Mitigating nitrous oxide emissions at a full-scale wastewater treatment plant. (15th October 2020)

• Record Type: Journal Article
• Authors: Duan, Haoran; van den Akker, Ben; Thwaites, Benjamin J.; Peng, Lai; Herman, Caroline; Pan, Yuting; Ni, Bing-Jie; Watt, Shane; Yuan, Zhiguo; Ye, Liu
• Is Part Of: Water research. Volume 185(2020)
• Publication Date: 2020-10-15
• Subjects: Nitrous oxide -- Wastewater treatment -- Full-scale -- Mitigation -- Nitrogen removal; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2020.116196
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: First reported N2 O mitigation strategy permanently implemented at full-scale. 35% N2 O emission reduction was achieved with 20% less operational cost. N2 O mitigation did not affect nutrient removal performance. Validated multi-pathway N2 O model at full-scale to evaluate mitigation strategies. Proposed a standard approach for mitigating N2 O emissions at full-scale plants. Abstract: Mitigation of nitrous oxide (N2 O) emissions is of primary importance to meet the targets of reducing carbon footprints of wastewater treatment plants (WWTPs). Despite of a large amount of N2 O mitigation studies conducted in laboratories, full-scale implementation of N2 O mitigation is scarce, mainly due to uncertainties of mitigation effectiveness, validation of N2 O mathematical model, risks to nutrient removal performance and additional costs. This study aims to address the uncertainties by investigating the quantification, development and implementation of N2 O mitigation strategies at a full-scale sequencing batch reactor (SBR). To achieve this, N2 O emission dynamics, nutrient removal performance and operation of the SBR were monitored to quantify N2 O emissions, and identify the N2 O generation mechanisms. N2 O mitigation strategies centered on reducing dissolved oxygen (DO) levels were consequently proposed and evaluated using a multi-pathway N2 O production mathematical model before implementation. The implemented mitigation strategy resulted in a 35% reduction in N2 O emissions (from the emission factor of 0.89 ± 0.05 to 0.58 ± 0.06%), which was equivalent to annual reduction of 2.35 tonne of N2 O from the studied WWTP. This could be mainly attributed to reductions in N2 O generated via the NH2 OH oxidation pathway due to the lowering of DO level. As the first reported mitigation strategy permanently implemented at a full scale WWTP, it showcased that the mitigation of N2 O emissions at full-scale is feasible and that widely accepted N2 O mitigation strategies developed in laboratory studies are also likely effective in full-scale plants. Furthermore, the close agreement between the validated and predicted N2 O emission factors (0.58% vs 0.55%, respectively), showed that the N2 O mathematical model is a useful tool to evaluate N2 O mitigation strategies at full-scale. Importantly this work demonstrated that N2 O mitigation does not necessarily require additional operational cost to meet reduction targets. In contrast, the N2 O mitigation applied here reduced energy requirements for aeration by 20%. Equally important, long-term monitoring identified that N2 O mitigation did not affect the nutrient removal performance of the plant. Finally, with the knowledge acquired in this study, a standard approach for mitigating N2 O emissions from full-scale treatment plants was proposed. Graphical abstract: Image, graphical abstract