A novel and cleaner technological process of extracting l-glutamic acid from fermentation broth by two-stage crystallization

The fermentative l-glutamic acid is one of the important bio-products in the world. In 2009, China produced 1.6 Mt of GA occupying more than 70% of the entire production globally. However, the problems of high sulfuric acid/liquid ammonia consumption and severe pollution in GA production process strongly limit the sustainable development of the fermentative GA industry. In this study, a novel GA extraction technology, two-stage crystallization technology (TSC), was proposed and testified in pilot scale aiming at reducing sulfuric acid/liquid ammonia consumption and wastewater pollution in GA production process. The proposed TSC process could totally recover 95% GA: extracting about 83% of GA from fermentation broth in the first-stage with isoelectric crystallization technique, and recovering more than 70% of remaining GA in isoelectric mother liquor in the second-stage with evaporative crystallization technique. With the proposed TSC process, consumption of sulfuric acid, liquid ammonia and other supplemental materials could be substantially reduced, while the amount of high concentrated wastewater decreased from 9.8 m3/t-GA to 1.6 m3/t-GA. Through further treatments of evaporation and centrifugation, the ammonium sulfate in the mother liquor originated from the second-stage crystallization could be recovered. The mother liquor after ammonium sulfate recovery could be consecutively concentrated into a substance in semi-molten state again, and then the substance can be manufactured as organic-inorganic compound fertilizers after quick cooling and extrusion granulating. Comparing with the existing process of isoelectric crystallization with ion exchange (IEIE), the TSC process has the advantages of high quality of GA product, less sulfuric acid/liquid ammonia consumption and no wastewater/emission gas disposals. Furthermore, the solid waste could be utilized as the value-added fertilizer at the same time. In this way, the proposed TSC process greatly promotes the economic and environmental effect of the GA production process.