Wastewater draining from massive pools of sewage sludge has the potential to play a role in more sustainable agriculture, according to environmental engineering researchers at Drexel University.

The study suggests that it's not only technically viable, but also could help to reduce the environmental and energy footprint of fertilizer production.

Today, the production of nitrogen for fertilizer is an energy-intensive process and accounts for nearly 2% of global carbon dioxide emissions. For this reason, researchers have explored alternatives to the Haber-Bosch nitrogen production process, which has been the standard for more than a century. 

One promising possibility, recently raised by some water utility providers, is gleaning nitrogen from the waste ammonia pulled from water during treatment.

“Recovering nitrogen from wastewater would be a desirable alternative to the Haber-Bosch process because it creates a 'circular nitrogen economy,” said Patrick Gurian, PhD, a professor in the College of Engineering who helped lead the research, which was recently published in the journal Science of the Total Environment.

According to Gurian, reusing existing nitrogen rather than expending energy and generating greenhouse gas to harvest nitrogen from the atmosphere poses a much more “sustainable practice for agriculture and could become a source of revenue for utilities.”

The team’s findings, led by Gurian and Sabrina Spatari, PhD, from Technion Israel Institute of Technology, suggest there is a complementary relationship that could result in a more sustainable path for both farmers and water management authorities.

Air-stripping, a method being explored by several facilities in North America and Europe, removes ammonia by raising the temperature and pH of the water enough to convert the chemical into a gas, which can then be collected in concentrated form as ammonium sulfate.

"In addition to ammonia sulfate production as a marketable product, the benefit of reducing the ammonia load in the side-stream before it is recycled into the wastewater stream at the wastewater treatment plant provides an additional justification for adopting air-stripping," the study said.

“This research suggests that water utility providers could also consider investing in technologies that would capture phosphorus and recycle it for agricultural use,” said Spatari.