . ~ ~ ~ * ~ It has been shown that optimum performance is highly dependent upon the correct matching of the flocculant properties (e.g. molecular weight and degree of hydrolysis) with the charge characteristics of the colloids present. Since the latter can vary widely with cane age, variety, district and time of year, it is to be expected that the optimum flocculant type will also change during the seas0n.l Over the past few years a consistent pattern of clarification difficulties has been experienced at Mount Edgecombe, particularly during dry periods in the second half of the season. The present study was undertaken in an attempt to monitor the seasonal variations in juice behaviour and to assess the relative effectiveness of a range of flocculants having differing degrees of hydrolysis.