Thermal drying: how to solve an environmental problem and obtain a value-added product

Grupo Neoelectra implements a thermal drying system driven by combined heat and power (CHP) at the company’s manure treatment plant in Artajona (Navarra). This enables the sludge produced in wastewater treatment plants to be treated and converted into agricultural fertiliser. The system is an excellent example of a successful public-private partnership between Neoelectra and Nilsa, the public waste management company in the area.

Untreated sewage sludge is an environmental problem that can affect soils and aquifers. Due to its high volume of organic matter and moisture, and the risk of the presence of pathogens such as salmonella, sludge hygienisation is very important to prevent land and groundwater contamination. Once treated, the resulting product becomes a very useful natural fertiliser for the agricultural sector.

Technologies that can be implemented for sludge treatment include thermal drying, anaerobic digestion, composting and incineration. Of these alternatives, thermal drying has a number of additional benefits, including lower combined treatment and management costs, and easier and safer storage and transport. This has made it the technology of choice for three wastewater treatment plants managed by publicly-owned company Navarra de Infraestructurales Locales (Nilsa). Nilsa has entrusted this thermal drying process to the Grupo Neoelectra pig manure treatment plant in Artajona (Navarra).

Fertiliser of high agricultural value

Sludge is waste in solid form that remains at the bottom of wastewater treatment plant tanks. It is a by-product of urban wastewater recycling and has great agronomic value as a fertiliser if properly treated. There is a high demand for this product in the agricultural sector, both in Spain and in the remainder of the European Union.

The location of Neoelectra’s plant in the area of Tudela – Tafalla, a region of very intensive agricultural activity, enables rapid distribution of the resulting fertiliser to agri-food farms in the area. The quality of these farms is acknowledged throughout Europe.

Circular economy model

Ecoenergía Navarra, the Artajona plant that manages this sludge, provides an excellent example of the circular economy, environmental sustainability and energy efficiency. The facility combines manure and sludge treatment and converts this waste into value-added products, whilst solving an environmental problem.

The plant is equipped with two 7.8 MW Wärtsilä gensets and a Liquified Natural Gas storage and distribution system. This CHP system produces electricity and heat simultaneously.

With respect to manure treatment, the plant treats waste from pig farms in the area, converting it into distilled water and biofertiliser through a CHP-driven drying process. CHP technology produces highly efficient electricity with low emissions, as well as the thermal energy used to supply the “Cultivos de Navarra” greenhouse, located alongside the facility.

Published in: Nº78 FuturENVIRO March – April 2021