Scientists transform ammonia in wastewater to fertiliser

Farmers worldwide have grappled with a severe fertiliser shortage. At the same time, wastewater professionals have dealt with the reality of ammonia-filled wastewater and the need to keep it at manageable levels — otherwise, the high levels could lead to fish kills, physiological changes in water-dwelling animals and organisms, and other unwanted effects.

In recent achievements that tackle both these matters, researchers have learned how to turn the ammonia in wastewater into fertiliser.

Scientists seek methods of more sustainable fertiliser production

When a Drexel University team investigated options for extracting the ammonia from wastewater for fertiliser, they had hopeful conclusions. One was that it’s a technically viable solution that may even give wastewater treatment facilities an additional revenue stream. Furthermore, the scientists believed this approach could reduce fertiliser production’s energy and environmental burdens.

However, the researchers wanted to explore particular methods for removing ammonia from the wastewater. They hoped to find the most cost-effective and worthwhile possibilities that wastewater plant decision-makers could pursue.

Studying air stripping to reduce high ammonia levels

The team focused on air stripping for their study, which included doing a life cycle analysis of the option. Their investigation revealed using air stripping to pull ammonia from wastewater to make ammonia sulfate fertiliser could promote a complementary relationship between farmers and wastewater plant leaders. Plus, the practice could pay off in environmental mitigation and economic gains.

The researchers also noted air stripping could minimise the high ammonia levels in the side stream before it gets recycled into the plant’s wastewater stream. The researchers focused on a wastewater treatment plant in Philadelphia, as well as several others in the United States and Europe when doing their economic feasibility study and the life cycle analysis associated with air stripping.

Air stripping is an above-ground wastewater treatment method that usually happens in a packed column tower. This method works by exposing contaminated water to clean airflow courtesy of a blower. The blower moves the clean air in the opposite direction of the water current and a sump at the tower’s base collects the cleaned water.

The researchers examined various factors as they assessed the feasibility of air stripping to remove ammonia in wastewater. Those included the costs of installing the air stripping equipment and maintaining it.

They also included the expenses related to the wastewater’s flow rate and how the costs might differ depending on the concentration of ammonia. The researchers calculated energy and transportation expenses associated with this approach. Examining all the aspects with such care resulted in thorough, realistic estimates.

Exciting results

Once the Drexel team had crunched all the numbers, the results showed that air stripping was a promising method for dealing with ammonia in wastewater and producing fertiliser in the process. More specifically, the option uses approximately 5–15 times less energy than the Haber-Bosch method of making nitrogen. The associated greenhouse gas emissions are also about 5–10 times fewer.

Air stripping to cope with ammonia in wastewater also had striking economic benefits. The data showed the overall costs of making fertiliser from wastewater were low enough that people could price them 12 times lower than Haber-Bosch-produced and still break even.

The researchers clarified that people would bring the most environmental benefits by applying this method to deal with high ammonia levels in wastewater. However, even at lower concentrations, this method remains cost-effective.

Another finding was wastewater plants might achieve energy savings by deploying air stripping to remove ammonia to cut the overall processing time needed to treat the water. It takes time and money for decision-makers to move forward with air stripping in their facilities. But, as this study shows, they can look forward to multiple advantages.

Farmers are increasingly investing in better methods. That may mean using robots or pursuing no-till agriculture. This research proves they may soon also get some of their fertiliser by fostering relationships with local wastewater treatment plants.

Going beyond ammonia in wastewater

The Drexel University researchers are just some of the ones interested in connecting wastewater to more sustainable fertiliser production. Another case involved Rice University, Arizona State University and the Pacific Northwest National Laboratory participants. They worked together to develop a process that converted nitrate levels of 2000 parts per million into ammonia. Then, unlike the Drexel team, this group relied on gas stripping to collect the ammonia.

Ammonium chloride and liquid ammonia are the products of a catalyst developed by engineers at Rice University to convert wastewater into useful chemicals. Image credit: Jeff Fitlow/Rice University.

The researchers found these two treatments brought the remaining nitrogen levels in the wastewater to drinkable levels. Previous research showed the team ruthenium was a suitable metal candidate for reducing nitrogen. However, they learned more recently that the outcomes were even better when combining ruthenium with copper.

Their tests showed this process works without the need for major infrastructure. It also had fewer carbon dioxide emissions than traditional ammonia production methods. People involved in this research clarified this option would not likely replace the ammonia industry. However, it would cause improvements toward more decentralised ammonia production, especially in high-nitrate areas.

In another instance, an Aalto University team developed a method for the recovery of nitrogen and phosphorus to create an ammonium sulfate solution people could use as fertiliser. Their experiments showed this option was kinder to the environment, less energy-intensive than other options and reduced nutrient discharges into waterways.

Perhaps the idea to focus on ammonia in wastewater came from the fact that the urine from humans and other animals contains it. Researchers from institutions located in three countries recently ran a real-world test to see how human urine used as fertiliser affected crop growth in Niger. The results showed a 30% increase in grain grown when using that fertilisation method compared to more conventional options.

Working towards effective and sustainable methods

Wastewater management professionals regularly deal with high ammonia levels and deploy various methods to reduce them. However, as these studies show, people can do more than remove substances from the water — they should consider going further by figuring out how those nutrients could become fertiliser for today’s farmers.

These new processes are not always easy and usually require significant forethought. However, as the studies here and elsewhere show, strategic nutrient extraction could be better for the planet than currently used methods and could help agriculture professionals deal with shortages.

*Emily Newton is the Editor-In-Chief of Revolutionized, a magazine exploring innovations in science and industry that shares ideas to promote a better tomorrow.

Top image caption: Rice University engineers have designed a catalyst of ruthenium atoms in a copper mesh to extract ammonia and fertilizer from wastewater. The process would also reduce carbon dioxide emissions from traditional industrial production of ammonia. Image credit: Jeff Fitlow/Rice University.