Microalgae grown on biogas digestate as biostimulants for crops

Resman, Lara (avtor), Mihelič, Rok (mentor), Acién Fernández, Francisco Gabriel (komentor)

In a study conducted in the ALS6 region of Europe (Ljubljana, Slovenia), the production of a microalgae consortium, primarily Scenedesmus dimorphus and S. quadricauda, on anaerobic digestate from food waste was investigated in three ponds (P1, P2, and P3) within a greenhouse. The impact of digestate quality and quantity, as well as seasonal variations, on microalgae productivity was examined. Based on measurements and observations, a simple Decision Support Protocol (DSP) was developed, based on easily measurable parameters (pH, temperature, electrical conductivity, dry matter, ammonium, nitrate, and nitrite nitrogen, delayed fluorescence index, and optical density). The produced microalgae biomass was tested for biostimulatory effects on plants using various bioassays: germination of white mustard (Sinapis alba) and auxin- and cytokinin-like efficiency tests with cucumber (Cucumis sativus) cotyledons. The biomass from the most productive pond (P2) was further processed through high-pressure homogenization and enzymatic hydrolysis to obtain cell extracts. These extracts were also tested with plant bioassays under controlled laboratory conditions and later in pot experiments in a greenhouse at different stages of cannabis (Cannabis sativa) development. Under optimal conditions, an average microalgae production of 11±1.5 g m-2 day-1 and a nitrogen use efficiency of 28±2.6 g biomass g-1 nitrogen input were achieved, following the DSP procedure. Positive effects on seedling germination and root formation in tested plants were observed, but no effect on plant growth or secondary metabolite production in cannabis was found. Valuable insights were gained into the potential of digestate-grown microalgae as biostimulants, though further optimization of cultivation conditions is needed to achieve specific biostimulatory effects.

• Jezik: Angleški jezik
• Ključne besede: microalgae, biogas digestate, open raceway ponds, microalgae productivity, decision support protocol, biostimulants, microalgae extraction, plant bioassays, biostimulant effects, Sinapsis alba, Curcumis sativus, Cannabis sativa, cannabinoids
• Vrsta gradiva: Doktorsko delo/naloga
• Tipologija: 2.08 - Doktorska disertacija
• Organizacija: BF - Biotehniška fakulteta
• Leto izida: 2025
• PID: 20.500.12556/RUL-170183
• COBISS.SI-ID: 241188355
• Datum objave v RUL: 02.07.2025

Sekundarni jezik

• Jezik: Slovenski jezik
• Naslov: Mikroalge, gojene na bioplinskem digestatu, kot biostimulansi za kulturne rastline

Izvleček

V študiji, izvedeni v regiji ALS6 v Evropi (Ljubljana, Slovenija), smo v treh bazenih (P1, P2 in P3) v rastlinjaku raziskovali pridelavo združbe mikroalg, predvsem Scenedesmus dimorphus in S. quadricauda, na anaerobnem digestatu iz prehrambenih odpadkov. Proučevali smo vpliv kakovosti in količine digestata ter sezonskih nihanj na produktivnost mikroalg. Na podlagi meritev in opazovanj smo razvili preprost protokol za podporo odločanju (DSP), ki temelji na enostavno merljivih parametrih (pH, temperatura, elektroprevodnost, suha snov, amonijev-, nitratni- in nitritni dušik, indeks zakasnjene flourescence ter optična gostota). Proizvedeno biomaso mikroalg smo preizkušali glede biostimulativnih učinkov na rastline, z uporabo različnih biotestov: kalitev bele gorjušice, Sinapis alba, ter testov avksinom in citokininom podobne učinkovitosti s kličnimi listi kumare, Cucumis sativus. Biomaso iz najproduktivnejšega bazena (P2) smo dodatno obdelali z visokotlačno homogenizacijo ter encimsko hidrolizo, da smo pridobili ekstrakte celic. Tudi te ekstrakte smo testirali z rastlinskimi biotesti v kontroliranih laboratorijskih razmerah ter pozneje v lončnih poskusih v rastlinjaku v različnih fazah razvoja konoplje, Cannabis sativa. Pri optimalnih pogojih smo dosegli povprečno proizvodnjo mikroalg v višini 11±1,5 g m-2 dan-1 in učinkovitost uporabe dušika 28±2,6 g biomase g-1 vnosa dušika sledeč postopku opisnem v DSP. Proizvedene mikroalge so pokazale pozitivne učinke na kalitev ter tvorbo korenin preizkušenih rastlin, niso pa imele učinka na rast rastlin ter na proizvodnjo sekundarnih metabolitov pri konoplji. S tem smo pridobili pomembne informacije o potencialu v digestatu gojenih mikroalg kot biostimulantov, pri čemer pa je potrebna nadaljnja optimizacija pogojev pridelave za dosego specifičnih biostimulativnih učinkov.

• Ključne besede: mikroalge, bioplinski digestat, odprti bazeni, mikroalgna produkcija, protokol za podporo odločanju, biostimulanti, ekstrakcija mikroalg, rastlinski biotesti, biostimulativni učinki, Sinapsis alba, Curcumis sativus, Cannabis sativa, kanabinoidi