Background Olive oil production generates huge quantities of waste that may have great environmental impact because of their high phytotoxicity, toxicity against aquatic organisms and suppression of soil microorganisms. Olive mill wastewater (OMWW) is composed of the olive fruit vegetation water, water used for washing and treating, and a portion of the olive pulp and residual oil. The polluting load of OMWW is caused by high chemical oxygen demand (COD) and five-day biochemical oxygen demand (BOD5), low pH, high concentrations of recalcitrant compounds such as lignin and tannins, and long-chain fatty acids. The lack of feasible and economically-viable alternative technologies makes the uncontrolled disposal of OMWW a serious environmental problem around the Mediterranean area. There is an urgent need for guidelines to manage these wastes through technologies able to minimise their environmental impact, and to promote a more sustainable use of resources. Objectives The objective of the RE-WASTE project was to demonstrate that olive mill wastewater (OMWW) can be a valuable resource for biogas energy production, whilst respecting existing environmental laws. It planned to develop and implement a demonstration plant to run an innovative and clean technology to treat and valorise olive mill effluents. A key aim was to extract natural compounds from OMWW, and to explore their potential uses in the food, pharmaceutical, cosmetic and animal feed industries. Results The RE-WASTE project established a pilot plant in the province of Benevento, in southern Italy, to treat olive mill wastewater (OMWW), and use it to obtain polyphenolic extracts, biogas and purified water, with significant potential environmental benefits for the environment. The project conducted a cost-benefit analysis that demonstrated good performance when the plant was operating at full capacity. Therefore, even given significant initial investment, the plant appears to be cost-effective. The pilot plant’s process led to the extraction of anti-oxidant extracts from OMWW (2.7 kg/m3 of treated OMWW). Two types of extract were obtained: a liquid-oily extract and a powder extract. The project team explored a number of potential markets for these, and showed that the polyphenolic extracts could be profitably sold for use in the functional foods and cosmetics sectors. The remaining organic content of OMWW can be used for producing biogas (methane), which in turn can be used to produce energy (1.6 m3 of methane/m3 of OMWW). The biogas contained about the 55% methane. Around 60% of the water left after the processing of OMWW is purified, and it was assessed, through analysis of COD, BOD5 and phenolic concentrations, to have the right characteristics for re-use in the olive oil extraction process. The technology can be implemented without the need for particular adaptations in legislation and policy. Moreover, laws allow olive oil producers to obtain an authorisation for treating their own OMWW, and this process is a standard and not time-consuming one, making the project’s technology easily replicable in Italy and other Mediterranean countries. It could also be adapted in the future within other agro-food sectors, for example, for processes in the dairy and canning sectors to eliminate pollution loads and recover added-value biomolecules. The project compiled a database of almost 100 companies belonging to two agro-food sectors and conducted 27 audits of companies that might benefit from the technology. The demonstration value of the RE-WASTE project was therefore high. Widespread uptake of the technology could bring major environmental benefits, linked to the complete use of all the organic matter residues from OMWW for energy production (biogas) and the possibility of re-using the purified water in industrial process (such as olive oil production). Indirect environmental benefit occur because the OMWW is no longer spread onto the land, thus avoiding the risk of contaminating soil and groundwater. From its in-depth cost/benefit analysis of two possible scenarios, the project showed that its technology could increase the income of olive oil producers. The scenarios were for two different plant sizes, running at full capacity for five months per year during the olive harvesting/processing season: a 20 m3/day plant installed in an existing olive oil company, and a 200 m3/day plant installed on a new industrial site. The total unit cost was 125.01 €/m3 of treated OMWW in the smaller plant, and 58.61 €/m3 in the larger plant. Revenues were received by both plants from the sale of the antioxidant extracts and the methane, and indirectly due to the avoidance of agronomic disposal (552.85 €/m3 combined). The return on investment (ROI) was 27.6% for the smaller and 49.6% for the larger plant. RE-WASTE disseminated its technical, environmental and economic results among olive oil industry operators and public bodies in Italy and the rest of Europe. This ensured that industry operators have the awareness and know-how to apply the project’s technology. Three demonstrative meetings at the pilot plant and a congress, co-organised by the Italian coordinating beneficiary (IOBM) and the Spanish beneficiary (Centro Tecnológico Nacional De La Conserva Y Alimentacion), were key activities in this respect. The project also organised courses targeting agro-industry technicians, produced documents on the ‘Technological demands and needs of the Spanish Olive Oil sector for treatment of OMWW’ and the ‘Valorisation of food sector by-products’, and published a series of scientific papers and articles. The project’s new technology helps implement relevant legislation at EU level, in particular, the Water Framework Directive (2000/60/EC), the Groundwater Directive (2006/118/EC), the Waste Framework Directive (2008/98/EC) and the Urban Wastewater Treatment Directive (91/271/EEC). Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).