Nitrous oxide (N2O) has emerged as a significant and multifaceted challenge for the water industry, prompting widespread concern and concerted efforts to mitigate its detrimental effects.
N20 and global warming
As a potent greenhouse gas, Nitrous oxide (N2O) contributes significantly to global warming and climate change, highlighting the urgency of addressing its presence in water treatment processes and wastewater management. With its considerable impact on environmental sustainability and public health, understanding the complexities and implications of N2O has become a critical priority for the water industry.
At the heart of the issue lies the role of N2O as a byproduct of the nitrogen cycle during biological nutrient removal (BNR) processes. Often employed in wastewater treatment facilities, BNR is essential for effectively removing nitrogen compounds from wastewater, preventing eutrophication and contamination of natural water bodies.
However, the unintended consequence of this process is the release of N2O, which significantly amplifies the carbon footprint of water treatment operations. The continuous discharge of N2O into the atmosphere not only contributes to the greenhouse effect but also exacerbates the overall environmental impact of wastewater treatment plants.
Measuring and controlling N20
The complex chemistry of N2O poses challenges in its measurement and control, necessitating advanced analytical techniques and precise monitoring systems. The quantification of N2O emissions demands meticulous attention to detail, often requiring sophisticated instruments and methodologies that are not readily accessible to all water treatment facilities. Consequently, the lack of comprehensive data and standardised protocols for N2O assessment further complicates efforts to regulate and reduce its release into the environment.
Speaking to Aquatech Online, Xylem’s Innovation Labs Accelerator Programme Lead, Dr Oliver Puckering, says: “Efficient monitoring of N2O emissions is a vital concern for wastewater utilities in their pursuit of comprehensive carbon inventories and meaningful mitigation targets. The 2019 Intergovernmental Panel on Climate Change (IPCC) guidelines introduced a tiered approach for N2O emissions estimation. However, these guidelines often underestimate actual emissions, leading to precision limitations in mitigation planning.
“N2O emissions are far from constant; they exhibit considerable variability and dynamic seasonal patterns influenced by factors like temperature, nitrogen loads and aeration demand patterns in treatment plants.”
Technology to reduce N20
The persistence of N2O in the atmosphere exacerbates its long-term environmental consequences, accentuating the need for sustainable and efficient strategies to minimise its impact. The water industry grapples with the imperative to adopt innovative technologies and operational practices that can effectively curtail N2O emissions while ensuring optimal treatment performance and regulatory compliance. Balancing the goals of environmental stewardship and operational efficiency presents a formidable challenge, requiring a comprehensive and integrated approach that encompasses technological innovation, regulatory frameworks and industry-wide collaboration.
Speaking to Aquatech Online, David Riley, head of carbon neutrality at Anglian Water, said: “I've witnessed great progress in reducing energy related carbon through efficiency programmes, vehicle fleets and renewable energy over the last 10 years, but reductions in N20 are lagging behind.
“The two key reasons are around the science and confidence in understanding measurement of emissions from different assets and processes and secondly the commercial challenge of financial savings in mitigating nitrous oxide emissions versus the investment required in supporting innovation and technology solutions.”
Dr Puckering adds: “Sensors capable of directly measuring N2O in liquid, gas, or both phases are available. While these sensors offer reliable measurements within their specified range, their large-scale implementation across multiple treatment plants remains a challenge. Nonetheless, they prove beneficial for conducting annual campaigns to measure N2O in specific locations within treatment plants, such as activated sludge basins.
“Empirical and risk-based models, incorporating parameters like dissolved oxygen, nitrite, nitrate, and computational fluid dynamics, offer a comprehensive understanding of N2O emissions. These models are appealing due to their ease of implementation and scalability, although they do face challenges related to validation and verification. Nevertheless, utilities worldwide are increasingly adopting these models in demonstration projects, accelerating the validation process.”
N20 research and development efforts
In the quest to address the N2O challenge, research and development efforts have intensified, focusing on the exploration of novel treatment methodologies and process modifications aimed at reducing N2O emissions.
