Valorization of Biomass into Micronutrient Fertilizers

Biological waste constitutes a resource that could be valorised into micronutrient fertilizers. Micronutrient fertilizers (berries seeds residues enriched with micronutrients—blackcurrant Ribes nigrum L., raspberry Rubus idaeus L., strawberry Fragaria × ananasa) produced via biosorption were developed. Micronutrient content was investigated by Scanning Electron Microscope with Energy Dispersive X-ray analysis (SEM-EDX) as an alternative method to Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) which is known as costly, time-consuming and sample-destructive method. X-ray mapping of SEM images and ICP-OES analysis showed the differences in the concentration of micronutrients on the materials surface (natural and enriched biomass—from 3 to 24 times). The highest content of micronutrients (ICP-OES) was achieved for enriched blackcurrant [Cu(II)-12.8 mg g−1, Zn(II)-10.8 mg g−1] and strawberry seeds [Mn(II)-5.13 mg g−1]. The highest atomic concentration of micronutrients was found on the surface (SEM-EDX) of enriched strawberry [24.5% for Cu(II), 8.43% for Mn(II) and 11.1% for Zn(II)]. It was shown that increasing content of micronutrient ions in biological material after biosorption was connected with decreased level of the following cations: Ca(II), Mg(II) and K(I) (ion exchange). The uniform distribution of micronutrient ions was observed on SEM micrographs. The structure of the surface, surface topography (steps, bends and broken edges) were also investigated. The content of micronutrients in biomass determined with ICP-OES and SEM-EDX revealed high correlations between these methods for manganese, zinc and copper ions (0.848, 0.739, 0.735, respectively). Described experiments showed that SEM-EDX was an efficient tool and an alternative for ICP-OES.