An Innovative Look into Ammonium Nitrogen Removal Using Algae and Zeolites as an Element of a Circular Bioeconomy

This work focused on the potential of simultaneously removing ammonium nitrogen from industrial wastewater using immobilized microalgae and powdered zeolite. Experiments were performed with different species and doses of microalgae embedded in spherical hydrogels in semicontinuous conditions. Ammonium nitrogen uptake by microalgae promoted the slow release of previously adsorbed ammonium nitrogen from zeolite that was then also absorbed by microalgae. Results showed that immobilized microalgae can reach a removal efficiency of up to 60% (C. vulgaris) and 42% (S. armatus). A higher removal efficiency was obtained for zeolites and immobilized C. vulgaris or S. armatus up to 86% and 79%, respectively. Moreover, a higher maximum sorption capacity for C. vulgaris (13.8 mg/g) was achieved than for S. armatus (5.5 mg/g). The recycling of spent hydrogel, zeolite, and wastewater is possible. Such an approach represents a circular bioeconomy loop.