A comparison of nitrogen removal systems through cost-coupled life cycle assessment and energy efficiency analysis

The global water crisis reflects the necessity of exploring the best approaches for the water supply. Therefore, for the first time, the current study compares nitrogen removal systems (NRSs) from life cycle assessment (LCA), economic, kinetic, thermodynamic, and synergistic perspectives. The assessed systems were sequential batch reactor (SBR), oxic/anoxic (OA), and oxic/anaerobic/oxic (OAO) bioreactors. Among all, the SBR configuration showed the best efficiency (98.74 %) for nitrogen removal. The environmental impacts notably presented by marine + freshwater ecotoxicity (53.76 %), and climate change categories (16.39 %), significantly because of metal emissions. Nonrenewable sources supplied 95 % of total energy demand. The operation of NRSs showed the most impact on human health (63.67 %) through CH4 and CO2 emissions. The total costs significantly belonged to the construction (<86.37 %) > amortization> operation. The influent COD illustrated the most role in environmental burdens (16.44 %) based on the sensitivity analysis. The removal reaction was endothermic, physical, non-spontaneous, and followed a pseudo-second-order kinetic model (R-2 > 0.98). The chemical exergy provided the major portion of the total calculated exergy (83 %). The exergetic efficiency of the system was 69 %, which was predominantly supplied by biogas (similar to 50.75 %). Accordingly, this study can present a stepwise guideline for further related investigations.

Automated summary

The study compares nitrogen removal systems (NRSs) from various perspectives and finds that the sequential batch reactor (SBR) configuration shows the best efficiency (98.74%) for nitrogen removal. The operation of NRSs has the most impact on human health (63.67%) through CH4 and CO2 emissions. The exergetic efficiency of the system is 69%, predominantly supplied by biogas (around 50.75%).