Whey permeate fouling of evaporators

Abstract

Whey permeate fouling was studied to gain a better understanding of the processes involved and find methods of alleviation. An apparatus was built which allowed study of fouling under industrial conditions. It was found that pretreatment by heating at 80°C for two minutes and then centrifuging at 630 g reduced fouling in the apparatus by 94%. This was attributed to precipitation of calcium phosphate in the solution bulk during preheating, which reduced the level of supersaturation. Heat treatment with the same conditions but without centrifuging reduced fouling by only 39%. Precipitate which forms in the bulk of solution fouls in later heat treatment processes and separation of the precipitated mineral is needed to minimise fouling. Storage time affected fouling. In the short term (about 2 weeks), fouling slightly increased with storage time. When held for longer times (about 1 month) whey permeate did not appreciably foul. The use of additives was also found to be an effective alleviation method, reducing fouling by 66% with 0.1% addition (by dry weight) of tetrasodium pyrophosphate. This addition would increase the price of a ton of lactose by $16.32 /ton. Nanoftltration, ion dialysis and electrodialysis were also examined, but rejected as being uneconomic. By observing the effect of preheating and storage time it was proposed that calcium phosphate exists in whey in two forms. The majority of the minerals are associated with non-protein nitrogen (NPN) species, which tends to provide stability and prevent precipitation. In the other form the calcium phosphate is in solution as free ions. When the NPN species release minerals due to cleavage by enzymes or denaturation by heat, the concentration of ionic species increases past the solubility product and precipitation occurs.