Ammonium recovery from different digestates using chabazite-rich tuff: towards scalable farm applications

The circular recovery and reuse of nutrients from wastewater is vital for achieving sustainability goals and the European Green Deal objectives. This study investigates the selective recovery of ammonium (NH4+) using a zeolitic tuff rich in chabazite zeolite. We focused on targeting its applicability for farm-scale applications from different anaerobic digestates undergoing various pre-treatments (screw compression, microfiltration and centrifugation). The results were compared with a zeolitic tuff rich in phillipsite and chabazite from a previous study. The tested wastewaters included swine, cattle and municipal solid waste digestates. Adsorption isotherms and kinetics were evaluated, considering key factors such as initial NH4+ concentration, contact time, competing ions (e.g. K+), total solids content and pre-treatment strategies. The adsorption process followed the Freundlich model, indicating heterogeneous multilayer sorption, whereas the kinetic data aligned with pseudo-first-order and intraparticle diffusion models. NH4+ removal efficiency was inversely correlated with K+ levels and solids content, with livestock-derived digestates enabling the greatest nitrogen recovery per gram of zeolitic tuff due to their favourable composition and kinetics. Among the tested pre-treatments, centrifugation proved most effective, improving active site accessibility. A preliminary field-scale trial using microfiltered swine digestate at a 3% solid-to-liquid ratio demonstrated the feasibility of batch operation, with an estimated nitrogen recovery of 715 kg N year–1. This work lays the foundation for future comparisons with other zeolitic tuffs, such as those rich in clinoptilolite, and it supports the principle of nutrient circularity in agriculture by reducing reliance on synthetic fertilizers.