What would happen if wastewater was turned into fertilizer?

Wastewater draining from sewage sludge ponds has the potential to play a role in more sustainable agriculture, according to a group of researchers from Drexel University.

A new study, looking at a process to remove ammonia from wastewater and convert it into fertilizer, suggests that it is not only highly feasible, but would also help reduce the ecological and energy footprint of fertilizer production, and even could provide numerous revenues for public water treatment services and facilities.

Fertilizer production is an energy-intensive process, accounting for almost 2% of global CO₂ emissions. Over the past few years, researchers have explored alternatives to a production process that has been the gold standard for decades. A new possibility that has been raised recently by some water providers would be to obtain nitrogen from the residual ammonia extracted from the water during water treatment.

According to the experts who have been part of this research, recovering nitrogen from wastewater would represent the creation of a circular nitrogen economy. This would mean that not only the already existing nitrogen would be reused, but also the energy expenditure would decrease and the generation of CO₂ would be limited. This would mean an improvement for agriculture, since it would be a sustainable practice that could become a strong source of income for public service companies in charge of water.

Ammonia has become a concern in recent years, as for aquatic environments it can cause excessive growth of vegetation in streams and rivers, endangering thousands of different species of fish and other animals that inhabit the waters. Eliminating this product that we find in our waters not only consumes a lot of time and space, but also represents a great consumption of energy.

That is why, one of the options that Europe and part of America are considering is the air stripping, which is responsible for eliminating ammonia by raising the temperature and pH of the water enough so that the chemical turns into a gas and, therefore, can be collected in a concentrated way as ammonium sulfate. However, the disassembly requires a complex study called life cycle analysis, of its technological and financial feasibility.

According to the researchers, converting wastewater to fertilizer presents an alternative to chemical production that is not as harmful to the environment and human health as the current process. In addition, they suggest that water service providers could invest in technologies that would capture phosphorus for recycling and use in agriculture.