Application of Plackett Burman Design for Citric Acid Production from Pretreated and Untreated Wheat Straw

A solid state fermentation method was used to utilize wheat straw as substrates for citric acid production by using Aspergillus niger ATCC ۹۱۴۲. The Plackett Burman design (PBD) of experiments was used to test the relative importance of the variables affecting production such as moisture content, age of spore, inoculum size, initial pH of substrate, methanol concentration, incubation temperature and time, as well as initial sugar concentration, steam time and type of solvent. In best condition, the microorganism produced ۴۷ g citric acid per kg dry crude wheat straw, with yield of ۹۳ % based on the amount of fermentable sugar consumed. The effect of pretreatment of wheat straw with HCl, NaOH and urea on the yield of production was also investigated by using PBD. Acid, alkaline and urea pretreatment of wheat straw increased citric acid concentration to ۱۱۵, ۸۵.۰ and ۱۰۹.۵ g/kg of dry wheat straw and yield to ۹۷, ۹۷ and ۹۶ % (respectively) based on available sugar consumed. Finally, up scaling was achieved to a ۲۰-L solid state fermentor (tray bioreactor) in which moisture was constant in gas phase and acid pretreated wheat straw was selected as the most efficient pretreated substrate. The produced acid concentration and yield in fermentor was ۶۰.۵۳ g/kg of dry wheat straw and ۲.۱۱ g/kg.day, respectively.

کلیدواژه ها:

Solid state fermentation ، Citric acid production ، Pretreatment ، Wheat straw ، Plackett-Burman design