Biostimulants and biofertilizers after pilot scale high pressure homogenization of Scenedesmus sp. grown in pig manure

Abstract

Microalgae are becoming an important source of high-value products such as biostimulants, biopesticides, and other low-value products like biofertilizers or aquafeed (fatty acids and carotenoids) among others. However, extracting the biomolecules contained in the microalgae cells is difficult due to the structure and composition of the microalgal cell wall. To overcome this drawback, mechanical cell disruption methods such as high-pressure homogenization (HPH), can be applied to facilitate extracting the compounds of interest. This work focuses on optimizing the extraction of two major groups of products from microalgae biomass - biostimulants and biofertilizers. The aim of this research is to study the effect of the HPH pre-treatment on the production of these different bioproducts starting with Scenedesmus sp. biomass grown in pig sludge as the raw material. For each product the pre-treatment of the wet biomass by HPH must to be optimized to select the optimal conditions for the pressure and the number of passes. A soft treatment of the wet biomass at 200 bar is enough to observe a 10% increase in the germination index (GI) of watercress seeds, while greater treatment intensities reduce the GI with respect to the untreated biomass, possibly because applying greater treatment intensities increases the concentration of the molecules responsible for the bioactivity thus causing a toxic effect on the seeds. In the case of biofertilizers, better results have been obtained at 600 bar, achieving a hydrolysis level of 72.9 %. Finally, the determination of the concentrations of phenolic compounds and salicylic acid, related with enhanced biostimulant activity, was carried out using spectrophotometric methods and High-Performance Liquid Chromatography- diode array (HPLC), respectively.