Bipolar membrane electrodialysis enhanced nutrient separation in manure treatment

To improve circularity in the agricultural sector, the nutrients nitrogen (N) and potassium (K) present in manure must be separated. This can be achieved by reverse osmosis (RO) under alkaline conditions where NH 4 + is converted to neutral NH 3 for selective permeation while K + is retained by the membrane. The NH 3 in the collected permeate can be concentrated after acidification, where the NH 3 is converted back to NH 4 + , in a second RO step to produce valuable liquid N-fertilizer. In this study, the OH - and H + required for the separation of the nutrients are produced in-situ by bipolar membranes. The process becomes more sustainable by saving on transportation, storage and dilution from aqueous alkali and acid. For system validation, first a water dissociation experiments were performed in a membrane stack with three compartments fed with NaCl solution. Follow-up experiments were done with artificial model solutions and co-digested manure digestate. The experiments showed that the NaCl feed and the artificial feed stream have a similar performance with effective productions of both OH - and H + of ~0.5 mmol/min. The real co-digested manure showed an effective OH - production for the conversion of NH 4 + to NH 3 , which was half of the effective production of the acid compartment. The resulting lower efficiency (40 instead of ~80%) in the base compartment is due to the presence of other OH - -consuming components present in the manure digestate. The surplus in H + production is useful as acid for other processes in manure treatment overall showing the potential of BMED integration. • Enhancing sustainability with novel integration of BMED in manure treatment • Reduction of transport and storage with on-site base and acid production via BMED • BMED enhances N/K separation while reducing water and chemical needs • Real digestate lowers OH - efficiency due to matrix effects