Wastewater may offer a new source of potassium fertilizer

Researchers in Germany reviewed 110 studies and found that wastewater streams could help replace some mined potash, with the best recovery method depending on the waste source. The findings point to a possible shift from treating wastewater only as a disposal problem to using it as a nutrient-recovery system for agriculture.

Why it matters: - Potassium is essential for crop growth, water regulation, and resilience. - Most fertilizer potassium still comes from mined potash, which can create saline waste, harm freshwater ecosystems, and leave supply chains exposed to geopolitical and economic disruption. - Wastewater already contains recoverable potassium, so capturing it could turn a disposal stream into an agricultural input.

What happened: - Researchers Cora Eichholz and Heidrun Steinmetz of RPTU Kaiserslautern-Landau reviewed 110 publications on potassium recovery from wastewater. - The paper was accepted on October 8, 2026, and published in Environmental Science and Ecotechnology. - The review examined human urine, livestock waste, industrial effluents, and municipal treatment streams as potential potassium sources.

The details: - The team used the Joanna Briggs Institute scoping-review framework and searched Scopus, then expanded the evidence base through citation-network analysis. - The 110 publications were sorted by wastewater source, treatment process, technology maturity, and fertilizer product. - The field is still dominated by lab work. - 61 studies reported laboratory-scale experiments. - 11 studies reached pilot scale. - About 34% of the evidence base relied on synthetic solutions rather than real wastewater. - Among 94 publications focused on specific technologies, potassium-struvite precipitation appeared in 40 studies, electrodialysis in 17, and ion exchange in 15. - Source-separated urine contained about 900 to 2,440 milligrams of potassium per liter. - Liquid digestate contained about 1,494 to 2,440 milligrams per liter. - Those concentrated streams are better suited to solid compound fertilizers such as potassium struvite. - Primary-settled municipal wastewater contained about 25 milligrams per liter. - That more dilute stream may fit liquid or single-nutrient products after concentration and separation. - Reported potassium recovery ranged from 15% to 98% for potassium-struvite precipitation. - Reported recovery ranged from 13% to 95% for electrodialysis. - Those recovery figures came from different conditions and are not directly comparable. - Ammonium and sodium can compete with potassium. - Membrane fouling, mineral scaling, energy use, and uncertain fertilizer purity remain practical barriers. - The review also notes that wastewater treatment plants usually prioritize nitrogen and phosphorus, leaving much potassium unused. - Previous studies have tested precipitation, membranes, and selective separation, but the results are scattered across different waste streams and operating conditions.

Between the lines: - The core takeaway is not just that potassium can be recovered, but that the fertilizer product should be defined first and the wastewater source chosen second. - A process that works in a clean lab mixture may underperform in real wastewater with fluctuating chemistry and competing ions. - The review suggests wastewater treatment plants could function as nutrient-recovery hubs, not only pollution-control facilities. - That shift depends on proving that recovered products are safe, usable, and consistent enough for agricultural markets.

What's next: - The authors call for sustained pilot testing and stronger product-quality evaluation before wastewater-derived potassium fertilizers can be deployed at scale. - Future work should test integrated treatment sequences with real, variable wastewater. - Researchers should measure equipment performance over longer operating periods. - Life-cycle assessment is needed to determine whether potassium recovery delivers environmental benefits beyond technical feasibility. - Practical deployment will also require contaminant screening for heavy metals and organic micropollutants and compliance with the European Union Fertilising Products Regulation. - The review says concentrated side streams could support solid, multi-nutrient fertilizers, while selected dilute streams could supply liquid potassium products for controlled cultivation systems such as hydroponics.

The bottom line: - Wastewater could become a meaningful potassium resource, but the path from lab results to commercial fertilizer still depends on real-world testing, product standards, and source-specific processing.