مرکز منطقه ای اطلاع رساني علوم و فناوري -

چكيده لاتين :

A solid state fermentation method was used to utilize wheat straw as substratesfor citric acidproduction by using Aspergillus niger ATCC 9142. The Placket! 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 47 g citric acid per kg dry crude wheat straw, with yield of 93 % based on the amount of fermentable sugar consumed The effect of pretreatment of wheat straw with HCI, 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 115, 85.0 and 109.5 g/kg of dry wheat straw and yield to 97, 97 and 96 % (respectively) based on available sugar consumed. Finally, up scaling was achieved to a 20-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 60.53 g/kg of dry wheat straw and 2.11 g/kg.day, respectively.