HOFOR Copenhagen Circular Water-Energy Nexus
HOFOR Copenhagen Circular Water-Energy Nexus
TL;DR: HOFOR Copenhagen is turning wastewater into a strategic energy and resource stream, using anaerobic digestion, heat pumps, and recovery technologies with BIOFOS and the VARGA project to produce green gas, district heating, and nutrients while moving toward carbon-neutral utility operations.
The water-energy nexus represents one of the most critical challenges for the modern green transition. Traditional water and wastewater treatment processes are highly energy-intensive, often accounting for a significant share of municipal electricity use. To meet net-zero commitments, utilities are shifting toward a circular water economy model that treats wastewater as a source of energy, nutrients, and heat rather than a liability to dilute and discharge. This shift reframes wastewater infrastructure as a platform for resource recovery and local energy production, tightly integrated with city-scale decarbonisation pathways.
From Linear Wastewater Treatment to Circular Water-Energy Systems
In a linear model, wastewater utilities consume large amounts of electricity to aerate, pump, and treat water before discharging effluent and disposing of sludge, with limited attention to the embedded energy and materials in the stream. A circular water economy reframes these flows as resource loops, where organic carbon becomes biogas, temperature gradients become a heat source for district networks, and nutrients such as nitrogen and phosphorus are recovered and redirected into food and industrial systems.
Anaerobic digestion is a central mechanism in this shift: by stabilising sewage sludge in oxygen-free digesters, utilities generate biogas that can be upgraded into biomethane, injected into gas grids, or converted into electricity and heat in combined heat and power units. When combined with high-efficiency heat pumps that extract low-grade heat from wastewater and with smart control of pumping and aeration, the overall energy balance of treatment plants can move from high consumption toward net-zero or even net-positive performance.
Governance and regulation determine how far utilities can push this transition, including tariffs that recognise energy and resource services, permitting frameworks for fertilizer products, and climate targets that incentivise investment in recovery technologies. Strategic trade-offs arise around where to allocate capital – for example, deeper resource recovery versus more conventional capacity expansion – and how to share costs and benefits between water customers, energy consumers, and taxpayers.
HOFOR Copenhagen and BIOFOS in the Circular Water Economy
In Greater Copenhagen, HOFOR and BIOFOS illustrate how a metropolitan utility can operationalise the circular water-energy concept at scale, serving around one million residents with integrated water, wastewater, gas, and district energy services. BIOFOS produces biogas from organic matter in wastewater at large treatment plants such as Lynetten and Avedøre, while HOFOR upgrades this biogas and injects it into the town gas network, increasing the renewable share of gas used by households and businesses.
The VARGA project at the Avedøre Wastewater Treatment Plant represents a lighthouse demonstration of a Water Resource Recovery Facility, combining carbon harvesting, biogas production, phosphorus recovery, and process optimisation to reduce greenhouse gas emissions and enable new resource value chains. In parallel, HOFOR’s role in replacing coal-fired heat and power generation at sites like Amagerværket with biomass units and integrating wastewater-sourced energy positions the water utility as a co-optimiser of urban energy and resource flows rather than a stand-alone service provider.
HOFOR aims for Copenhagen’s town gas to reach 100 percent carbon-neutral content by 2025 by upgrading biogas from BIOFOS wastewater treatment plants and integrating it into the city’s gas grid.
Take-Out
HOFOR Copenhagen’s circular water-energy strategy shows how wastewater utilities can evolve into water resource recovery hubs that supply low-carbon gas, heat, and nutrients while meeting core treatment obligations. For other utilities, the key lesson is to design integrated portfolios that align digestion, heat recovery, and nutrient capture with citywide climate targets and energy planning.
Expert Follow-Up Questions
How does anaerobic digestion of wastewater sludge support HOFOR’s energy goals?
Anaerobic digestion converts the organic fraction of wastewater sludge into biogas, primarily methane and carbon dioxide, which BIOFOS produces at major treatment plants in the Copenhagen area. HOFOR then upgrades this biogas to biomethane quality and injects it into the town gas grid, directly displacing fossil natural gas and helping move the gas supply toward carbon neutrality by 2025.
What makes the VARGA project at Avedøre a “water resource recovery” facility rather than a traditional plant?
The VARGA project goes beyond conventional treatment by systematically harvesting carbon for biogas, recovering phosphorus from sludge streams, and testing process changes that lower nitrous oxide and other greenhouse gas emissions. This integrated approach treats wastewater as a feedstock for energy and nutrient cycles, turning the plant into a resource platform that can support agriculture, energy systems, and industrial users, not just effluent quality targets.
How is district heating linked to wastewater and the circular water economy in Copenhagen?
Large-scale heat pumps can extract low-temperature heat from treated wastewater or sewer flows and upgrade it to district heating supply temperatures, effectively turning wastewater streams into a renewable heat source. In Copenhagen, this concept complements the shift away from coal at plants like Amagerværket and allows HOFOR to co-optimise water and energy assets in service of citywide decarbonisation.
What policy or regulatory conditions enable HOFOR’s circular water-energy projects?
National and municipal climate goals, such as Copenhagen’s ambition for carbon neutrality and sectoral objectives for energy-neutral water and wastewater services, create a clear mandate to invest in recovery technologies. Supportive frameworks for biogas grid injection, renewable gas certification, and the use of recovered phosphorus as fertilizer further improve the business case for projects like VARGA and BIOFOS biogas upgrading.
How transferable is HOFOR Copenhagen’s model to other cities and utilities?
The exact technology mix will vary, but the core principles – integrating digestion, gas upgrading, heat recovery, and nutrient capture with city energy plans – are broadly replicable in metropolitan regions with centralised plants. Critical success factors include strong utility–municipality partnerships, clear climate targets, and the ability to monetise multiple value streams from wastewater beyond basic treatment services.
Water Utility of the Future – HOFOR Copenhagen
For a detailed look at how water operations are being co-optimised with energy production – including project economics, technology configurations, and governance arrangements – access the full Water Utility of the Future – HOFOR Copenhagen report.
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