Researchers study sludge-based solution to algal blooms

Researchers in Scotland are investigating the potential of converting sewage sludge into a mineral-rich material that could be used to treat growing, climate-change-associated instances of eutrophication and algal blooms in lochs and rivers.

The research project, funded by the Industrial Biotechnology Innovation Centre and Scottish Water, is assessing the viability of a water filter derived from sewage sludge to remove phosphorus from wastewater. This could deprive algal blooms of a chief nutrient.

The filter is made from biochar – a charcoal-like substance created when a carbon-containing material, in this case, sewage sludge, is treated at 500ºC in the absence of oxygen. According to the researchers, sewage sludge biochar, used at scale, “could play an important role in treating water at the point of discharge to prevent algal blooms from forming.”

And they point out that natural reserves of phosphorus – needed in many household products including cleaning fluids and matches – are depleting “at an alarming rate.” So the Scottish sewage sludge process “could open up new avenues for collecting phosphorus”.

The researchers said using biochar derived from sewage sludge is completely safe and sanitary, with any residual toxins, pharmaceuticals or pesticides destroyed during the heating process.

The sludge used to create the biochar is being supplied by Scottish Water, while its commercial subsidiary, Scottish Water Horizons, is testing the biochar at its Waste Water Development Centre in Bo’ness. 

According to Scottish Water about 130,000 tonnes of human waste from the sewage system are disposed of  each year in Scotland at a cost of some £6 million. Most of it is used as fertiliser or incinerated. But proposed changes to regulations dictate the development of other disposal methods.

Experts at the University of the Highlands and Islands are studying biochar in filtration systems, supported by water treatment specialist, AL-2 Teknik.

Lead academic on the project, Dr Szabolcs Pap, said: “While phosphorus causes challenges for the environment and sectors it is also an element that we all use in everyday products. Natural stores are depleting, so this circular bioprocess could lead to new opportunities to recover the nutrient from wastewater and create new supply chains here in Scotland.

“At the same time, water companies are under increasing pressure to reduce waste and find alternatives for bioresources from sewage, so there is an additional benefit in terms of sustainability. Biochar can be a valuable material with a range of potential applications, but the global market is still in its infancy.”

The next stage of the research will include on-site tests at some of Scottish Water’s smaller treatment works, alongside ongoing conversations with regulators and development agencies about the emerging market for commercialising biochar in Scotland.

AL-2 Teknik has already supplied systems in Europe and one in the US, creating biochar from different bioresources. The company is understood to see the sludge project as a basis for opening its first facility in Scotland.