Life cycle assessment of side stream removal and recovery of nitrogen from wastewater treatment plants

In the light of a circular economy, the Nijhuis Ammonia Recovery system (AECO-NAR) was developed to not only remove nitrogen from wastewater streams, but also produce ammonium sulfate (AS), used as fertilizer, in a single plant. The goal of this paper was to quantify the environmental impacts of side stream ammonia recovery with the AECO-NAR system and compares them with the impacts of side stream nitrogen removal combined SHARON (partly nitrification)-anammox plant. For this, an environmental life cycle assessment was performed with a functional unit (FU) of the treatment of 1 kg of total dissolved nitrogen inflow. Since AS obtained by the AECO-NAR is a by-product of the ammonia removal process, allocation was based on system expansion. Foreground inventory data were obtained from a full-scale plant. ReCiPe2016 was used to determine human health and biodiversity impacts. Results show that due to the production of AS in an integrated water treatment and production system, the AECO-NAR avoids impacts of current AS production, leading to negative impact scores. Impacts per FU decrease with increasing inflow concentrations of ammonia. Main improvement options are the use of renewable energy and the replacement of the cleaning chemical citric acid with a sustainable alternative. Total impacts of the AECO-NAR system diminish when comparing the system to the biological SHARON-Anammox system, due to production of AS fertilizer product. Due to the fertilizer production step being integrated in the side stream treatment, the complete system is beneficial over ammonia recovery and wastewater treatment as separate systems.