Evaluation of the economic and environmental benefits of partial nitritation anammox and partial denitrification anammox coupling preliminary treatment in mainstream wastewater treatment

Anaerobic ammonium oxidation (anammox) technology is considered the best alternative for current wastewater treatment to improve resource recovery and energy efficiency. Evaluation of the economic and environmental benefits of partial denitrification anammox (PDA) and partial nitritation anammox (PNA) from a plant-wide perspective, which are the two most common mainstream anammox processes, is crucial for guiding the development direction of anammox, but research is still lacking. In this study, two plant-wide processes with chemically enhanced primary treatment-PDA (CEPT-PDA) and high rate activated sludge-PNA (HRAS-PNA) as the core units respectively, were firstly proposed and analysed, and life cycle assessment (LCA) was conducted to assess environmental impacts (EIs). The results of energy and economic analysis showed that the net energy consumption of CEPT-PDA and HRAS-PNA was 0.11 kwh/m3 and 0.16 kwh/m3 respectively; however, the operating cost of CEPT-PDA was 16.54% higher than that of HRAS-PNA due to the requirement for more chemicals. Compared with CEPT-PDA, the total EIs of HRAS-PNA decreased by 14.80%. The EI categories related to human toxicity and ecotoxicity contributed greatly to total EIs, accounting for 95.81% in CEPT-PDA and 96.75% in HRAS-PNA. Major environmental impacts were attributed to coagulant and energy consumption in two processes. In addition, improving the iron recycling efficiency was more beneficial for CEPT-PDA and further narrowed the gap between CEPT-PDA and HRAS-PNA on EIs. This study identifies that CEPT-PDA is competitive in the engineering application of mainstream anammox but reducing iron addition is a prerequisite.