User Story: Enabling Greenhouse Gas Mitigation Through Nitrogen Monitoring
Tracking of Greenhouse Gas (GHG) emissions from activities related to water treatment has changed pace and focus over the years. Prior to the 1990s, GHGs were not a concern for the industry, which at that time was more looking at methane capture as an energy source. In the 2000’s the Intergovernmental Panel on Climate Change (IPCC) began including wastewater treatment in GHG inventories, and out of this, researchers began quantifying methane (CH4) and nitrous oxide (N2O) from treatment activities.
Fast forward to the late 2010’s, and monitoring and reporting studies revealed that N2O was being emitted at levels of concern, which precipitated wider and more focussed monitoring campaigns. IPCC guidelines provided default emission factors for the industry, but when these we applied site specifically, it became apparent that the need for enhanced monitoring and data collection on a site-specific basis was required.
The Paris Agreement in 2015 increased pressure on the wastewater sector to reduce emissions, and utilities engaged with the sensor and analysis sector to find pathways to better data to support mitigation and decision-making steps. The use of the Carbon Accounting frameworks allowed integrated GHG reporting.
This is largely where the Wastewater market remains, and it falls to the most innovative of groups to take the next steps beyond reporting, but to actual control. This is a complex topic, requiring specialist skills from data and process scientists to unravel the data trends coming from online and real-time monitoring of critical parameters, and applying these findings to both real-time control and process models to mitigate and control N2O emissions.
To find out more, we have spoken to two of the UK’s leaders, tackling GHG emissions from their facilities through dedicated teams focused on carbon neutrality.
History of GHG monitoring
David Inman, Innovation Projects Manager at Anglian Water, tells us that Anglian began its work in greenhouse gas measurement as far back as 2012 at an activated sludge plant in the west of the Anglian region. The initial findings provided an understanding that N2O contributes significantly to the overall wastewater treatment carbon balance, prompting the use of the Carbon Accounting Workbook to report on emissions. This initiative, commencing with the Innovation Team and Carbon Neutrality Team, is now led by an Asset Delivery Team focusing on mitigation in AMP8, with a focus on linking plant efficiency to carbon reduction.
Bharani Sri and Hannah Laywood, both Process Emission Leads at Severn Trent Water, tell us that their journey in GHG emissions took a defined focus when Severn Trent Water initiated its Triple Carbon Pledge: 100% electric vehicles, 100% renewable energy, and 100% net zero carbon emissions, identifying N2O as the largest contributor of direct emissions. Initial assessment of the Carbon Accounting Workbook revealed potential inaccuracies, prompting more direct measurement strategies. With tightening legislation such as the UK’s Net Zero 2050 initiative and industry-wide ambition, N2O mitigation has become a strategic priority for both utilities.
Challenges
Despite its importance, measuring N2O remains technically challenging. Opportunities to measure in the liquid and gaseous phase exist and offer insights into the levels of GHG’s being emitted from processes. In addition, the seasonal variation in emissions required studies to be performed over a 12-month period, just to capture baseline levels. However, N2O is a secondary byproduct of nitrogen transformations, making direct measurement less actionable for operators. This leaves the wastewater industry with the challenge of identifying control levers in their processes to action change.
In the early baselining and quantification studies, Anglian Water found discrepancies between IPCC figures and outputs from the Carbon Accounting Workbook, necessitating a re-baseline. While energy efficiency gains (e.g. replacing pumps) are relatively easy, process emissions, particularly N2O, are more complex. David noted the additional challenge in monitoring air flows within activated sludge plants, where aeration is typically controlled by power usage, but there is poor visibility into actual air distribution within ASP lanes. With air playing a critical role in the chemistry of nitrogen transformation, this presents further challenges for control.
