‘Pooholes’ filled with eco-friendly material made from wastewater

The grit remaining from wastewater treatment can be used to effectively fill potholes in an environmentally friendly way, researchers have said.

Currently, potholes are filled with hydrocarbon-containing asphalt, which can leach out and pollute the nearby environment.

“We had an idea to divert wastewater grit from landfills and turn it into a marketable product,” said researcher Zhongzhe Liu at California State University-Bakersfield.

“We formulated it into a ceramic mortar that could be used as a patch for pothole repair.”

The substance, known as grit assisted patch (GAP), is ultimately safer for the environment than hydrocarbon-based asphalt.

Grit, a heavy, unbiodegradable solid, is made with processed wastewater containing sewage, food scraps and other waste and is processed at treatment plants.

The result is clean water that is released into waterways, but also solids from the preliminary treatment that are mostly sand and gravel, and this is referred to as grit.

Because grit contains pathogens and impurities that make it unsuitable for direct recycling, it is usually taken to a landfill and buried.

Instead, the researchers incorporated it into a chemically bonded phosphate ceramic (CBPC). CBPCs are routinely used to treat hazardous or radioactive waste for disposal, but no one had used this yet on wastewater products.

Because a CBPC contains ingredients that would inactivate microbes, the researchers thought this could be a good way to kill pathogens and end up with a material that could be safely applied to roads.

“In the first step of making a CBPC, we mix the wet grit with calcium oxide and magnesium oxide, which form an alkaline grit slurry that prevents the proliferation of pathogens,” Liu said. “The second step is to add a weak acid, potassium dihydrogen phosphate, into the pathogen-minimised alkaline slurry to form the grit-CBPC mortar.”

The researchers said that using grit also negates the need to use polycyclic aromatic hydrocarbons, which is used in normal patching materials that are a risk to human health.

When testing GAP in the lab, they demonstrated that it has a compressive strength comparable to asphalt pavement, and they believe its longevity will be superior to that of asphalt-based patches.

They are also working on improving its compressive strength even further, so it could potentially be used for other applications, such as building wheel stops at the end of parking spots.

In 2018 the government promised an extra £100m to repair the UK’s potholes following severe cold weather. 

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