When olive oil is produced commercially, olives are crushed and mixed with water in mills. The oil is then separated out and saved, while the leftover water and solid residue are discarded – and that can be problematic. Help may be on the way, however, as scientists have devised a process of converting olive mill wastewater into biofuel, fertilizer and clean water.

As things currently stand, there's no good way of disposing of the wastewater. Dumping it in waterways pollutes them, while pumping it directly onto farm land damages the soil and reduces crop yields.

That's why a team led by Mejdi Jeguirim of France's Mulhouse Institute of Materials Science has taken a different approach. The scientists started by mixing the wastewater with cypress sawdust, which is another waste product that's common in the Mediterranean, where 97 percent of the world's olive oil is produced.

That mixture was rapidly dried, and the water was collected as it evaporated – that water was clean, and could be used to irrigate crops. The remaining dried material was then subjected to pyrolysis, which is a process wherein organic material is exposed to high temperatures in the absence of oxygen. This caused it to decompose into combustible gas and charcoal pellets.

That gas was collected and condensed into bio-oil, which could ultimately be used as a heat source for the drying and pyrolysis processes. The charcoal, meanwhile – which contains high amounts of nutrients such as potassium, phosphorus and nitrogen – was gathered and used as a crop fertilizer. In field tests, it was found that the pellets "significantly improved plant growth."

A paper on the research was recently published in the journal ACS Sustainable Chemistry & Engineering.