Assessment of Granulated Fertilizers from Waste Materials

Abstract: Waste residues generation increases year after year and how to treat these waste materials is often a problem. In this study it will be studied two waste materials: fly ashes and sewage sludge.
Nowadays Northern Sweden is exporting some of their fly ashes to Norway (to Langøya Island) but in a short period of time Norway will not accept these wastes anymore because of the rehabilitation plan of the island. Other alternatives for this waste material are use them to land filling, but it is not an attractive alternative given that it is costly and consumes landfill space.
On the other hand, the sewage sludge is another waste material from the waste water treatment that nowadays is used to obtain biogas, compost soil, heat, electricity, etc. Both materials, fly-ash and sewage sludge, have the common properties of containing nutrients such as P, N, S, Ca, etc. Therefore, these waste materials are attractive substitutes for synthetic fertilizers in forestry and agriculture.
Nevertheless, the use of these materials is often limited due to the presence of potentially toxic elements and substances. Moreover, spreading of loose ashes and dried sludge can lead to rapid wash out of nutrients as well as cause difficulties of spreading itself (e.g. due to the dusting). It is therefore necessary to assess and modify properties (e.g. through the granulation) of these and similar waste materials in order to take advantage of their beneficial properties.
This study focuses on assessing fly ash and sludge collected in Northern Sweden as potential fertilizers. The effects of mixing these two materials with a binder (peat or gypsum) on soil chemical properties were evaluated. The obtained results are used to identify the key mechanisms responsible for nutrients leaching and determine properties that need to be modified in order to have a higher-value material.