Advanced Water Management Centre, The University of Queensland, Brisbane, QLD, Australia; School of Chemical Engineering, The University of Queensland, Brisbane, QLD, Australia.
South Australian Water Corporation, Adelaide, SA, Australia; School of Natural and Built Environments, University of South Australia, SA, Australia; College of Science and Engineering, Flinders University, SA, Australia.
Water Res. 2020 Oct 15;185:116196. doi: 10.1016/j.watres.2020.116196. Epub 2020 Jul 16.
Mitigation of nitrous oxide (NO) emissions is of primary importance to meet the targets of reducing carbon footprints of wastewater treatment plants (WWTPs). Despite of a large amount of NO mitigation studies conducted in laboratories, full-scale implementation of NO mitigation is scarce, mainly due to uncertainties of mitigation effectiveness, validation of NO 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 NO mitigation strategies at a full-scale sequencing batch reactor (SBR). To achieve this, NO emission dynamics, nutrient removal performance and operation of the SBR were monitored to quantify NO emissions, and identify the NO generation mechanisms. NO mitigation strategies centered on reducing dissolved oxygen (DO) levels were consequently proposed and evaluated using a multi-pathway NO production mathematical model before implementation. The implemented mitigation strategy resulted in a 35% reduction in NO 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 NO from the studied WWTP. This could be mainly attributed to reductions in NO generated via the NHOH 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 NO emissions at full-scale is feasible and that widely accepted NO mitigation strategies developed in laboratory studies are also likely effective in full-scale plants. Furthermore, the close agreement between the validated and predicted NO emission factors (0.58% vs 0.55%, respectively), showed that the NO mathematical model is a useful tool to evaluate NO mitigation strategies at full-scale. Importantly this work demonstrated that NO mitigation does not necessarily require additional operational cost to meet reduction targets. In contrast, the NO mitigation applied here reduced energy requirements for aeration by 20%. Equally important, long-term monitoring identified that NO mitigation did not affect the nutrient removal performance of the plant. Finally, with the knowledge acquired in this study, a standard approach for mitigating NO emissions from full-scale treatment plants was proposed.
减少一氧化二氮（NO）排放对于实现污水处理厂（WWTP）减少碳足迹的目标至关重要。尽管已经在实验室进行了大量的 NO 减排研究，但实际应用却很少，主要原因是 NO 减排效果的不确定性、NO 数学模型的验证、对营养物质去除性能的风险以及额外的成本。本研究旨在通过在全尺寸序批式反应器（SBR）中研究 NO 减排策略的量化、开发和实施来解决这些不确定性。为此，监测了 NO 排放动力学、营养物质去除性能和 SBR 的运行情况，以量化 NO 排放并确定 NO 的生成机制。随后，提出并评估了以降低溶解氧（DO）水平为中心的 NO 减排策略，在实施之前使用多途径 NO 产生数学模型进行了评估。实施的减排策略使 NO 排放量减少了 35%（从排放因子 0.89±0.05 减少到 0.58±0.06%），相当于从研究中的 WWTP 每年减少 2.35 吨的 NO。这主要归因于 DO 水平降低导致通过 NHOH 氧化途径生成的 NO 减少。作为第一个在全尺寸 WWTP 中永久实施的减排策略，它展示了在全尺寸范围内减排 NO 是可行的，并且在实验室研究中广泛接受的 NO 减排策略在全尺寸工厂中也可能有效。此外，验证和预测的 NO 排放因子之间的密切一致性（分别为 0.58%和 0.55%）表明，NO 数学模型是评估全尺寸工厂中 NO 减排策略的有用工具。重要的是，这项工作表明，NO 减排不一定需要额外的运营成本来达到减排目标。相比之下，这里应用的 NO 减排减少了 20%的曝气能源需求。同样重要的是，长期监测表明，NO 减排不会影响工厂的营养物质去除性能。最后，根据本研究获得的知识，提出了一种从全尺寸处理厂中减排 NO 的标准方法。
