Biodegradation of synthetic and naturally occurring mixtures of mono-cyclic aromatic compounds present in olive mill wastewaters by two aerobic bacteria

Two bacterial strains, Ralstonia sp. LD35 and Pseudomonas putida DSM 1868, were assayed for their ability to degrade the monocyclic aromatic compounds commonly found in olive mill wastewaters (OMWs). The goal was to study the possibility of employing the two strains in the removal of these recalcitr ant and toxic compounds from the effluents of anaerobic treatment plants fe d with OMWs. At first, the two strains were separately assayed for their ab ility to degrade a synthetic mixture of nine aromatic acids present in OMWs , both in growing- and resting-cell conditions. Then, due to the complement ary activity exhibited by the two strains, a co-culture of the two bacteria was tested under growing-cell conditions for degradation of the same synth etic mixture. Finally, the degradation activity of the co-culture on two fr actions was studied. Both fractions one deriving from natural OMWs through reverse osmosis treatment and containing low-molecular weight organic molec ules, and the other obtained from an anaerobic lab-scale treatment plant fe d with OMWs, were rich in monocyclic aromatic compounds. The co-culture of the two strains was able to biodegrade seven of the nine components of the tested synthetic mix (2, 6-dihydroxybenzoic acid and 3, 4, 5-trimethoxybenz oic acid were the two undegraded compounds). In addition, an efficient biod egrading activity towards several aromatic molecules present in the two nat ural fractions was demonstrated.