Navigating the decarbonization of water and wastewater utilities

Establishing an engineering-led decarbonization strategy

For carbon reduction commitments to succeed, it is essential that targets are supported by a clear, realistic, and achievable strategy. This enables organizations to better understand what their decarbonization journey requires, and how to prioritize, manage, and measure progress.

In the UK, New Zealand, and United Arab Emirates, Mott MacDonald has played an instrumental role in enabling clients in the water and wastewater industry to develop decarbonization roadmaps that meet legislative, regulatory, and stakeholder obligations. an international specification that provides an effective, proven framework for building robust, engineering-led plans for an entire value chain. In 2016 and 2023, Mott MacDonald co-authored editions of PAS 2080.

Where PAS 2080 excels is by guiding organizations to measure their baseline climate impacts to clearly establish roles and responsibilities across both the organization and its value chain, and by considering asset emissions across the entirety of the infrastructure lifecycle. It helps decision makers consider a carbon reduction hierarchy for their assets, and whether emissions can be avoided (using less resources, or none at all), shifted (using less carbon intensive materials, approaches or technologies for example), or improved (increasing the efficiency of existing activity). This enables better, consistent governance and decision making when it comes to addressing different sources of emissions, as well as informed prioritization, collaboration, and ultimately the measurement of progress.

Avoiding emissions and improving efficiency

Putting strategy into action, decarbonization can also mean improving the efficiency of your organization, including avoiding carbon and resource intensive activity.

One example can be found in the Catskill Mountains, where high up reservoirs are connected to New York City through a 91-mile aqueduct built more than 100 years ago. Maintaining, rather than replacing the aqueduct, is a cost-effective and carbon efficient option. Supporting the New York City Department of Environmental Protection, Mott MacDonald utilized digital tools, including building information modeling (BIM) and geographic information systems (GIS), to reduce the scope of rehabilitation construction and allow the existing aqueduct to be retained in good repair for another century. 

Addressing construction and design emissions

Supported by the PAS 2080 framework, where new assets are required, Mott MacDonald also helped water and wastewater organizations to lower their carbon footprint. Construction and maintenance can be carbon intensive because producing and transporting construction materials and assembling them to create operational assets can require carbon intensive processes.

Working with Wellington Water in New Zealand, Mott MacDonald utilized its Carbon Portal tool to better understand the carbon involved in using different materials for planned water and wastewater assets. With a better understanding of its potential construction emissions, it could then make better decisions on where emissions could be avoided, where they could be shifted, and where they could be improved on its projects.

This can also influence better design decisions. Working with Severn Trent, a water and wastewater utility company in the UK for the revival of its Witches Oak wastewater treatment plant, Mott MacDonald supported the design and delivery of a nature-based solution that reduced the requirement for energy and chemical use. By using a series of floating wetlands, which rise and fall with the load and seasons, the natural processes of the ecosystems including the different vegetation, root mass, and microbial communities could remove between 40-60% of the asset’s total nitrogen and suspended solids.

Alongside low-carbon construction approaches and materials, it means a substantial improvement in the asset’s whole life carbon emissions, compared to conventional treatment. It’s also improving the resilience of the Witches Oak facility to extreme weather events.

Tackling operational carbon and improving performance

Addressing operational carbon is also key. Mott MacDonald has been investigating methods and technologies to measure and mitigate nitrous oxide and methane emissions from wastewater treatment plants.

One of the challenges the water industry faces is treatment to remove emergent pollutants and meet new health standards. Ever tighter treatment standards are creating demand for new assets and increasing energy demand, including recent regulation to control a family of chemicals known as per- and polyfluoroalkyls – PFAS.

However, carbon saving opportunities can be found. To address the problem of PFAS in wastewater biosolids, Mott MacDonald is working with Iowa State University (ISU) and Philadelphia Water Department (PWD), with funding from the US Department of Energy (DOE). Together, they are piloting autothermal pyrolysis, a process that removes the PFAS and produces a solid biochar, which contains sequestered carbon. It additionally can reduce the volume of the biosolids by 80-90%, which translates into large savings on haulage.

Meeting your unique needs

While PAS 2080 sets a proven, measurable, and accountable framework for guiding your water and wastewater strategy, Mott MacDonald knows that every water and wastewater organization has a unique operating context, and every asset requires the right experience and expertise to reduce different sources of emission. We’re here to help you navigate your journey.