The CLOSECYCLE project builds partly on the experiences and results of the Interreg North Sea project SOILCOM. This is especially the case for the composting of organic residual wastestreams. In SOILCOM, partners investigated the characteristics of these composts. Recently, an interesting scientific article was published.
Composting is a widely used method for processing organic waste, turning it into a valuable product for soil improvement and use in growing media.
The study in SOILCOM explored how the characteristics of composts produced across the North Sea Region vary, and what factors contribute to these differences.
Researchers analyzed 107 compost samples, grouped by two composting practices—farm-made and commercially produced—and by three types of feedstocks:
- Manure mixed with other wastes
- Green waste
- Fruit, vegetable and garden waste (FVG)
Each compost was measured for 67 physical, chemical and biological properties. The results showed large variation between composts. For example, total microbial biomass differed by up to a factor of 20, and potassium content by a factor of 11. Such wide ranges highlight how important it is to characterize compost properly so it can be matched to its intended use.
The organic matter (OM) content varied from 14% to 73% of dry matter. Belgian composts generally had higher OM levels than those from the Netherlands, Denmark, Germany and Scotland. Higher OM content was also linked to higher microbial biomass, greater cation exchange capacity, and higher nitrogen (N) and phosphorus (P) levels.
Farm-produced composts showed higher microbial biomass than commercial composts, regardless of their organic matter level. Compost made from green waste tended to have lower N and P contents compared to compost from FVG or manure-based feedstocks.
Overall, this study provides a clear overview of the wide range of compost qualities found in the region. These findings offer a useful benchmark and support future steps toward producing tailor-made compost with characteristics suited to specific applications.