From Wastewater to Green Gas: How Aa en Maas Is Turning a Net-Zero Ambition into a Systems Strategy
Exec Exchange – Episode highlight with Pieter Verlaan, CEO, Waterschap Aa en Maas (The Netherlands)
What does it take for a wastewater authority to seriously aim for energy self-sufficiency—and not treat it as a branding slogan?
In this episode of The Exec Exchange, Dr. Piers Clark speaks with Pieter Verlaan, Chief Executive of Dutch water authority Aa en Maas, about how his organisation—and the wider Dutch water authority network—is systematically re-engineering wastewater treatment to become a producer of energy and resources, not just a cost centre.
A Regional Authority in a National Network
Aa en Maas is one of 21 regional water authorities in the Netherlands. Its jurisdiction:
- Southern North Brabant, in the south-east of the country
- Around 1 million inhabitants
- 600–800 employees managing wastewater, water levels and water quality
Geographically, it’s classic Dutch territory:
- Flat by global standards (only ~30 m difference between high and low),
- But with enough variation to matter operationally.
Each water authority owns and operates its own assets, but they collaborate closely through a national “Energy & Resource Factory” – a joint initiative created when early pioneers realised 15 years ago that biogas from digesters was more than a curiosity.
“We said: we can produce energy out of our systems, and we can recover a lot of resources and raw materials from our wastewater treatment plants.”
The Energy & Resource Factory: From Pilot Idea to Strategic Platform
The Dutch water authorities’ Energy & Resource Factory is now a mature network organisation, not a one-off project.
It brings together:
- All 21 water authorities,
- Shared R&D and innovation,
- Joint fundraising,
- And coordinated work with regulators and ministries to remove legislative barriers.
Many of the activities Aa en Maas is now deploying simply weren’t legally possible 15 years ago. The network has helped:
- Shape EU and national frameworks,
- Secure permits for new energy and resource recovery routes,
- Build confidence with industrial offtakers and the public.
Pieter served as chair of this network, and Aa en Maas deliberately set out to be a front-runner:
“Every installation we design or redesign is built on the principles of getting close to energy self-sufficient.”
Beyond “Just” Anaerobic Digestion
At the core of the energy-neutral ambition is anaerobic digestion (AD) – but not as a standalone bolt-on.
1. Classic AD, Optimised
Aa en Maas operates digesters that produce:
- Biogas (methane + CO₂) from sewage sludge
- Enhanced with additional high-calorific streams, including recovered toilet paper and other fibre-rich materials
2. From Biogas to “Green Gas”
The biogas is then upgraded:
- CO₂ is removed to increase methane concentration
- The resulting “green gas” is certified and suitable as a natural gas substitute
Rather than immediately injecting into the public grid, Aa en Maas has taken a direct-to-industry route:
“We deliver directly to some international industrial firms… That’s the best way to do it so we don’t have losses in the grid and we avoid complexity with grid permits.”
One flagship partnership:
- A major global brewer (yes, the one in the green bottles) uses Aa en Maas green gas to supply around half of the energy demand at one of its large production sites.
When the project started, the brand didn’t want its name linked publicly to “wastewater”. Now, that’s flipped:
“Heineken is very proud that they have green gas which is totally circular.”
3. Extracting More Energy from the Same Sludge
To get more energy per kilogram of sludge and cellulose, Aa en Maas deploys pre-treatment technologies such as:
- Thermal hydrolysis
- High-pressure, high-temperature “crunching” of fibres
- Other disintegration techniques (some full-scale, some still experimental)
These processes:
- Break down complex structures (e.g. toilet paper cellulose),
- Increase biodegradability in the digester,
- Boost biogas yields and shorten retention times.
Energy Neutrality: A System-Level Target
Crucially, energy self-sufficiency is not being pursued plant-by-plant.
- The ambition is set at the level of the water authority as a whole.
- Some sites will always be net consumers; others can be net producers.
This approach aligns with the revised EU Urban Wastewater Treatment Directive, which now explicitly encourages (and in some areas demands) greater energy efficiency, resource recovery and pollution reduction.
For Aa en Maas and its peers, that means a combined programme of:
- Energy generation (biogas/green gas, heat, possibly solar/wind)
- Energy efficiency (optimised aeration, process control, pumping strategies)
- Load management (aligning energy-intensive operations with renewable availability)
Only by optimising the whole system—not just one flagship plant—does the energy-neutral ambition become technically and economically credible.
Beyond Energy: From Wastewater to Resource Hub
Energy is only one dimension of the transformation. Aa en Maas and the Dutch water authorities are also building a serious resource recovery portfolio, including:
- Phosphorus and nitrogen recovery for fertiliser applications
- Removal of pharmaceutical residues to protect surface waters
- Emerging work on PFAS and other persistent micropollutants
A national programme is actively testing and scaling methods to:
- Remove these substances more effectively,
- Where feasible, recycle them into valuable products,
- And reduce the long-term environmental and regulatory risks.
This changes the narrative. As Pieter puts it:
“Our business is not very sexy if you tell people you work in wastewater treatment. But when you explain what you’re actually doing for society, people get enthusiastic.”
Leadership, Responsibility and “Never Give Up”
Pieter has been CEO for just under a year, after almost a decade in the organisation. His engineering background and long-standing fascination with water management are evident, but so is his sense of responsibility:
- Public money,
- Public health,
- Long-lived infrastructure whose performance shapes environmental outcomes for decades.
“It’s a great responsibility. I feel that every day… but it’s a great business. I’m very proud.”
Asked what he owes his parents, he gives an answer that could be a strapline for the entire Dutch water sector:
“Never give up. With hard work and not giving up, you can do things you thought were impossible.”
That mindset is exactly what’s required when you’re trying to turn wastewater utilities into energy-neutral, resource-producing, pollution-removing hubs—within the constraints of regulation, cost, and public perception.
Why This Episode Matters for Water Leaders
If you’re leading—or advising—a water or wastewater utility and wrestling with:
- How to move beyond pilots to full-scale energy and resource recovery
- How to aggregate assets to hit energy-neutral targets at system level
- How to structure industrial offtake agreements (e.g. green gas to major users)
- How to navigate regulation and public perception around “wastewater-based” products
…this episode with Pieter Verlaan offers a clear, pragmatic view of what a front-running utility is already doing today.
From thermal hydrolysis and green gas a medicines and PFAS removal, Aa en Maas shows that the route to energy neutrality is not a single technology—it’s a disciplined, multi-decade systems strategy backed by collaboration, policy influence, and a refusal to give up.
To dive deeper into the story, listen to Episode 19 of The Exec Exchange: “Meeting the ambition to be energy neutral”con Pieter Verlaan, CEO of Aa en Maas, The Netherlands.