Decarbonizing the water industry

For more information, please see our blog on why the world will need even more desalinated water in the future.

Watch Ana Lopez answering the question: "Why is water scarcity a growing global concern?"

The “water-energy nexus” refers to the interdependent relationship between water and energy resources. This interdependence means that changes in the availability or efficiency of one resource directly affect the other.

Supplying, treating, and distributing water – and treating wastewater – all require energy. The amount of energy required depends on the type of water supply and treatment. Conversely, water is essential for producing energy, whether for cooling in power plants, hydropower generation, or extraction of fossil fuels.

The type of energy used impacts greenhouse gas (GHG) emissions. Renewable energy sources, such as solar and wind, produce very low emissions compared to carbon-based energy sources like coal and natural gas. Thus, utilizing renewable energy for water-related processes can significantly reduce their carbon footprint. Actual GHG emissions depend on the mix of energy sources used in a particular region.

For further insights, please see our blog about renewable energy and SWRO and our case story  on how an SWRO plant runs exclusively on solar power.

Decarbonizing high-pressure membrane processes such as seawater reverse osmosis (SWRO) used for desalination and zero liquid discharge (ZLD) used for wastewater treatment is crucial due to three key reasons:

1. Increasing necessity: With growing water scarcity, industrial pollution, and the impacts of global warming, the demand for SWRO and advanced wastewater treatment processes like ZLD is rising. These treatments are essential for ensuring an adequate water supply and protecting the environment.
2. High energy intensity: SWRO and ZLD processes are energy intensive. Depending on the mix of energy sources, high energy consumption results in significant greenhouse gas (GHG) emissions. Reducing the carbon footprint of these processes is vital to mitigate their negative impact on climate change.
3. Technological advancements: Utilizing the best available technology can dramatically reduce both GHG emissions and operational costs. By adopting energy-efficient technologies and renewable energy sources, the environmental and financial sustainability of these critical water treatments can be greatly enhanced.

 For more information, please see our blogs on the carbon footprint of potable water and  why energy-efficient membrane processes will drive ZLD and MLD growth.

Watch Darren Williams answering the question: "Why is it essential to decarbonize water treatments like desalination and ZLD?"

Desalination, including seawater reverse osmosis (SWRO), uses significantly more energy than other sources of fresh water, such as surface water and groundwater.

To compare energy needs, industry stakeholders use Specific Energy Consumption (SEC) data. SEC is a measure of the energy required to produce a specific amount of treated water, usually expressed in kilowatt-hours per cubic meter (kWh/m³). It is a key metric for understanding the energy efficiency of water treatment processes.

Using SEC, we can easily compare the energy requirements of different water sources:

• Surface water typically requires the least energy for treatment and distribution, with SEC values generally below 0.5 kWh/m³.
• Groundwater requires more energy than surface water due to the need for pumping, but still far less than desalination, with SEC values around 0.5 to 1 kWh/m³.
• Desalination has historically had very high SECs, with the first thermal plants as high as 27 kWh/m³. Subsequent generations of SWRO, now the dominant desalination technology, reduced SEC dramatically. Today, the SECs of many SWRO plants range from 2.5 to 5 kWh/m³.

The SEC of SWRO varies depending on factors such as the quality of the source water, plant design, and the technology used. Cutting-edge technologies and optimized processes can substantially reduce the energy required. For instance, the DESALRO 2.0 project set a new world record in SWRO energy efficiency with an SEC of 1.8 kWh/m³.

For more information, please see our blog on the carbon footprint of potable water.

One of the primary challenges in SWRO processes is the significant energy required for high-pressure pumps that force seawater through membranes. This high-pressure requirement represents the largest energy usage of SWRO plants, accounting for approximately 70% of a typical plant’s total energy consumption. Intake pumps and pre-treatment processes make up most of the remainder.

SWRO plants can, first and foremost, reduce their carbon footprint through strategies and component choices aimed at improving the energy efficiency of high-pressure processes. Three components in particular have the greatest influence on energy efficiency and minimizing greenhouse gas emissions:

1. High-pressure pumps: The type of high-pressure pumps specified for use has significant consequences for energy consumption. Positive displacement pumps are more energy-efficient than centrifugal pumps and provide substantial energy savings.
2. Energy recovery devices (ERD)s: In addition to high-pressure pumps, ERDs play a crucial role by recovering and reusing energy from the high-pressure brine stream that would otherwise be wasted. This significantly lowers the overall energy demand by reducing the high-pressure pump’s workload.
3. Membranes: Membrane efficiency is another critical factor. High-quality membranes with better permeability and lower fouling rates save energy by requiring less pressure to achieve the same water output, again reducing the high-pressure pump’s energy requirements.

Furthermore, automation and operational tweaks also contribute to energy savings. Marginal improvements through optimized operations, such as adjusting flow rates and pressure settings, can cumulatively result in significant energy reductions.

Finally, SWRO plants also reduce their carbon footprint by sourcing their energy from renewables such as solar and wind rather than using electricity generated from coal or gas.

For more information, please see our blog on how much energy and CO₂ can be saved by retrofitting existing desalination plants.

Positive displacement high-pressure pumps are more energy efficient than centrifugal high-pressure pumps for several reasons.

