OneWater Reflections Mar 28, 2024

Demystifying Wastewater Decarbonization

By Emma Shen

OneWater Reflections

With the impacts of the climate emergency increasingly clear to society and global leaders, we’re seeing more countries, cities and companies set net-zero emission goals. These goals need to be cascaded down to different sectors, as each sector faces different challenges and opportunities.

The water sector contributes to about 2% of the global carbon footprint – this is about the same as the shipping industry, and likely underestimated as methodologies are not well established for all water sector greenhouse gas (GHG) sources. 

Over the past decade, there have been significant efforts to reduce energy consumption and the associated GHG emissions across the water sector, through a combination of reducing energy consumption, maximizing energy recovery and increasing the purchase of renewable energy and technology advancements which have made ‘net-zero’ energy a possibility. However, it is important to recognize the significant gap to achieving ‘net-zero emission’, because we produce GHG emissions as byproducts of the wastewater and sludge treatment processes – nitrous oxide (N2O) and methane (CH4), referred to as ‘process emissions’. These emissions can make up more than 2/3 of the total emissions for a typical water resource recovery facility (WRRF), and in some regions already account for more than 90% of the WRRF carbon footprint (e.g., where the local electricity grid is almost decarbonized). Tackling process emissions remains the key challenge for decarbonizing the wastewater sector, but also the most significant opportunity to make an impactful reduction in the near term – if we act now! This is a fast-evolving area with plenty of development and collaborations globally. 

Jacobs has been working with our water sector clients around the world to develop decarbonization strategies and set meaningful GHG reduction commitments. The key is to establish a transparent framework that clearly defines the boundary (i.e., the scope of GHG emissions to be included), the methodologies used to quantify these emissions, the associated limitations (e.g., data quality, level of uncertainties), opportunities for improvement and, importantly, any changes from the previous methodologies used. These will enable us to ‘re-baseline’ the GHG emissions to include additional emission sources and refine the reduction targets as the quantification methodologies continue to evolve and improve. When setting the reduction targets, it is important to consider the ‘possibility’ and ‘reality’ of GHG mitigation opportunities in the context of local conditions (for example, opportunities targeting electricity saving or renewable generation will have smaller impacts on GHG reduction for a ‘clean’ energy grid than a ‘dirtier’ grid), the technical feasibility (including whether the reduction can be reliably quantified), and operational and financial impacts.  We need to acknowledge the challenges and limitations when making net-zero ambitions – recognizing that it is not possible to achieve net-zero emissions cost-effectively based on technologies available today, while having faith in science and technology development that innovative net-zero solutions will become more established in the long term. 

It is worth noting that many of the decarbonization solutions offer co-benefits, such as improved energy efficiency and associated cost saving, enhanced process performance, stability and/or resiliency, or process intensification that can defer capital spending for major capacity expansions. It is important that we incorporate decarbonization into long-term facility planning and capital delivery processes, such that net-zero solutions can be identified and evaluated along with other ‘conventional’ solutions for asset renewals, growth, and efficiencies, and be incorporated into future designs and operations. 

About the author

Emma Shen

Dr. Ruqiao (Emma) Shen is Jacobs Global Principal for Wastewater Energy Optimization and Sector Decarbonization. An expert in wastewater treatment plant performance assessments and process upgrades evaluation, process modeling and energy optimization, Emma leads a Jacobs team at the forefront of the global conversation about the paradigm shift toward a low-carbon, low-energy and climate-resilient water sector.

Get to know Emma