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Carbon Zero Grand Challenge

The race to act on climate is on and the water sector must do its part.
Help us take the world’s water to net zero emissions and beyond!

Challenge Overview

The S$6.5 million (approximately US$4.8 million) Carbon Zero Grand Challenge seeks to incentivize innovative solutions that can help PUB achieve net-zero emissions by mid-century and scale to water facilities around the globe. PUB is seeking carbon capture, utilization, removal, and other solutions at any technology readiness level that can be integrated with its operations and reach commercial scale within a decade or sooner. 

The grand challenge will have two phases of competition and a pilot-scale demonstration over approximately 45 months. In the Proposal Phase, solvers will submit a detailed proposal addressing net carbon abated, cost, and other critical aspects of their solution. Up to six will be awarded S$250,000 each to develop a Proof of Concept. In the Proof of Concept Phase, solvers will develop a desktop simulation and/or lab-scale study and a detailed design for a pilot project. Up to two will be awarded S$2.5 million each to demonstrate a ~1 kiloton-scale version of their solution at a PUB facility in Singapore.


As an island city-state, Singapore’s geography inherently limits its access to natural resources. For this reason, Singapore has always been an innovator and a leader in identifying clean, efficient, and cost-effective solutions for energy, water, and the environment. 

PUB, Singapore’s national water agency, manages the nation’s water supply, water catchment, and used water in an integrated way. In 2020, PUB also took on the responsibility of protecting Singapore’s coastline from sea-level rise as the national coastal protection agency. 

The global water sector contributes approximately 5% of greenhouse gas (GHG) emissions but has not yet received significant attention in climate debates. Although Singapore’s local water sector emissions represent less than 1.5% of the city-state’s total emissions, in today’s climate, every contribution counts. 

The Sixth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC) that was published in August 2021, reinforced the reality that urgent and aggressive action is needed to keep global temperature rise below 2°C, as committed to in the Paris Agreement. Every sector must play its role, including the water sector. That is why PUB has set a goal to achieve net zero carbon emissions by mid-century. 

The Carbon Zero Grand Challenge seeks to focus the attention of innovators, investors, and thought leaders on water sector emissions in order to accelerate the deployment of innovative solutions to address Singapore’s net zero carbon emission goals and scale to water facilities around the globe. ​

Emissions to be Addressed

As an organization, PUB’s emissions in 2020 are approximately 460 kt CO2e as reported in PUB's Sustainability Report 2020/2021​. To achieve its net-zero goal, PUB will need to implement new technologies and solutions to address emissions associated with its water facilities. PUB has built a robust and diversified supply of water, including NEWater facilities that recycle used water and desalination facilities that convert seawater to drinking water (see FIGURE 1).

However, many of these processes are inherently energy-intensive and PUB’s emissions are projected to increase with population rise and economic growth in the coming decades. By mid-century, emissions could double to 1 MtCO2e. ​

PUB is already working to reduce its carbon footprint by replacing carbon-emitting energy sources with solar PV deployed on facility rooftops and at reservoirs, and reducing carbon emissions through energy efficiency, lowering desalination energy and conservation. These efforts are expected to abate approximately 600 kt CO2e/year of emissions by mid-century. 

While current efforts can reduce PUB’s future carbon footprint substantially, PUB is seeking solutions to remove an additional 400 kt CO2e/year associated with its facilities that will require solutions such as carbon capture, utilization and storage (CCUS) and carbon removal (see FIGURE 1 and TABLE 1).

PUB Water Loop​​​​​​​


Projected Emissions from PUB

Description​Annual Estimated Projection
Total PUB emissions 1,000 kt CO2e
​Emissions for which solutions have already been identified 600 kt CO2e
Emissions requiring new solutions (focus of this grand challenge) 400 kt CO2e
Scope 1 emissions (within emissions requiring new solutions) 200 kt CO2e
Scope 2 emissions (within emissions requiring new solutions)​200 kt CO2e

PUB’s projected Scope 1 emissions that will require new solutions (200 kt CO2e/year) are associated with its four water reclamation facilities and come from two sources: 

● ​​​Approximately 100 kt CO2e/year from anaerobic digester processes that result in an emissions stream containing approximately 35% carbon dioxide; 62% biomethane; and 3% mixed gases that are primarily hydrogen sulfide and nitrous oxide.
● ​​Approximately 100 kt CO2e/year of mostly nitrous oxide emissions from nitrification/denitrification that happens in the aerobic wastewater treatment processes.​

FIGURE 2 illustrates a typical water reclamation process and the sources of Scope 1 emissions.

