Cultivation experiment with sewage‑sludge biochar

Client

NSR (Nordvästra Skånes Renhållnings AB) is a municipal waste management company focused on developing circular and sustainable solutions. One of their initiatives is the production of biochar, where garden waste and other organic materials are converted through pyrolysis – a process that occurs without oxygen.

Biochar is used both as a soil enhancer and to sequester carbon long-term, which helps reduce climate impact. NSR’s biochar project is a key part of their strategy to close the loops and create local solutions for sustainable development

Background

Our wastewater systems produce large amounts of sludge that need to be managed. At the same time, the sludge can be viewed as a resource because it contains significant quantities of nutrients such as nitrogen, potassium, and especially phosphorus. After treatment and with the appropriate permits, sludge can be used as a fertilizer on agricultural land.
Another option is to convert the sludge into biochar through pyrolysis. This process can help reduce harmful substances while preserving a large share of the nutrients, which can then be returned to the soil. Sewage‑sludge biochar differs from biomass‑based biochar in that it contains a higher proportion of ash‑forming compounds and more nutrients—particularly phosphorus.

The Project

NSR is now interested in examining how sewage‑sludge biochar performs as a fertilizer for plants with high phosphorus requirements. In this project, you will explore this through a cultivation experiment on one or several crops – for example cereals and/or grasses. NSR has access to sewage‑sludge biochar produced through pyrolysis at different temperatures, ranging from 650 to 950 °C. Chemical analyses of these biochar samples have already been carried out.

Through the project, NSR wants to determine:

• the significance of pyrolysis temperature for the function of sewage‑sludge biochar as a fertilizer and soil improver
• how much of the phosphorus in the biochar is water‑soluble and therefore available to plants (this needs to be tested in the project)

Before cultivation begins, the biochar needs to be charged to achieve a favorable nutrient composition, or alternatively, supplementary nutrients can be added directly to the soil. The cultivation experiment can be conducted in raised beds outdoors or in a greenhouse, with planning and sowing in March/April and harvesting in July/August. Crop growth is documented continuously during the cultivation period, and the final yield is weighed.

Final delimitations are made in consultation with the school supervisor and the project client. Both the student and the client should be aware that appropriate academic grounding must be applied in the work