Riley adds: “Things are changing, with investment in measurement and monitoring and the urgency that now exists to tackle and drive down this very damaging greenhouse gas.”
Innovative approaches, such as the optimisation of aeration strategies, the implementation of advanced process controls and the utilisation of tailored microbial communities, have shown promising potential in minimising N2O generation while maintaining robust treatment efficacy.
Wastewater treatment plants in Denmark, Australia, and the UK, for example, have united under the banner of the Net Zero Partnership, to tackle N20. The collaborative effort, initiated by Aarhus Vand, Melbourne Water, and Severn Trent aims to curb carbon emissions collectively by one million tonnes annually, highlighting the critical importance of international cooperation in addressing climate challenges.
Over the past year, the three partner organisations closely monitored N2O emissions in both gas and liquid phases, producing significant insights into emission patterns and effective mitigation strategies. Their findings have prompted vital discussions about the urgent need for comprehensive regulation of N2O emissions, considering its substantial contribution to global warming.
Real-time monitoring of N20
Their comprehensive study sheds light on the intricate dynamics of N2O emissions within the context of biological wastewater treatment. Researchers emphasize the significance of the nitrification-denitrification process in generating N2O, highlighting the impact of various operational conditions and microbial compositions on seasonal emission variations.
The report underscores the necessity for standardised methodologies to accurately calculate emission factors and advocates for the development of common monitoring and reporting techniques, fostering a unified approach to combating N2O emissions globally.
Dr Puckering says: “Real-time monitoring of N2O emissions, whether through direct measurement or modeling, is crucial for informed mitigation strategies. Decision support systems employing machine learning use N2O monitoring data to optimise operational conditions, including oxygen control and the return of activated sludge. This minimises N2O generation and thus the risk of emissions via gas stripping during nitrification and denitrification processes while meeting treatment requirements.
“It's important to understand, though, that while mitigation solutions can reduce N2O emissions, they may not entirely eliminate N2O production intrinsic to biological treatment processes,” he says.
“Therefore, utilities should consider a gradual shift to alternative treatments, like physical, chemical, and algae-based methods, with the aim of replacing conventional activated sludge processes, which were originally developed over 100 years ago. These alternatives not only prevent N2O production but also enable resource recovery from wastewater, such as optimising biogas production alongside reclamation of nutrients and capture of carbon.”
Measuring N20’s impact
In a recent whitepaper by Royal HaskoningDHV, the impact of N20 emissions from wastewater treatment plants (WWTPs) was explored in light of the challenges faced by water companies in achieving 'Net Zero' targets by 2030.
The study underscores the significance of controlling N2O emissions, highlighting the strong correlation between high ammonia loads and elevated N2O levels in the treatment process. By implementing Advanced Process Control, a comprehensive approach leveraging artificial intelligence and domain knowledge, effective strategies for minimising N2O emissions can be devised.
To help address the multiple enabling technology needs, Xylem has tasked its Innovation Labs team to define the current and emerging technological landscapes, identify the most promising options, and help accelerate broader deployment into the market.
This team is working in close support to both internal and external global N2O working groups with the latter including consultants and utilities. Collaborative initiatives and knowledge-sharing platforms have played a pivotal role in fostering a collective understanding of the N2O challenge, facilitating the exchange of best practices, and fostering the dissemination of cutting-edge research within the water industry.
As the water industry continues to navigate the complexities of N2O management, the imperative to prioritise sustainability, innovation, and collaboration remains paramount. Harnessing the collective expertise and technological advancements within the industry will be crucial in devising comprehensive and tailored strategies that address the multifaceted challenges posed by N2O, ensuring the continued preservation of environmental integrity and the promotion of sustainable water management practices.
By embracing a holistic and forward-thinking approach, the water industry can pave the way for a more resilient and environmentally conscious future, effectively mitigating the impact of N2O and fostering a sustainable balance between water treatment and global environmental well-being.