Scientists create biofuel from waste water used to make olive oil
Researchers at Mulhouse Institute of Materials Science in France have developed a way to transform the polluting waste water that derives from olive oil production into fertiliser and biofuel. Olive mills in Mediterranean countries produce about eight billion gallons of waste water, much of which is disposed of irresponsibly. The scientists embedded the waste water into another waste product, cypress sawdust, then exposed the material to high temperatures without oxygen, a process known as pyrolysis. The material then decomposes into combustible gases and charcoal, the former of which can be condensed into biofuel and the latter used as a fertiliser.

During processing, olives are crushed and mixed with water in mills. The oil is separated out of this mixture, and the dirty water and solid residue are discarded. In Mediterranean countries, where 97 percent of the world's olive oil is produced, olive mills generate almost 8 billion gallons of this wastewater annually. Disposing of it has become problematic. Dumping it into rivers and streams can potentially contaminate drinking water and harm aquatic life. Pumping it onto farm land damages the soil and reduces crop yields. Some researchers have tried burning the wastewater with mixtures of solid waste from the mills or waste wood. But these approaches have either been too costly or have produced excessive air pollution. Mejdi Jeguirim and colleagues took a different approach. They wanted to see if they could convert olive mill wastewater (OMW) from a pollutant into sustainable products for practical use. The researchers first embedded OMW into cypress sawdust – another common Mediterranean waste product. Then they rapidly dried this mixture and collected the evaporated water, which they say could be safely used to irrigate crops. Next, the researchers subjected the OMW-sawdust mixture to pyrolysis, a process in which organic material is exposed to high temperatures in the absence of oxygen. Without oxygen, the material doesn't combust, but it does thermally decompose into combustible gases and charcoal. The researchers collected and condensed the gas into bio-oil, which could eventually be used as a heat source for OMW-sawdust drying and the pyrolysis process. Finally, they collected the charcoal pellets, which were loaded with potassium, phosphorus, nitrogen and other nutrients extracted from the breakdown of OMW-sawdust mixture during pyrolysis. Used as biofertilizers, the researchers found that after five weeks these pellets significantly improved plant growth, including larger leaves, compared to vegetation grown without them. The authors acknowledge funding from the PHC Utique program of the French Ministry of Foreign Affairs and Ministry of Higher Education and Research; the Tunisian Ministry of Higher Education and Scientific Research in the GEDURE project; and the MICA Carnot Institute. " Olive Mill Wastewater: From a Pollutant to Green Fuels, Agricultural Water Source and Biofertilizer