Mashreki Sami has defended his thesis about graywater management.
8 September 2025
Greywater could be a resource – but bacteria remain a challenge
Reusing water from showers, washing and dishwashing could ease pressure on water resources and help create more sustainable cities. In his doctoral thesis at Luleå University of Technology, Mashreki Sami shows that decentralized greywater treatment systems can be highly effective – but that bacteria still pose a hurdle.
"Greywater makes up as much as 90 percent of household wastewater. If treated properly, it can become a valuable resource for irrigation in agriculture or green urban areas," says Mashreki Sami, PhD in Urban Water Engineering at Luleå University of Technology.
Capturing microplastics
The thesis examines different systems: small-scale package plants, sand filters, green walls and a constructed wetland. The results show that organic matter and nutrients could be removed with up to 99 percent efficiency, and that several filter materials also retained microplastics.
But when it comes to bacteria such as E. coli and enterococci, the results were more mixed. The constructed wetland performed best, yet even there additional hygienisation steps were needed to meet EU standards for reuse.
"The results demonstrate both strengths and weaknesses. We see that the systems can clean the water effectively, but there are still health risks that need to be addressed," says Mashreki Sami.
A piece of the puzzle for sustainable cities
The thesis highlights that decentralized systems can play an important role in future water supply, especially since water stress areas are more frequent in today’s society.
"With the right technology, greywater can become part of the water-food-energy nexus and contribute to more resource-efficient cities," says Mashreki Sami.
Mashreki Sami defended his thesis Decentralized greywater systems: performance, microbial risk and microplastics at Luleå University of Technology. Opponent was Professor Eran Friedler from Technion – Israel Institute of Technology.
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