An environmentally-friendly strategy for the valorization of olive mill wastewater converts it from a pollutant to an asset. Source: Marco Ossino/Shutterstock.com

The milling of olives produces olive oil, a very useful commodity, and vast volumes of wastewater that pose management and disposal problems.

About 97 percent of the world’s olive oil is produced in the Mediterranean region, where olive mills generate 8 billion gallons a year of wastewater. Discharging this waste into waterways impacts aquatic ecosystems and degrades drinking water quality, and disposal onto agricultural land reduces soil fertility.

Researchers from France and Tunisia sought to address this pollution problem by transforming the wastewater into value-added products. Wastewater mixed with another waste product—cypress sawdust—was dried to release water that can be reused for agricultural purposes.

The mixture was then pyrolyzed to yield combustible gas and charcoal. The gas was condensed into bio-oil, a green fuel that can be used as a heat source for the wastewater-sawdust drying and the pyrolysis processes.

The charcoal pellets, which were loaded with potassium, phosphorus, nitrogen and other nutrients, were tested as biofertilizer. Five weeks after land application, the pellets significantly improved rye grass growth.

Scientists from Institut de Science des Matériaux de Mulhouse (France), Water Research and Technologies Centre (Tunisia), Higher Institute of Sciences and Technology for Environment (Tunisia) and Rittmo Agroenvironment (France) participated in this research.