Typical Water Reclamation Process and Scope 1 Emissions


The remaining Scope 2 emissions (200 kt CO2e/year) are due to the electricity used to power PUB’s facilities, for example water treatment plants, desalination plants, NEWater Factories and used water treatment plants.

Approaches In-Scope for this Grand Challenge

This grand challenge seeks solutions that :

1) Directly address emissions associated with PUB’s water facilities, as described in the section above; and
2) Have the potential to be deployed at commercial scale within a decade or sooner

Such solutions may include: 

● Carbon capture, utilization, and storage (CCUS) technologies that can be integrated with PUB’s water treatment or desalination operations
● Approaches for addressing greenhouse gas (GHG) emissions associated with PUB’s facilities, while still maintaining PUB’s ambition to achieve energy self-sufficiency through the use of biogas/biomethane generated from anaerobic digestion
● Approaches for carbon dioxide removal (CDR), that remove CO2 from the atmosphere that could be integrated with PUB operations
● Approaches for carbon dioxide removal (CDR) that remove CO2 from seawater that could be integrated with PUB operations
● Any other approaches that directly address emissions associated with PUB’s water facilities and are not out of scope, as described below 

Solutions that do not directly reduce or remove GHG emissions associated with PUB’s water facilities are out of scope for this grand challenge. These include: 

● Approaches to replace grid power used by PUB’s facilities with commercially available renewable power generation sources, such as rooftop solar PV
● Approaches involving tree planting, soil sequestration, or similar offset schemes
● Approaches addressing any Scope 1 emissions associated with vehicles or travel
● Approaches addressing any Scope 1 or Scope 2 emissions associated with building heating or cooling systems ​

Grand Challenge Structure and Timeline

The grand challenge will focus on accelerating the development of innovative concepts through proof of concept and an initial field demonstration. The grand challenge will include two phases of competition and a pilot-scale demonstration, as follows: 

Proposal Phase: Solvers will submit a proposal for their solution, including any relevant data or other credible supporting information; up to six1 will be chosen to move onto the next phase
Proof of Concept Phase: Solvers will develop a desktop simulation and/or lab-scale study based on PUB’s conditions (which will be outlined in the submission template) and a detailed design for a pilot project; up to two will be chosen to develop a pilot project
Pilot Project: Winners from the Proof of Concept Phase will build and demonstrate an approximately 1 kiloton-scale version of their solution at a PUB facility in Singapore and develop a plan to achieve commercial scale within a decade or sooner 

The grand challenge will last a total of approximately 45 months, including approximately 21 months for the two phases of competition and 24 months for the pilot project. TABLE 2 provides the expected timeline for the grand challenge.

Grand Challenge Expected Timeline

Grand Challenge opens; Proposal Phase commences --October 19, 2021
Solvers register and develop submissions 4 monthsOctober – February 2022
Proposal Phase registration deadline and submission deadline--February 24, 2022
Proposal Phase evaluation 3 monthsMarch – May 2022
Proposal Phase awards announced--June 2022
Proof of Concept Phase commences; Solvers selected to participate in this phase develop proof-of-concept submissions9 months​​​​

June 2022 to March 2023
Proof of Concept Phase submission deadline--March 2023
Proof of Concept Phase evaluation3 monthsQ2/Q3 2023
Proof of Concept Phase awards announced --Q3 2023
Pilot Project, including 6-12 months of operation24 months Q3 2023 ​to Q3 2025
PUB is seeking to select a variety of solutions that address emissions in different ways to move forward to the Proof of Concept Phase and the Pilot Project Phase. However, the distribution of awards across solutions or types of technology will ultimately depend on the quality of submissions.
Key Performance Criteria

In the Proposal Phase and the Proof of Concept Phase, solvers must address the Key Performance Criteria for this grand challenge, as described in TABLE 3.