Severn Trent Water observed that early measurements at their Spernal WWTP site aligned with IPCC figures, which, if applied network-wide, would imply significantly high emissions. This led to an expanded measurement campaign to multiple facilities enabling comprehensive evaluation of nitrous oxide emissions across facilities, and benefit of measuring key parameters in the process, namely, ammonium, dissolved oxygen, nitrate, nitrite, airflow and pH. Bharani and Hannah pointed to major operational pain points, such as installation and data integration of so many sensors, maintaining this equipment to ensure data flow continuity, and securing telemetry infrastructure.
Solutions
The water industry is looking for a robust solution which is practical from an operational perspective. While evaluating many technologies, one thing is clear: the least number of sensors necessary should be deployed, and a method of controlling N2O before its formation is a favoured pathway. An attractive strategy involves monitoring the chemical precursors to N2O, specifically nitrite NO2 and nitrate NO3, which are pathways in the biological processes that result in N2O formation. Using real-time measurements of these compounds, operators can gain meaningful insight into plant conditions and proactively manage emissions.
Severn Trent Water is also pursuing NO2 and NO3 monitoring as a mitigation strategy. Their five-year plan involves testing a range of sensors and data sets to develop predictive models to optimise process and control N2O. The plan includes a 12-month evaluation period to capture seasonal variation, with monthly data reviews to identify early learnings, and long term machine learning studies to uncover hidden insights. Site-specific approaches are being considered, with their Minworth WWTP site focusing on process control and the Strongford facility targeting a full digital twin of site operations. Bharani and Hannah agree that the research highlights the importance of the nitrite in the nitrification pathway, but this must be proven out on a full-scale biological treatment plant, and nitrite as a parameter may be important, but in isolation, it is not the full solution. The approach in their studies of having a reference lane and a study lane in parallel will offer a level of operational insight never seen before.
Evidence
Aquamonitrix technology is being trialled across multiple UK sites, including the AW Whittlingham site and STW Minworth site, to support real-time nitrogen monitoring with the objective of enabling proactive emissions control.
Works outside of the UK, and particularly in the Netherlands, has established the correlation between Nitrite and Nitrous Oxide in the gaseous phase on a full scale and fully covered activated sludge lane.
Both Severn Trent and Anglian Water have received substantial funding under the Net Zero Enhancement funding from OFWAT, which reflects confidence in their approach and innovation strategy. These awards are the only ones of their kind in the UK and reflect the leading roles both utilities are taking in making advancements in this critical area.
The topic of climate change creates different mood music in different territories, but when you speak with David, Bharani, and Hannah, it is evident that they are focused on delivering effective and practical solutions for their utilities and, ultimately, their customers and the environment.
Severn Trent Water is pursuing a science-based target of a 45% reduction in emissions by 2030, despite the UK’s broader 2050 legislative target. Their active evaluation of datasets and early field trials indicates strong institutional support for innovative, data-driven control strategies.
“Our Science Based Target commits us to a 46% reduction in our direct operational Scope 1 and 2 emissions by 2031.”
Likewise, Anglian Water has self-imposed targets that it will pursue. Its goal is to generate 45% of its energy from renewable sources by 2025 and become a fully net-zero carbon business by 2030. This includes managing and reducing emissions by installing monitoring equipment at four large Anglian Water sites to obtain data to assist with the plan to achieve net-zero emissions by 2030.
Join the movement
The topic of GHG reduction in Wastewater activity is growing on a global scale. Some territories faster than others. Groups of professionals in this space are creating information sharing platforms, such as the Sensors in Water Interest Group (SWIG), who have held 2 consecutive seminars on Nitrous Oxide “It’s no Laughing Matter”, attended by a global audience of thought leaders in this area. It will come as no surprise that David, Bharani and Hannah Laywood are regular contributors on these platforms.
With the best minds working on this challenge, science-based solutions will emerge. We have a collective responsibility to address climate change, and within the biological water treatment sector, this is the biggest issue to target.
Contact us at Aquamonitrix to learn how you can join the monitoring campaigns and start your journey to managing GHG emissions from your assets.
