Medieval alchemists sought to literally turn non-valuable substances into gold. Now some scientists have discovered a figurative equivalent method to transform sewage sludge into food for animals and fuel for automobiles, according to research published in Nature Water.
Sewage sludge — the thick, organic, and, yes, smelly wastewater treatment byproduct— represents a massive and costly problem. The world’s cities produce over 100 million tons of the stinky substance. It often clogs treatment plants and costs billions to process. More than 100 million tons of dry sludge accumulates globally every year. This is especially problematic in “megacities.” Their combination of massive population and density renders a haste to make something from this waste.
“The ever-increasing generation of sewage sludge in megacities places a substantial burden on waste treatment systems,” according to the paper. “The complex and resilient structure of sludge renders conventional pretreatment and biological reclamation methods time-consuming, energy-inefficient and environmentally burdensome.”
Solar-Powered Solution?
A team of scientists from Singapore and China developed an approach that addresses multiple issues. Their method could process the waste into something useful rather than noxious — hydrogen and protein. The hydrogen could then power vehicles, and the protein could feed animals.
The researchers developed a three-step, solar-powered process that taps into mechanical, chemical, and biological techniques.
First, they ground down the sludge to begin breaking down its structure. Adding a catalyst also helps separating out molecular components, like heavy metals, which can then be removed and contained.
Next, the remaining organic material undergoes electrolysis, powered by solar energy. This is where much of the magic happens. Instead of simply breaking down the sludge, the system turns it into something useful. The positively charged anode triggers electrochemical oxidation of the waste, resulting in volatile fatty acids — including acetic acid. The negatively charged cathode then splits water into hydrogen and oxygen.
Finally, the solid components are fed to microbes. Those bacteria transform the acetic acid into protein that can then be used for animal feed.
Read More: Scientists Just Created a Bacteria That Eats CO2 to Reduce Greenhouse Gases
Reducing CO2 Emissions
Proof-of-concept tests revealed that the NTU team’s process is more efficient than conventional techniques like anaerobic digestion — through which bacteria break down organic waste to produce biogas and nutrient-rich residue.
It recovers significantly more resources, completely removes heavy metal contaminants, has a smaller environmental footprint, and offers better economic feasibility.
The study touts some impressive numbers. The process recovers over 91 percent of the organic carbon from the sludge, with 63 percent of it transformed into single-cell proteins. It also reduces CO2 emissions by 99.5 percent compared to other sludge-processing methods, like anaerobic digestion.
“Proof-of-concept tests revealed that the NTU team’s process is more efficient than conventional techniques like anaerobic digestion — through which bacteria break down organic waste to produce biogas and nutrient-rich residue,” according to a Nanyang Technical University, Singapore press release. “It recovers significantly more resources, completely removes heavy metal contaminants, has a smaller environmental footprint, and offers better economic feasibility.”
To see if this technique is truly feasible, other groups must replicate it. Then, once the process is further validated, its scale will need to be increased. If a larger version of the process can, indeed serve cities, it could prove that we can, indeed, transform sludge into a kind of gold.
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Nature Water. Solar-driven sewage sludge electroreforming coupled with biological funnelling to cogenerate green food and hydrogen
Statistica. Sewage sludge produced and disposed in Europe in 2021, by country
Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
