Fermentative decolorization of olive mill wastewater by Lactobacillus plantarum

Abstract

The effects of Lactobacillus plantarum growth on reductive decolorization and biodegradation of phenolic compounds were evaluated. L. plantarum growth on fresh Olive Mill Wastewaters (OMW) for 6 days produced an increase in the number of viable cells and decrease of pH due to the production of lactic acid. The growth of L. plantarum led to the depolymerization of phenolic compounds of high molecular weight, with a resultant decolorization of fresh OMW and significant reduction of total phenols, in proportion to the dilution of OMW. Approximately 58% of the color, 55% of the chemical oxygen demand (COD) and 46% of the phenolic compounds were removed when OMW was diluted ten times. During fermentation COD and color removal increased while the number of viable cells remained constant because L. plantarum growth resulted in an increase in total suspended solid (TSS) corresponding to phenolic compounds adsorbed on cells. The removal of phenolic compounds was associated with depolymerization, their partial adsorption on the cells and biodegradation of certain simple phenolic compounds. Moreover, L. plantarum produced an inverse reaction of auto-oxidation in the oxidized phenolic compounds contained in black stored OMW by reductive depolymerization, while at the same time leading to decolorization.