'Waste not, want not' in the olive industry
Food processing usually presents an environmental cost and the Mediterranean olive industry is no exception. Olive mill wastewater (OMW) is a significant pollutant in both waterways and on land due to the presence of phenolic compounds. Ironically, phenols are produced by plants as their defence against pathogens but they can therefore affect the delicate balance of microbiota of soils and water. Composed of partner countries that produce the olive crop, the EU funded project NEWTECHOMW aimed to develop new technologies to minimise the phenol content of OMW. The team of scientists based at the University of Naples Federico II in Italy have been particularly active in their research endeavours on olive waste. One of their research packages involved the investigation of the action of different biological and abiotic catalysts on OMW. A commercial enzyme laccase and the strong oxidative catalyst birnessite were compared for their remedial action. Germination tests on tomato and garden pepperwort seeds showed that laccase was more effective at reducing phenol content in whole OMW than in concentrated extract of the waste. Further exploration showed this differential effect was dependent on the type of laccase and the phenol present. Overall, however, the inorganic catalyst was better at transforming phenols and removing antibacterial activity. Phytotoxicity was reduced but not removed completely by either type of catalyst. As with any complex waste processing treatment, the remedies are usually far from straightforward. The level of phytotoxicty recorded depended on the seed type used. The data also suggested that compounds other than phenols in the mixture may be responsible for the phytotoxicity. Nevertheless, the data collected by the team has shown that toxicity of OMW can be reduced using catalytic agents. Olive products are gaining in popularity and the industry is valuable in southern Europe. The successful detoxification of olive waste and subsequent use of the residue for fertigation stands to enhance conditions in rural communities.