Facultative lagoons remain an essential part of regional wastewater treatment in Victoria. They are simple to operate, tolerant of variable loads and capable of producing recycled water suitable for agricultural reuse. Yet their passive design also creates a climate challenge.
In the absence of oxygen, the lower layer of a lagoon becomes anaerobic, producing methane as organic material breaks down. For utilities with large lagoon assets, methane from these systems represents a significant portion of scope 1 emissions.
Coliban Water’s Climate Innovation Challenge project proposes a practical response. The organisation is trialling solar-powered aeration systems that can disrupt anaerobic conditions and reduce methane generation by up to 50 per cent.
The project received $75,000 in funding as the Joint Winner of the 2025 Water Minister’s Climate Innovation Challenge, positioning it as a leading example of how renewable energy can be used to reduce direct emissions in wastewater operations.
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Why do facultative lagoons generate methane?
A facultative lagoon stratifies into three layers. The upper aerobic layer supports oxygen-dependent microbial activity, while the lower anaerobic zone lacks oxygen entirely. It is within this lower zone that methanogens convert organic matter into methane. The process is biologically efficient but produces a greenhouse gas with a global warming potential many times greater than carbon dioxide.
Coliban Water identified that the size and stability of the anaerobic zone heavily influences the methane emissions profile of its lagoon systems. Seasonal temperature shifts, loading patterns and organic loading rates all affect stratification. Without intervention, methane generation continues year-round.
How can solar lagoon aeration reduce methane emissions?
Mechanical aeration is not new, but high energy requirements and limited power availability have historically constrained its application to large regional lagoons. Coliban Water’s approach pairs low-energy aerators with dedicated solar generation, providing daytime aeration without increasing grid demand or requiring costly electrical upgrades.
The aerators deliver diffused oxygen through the upper and mid layers of the lagoon. This oxygen suppresses anaerobic conditions and supports microbial pathways that favour carbon dioxide production over methane. Although carbon dioxide remains an emission, the shift away from methane represents a substantial net climate benefit.
Intermittent solar-driven aeration is also well-suited to lagoon dynamics. During daytime operations, the aerators break down stratification and oxygenate the water column. At night, the system relies on residual dissolved oxygen, meaning the lagoon remains partially oxygenated until solar input resumes. This cyclical pattern is sufficient to prevent the formation of fully anaerobic zones in many lagoon configurations.
What are the expected performance and energy impacts?
Coliban Water’s modelling suggests that methane emissions could be reduced by up to 50 per cent, with corresponding reductions in nitrous oxide generation due to improved aerobic stability. The project also anticipates improvements in recycled water quality, including reduced odour potential and more stable nutrient removal.
Energy savings are another major advantage. Solar-powered aerators operate independently of the grid, meaning the project avoids the electricity use associated with traditional aeration systems. This aligns with state targets to reduce reliance on offsets by lowering emissions at the source.
The first implementation will occur at Kahuna, a high-priority lagoon site with limited grid access. A successful demonstration at this site would support a broader rollout across Coliban Water’s lagoon portfolio and potentially across regional Victoria.
What does the project mean for the sector?
Facultative lagoons make up a significant percentage of Australia’s wastewater treatment assets, particularly in regional areas. They are reliable and cost-effective, but are increasingly scrutinised for their emissions intensity. This project provides utilities with a pathway to reduce lagoon-related emissions without replacing entire treatment systems or committing to energy-intensive upgrades.
The $75,000 Climate Innovation Challenge funding accelerates the trial and enables data collection essential for future investment decisions. As Victoria moves toward its 2030 climate targets, projects like this show how operational assets can become part of the emissions solution, not just contributors to the problem.
Coliban Water’s solar lagoon aeration project demonstrates how targeted engineering interventions can reshape the emissions profile of legacy treatment systems. With strong replication potential, it stands as one of the most immediately scalable innovations emerging from this year’s challenge.