Key Performance Criteria for this Grand Challenge

​​​CriteriaDescriptionCalculation/Unit of Measurement
Net carbon abatedThe amount of CO2e permanently reduced or removed annually-Expressed in CO2 equivalent (CO2e)
CostThe projected cost per metric ton of CO2e abated for the solution at full commercial scale (100 kt/yr)-Expressed in S$/metric ton of CO2e
-Using the techno-economic analysis guidelines explained below
FootprintThe physical footprint of the solution at pilot scale (approximately 1 kt/year) and at full commercial scale (100 kt/year-Expressed in m2​

Techno-Economic Analysis Guidelines

For the techno-economic analysis, solvers should provide cost estimates that are reasonably accurate and precise, and presented in such a way that the major cost factors can be broken out and analyzed for error, uncertainty, and sensitivity. The analysis should include all costs over the life of the project on a levelized basis. 

Solvers should calculate cost as follows: 

S$/tonne of CO2e abated =
(Capital Expense plus Operating Expense minus Revenues)
divided by # of metric tons of CO2e abated 

• Capital Expense includes materials, equipment, and any other capital expenditures
• Operating Expense includes energy, chemicals or other process inputs, personnel, maintenance, and any other operating expenditures
• Revenues include proceeds from the sale of any product derived from CO2 captured and utilized by the project
• The standard cost of electricity is S$110/MWh
• The emission factor for grid electricity is 0.4 kg CO2 per kWh
• The standard Discount Rate is 4%
• To convert costs to Singapore dollars (S$), solvers should use the exchange rates listed for October 19, 2021 via this website.


This grand challenge will offer up to S$6.5 million (approximately US$4.8 million)2 in awards and an opportunity to demonstrate a pilot-scale version of the solution at a PUB facility in Singapore. 

Solvers will be selected for an award at the end of the Proposal Phase (up to 6 winners with S$250,000 each) and at the end of the Proof of Concept Phase (up to 2 winners with S$2.5 million each). To receive an award, solvers must accept the Conditions of Contract. See the Conditions of Contract template here. Solvers will not receive the total award funding upfront when the award is announced; rather, solvers will propose (and PUB will need to approve) a payment schedule based on key technical milestones for personnel and reimbursable expenses associated with activities that will be conducted in the subsequent phase. The payment schedule and reimbursable expenses will be part of the submission requirement for each of the two phases of competition. 

For example, Solver A is selected for an award based on their Proposal Phase submission. Solver A is now eligible to receive up to S$250,000 over the course of the Proof of Concept Phase. In their Proposal Phase submission, Solver A proposed S$50,000 for reimbursable expenses and two payments for personnel based on technical milestones: one for S$50,000 that occurs when the lab-scale equipment has been set up and one for S$150,000 that occurs when Solver A submits their Proof of Concept Phase submission. If PUB agrees to this payment schedule and Solver A meets both milestones and provides receipts/invoices for the reimbursable expenses, Solver A will receive all payments, totaling S$250,000.

TABLE 4 summarizes the award distribution.

Award Distribution for the Grand Challenge
​​​AwardeesTotal Amount AvailableAmount Available Per AwardeePayment Schedule
​​​​Proposal Phase WinnersS$1,500,000S$250,000 X 6 awardsBased on milestones and reimbursable expenses proposed by the solver and approved by PUB; all milestones and reimbursable expenses must be completed by the Proof of Concept Phase submission deadline (March 2023)
​​​​Proof of Concept Phase WinnersS$5,000,000S$2,500,000 X 2 awardsBased on milestones and reimbursable expenses proposed by the solver and approved by PUB; all milestones and reimbursable expenses must be completed by the end of the Pilot Project (Q3 2025)​

2 This amount reflects currency exchange rates accessed on October 6, 2021 found here​

How do I compete?

To participate in the grand challenge, solvers must: 

● Register to compete on the grand challenge website
● Complete and execute the Team Agreement
● Complete and submit the submission forms below by the applicable deadlines ​

Plese refer to this link for details on what you need to submit.