Net-zero: net gain

Energy revolution

Water and wastewater treatment processes are energy hungry. Historically, the energy sector has been slower than the water industry to decarbonise.

Water providers have long been investing in measures to minimise their grid electricity use to achieve net-zero. They have radically improved their energy efficiency, and they generate renewable energy using biogas from wastewater sludge, and on-site solar and wind installations. These power sources have enabled the water providers to stop using natural gas as a heat source for wastewater treatment; they no longer require diesel generators for back-up power.

Water providers’ embrace of renewables has been assisted by government incentives to increase the production and use of biogas as a green fuel. Conventional sludge treatment has been replaced with advanced anaerobic digestion (AAD) to increase biogas production. Biogas fuels high-efficiency combined heat and power engines that meet the thermal energy requirements of the digestion process itself, and generate electricity to run the rest of the wastewater treatment process. Surplus gas and electricity are used to power vehicles or are sold to the grid.

Water and electricity regulation have been changed to enable the providers to generate renewable electricity at scale – some water companies are nationally significant electricity producers. And with government support, water and energy providers have together developed facilities to produce hydrogen – an important part of the net-zero energy system.

A chemical engineering process called reforming converts biogas into ‘grey’ hydrogen – carbon is a by-product that is captured and stored. The companies also produce ‘green’ hydrogen from water, using surplus renewable electricity to power electrolysis. It is a thirsty process: water demand is met by working with customers to reduce consumption and by using digital solutions to identify and fix leaks, limiting losses from the water network.

Radical efficiency

Incremental energy and carbon savings have been achieved through painstaking attention to the operating efficiency of processes and plant, aided by digitalisation.

And major steps to decarbonisation have been achieved through the systems approach to water resource management.

New farming and land management practices, and the water providers’ use of nature-based solutions, are reducing the amount of treatment needed to bring raw water up to potable standard. Meanwhile, water and environmental regulators permit flexible wastewater discharge standards, based on the quality of the receiving water body and its ecological health.

Effluent is heavily diluted in rivers swelled by winter rain and pollutants are quickly broken down, enabling the water companies to relax the treatment standard, reducing energy use and carbon emissions. The highest treatment standard must be achieved when river flow is low in summer, so as not to harm plant and animal life or pose a risk to river users’ health. Treatment is adjusted in real time, informed by data on pollution load in the incoming wastewater stream, and on the receiving water body.

Nature-based solutions have reduced the need for treatment, saving energy and chemicals. In some locations, this enables water providers to meet increasing demand without building new water treatment facilities, so avoiding capital carbon emissions.

Difficult emissions

In the early 2020s, water industry research and new monitoring systems enabled providers to accurately quantify the emissions of methane and nitrous oxide – both powerful greenhouse gases –from their wastewater treatment facilities.

These releases posed a serious obstacle to providers’ net-zero mission and they have responded by designing all new facilities to minimise and capture the gases; they continue to implement programmes to retrofit existing facilities.

The water industry has moved faster than society at large in decarbonising its vehicle fleet. All of the industry’s vehicles run on renewables – cars and light goods vehicles are electric and heavy vehicles are powered by biogas or hydrogen fuel cells. The transition from fossil fuels has been supported by the transport sector, which has worked with the water industry to provide charging and fuelling infrastructure where needed.

Service providers have invested in large-scale carbon sequestration projects to offset their process-related carbon, and continue to do so, using their own land and working with other landowners to develop nature-based solutions, such as tree planting and peatland restoration. Nature-based carbon sequestration, flood mitigation and water treatment are complementary – the providers develop schemes to deliver multiple benefits.

Net-negative

Overall, the water industry’s actions to cut carbon emissions have delivered cost savings that have enabled reinvestment in new carbon initiatives, creating a positive feedback loop.

By 2040, the industry is providing more green energy than it needs and sequestering more carbon than it produces. It has become carbon negative – a supporter of national efforts to achieve net-zero.