According to UN-Habitat, over 100 million tonnes of sewage sludge are generated globally each year. Common disposal methods - including incineration or landfill - are time-consuming, energy-inefficient, and contribute to environmental pollution.
To tackle this problem, NTU researchers created a three-step solar-powered process that integrates mechanical, chemical, and biological techniques.
Proof-of-concept tests showed that the NTU team’s process is more efficient than conventional techniques like anaerobic digestion. It is said to recover ‘significantly more’ resources, removes heavy metal contaminants, has a smaller environmental footprint, and offers better economic feasibility.
In a statement, research lead Associate Professor Li Hong from NTU’s School of Mechanical and Aerospace Engineering (MAE) and the Energy Research Institute @ NTU (ERI@N) said, “Our method transforms waste into valuable resources, reducing environmental damage while creating renewable energy and sustainable food. This exemplifies the circular economy and contributes to a greener future.”
Three-step process
The process begins by mechanically breaking down the sewage sludge. A chemical treatment separates heavy metals from organic materials, including proteins and carbohydrates.
Next, a solar-powered electrochemical process uses specialised electrodes to transform the organic materials into products, such as acetic acid, which is a key ingredient for food and pharmaceutical industries, and hydrogen gas.
Finally, light-activated bacteria are introduced to the processed liquid stream to convert nutrients into a single-cell protein suitable for animal feed.
A viable solution
According to NYU, lab tests showed the new method recovers 91.4 per cent of the organic carbon in sewage sludge and converts 63 per cent of the organic carbon into single-cell protein without producing harmful by-products. In comparison, traditional anaerobic digestion typically recovers and converts around 50 per cent of organic materials in sewage sludge.
The solar-powered process achieves an energy efficiency of 10 per cent, generating up to 13 litres of hydrogen per hour, which is around 10 per cent more energy efficient than conventional hydrogen generation methods.
The NTU process reduces carbon emissions by 99.5 per cent and energy use by 99.3 per cent compared to traditional methods.
The NTU research team said the newly developed process is promising, but more studies are needed to determine if it can be scaled up. Their work is published in Nature Water.
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