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Nuggets Of Treasure: New Process May Turn Sewage Into Valuable Chemicals

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Jack Dunhill

Social Media Coordinator and Staff Writer

clockMar 4 2022, 14:19 UTC
sewage

Searching for treasure just got a whole lot less glamorous. Image Credit: Mike Laptev/Shutterstock.com

It turns out one man’s poop might be another man’s treasure, as a team of scientists from Stanford may have found a way to take extremely toxic by-products of sewage treatment and turn them into precious resources for agriculture and even electronics.

The team believes it could allow for far more efficient water reuse – something desperately needed with so many countries lacking access to clean water – while turning a toxic waste product into one with important uses in multiple industries.  

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“We are always looking for ways to close the loop on chemical manufacturing processes,” said senior author Will Tarpeh, an assistant professor of chemical engineering at Stanford University, in a statement.  

“Sulfur is a key elemental cycle with room for improvements in efficiently converting sulfur pollutants into products like fertilizer and battery components.” 

Their results were published in the journal ACS ES&T Engineering.

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As scientists scramble to find cost-effective treatment options for the vast amount of sewage people produce, one method has been highlighted as a strong contender: anaerobic filtration.

This process involves wastewater flowing through a filter full of active biomass, which traps and degrades solids and unwanted particles in the water. It is efficient, requires no electricity, and effectively removes solids from wastewater and even water that has already gone through treatment.

Like all good things, however, anaerobic filtration has a problematic downside – it produces large amounts of sulfide. Sulfide is toxic, and large quantities of it are extremely difficult to deal with. Current management techniques of the by-product produce further toxic chemicals, which corrode pipes and make further disinfection of the water difficult. 

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In the pursuit of a better alternative, researchers wondered how to turn the sulfides into something usable. One such use is sulfur-containing fertilizers, widely used by farmers as sulfur is a major nutrient required by plants. However, turning these by-products into fertilizer is a process that hasn’t been fully developed yet. 

Using electrochemical sulfur oxidation, the researchers began turning the wastewater sulfides into useful products and analyzed the process with microscopy to determine where the reaction may be limited, plus any blockages that may stop sulfur recovery.

They successfully fine-tuned the process, claiming it could be powered by renewable energy and used at scale for the treatment of entire cities. If it were to be combined with other recovery techniques that capture nitrogen, it could even directly produce ammonium sulfate fertilizer.  

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The team now hopes the process can be further optimized and even implemented as a way to reduce the toxic output of wastewater, reduce pollution, and finally use the by-products in a positive way.  

“Hopefully, this study will help accelerate adoption of technology that mitigates pollution, recovers valuable resources and creates potable water all at the same time,” said lead author Xiaohan Shao, a PhD student in civil and environmental engineering at Stanford, in a statement. 


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