Dynamic ammonium retention for nutrient separation from manure digestate
Year: 2024
Type: article
Abstract: Extensive nitrogen emissions with negative impact on nature and the environment urge effective valorization of manure and fractionation of nutrients to enable precision fertilization. Typically, manure is fed to a digester to produce biogas. The remaining digestate is then mechanically separated into a solid phosphorous-rich fraction and a liquid fraction containing both NH4+ and K. These ions are difficult to separate due to their very identical size and charge. We show that with smart tuning of the pH to control the NH3/NH4+ equilibrium, membranes can produce dedicated N and K-rich streams. The increased pH switches the equilibrium towards neutral NH3 that permeates more easily through the membrane than charged NH4+ and K+ ions. Experiments with both artificial NH4Cl/KCl mixtures as well as real digestate and four different membrane types, ranging from open nanofiltration (NF) to sea water reverse osmosis (RO) membranes were performed. At neutral pH, no N/K selectivity was observed, not for single components nor for mixtures. When the pH was increased towards alkaline environment, distinct selectivity for N/K was obtained both with model solutions and real digestate. At a suitable pH of 10, with > 80% of the total ammonia present as NH3, the RO BW showed a significant N/K selectivity of 35 in the crossflow system. Additional RO steps at low pH allows subsequent concentration of the formed NH4+ and K+ fractions. The presented dynamic pH approach proofs that in a two-step RO system both N, and K-enriched fertilizers can be produced from real digestate.
Source: Waste Management
Institution: Eindhoven University of Technology
Language: English
Subfield: Water Science and Technology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,280
Award: No time to waste
OpenAlex ID: W4404021444