Wednesday, November 11, 2015
Exhibit Hall 1 (Salt Palace Convention Center)
Techno-economic and environmental assessment of Citric Acid Production by Aspergillus niger
Chacón Yessica1, Daza Laura1, Cardona Carlos A1**.
1 Universidad Nacional de Colombia sede Manizales, Instituto de Biotecnología y Agroindustria, (+57) (6) 8879400 ext 55354.
** Corresponding author: firstname.lastname@example.org
Citric acid is an organic acid with high application in food industry as acidulant in soft drinks and confectionery . In 2009, it was reported a world production of approximately 1,6 million ton . Different fermentation techniques in which predominates submerged fermentation in different feedstocks of accessible cost (sucrose, glucose and cane molasses, among others) give high yields  . In Colombia sucrose from sugar cane is used as substrate for citric acid production using the strain Aspergillus niger, based on the advantage of this microorganism to have an extra cellular mycelial bound invertase that hydrolyzes sucrose under acid conditions in the fermentation .
However submerged fermentation, different factors influence the production of other compounds reducing yields and obtaining oxalic or gluconic acids instead of citric acid. In this way the carbon source and other macronutrients as nitrogen, phosphorus and trace elements represent determinant factors in conidia growth and acid accumulation . Carbon source in the medium should be adequate, since a low concentrations byproducts as the oxalic acid are generated and at high concentrations polyol can be obtained, leading to low yields of the interest product . Nitrogen source leads to decrease pH, being ammonium sulfate of the most use because it increases the production of citric acid without oxalic acid formation. However, fermentation media with low levels of ammonium nitrate to prevent the formation of oxalic acid and without affecting the C/N ratio have been reported  . High phosphorus contents easily lead to the formation of oxalic acid, hence low levels of phosphate are necessary. The most appropriate phosphate source use is potassium dihydrogen phosphate  . Finally, different divalent metals (such as Zn, Mn, Fe, Cu and Mg) as trace elements inhibit the accumulation citric acid, while others (Mg, Cu) balance this effects and are necessary for the fungus growth and acid production  . Fermentation process of A. niger for citric acid production is carried out at temperatures between 28°C-30 °C during 5-14 days with continuous agitation and tolerable aeration rate. High pH leads to oxalic and gluconic acids production due to the glucose oxidase enzyme activation  . Low pH is advisable to performe this fermentation.
The aim of this work was to evaluate the citric acid production from glucose as carbon source using A. niger as microorganism. The study was carried out in the fermenter Liflus GX (BIOTRON, INC-HANIL). Biomass concentration, citric acid and total reducing sugars concentrations were followed using the techniques of dry weight, HPLC and the Saffran-Densted Method to 418 nm, DNS (3,5-dinitrosalicylic acid) Method to 540 nm, respectively.
The techno-economic analysis was developed using the commercial software Aspen Plus V8.2 (ASPEN TECHNOLOGY USA) to simulate the process for obtaining the material and energy balances. These balances were use in the commercial software Aspen Process Economic Analyzer V8.2 (ASPEN TECHNOLOGY USA) to calculate the production cost per kg of citric acid considering the reported values in Colombia for tax rate (25%)m interest rate (17%), electricity and water costs  . The study was performed for a period of ten years using the straight-line method for depreciation of capital. The environmental assessment was performed using the Waste Algorithm Reduction (WAR), developed by the Environmental Protection Agency (EPA) .
The results obtained allowed concluding the determinant factors in the citric acid production to reach an economic and environmental competitiveness of the most common production process in the field of biotechnology.
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