Wastewater mining for circular potassium fertilisers: A critical scoping review of technologies, product formulations, and up-scaling challenges
- 1Department of Resource-Efficient Wastewater Treatment, RPTU Kaiserslautern-Landau, Paul-Ehrlich-Straße 14, Kaiserslautern, 67663, Germany
Abstract
Potassium (K) is an essential plant macronutrient and an irreplaceable resource for global food production. Today, agricultural potassium comes almost entirely from mined potash, an energy-intensive practice linked to severe ecological pressures—such as the salinisation of vulnerable river systems—and heavy dependence on a few exporting nations. Recovering potassium from wastewater offers a tangible path toward circular nutrient management, yet research on K recovery has largely been overshadowed by efforts focused on nitrogen and phosphorus. This scoping review critically evaluates 110 peer-reviewed publications using the Joanna Briggs Institute framework combined with citation network analysis to assess where the field genuinely stands. Our analysis reveals that research remains predominantly in its infancy: roughly 34% of studies rely on synthetic solutions in simplified lab-scale setups, with investigations centring on K-struvite precipitation (approximately 43%), electrodialysis, and ion exchange. These processes face acute operational hurdles under real-world conditions, severe competition from counter-ions (NH4+ and Na+), scaling challenges, and a lack of long-term sorbent regeneration and stability data. Crucially, we show that the wastewater stream choice fundamentally dictates the feasible fertiliser formulation. High-strength, nutrient-rich streams—such as source-separated urine (900–2440 mg K L−1) and liquid digestate (1494–2440 mg K L−1)—are naturally suited for producing solid compound fertilisers (predominantly K-struvite), whereas low-concentration municipal WWTP effluents (approximately 25 mg K L−1) offer a more favourable stoichiometric balance for isolating liquid or single-nutrient fertilisers (e.g., KCl for precision hydroponics). However, before these secondary fertilisers can enter the agricultural market, critical gaps must be resolved regarding product purity, compliance with the European Union Fertilising Products Regulation (particularly heavy metal and organic micropollutant thresholds), and synergistic multi-stage process design. Ultimately, moving potassium recovery from laboratory curiosity into existing wastewater infrastructure demands rigorous pilot testing with dynamic, real effluents alongside holistic life-cycle assessments.
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BibTeX
@article{eichholz2026wastewater,
title = {{Wastewater mining for circular potassium fertilisers: A critical scoping review of technologies, product formulations, and up-scaling challenges}},
author = {Cora Eichholz and Heidrun Steinmetz},
journal = {Environmental Science and Ecotechnology},
year = {2026},
month = oct,
doi = {10.1016/j.ese.2026.100777},
url = {https://doi.org/10.1016/j.ese.2026.100777},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Wastewater mining for circular potassium fertilisers: A critical scoping review of technologies, product formulations, and up-scaling challenges
AU - Cora Eichholz
AU - Heidrun Steinmetz
PY - 2026
DA - 2026/10/08
JO - Environmental Science and Ecotechnology
DO - 10.1016/j.ese.2026.100777
UR - https://doi.org/10.1016/j.ese.2026.100777
AB - Potassium (K) is an essential plant macronutrient and an irreplaceable resource for global food production. Today, agricultural potassium comes almost entirely from mined potash, an energy-intensive practice linked to severe ecological pressures—such as the salinisation of vulnerable river systems—and heavy dependence on a few exporting nations. Recovering potassium from wastewater offers a tangible path toward circular nutrient management, yet research on K recovery has largely been overshadowed by efforts focused on nitrogen and phosphorus. This scoping review critically evaluates 110 peer-reviewed publications using the Joanna Briggs Institute framework combined with citation network analysis to assess where the field genuinely stands. Our analysis reveals that research remains predominantly in its infancy: roughly 34% of studies rely on synthetic solutions in simplified lab-scale setups, with investigations centring on K-struvite precipitation (approximately 43%), electrodialysis, and ion exchange. These processes face acute operational hurdles under real-world conditions, severe competition from counter-ions (NH4+ and Na+), scaling challenges, and a lack of long-term sorbent regeneration and stability data. Crucially, we show that the wastewater stream choice fundamentally dictates the feasible fertiliser formulation. High-strength, nutrient-rich streams—such as source-separated urine (900–2440 mg K L−1) and liquid digestate (1494–2440 mg K L−1)—are naturally suited for producing solid compound fertilisers (predominantly K-struvite), whereas low-concentration municipal WWTP effluents (approximately 25 mg K L−1) offer a more favourable stoichiometric balance for isolating liquid or single-nutrient fertilisers (e.g., KCl for precision hydroponics). However, before these secondary fertilisers can enter the agricultural market, critical gaps must be resolved regarding product purity, compliance with the European Union Fertilising Products Regulation (particularly heavy metal and organic micropollutant thresholds), and synergistic multi-stage process design. Ultimately, moving potassium recovery from laboratory curiosity into existing wastewater infrastructure demands rigorous pilot testing with dynamic, real effluents alongside holistic life-cycle assessments.
SN - 2096-9643
SN - 2666-4984
ER -