Recovery of ammonium and nitrate from wastewater using adsorption-based techniques: A review

Approximately 312 billion m³ of municipal wastewater is generated worldwide annually containing ∼16.6 million tonnes of nitrogen which could meet ∼17 % of the global agricultural demand. Nitrogen recovery from wastewater would thus be economically significant, improve security of supply for fertilizers, prevent eutrophication of water bodies, and curb the large carbon footprint of synthetic nitrogen fertilizer production. Currently, nitrogen recovery from wastewater is not a common practice and the conventional nitrogen removal process via microbial nitrification/denitrification causes nitrogen to be lost into the atmosphere. This review provides an overview of ammonium and nitrate recovery via adsorption technology from a techno-economic perspective. An adsorption process can be used in combination with other techniques (e.g., ammonia stripping, membrane separation, struvite precipitation, or microbial assimilation) as a pre-concentration method. The most studied adsorbents are zeolites, biochars, activated carbons, and ion-exchange resins where the highest reported adsorption capacities in a flow-through process aiming for nitrogen recovery are ∼80 mg/g for ammonium and ∼360 mg/g for nitrate. The few existing full-scale plants, economic assessments, and life-cycle analyses point out that adsorption-based nitrogen recovery can achieve lower costs, smaller environmental impact, and higher treatment efficiency than the status quo. Thus, adsorption technology could be an important part of the toolbox when shifting towards a circular economy of nitrogen.