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The STC heat transfer system is a consolidated process that Aqualogy has designed to contribute to the thermal drying of sludge and biomass at low temperatures using its own technology based on the application of solutions using residual energy and heat pumps.

Its low-temperature drier reduces the volume of sludge, both industrial and urban, from wastewater treatment plants and various industrial processes, facilitating the use of various types of residual energy, which can be easily transported and used for agricultural purposes or as an alternative fuel.

Diana Permuy Vila Contact

Wet sludge is introduced into the drier and homogenously deposited on the drying belt by means of an extruder that facilitates the flow of air and the transfer of heat. The system admits any heat source that allows it to operate with a hot water circuit (75/90ºC).

The belt carries the sludge through a closed tunnel, where air is circulated at 65/80ºC, condensing the humid air in such a way that water is only extracted to the exterior. The belts cover the entire tunnel to prevent the generation of dust and possible obstructions.

Once dry, the resulting product is easy to transport, having lost as much as 70% of its volume, guaranteeing a dry content rate of 90%.


Its low-temperature operation maximises the use of residual energy, such as exhaust gases from cogeneration or cooling water from engines.


An experienced and multi-disciplinary team covers all the phases of the project, from design and manufacturing through to assembly and maintenance. The driers are fully assembled and tested in the factory to make the process as easy as possible for the customer.


Outside the scope of application of the ATEX Directive (zero risk of explosion or fire).
It does not generate dust.


The drier can be adapted to the energy needs of any customer. The 75/90ºC hot water used in the process can be obtained from various energy sources, such as natural gas boilers, cogeneration engines and heat pump technologies.


Reduction of environmental impact. It limits greenhouse gas emissions. Its cold source and closed air system inside the tunnel reduce both the size of the deodorisation system and the emission of odours.

Easy to use

Quick and fully automated commissioning process.
Partial maintenance without shutdowns.
Easy access to all the equipment.


Possibility of maintenance contracts for up to 15 years.
Extremely safe and efficient technology.

CEMEX CEMENT PLANT (Alicante, Spain)

Urban sludge facility with a 60,000 t/year capacity equipped with two driers with a capacity of 3,000 l/h of evaporated water per unit. The heat necessary for the drying process is generated using hot water (recovery of residual energy from the cement plant). Installation completed in 2011.

This facility is located at CEMEX’s San Vicente del Raspeig cement factory and is designed to be an external treatment centre (multi-management) for sludge from various treatment centres located in Alicante and its surrounding area.

The main innovation is that the heat used for drying is excess heat recovered from the cement factory.

This cuts down on CO2, as primary energy is not used in the drying process. The dried sludge can be used for agriculture or be sent to the cement plant for energy use.


Urban sludge facility with a 70,000 t/year capacity equipped with two driers with a capacity of 3,625 l/h of evaporated water per unit. The heat necessary for the drying process is provided by cogeneration engines (exhaust gases + heat from the engine block). Installation completed in 2007.

With this installation, the companies ACCIONA Agua and EMASA have given us the opportunity to take advantage of maximum treatment capacity per line (4,000 l/h/drying line). The treatment plant's location, close to a shopping centre, made it necessary to construct a special building to confine the facilities using elaborate architectural techniques.

The parties have signed a five-year full guarantee contract.

SHANGANAGH WWTP (Dublin, Ireland)

Installation for digested sludge with an 18,000 t/year capacity equipped with two driers with a capacity of 1,500 l/h of evaporated water per unit. The heat necessary for the drying process is provided by hot water used by cogeneration engines (gases and engine cooling) and a biogas boiler. Installation completed in 2012.

The SDD consortium, made up of Drace Medio Ambiente, Dragados and the Irish building contractor Sisk, has provided us with the opportunity to participate in the Shanganagh wastewater treatment plant, which serves the southeast area of Dublin, and is in turn part of a 25-year BOT project.

To meet this challenge we have taken great pains to standardise our system and implement continuous improvements while adapting to different work cultures. The support of the professional teams working for our customers allowed us to successfully complete this project.

SAINT-MARCELLIN WWTP (Rhône-Alpes, France)

Installation for digested sludge with a 6,000 t/year capacity equipped with a drier with a capacity of 560 l/h of evaporated water per unit. The heat necessary for the drying process is obtained from the hot water from a biomass (wood) boiler. Installation completed in 2013.

With this project, the company Degrémont Services has given us the opportunity to design a single-block facility that incorporates a biomass (wooden shavings) boiler as the heat source to dry sludge.

Single-block units are a simple and competitive solution for the treatment of industrial sludge and for small urban wastewater treatment plants. Their great advantage is the possibility of turnkey projects, minimising on-site assembly time.