A tree seed once linked to Ancient Egyptian water cleaning is now showing promise against one of today’s biggest drinking water problems.

A recent study found seeds from the moringa tree matched or outperformed alum, a common chemical coagulant, in removing aged PVC microplastics from water. The research was led by Gabrielle Batista at São Paulo State University, UNESP, Brazil, and published in ACS Omega.

The study compared alum with a salt-based extract made from moringa. Both removed more than 98 percent of PVC particles from water. Moringa was also more consistently reliable across a wider pH range.

The PVC particles tested were about 15 micrometres in size, small enough to slip through standard filters. Both coagulants work by neutralising the negative electrical charge that makes microplastic particles repel each other and avoid filtration. Once neutralised, the particles clump into larger aggregates, called flocs, which can then be caught by a sand filter.

Researchers also found moringa worked as effectively for in-line filtration as it did for direct filtration. That means it could remove the need for the flocculation step, which binds coagulated particles together and can add cost and energy use.

The findings come as Europe steps up scrutiny of microplastics in drinking water. In 2024, the EU increased monitoring protocols after researchers warned last year that very small particles may still be passing through treatment systems and into the blood and organs.

Microplastics are plastic particles less than 5 millimetres long. They come from sources including car tyres, paint, textiles and degraded plastic packaging. Beyond possible links to cancer, heart attacks and reproductive problems, they can also absorb and carry other hazardous pollutants through ecosystems and into the food chain.

European countries currently use physical and chemical methods to remove microplastics from wastewater. Alum is widely used because it helps separate microplastics and other contaminants for removal. But improper use can raise aluminium levels in water, which have been linked to potential neurological disorders, including Alzheimer’s disease.

Alum also produces large amounts of sludge during coagulation. That waste is difficult to manage and usually goes to landfill, where it can leach toxins into soil and waterways. Its production also relies on bauxite strip-mining in tropical regions, including Australia, Brazil, Guinea, Guyana and Jamaica, which can lead to deforestation and habitat loss. Processing the raw material also requires significant thermal energy and releases emissions.

Moringa has long been used for water purification and is thought to have been used by Ancient Egyptians to remove bacteria and reduce turbidity. The crop grows quickly, resists drought and needs little water. It also acts as a carbon sink, grows in arid and degraded soils, and supports biodiversity.

The researchers said one issue still needs further scrutiny: the leaching of dissolved organic carbon during treatment, which could complicate downstream processes. They also said moringa still needs to be tested for efficacy at scale.

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