Biological pretreatment and ethanol production from olive cake

Olive oil is one of the major Mediterranean products, whose nutritional and economic importance is well-known. However the extraction of olive oil yields a highly contaminating residue that causes serious environmental concerns in the olive oil producing countries. The olive cake (OC) coming out of the three-phase olive oil production process could be used as low price feedstock for lignocellulosic ethanol production due to its high concentration in carbohydrates. However, the binding of the carbohydrates with lignin may significantly hinder the necessary enzymatic hydrolysis of the polymeric sugars before ethanol fermentation.
Treatment with three white rot fungi, Phaneroachaete chrysosporium, Ceriporiopsis subvermispora and Ceriolopsis polyzona has been applied on olive cake in order to investigate the potential for performing delignification and thus enhancing the efficiency of the subsequent enzymatic hydrolysis and ethanol fermentation process steps. It has been concluded that the conditions tested were not adequate for reaching satisfactory delignification and thus studying different conditions (humidity, pH and nitrogen levels) is necessary.
Another possibility for lowering the cost of bioethanol is the use of microbial strains, which possess the ability for hydrolysis of complex carbohydrates. Thus, the addition of enzymes could be eliminated to a minimum extent for reaching a satisfactory degree of fermentable sugars release from a biomass. In that concept, the hydrolytic, ethanol-producing Thermoanaerobacter ethanolicus has been applied on olive cake supplemented with glucose in order to evaluate any inhibitory effect that olive cake might have on the microbial growth and metabolism. It was shown that the strain was able to grow and produce ethanol up to a TS content of 100 g per L. Further investigation of the pH role on the ethanol yield will take place.