Microalgae are microorganisms with the capacity to contribute to the sustainable and healthy food production, in addition to wastewater treatment. The subject of this work was to determine the potential of Scenedesmus obliquus microalga grown in brewery wastewater to act as a plant biostimulant. The germination index of watercress seeds, as well as the auxin-like activity in mung bean and cucumber, and in the cytokinin-like activity in cucumber bioassays were used to evaluate the biostimulant potential. Several biomass processes were studied, such as centrifugation, ultrasonication and enzymatic hydrolysis, as well as the final concentration of microalgal extracts to determine their influence in the biostimulant activity of the Scenedesmus biomass. The results showed an increase of 40% on the germination index when using the biomass at 0.1 g/L, without any pre-treatment. For auxin-like activity, the best results (up to 60% with respect to control) were obtained at 0.5 g/L of biomass extract, after a combination of cell disruption, enzymatic hydrolysis and centrifugation. For cytokinin-like activity, the best results (up to 187.5% with respect to control) were achieved without cell disruption, after enzymatic hydrolysis and centrifugation at a biomass extract concentration of 2 g/L.

Amino acids concentrates derived from microalgae biomass through enzymatic protein hydrolysis can improve plant growth by saving the energy that is required for amino acid synthesis from conventional mineral fertilizer resources. To obtain high enzymatic hydrolysis yields, pre-treatment of microalgae biomass prior to enzymatic hydrolysis is suggested for facilitating enzyme access to proteins.Pulsed electric field (PEF) treatment was introduced as a pre-treatment to fresh and concentrated (50 g•kg sus −1 to 80 g•kg sus −1) Scenedesmus almeriensis biomass prior to enzymatic hydrolysis. The concentrated microalgae suspension was treated at an initial conductivity of σ = 1 mS•cm −1 with 1 μs long pulses at an electric field strength of 40 kV•cm −1 and a treatment energy of 75 kJ•kg sus −1 and 150 kJ•kg sus −1 . For benchmarking, additional biomass samples were processed by high pressure homogenization (HPH) at 2 kbar and up to 5 passes. Enzymatic hydrolysis was performed by applying the commercial enzymes Alcalase 2.5 L and Flavourzyme 1000 L for 180 min. The amino acids content in supernatant was determined by using the ortophthaldialdehyde (OPA) assay. PEF treatment at both energy inputs and HPH treatment at 2 kbar, 5 passes, revealed the same hydrolysis kinetics and the same final value of the degree of hydrolysis (DH) of 50% ± 2%. The energy demand for PEF pre-treatment amounts to 0.75 MJ•kg dw −1 when processing biomass at 100 g dw •l −1 . After both pretreatments, incomplete protein hydrolysis could be detected by SDS-PAGE analysis of residual biomass. Most feasible, hydrophobic protein fractions and protein aggregation impede complete protein hydrolysis by the applied enzyme cocktail.Since PEF treatment preserves cell shape and biomass separability and thus enables cascade processing, it is suggested as alternative downstream processing method for the production of amino acids concentrates from microalgae biomass.

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