A heat-pump-based sludge drying system aimed at smaller wastewater treatment works is being promoted in the UK as a means of reducing sludge volumes while making use of surplus renewable electricity.
The HUBER Cold Air Dryer HPS is designed for wastewater treatment plants serving up to 50,000 population equivalents (PE), with capacity to handle up to 3,000 tonnes of dewatered sludge per year.1
Developed by German wastewater technology specialist HUBER, the system is intended in particular for smaller treatment works where sources of waste heat – which can be used by conventional thermal sludge dryers – are unavailable.
Instead, the HPS (Heat Pump System) uses electricity to operate a heat pump that conditions the drying air. Moist air leaving the sludge is cooled and dehumidified before being reheated and recirculated through the drying chamber in a closed-loop process.2 HUBER says drying takes place at around 40°C.3
The company suggests the technology could be particularly useful at wastewater treatment works equipped with solar PV, wind generation, CHP or battery storage, allowing surplus electricity to be used for sludge treatment once the site’s immediate electricity demand and storage requirements have been met.
“Instead of exporting electricity to the public grid for little return, the available energy can be utilised for an essential operational task – sludge drying,” said Dale Foster, business development manager at HUBER Technology UK.
Reducing the water content of sludge can substantially decrease the volume requiring storage and transportation. HUBER Technology UK said this could be particularly relevant to smaller or difficult-to-access sites where thin or dewatered sludge otherwise has to be regularly tankered to larger regional treatment centres.1
The dryer has a modular design, with between one and five drying modules specified according to the amount of water that needs to be evaporated. It can be supplied as a factory-assembled containerised unit, with electrical systems already tested, reducing the amount of installation work required on site. An installation within an existing building is also possible.2
HUBER’s larger Belt Dryer BT and RotaDry Disc Dryer systems are aimed at medium-to-large wastewater treatment facilities where suitable heat sources are available. The HPS has been developed to extend sludge drying to smaller applications without access to such heat.
The manufacturer says the optimum configuration will depend on site-specific factors including sludge quantity and dry-solids content, the required drying target, electricity-generation and plant-load profiles, and available energy storage.
HUBER first announced the HPS as an addition to its sludge-drying portfolio in July 2025. The company says it began developing the technology in 2024.3
Notes
[1] Water Briefing, “Innovative Cold Air Sludge Drying solution fills critical gap for smaller wastewater treatment plants”, 29 September 2026.
[2] HUBER, “New product: HUBER Cold Air Dryer HPS”, 31 July 2025.
[3] HUBER, HPS product/brand information.
