Oxalic acid production by Aspergillus niger - Part II: Optimisation of fermentation with milk whey as carbon source

Oxalic acid is formed by Aspergillus niger at nearly neutral pH values. In this study the applicability of milk whey as a carbon source was investigat ed, both in shaking flask experiments and in a stirred tank reactor. The in fluence of pH on oxalic acid formation showed that the maximum production r ate and higher concentration of the product are observed at pH 6. At pH 7 t he same production rate was obtained although at a lower oxalic acid concen tration. The process was shown to be inhibited by product from an oxalic ac id concentration of about 10 kg/m(3) and its behaviour was fitted by Luong' s equation. In a 10-dm(3) strirred tank ferment the stirrer speed was varie d in a range from 100 to 600 rpm. At values between 200 and 400 rpm, maximu m production rates of oxalic acid of 6.8 kg/m(3).d and 6.5 kg/m(3).d were r eached, respectively. A final concentration of 41.4 kg oxalic acid/m(3) was reached operating at 400 rpm.