Making fertiliser from wastewater is feasible, study shows

Gleaning nitrogen from the waste ammonia from wastewater during treatment could be an alternative to the Haber-Bosch nitrogen production process, according to researchers at Drexel University.

Circular nitrogen economy

“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 Drexel’s College of Engineering. “This means we are reusing existing nitrogen rather than expending energy and generating greenhouse gas to harvest nitrogen from the atmosphere, which is a more sustainable practice for agriculture and could become a source of revenue for utilities.”

A process called air-stripping removes ammonia from wastewater 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.

Cost-effective even at low concentration

Findings of a life-cycle analysis show that air-stripping emits about 5 to 10 times less greenhouse gas than the Haber-Bosch nitrogen-producing process and uses about 5 to 15 times less energy. The study suggests that recovering ammonia can be cost-effective even at low concentration.

Air-stripping however produces fertiliser in smaller amounts than the industrial Haber-Bosch process. But, being able to collect and reuse any quantity of resources helps to improve the sustainability of commercial agriculture and prevents them from becoming water pollutants, the reseachers say.

For various reasons, global fertiliser prices have skyrocketed, especially nitrogen prices. How are crop growers worldwide coping with this? And what new precision techniques can help growers apply fertiliser as efficiently as possible? These articles provide answers.