How to transform 8 billion gallons of olive oil wastewater into a green biofuel

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Olive oil may not seem like a typical perpetrator of industrial-scale pollution, but its production leaves a surprising amount of waste in its wake. Making olive oil relies on mixing vast amounts of water with the mashed up olives in a mill, a process that annually generates eight billion gallons of discarded wastewater in Mediterranean countries, where 97% of olive oil is made. The waste is usually left to sink into the soil, or flow into water bodies, which can trigger toxic algal blooms and contaminate drinking water.

But now researchers have developed a three-step method to tackle this problem, most notably transforming the waste into a valuable biofuel.

The team of Tunisian and French scientists devised a method that relies on mixing the olive mill wastewater with another waste product–sawdust. First, they evaporated the water out of this mixture, which was repurposed to irrigate crops. Then they subjected the sawdust mixture to pyrolysis, a high-heat process that allowed them to capture emitted gases from the mixture and convert it into a sustainable biofuel. Finally, the dried out remains were conveniently recycled as a nutrient-rich fertilizer for crops. By the end of this process, every bit of waste had been repurposed.

The scientists’ low-cost method could solve a problem that has, for decades, dogged the olive farming industry. It’s also a further piece of evidence that the agricultural industry as a whole can take steps to transform its reputation as a major polluter–in small, inventive, and sometimes unexpected ways.

Source: Haddad et. al. “Olive Mill Wastewater: From a Pollutant to Green Fuels, Agricultural Water Source and Biofertilizer.” ACS Sustainable Chemistry and Engineering. 2017.

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