Zeolite Ion Exchange to Facilitate Anaerobic Membrane Bioreactor Wastewater Nitrogen Recovery and Reuse for Lettuce Fertigation in Vertical Hydroponic Systems

Ammonia-nitrogen recovered from synthetic anaerobic membrane bioreactor (AnMBR) permeate facilitated by natural zeolite (clinoptilolite) ion exchange was released during regeneration with tap water into a recirculating, vertical hydroponic system to demonstrate a potential method for nitrogen recovery and reuse from domestic wastewater. Exhausted clinoptilolite leached ammonium into the tap water, which was then used for the hydroponic fertigation of butter crunch lettuce (Lactuca sativa) in vertical hydroponic towers. Crop mass and pigment development of lettuce grown in the zeolite desorption solution were favorable compared to the control (consisting of diluted, synthetic AnMBR permeate). Nitrification occurred faster in the desorption solution compared to the control, resulting in an 11% and 19% increase in fresh and dry mass, respectively, and greater chlorophyll-a and chlorophyll-b development. A system is proposed for implementing vertical trickling hydroponic systems integrated with zeolite regeneration to realize a reusable nutrient recovery system. This work demonstrates the potential of the proposed nutrient recovery system to simultaneously attenuate AnMBR ammonia-nitrogen content, while providing a renewable source of nitrogen for use in soilless agriculture.