Wastewater could be the secret to eco-friendly fertilizer
Each year, billions of tons of human and agricultural waste flow through wastewater treatment plants, rich with the same essential nutrients that feed crops—nitrogen, phosphorus, and potassium. For decades, these valuable elements were treated as pollutants to be removed and disposed of. But a quiet revolution is underway. Across the world, scientists, engineers, and cities are rethinking wastewater not as waste, but as a renewable resource. The emerging field of nutrient recovery—extracting these concentrated elements from sewage and biosolids—is proving to be a cornerstone of a circular economy, turning a pollution problem into a sustainable fertilizer solution.
The promise of nutrient recovery lies in its triple win: environmental protection, economic value, and climate benefits. Environmentally, recovering nutrients keeps them out of rivers and oceans, where they can cause serious damage. When excess nitrogen and phosphorus leak into waterways, they trigger algal blooms that choke out oxygen and kill marine life—a process known as eutrophication. One of the most dramatic examples is the “Dead Zone” in the Gulf of Mexico, a region the size of New Jersey that becomes uninhabitable for fish and other aquatic species each summer due to nutrient pollution washing off farmland and sewage systems. By capturing these nutrients before they reach waterways, cities can help prevent such ecological disasters while producing a valuable agricultural input.
There’s also a question of resource security. Phosphorus, one of the key nutrients in fertilizer, is a non-renewable mineral mined primarily from phosphate rock, with the majority of global reserves concentrated in just a handful of countries. This makes the global food system vulnerable to geopolitical shocks and price volatility. Recovering phosphorus from wastewater in the form of a mineral called struvite—magnesium ammonium phosphate—creates a reliable and renewable domestic supply. It also closes the loop between cities and farms, ensuring that what flows out of urban wastewater systems can be returned to agricultural soils sustainably.
The climate benefits are equally compelling. Producing synthetic nitrogen fertilizer through the Haber-Bosch process consumes vast amounts of natural gas and energy, releasing large quantities of greenhouse gases. Recovering existing nitrogen from wastewater, by contrast, requires far less energy, dramatically reducing the carbon footprint of fertilizer production. At the same time, the responsible use of biosolids—nutrient-rich solids safely treated and processed—can return organic carbon to soils. This not only improves soil structure and microbial health but enhances water retention, making farmland more resilient to drought. Unlike synthetic fertilizers, which can degrade soil over time, recovered nutrients can help restore its vitality.
A growing range of technologies is making nutrient recovery practical at scale. One of the most established methods is struvite crystallization, which captures phosphorus by inducing it to form a solid crystal that can be filtered, dried, and sold as fertilizer. Newer approaches such as pyrolysis and gasification transform sewage sludge into biochar—a nutrient-rich, carbon-stable material that can be safely applied to fields. Biological systems are also gaining traction. Researchers are experimenting with microalgae and duckweed that thrive in nutrient-rich wastewater, naturally absorbing nitrogen and phosphorus that can later be harvested and used as biofertilizer.
Real-world examples are proving the concept viable. In Kobe, Japan, the local utility has operated a full-scale struvite recovery facility for years, producing high-quality fertilizer marketed to farmers. In Europe and North America, several water treatment facilities have partnered with companies specializing in recovered nutrient products, such as Ostara Nutrient Recovery Technologies, which sells its “Crystal Green” fertilizer made entirely from wastewater-derived phosphorus. Farmers using these products report strong yields and improved soil health, showing that sustainability and productivity can go hand in hand.
Ultimately, recycling nutrients from wastewater is not a futuristic idea—it’s an unavoidable necessity. Phosphorus cannot be manufactured, and global reserves are declining. As the cost of climate damage rises and the pressure on food systems grows, the logic of nutrient recovery becomes undeniable. The future of fertilizer may well depend on closing the loop between what we flush away and what feeds the world. In the circular economy of tomorrow, even wastewater will have value, nourishing both the soil and the planet that sustains us.
