Investing in wastewater energy efficiency for a greener future

Energy efficiency


Expenditure on infrastructure such as wastewater treatment systems represents investment in what are long-life assets, meaning there is good reason to make decisions based on whole life costs rather than just the upfront capital costs. But what if more efficient equipment could reduce overall costs and at the same time deliver much-needed cuts in greenhouse gas emissions? A recent report by international technology company Xylem provides an assessment to support precisely this idea. Keith Hayward takes a closer look at the findings.

The report on wastewater treatment efficiency and greenhouse gas emissions released recently by international technology company Xylem offers some persuasive figures, including a top-line figure that a positive economic return totalling $40 billion across the USA, Europe and China could be achieved if a range of efficiency measures were to be implemented. Governments are increasingly on the lookout for ways to reduce greenhouse gas emissions. According to the analysis presented by Xylem, investment in efficient wastewater treatment equipment would in many cases not only reduce power demand and in turn cut greenhouse gas emissions, but would do so at either no net cost or with an overall cost saving.

Wastewater treatment is estimated to use around 0.8-1.0% of total electricity generated in developed locations such as the USA and Europe. It is therefore not the largest consumer of power, but it is nonetheless a significant user. The types of technologies advocated by Xylem already exist, unlike many of the solutions to deal with greenhouse gases upon which the world’s long-term hopes are being pinned. A shift to highly efficient wastewater treatment would therefore seem to be a no-regrets contribution.

The analysis was carried out for Xylem by Vivid Economics. It investigated the application of 18 different opportunities in wastewater management to cut emissions arising from the use of electrical power. According to the study, nearly half of the electricity-related emissions in wastewater management can be abated at a negative or neutral cost using these measures.

Xylem Powering the Wastewater Renaissance
Xylem's Powering the Wastewater
Renaissance report (c) Xylem Inc.

The opportunities assessed in the study covered use of high efficiency pumping, variable speed pumping, variable speed blowers, high efficiency mixing, optimised control systems, and improved biogas production in wastewater transport, secondary treatment, and / or sludge treatment, use of efficient air scour blowers and filter system controls in tertiary treatment, as well as optimised new plant for secondary, tertiary, and aerobic and anaerobic sludge treatment.

Around one third of electricity-related emissions could be abated in Europe and USA using the options assessed, with most implemented at a negative or neutral cost, according to the study. In China almost 60% of the emissions could be abated using these measures, all at a negative or neutral cost. In all, over 20 million metric tons of carbon dioxide equivalents could be abated annually at negative or neutral cost across the three study areas. Scaled up to the global level, the study estimates a potential to abate nearly 44 million metric tons of carbon dioxide equivalents annually. To put this in perspective, according to the US EPA, the total global annual emission of all greenhouse gases for 2010 was around 46 billion metric tons of carbon dioxide equivalents.


Behind the numbers

The study used two methods to assess the potential benefits of the different options. One was to prepare what are known as marginal abatement cost curves. These pull together both the emission reductions and the positive or negative abatement costs associated with each of the various options to create an overall picture of the reduction that can be achieved and the financially most attractive options contributing to this reduction. The other was to evaluate the internal rate of return of the different options, which is a way to identify the most attractive options for a range of different possible future carbon costs.

Behind the findings are quite a number of assumptions and caveats that need to be kept in mind. For example, the findings represent a comparison between carrying out end of life replacement with low or medium efficiency equipment and with high efficiency equipment. An asset life of 20 years is assumed. The calculations are also based on all assets being replaced immediately. This would not be the case, and it is likely that the farther into the future assets are replaced, so the emissions savings associated with them would be reduced since there is likely to be an increasing shift over time towards lower emission energy sources.

Also, the main findings represent just part of the overall carbon and energy picture of wastewater treatment. The efficiency measures that the report advocates help address the emissions relating to electricity use. They do not address the direct release of greenhouse gases from wastewater handling and treatment. Such fugitive emissions are important. In China, they account for 90% of wastewater sector emissions, both because there tend to be more greenhouse gas emissions when there is little or basic on-site treatment, and because the lower level of secondary treatment here means there is proportionately less power use. But even in Europe and the USA, fugitive emissions account for around two thirds of all wastewater sector emissions, and based on a US EPA assessment cited in the report, it is concluded that the high cost of dealing with these emissions means they are unlikely to feature in climate policy.

Importantly, the assessment is also based on all wastewater treatment plants using conventional activated sludge as the secondary treatment process. The report acknowledges that the process is not widespread in China and notes that there is a case for a further assessment for China. For Europe and USA, the results show there are substantial gains to be had from installing high efficiency blowers and aeration control in the secondary treatment stage. However, the report does not consider what alternatives there may be to conventional activated sludge and in turn what the energy implications of this may be.


The case for change

Nonetheless, there is, Xylem argues, a clear financial case for investment in the types of wastewater treatment efficiencies set out in the report, raising the question as to just why such options are not being pursued to a greater extent.

The main case made by Xylem in the report is that the primary barriers to adoption are awareness of the opportunity and willingness to adopt existing solutions that have a higher initial capital cost and a lower ongoing operating cost.

‘What’s missing is the enabling framework to incentivize investment and accelerate widespread adoption of these advanced, sustainable solutions,’ says Patrick Decker, President and CEO of Xylem in the foreword to the report.

Xylem says that two levers identified in the report would accelerate adoption of highly efficient wastewater technologies: new financing models that incentivize investments in low-carbon technologies, which would assist with the initial higher capital costs that often come with these advanced technologies; and increasing the energy efficiency standards of wastewater equipment, which would ensure broader adoption.

The challenge is one of just how to move the sector down this route. Xylem makes a number of proposals, including developing the assessment method further, looking at different policy instruments, building data sources, and carrying out fieldwork to better understand just what the barriers to progress are.

The report also issues are rallying call to try to stimulate action. ‘Now is the time for the industry and all stakeholders in the climate change agenda to work together to overcome these barriers to adopting high efficiency wastewater treatment technologies, which will result in greater productivity of wastewater operations, and a meaningful step forward in tackling climate change,’ the report concludes, with CEO Decker adding: ‘Infrastructure investments today can have positive environmental and economic consequences for decades. Importantly, the pragmatic solutions identified in this report pay for themselves and, in many cases, unlock new capital that can be invested in additional infrastructure improvements. As we address the effects of a growing global population and its accompanying strain on natural resources, the public and private sectors must come together to identify and implement new ways to realize the full potential of a low-carbon economy.’

To download the report, Powering the wastewater renaissance: energy efficiency and emissions reduction in wastewater treatment, visit:

See also interview with Al Cho, Xylem VP Strategy and Business Development: The water sector energy efficiency opportunity


  • Xylem, water and energy, municipal wastewater, sewage, energy efficiency