Research into processing waste-water purification sludge into valuable mineral fertilisers and organic soil improvers with existing and new technologies contributes to solutions in the water, food and ecology nexus. The project is partly made possible with TKI Delta Technology.

Reason for the project

Water boards in the Netherlands are seeking out alternative sales routes for purification sludge, with the aim being sustainability, generating energy and reusing nutrients. Current sales routes, whereby sludge is burned, result in high costs and to a loss of valuable nutrients and organic material. Reusing sludge in agriculture is an efficient and inexpensive way of returning nutrients and organic material to the soil and thus maintaining the soil’s quality and fertility. In the Netherlands, sludge has no longer been used in agriculture since the 1990s due to the presence of heavy metals, the product’s negative image and the increasing competition with animal manure. However, the future presents new opportunities for the sale of l sludge in agriculture. Techniques are now available that considerably improve the agricultural and environmental quality of purification sludge while there is also increased understanding of the behaviour of contaminants in the environment, meaning factors such as land usage and bio-availability can be included in assessing the environmental risks of using the product in agriculture. These trends result in future prospects for processing purification sludge into a clean and impeccable product which also complies with the end user’s criteria.

Aim of the project

  • Processing purification sludge into valuable mineral fertilisers and organic soil improvers with existing and new techniques.
  • Assessing the agricultural and environmental value (environmental risk analysis) of purification-sludge products and determining these products’ suitability for various applications in agriculture.
  • Elaborating promising routes for processing sludge and selling the products to the agricultural sector.
  • Increasing the acceptance of using purification-sludge products in agriculture.

Description of the activities

Purification sludge is processed by the partners involved using fermentation and composting and the products resulting from this are analysed by Alterra and assessed for agricultural and environmental value. The products’ agricultural properties are compared with the user-specific criteria. The environmental assessment evaluates the environmental risks regarding contaminants such as heavy metals and organic micro pollutants. Based on the results, Alterra determines the products’ suitability for various applications in agriculture. Tests are also conducted which indicate whether the products’ quality can be further improved and adjusted using existing techniques and those yet to be developed. Based on the results, promising routes are devised that lead to purification sludge being sustainably processed into soil improvers and fertilisers.

Expected results

The project formulates prospects for sustainably processing purification sludge into fertilisers and soil improvers that can be sold in agriculture. Regarding the current, expensive sales routes, using sludge in agriculture provides the water sector with a substantial financial benefit.

Promising processing routes for purification sludge are to be elaborated in a subsequent PPS.

Innovative nature of Sludge2Soil

Innovative projects are being used in this project for processing sludge into clean, high-quality fertilisers and soil improvers. Knowledge gained from this project can be further used in other projects focused on reusing nutrients and valorising residue and waste streams. This project thus contributes to creating a circular economy.

Knowledge transfer

Project results are shared with the water sector by publishing the results and through presentations at relevant meetings. The project's progression can also be followed on the project website. For promising routes, water boards and businesses will actively be sought out that wish to participate in follow-up research to make new processing and sales routes marketable by performing pilots with new/improved techniques and pot tests with the products. A workshop is organised for this purpose in mid-2016.