RECOVERY OF CALCIUM TARTRATE AND CALCIUM MALATE IN EFFLUENTS FROM GRAPE SUGAR PRODUCTION BY ELECTRODIALYSIS

This paper deals with the recycling of concentrate during the electrodialysis treatment at 60-degrees-C of grape must in order to decrease the effluent pollution volume and to increase the concentration of tartaric and malic acid in the recovery of their insoluble salts. The concentrate extracted slightly below the threshold of salts crystallization is cooled (5-degrees-C for 48 h) and crystals of potassium salts are recovered. This concentrate is next recycled, extracted and cooled. The final effluent volume is fifteen times lower than that of the initial must. The cold storage of primary and secondary concentrates eliminates, respectively, 80% and 87% of tartaric acid, 15% and 14% of malic acid. When calcium chloride is added to the effluents, the tartaric acid recovery rate can be 60-75%, while that of malic acid is in the range 29-55%. Maximum recoveries can only be achieved when the effluent concentration is raised to 165 g of malic acid per liter.