School of Chemical Engineering, the University of Queensland, St. Lucia, Queensland 4072, Australia.
Advanced Water Management Centre (AWMC), the University of Queensland, St. Lucia, Queensland 4072, Australia.
Environ Sci Technol. 2021 Jun 1;55(11):7208-7224. doi: 10.1021/acs.est.1c00840. Epub 2021 May 12.
Nitrous oxide (NO) emissions account for the majority of the carbon footprint of wastewater treatment plants (WWTPs). Many NO mitigation strategies have since been developed while a holistic view is still missing. This article reviews the state-of-the-art of NO mitigation studies in wastewater treatment. Through analyzing existing studies, this article presents the essential knowledge to guide NO mitigations, and the logics behind mitigation strategies. In practice, mitigations are mainly carried out by aeration control, feed scheme optimization, and process optimization. Despite increasingly more studies, real implementation remains rare, which is a combined result of unclear climate change policies/incentives, as well as technical challenges. Five critical technical challenges, as well as opportunities, of NO mitigations were identified. It is proposed that (i) quantification methods for overall NO emissions and pathway contributions need improvement; (ii) a reliable while straightforward mathematical model is required to quantify benefits and compare mitigation strategies; (iii) tailored risk assessment needs to be conducted for WWTPs, in which more long-term full-scale trials of NO mitigation are urgently needed to enable robust assessments of the resulting operational costs and impact on nutrient removal performance; (iv) current mitigation strategies focus on centralized WWTPs, more investigations are warranted for decentralised systems, especially decentralized activated sludge WWTPs; and (v) NO may be mitigated by adopting novel strategies promoting NO reduction denitrification or microorganisms that emit less NO. Overall, we conclude NO mitigation research is reaching a maturity while challenges still exist for a wider implementation, especially in relation to the reliability of NO mitigation strategies and potential risks to nutrient removal performances of WWTPs.
一氧化二氮（NO）排放占废水处理厂（WWTP）碳足迹的大部分。自那时以来，已经开发了许多减少 NO 的策略，但仍缺乏整体观点。本文回顾了废水处理中减少 NO 的最新研究。通过分析现有研究，本文提出了指导 NO 减排的基本知识和减排策略背后的逻辑。在实践中，减排主要通过曝气控制、进料方案优化和工艺优化来实现。尽管越来越多的研究，但实际实施仍然很少，这是气候变化政策/激励措施不明确以及技术挑战的综合结果。确定了减少 NO 的五个关键技术挑战和机遇。有人提议：(i) 量化整体 NO 排放和途径贡献的方法需要改进；(ii) 需要可靠而简单的数学模型来量化收益并比较减排策略；(iii) 需要对 WWTP 进行定制风险评估，其中更需要长期进行全规模减少 NO 的试验，以便对由此产生的运营成本和对养分去除性能的影响进行稳健评估；(iv) 当前的减排策略侧重于集中式 WWTP，需要对分散式系统进行更多调查，特别是分散式活性污泥 WWTP；以及 (v) 通过采用促进 NO 还原反硝化或排放较少 NO 的微生物的新策略，可以减少 NO。总的来说，我们得出结论，减少 NO 的研究正在达到成熟阶段，但仍存在广泛实施的挑战，特别是在减少 NO 策略的可靠性和 WWTP 养分去除性能的潜在风险方面。
