Biodegradation of phenol compounds in vinasse using Aspergillus terreus and Geotrichum candidum

Amongst the methods for the purification of vinasse, anaerobic digestion features some advantages that make it particularly suitable for processing this type of waste. However, its efficiency is somewhat decreased by the presence of phenol compounds. The prior removal of these compounds make the vinasse more amenable to anaerobic digestion. A possibility of reducing the phenolic content is through an aerobic biological pretreatment by some Fungi. So, in the framework of broader research directed towards the purification of vinasse by two-stage treatment (an aerobic fermentation followed by an anaerobic digestion), this work studies exclusively the aerobic stage of Aspergillus terreus and Geotrichum candidum. The study is aimed at finding the most suitable microorganism for removing phenolic compounds. The fermentations follow Monod kinetics. The mathematical model is used in order to compare the microorganisms behaviour, and it allows the prediction of the removal of phenols. The extent of removal, in the fermentation by A. terreus, of total phenols and o-diphenols was c. 66 and 94%, respectively; in the case of G. candidum, the results were c. 70 and 91%. For A. terreus, the maximum specific growth rate is mu(max) = 0.06 h(-1), the constant K-s = 13,525 mg COD 1(-1), the growth yield is Y-X/S = 0.38 mg cells per mg COD and the efficiency on degrading phenolic compounds is E = 0.033 mg total phenols per mg cells. For G. candidum, these constants are mu(max)' = 0.047 h(-1), K-s' = 4558 mg COD 1(-1), Y-X/S' = 0.39 mg cells per mg COD and E' = 0.036 mg total phenols per mg cells. Though both microorganisms behave in a similar way, G. candidum seems to be slightly better for removing phenols from vinasse. (C) 1997 Elsevier Science Ltd.