STOKHOLM, July 11 — The slurry that forms in sewage plants is full of nutrients.

But many farmers won’t use it on fields because toilet waste has been contaminated with pollutants.

"Today we mix all the waste waters into one big pipe. So we have the large flows from all the open areas in the city and there we have lots of heavy metals and pollutants from cars and from all the streets...and it’s getting mixed with the beneficial fractions from the toilet water because urine and faeces are really good fertiliser but we should not mix them with other waste waters from the urban areas,” Lund University doctoral student Hamse Kjerstadius said.

Kjerstadius helped waste water managers in Helsingborg find a solution that could have many eco benefits.

"We separate the waste water already at the source in the household. We have the toilet waste water into one pipe, and the food waste into a separate pipe, and the remaining household waste water — the grey water — goes into a third pipe,” Kjerstadius said.

"So there’s three pipes leaving the household and that means we can have a lot more efficient treatment down at the waste water treatment plant, and recover much more resources from the waste water.”

Engineers hope to increase nutrient returns to farms sevenfold.

Biogas production from sewage sludge could double.

The system is being fitted in hundreds of homes and businesses in Oceanhamnen, a new city district being built.

Sewer networks across Sweden need updating and other cities could adopt the plans. — Reuters