Fundamental design differences contribute to the superior efficiency of positive displacement pumps. They are designed to move a fixed amount of fluid with each cycle, which makes them inherently more efficient as they avoid the energy losses associated with the high-speed rotational motion of centrifugal pumps. This characteristic allows positive displacement pumps to achieve higher energy efficiency across various applications and sizes.

Another key advantage of positive displacement pumps compared to centrifugal pumps is that they maintain their high efficiency across a wide range of flow pressure rates. This means they can handle varying conditions (e.g., seasonal variations in seawater temperature and salinity) without a significant drop in performance.

By leveraging these advantages, positive displacement high-pressure pumps can significantly reduce the energy consumption of processes like seawater reverse osmosis (SWRO), ultimately contributing to a lower carbon footprint and financial burden.

 For more information on the energy efficiency advantages of positive displacement pumps compared to centrifugal pumps, please see this article from Pumps & Systems.

Despite the potential for significant energy efficiency improvements in SWRO, many operators are hesitant to adopt these changes for several reasons.

A primary barrier is the lack of awareness about the water-energy nexus and the true financial and environmental costs associated with current practices. Some operators and most end users may not fully understand the actual costs of energy inefficiencies, nor are they aware of realistic alternatives to legacy solutions. This knowledge gap can prevent SWRO stakeholders from making informed decisions that could lead to reduced environmental impact and substantial financial savings.

Another significant factor is the focus on upfront costs (CAPEX) rather than operational expenditures (OPEX) and the total cost of ownership (TCO). Energy-efficient technologies often require higher initial investments, and without a clear understanding of the long-term financial benefits, operators may opt for cheaper, less efficient solutions. This short-term financial focus can be a major deterrent to adopting new, more efficient technologies that provide substantial long-term economic and environmental advantages.

Furthermore, the absence of carbon pricing or taxation to incentivize energy efficiency improvements also plays a role. Without financial incentives or penalties related to carbon emissions, there is less motivation for operators to invest in energy-efficient solutions. Carbon pricing mechanisms could provide the necessary economic motivation to drive the adoption of technologies that improve energy efficiency and reduce greenhouse gas emissions.

Calculating the environmental and financial impacts of retrofitting desalination plants with the most energy-efficient equipment involves several steps:

1. Assess the plant’s current technology and SEC: Begin by evaluating the plant's existing technology and determining its SEC. This will provide a baseline for comparison.
2. Calculate the financial and GHG impacts of your current setup: Analyze the financial costs associated with the current setup, including energy costs, maintenance, and operational expenses. Additionally, calculate the GHG emissions based on the type of energy used and the amount consumed. This will give a clear picture of the financial and environmental impacts of the current operations.
3. Compare the existing setup to best-in-class technologies and SECs: Research and identify the most energy-efficient technologies available for your desalination needs, such as advanced high-pressure pumps, ERDs, and high-efficiency membranes. Compare the SEC of the plant if it utilized these best-in-class technologies to its current SEC to understand the potential energy savings.
4. Budget for retrofit costs and calculate the payback period: Estimate the costs associated with retrofitting the plant, including the purchase and installation of new equipment, any necessary infrastructure modifications, and potential downtime during the retrofit process. Calculate the payback period by comparing the upfront retrofit costs to the annual savings in energy costs and reduced maintenance expenses. The payback period is the time it takes for the savings to cover the initial investment.

By following these steps, decision-makers can comprehensively evaluate the environmental and financial impacts of retrofitting their desalination plant, making it easier to decide on the best course of action.

For more detailed insights, please refer to our blog Retrofits: The key to improving energy and cost efficiency for SWRO’s installed base.

While maximizing the overall energy efficiency and sourcing electricity from renewable sources have the greatest impact on SWRO’s GHG emissions, a more comprehensive approach has additional advantages:

Choose quality components and designs: Investing in high-quality design and components is crucial. Buying and maintaining one good, durable item often saves GHG emissions and financial costs in the long run compared to repeated purchases of cheaper alternatives that break down and need frequent replacement. This approach not only reduces waste but also minimizes the carbon footprint associated with manufacturing and transporting multiple products over time.

Consider the entire value chain: SWRO decision-makers should look at the entire value chain to understand and mitigate scopes 1, 2, and 3 emissions, with a particular focus on refurbishment, repair, and end-of-life considerations:

• Scope 1 (direct emissions from owned or controlled sources):  Most SWRO plants purchase their electricity (see Scope 2), but some produce it themselves. Reducing the emissions related to electricity generation by using renewable energy sources such as wind or solar rather than diesel generators, for example, lowers scope 1 emissions substantially.
• Scope 2 (indirect emissions from the generation of purchased electricity): In addition to the energy-efficiency optimizations described above, SWRO operators can purchase their electricity from renewable sources such as wind and solar.
• Scope 3 (all other indirect emissions that occur in the value chain, including upstream and downstream and vendor activities): This includes emissions from the production and transportation of components and consumables, waste disposal, and employee commuting. Emphasizing repair over replacement extends the lifespan of existing equipment, reducing the need for new manufacturing and transport, and thus reduces associated emissions. Considering the end of life of components and planning for their refurbishment or recycling can also significantly lower the overall environmental impact.

Watch Georg Herborg answering the question: "In addition to the energy efficiency of key components, what else should decision makers consider to reduce the carbon footprint of SWRO?"