Olive mill wastewater: a health-boosting tonic hiding in the leftovers

A by-product of the olive oil production process is packed with compounds that lower your cholesterol and reduce your risk of developing cancer.

- DR EMMA BECKETT

Olive oil is well known for its health benefits. The star of the Mediterranean diet, it's rich in good fats, packed with antioxidants that have anti-inflammatory properties, and linked to a variety of improved health outcomes.

The olive oil production process does create a lot of waste products, though. Luckily, however, it seems one of them olive mill wastewater might be a potentially health-boosting product in its own right.

Admittedly, olive mill wastewater, or 'OMW' as it's typically called in the scientific literature, isn't a particularly appetising name for a trendy, new, nutrient-dense supplement. But, olive mill wastewater is exactly what the name suggests - the wastewater from olive oil production.

It's one of many byproducts created when olives are milled and the oil is separated and filtered. To reduce such byproducts and improve profits, the waste is 'valorised' reused, recycled, composted or converted into more useful things that have value, including materials, chemicals or fuels.

The solid waste products from olive oil production - olive pomace, olive oil sediment, olive pit residue and spent olive cake – can all be used as animal feed, compost or biomass fuel.

The liquid waste from the extraction process, which includes water added as part of the processing, is the olive mill wastewater, a dark, cloudy, bitter and slightly acidic liquid-millions of litres of which are generated each year. As a byproduct, it's considered the most harmful waste from olive oil production - its high organic load and phenolic content are a significant environmental concern. If it's not properly managed and treated before release (which adds to the cost of production), it can contaminate waterways and soil, and be toxic to plants and animals.