Citric Acid Recovery from Fermentation Broth

The fermenting broth was filtered using Whatman filter paper No. 1 to remove the fungal biomass. The citric acid in the filtrate was recovered by the double precipitation method [44 , 50 (link)] using Ca(OH)₂ and H₂SO₄ in a stepwise manner to separate citric acid from the fermenting broth. To 500 ml of the filtrate, 30 g of Ca(OH)₂ was added and agitated briefly at 60 °C. The calcium citrate precipitate that was formed was recovered, diluted with distilled water (1:10) and further treated with conc. H₂SO₄ (10:1). The sequence of the recovery process of citric acid is depicted in Fig. 3. The quantification of the citric acid was done on HPLC Infinity 1260 (Agilent Technologies, USA) [5 (link), 38 (link)] at a wavelength of 211 nm using a diode array detector (DAD). The citric acid (Sigma-Aldrich, Darmstadt, Germany) was prepared by dissolving 0.001 g in 10 ml of sodium phosphate buffer and used as standard. Acetonitrile buffer at 70:30 (pH 6.5) was used as the mobile phase at a flow rate of 1.0 ml/min. The temperature of the column (Primesep D, 100 Å, 5 μm, 4.6 × 150 mm) was maintained at 35 °C during the analysis.
Fig. 3

Scheme for the recovery and purification of citric acid