Abstract
This study aimed at valorizing digestate through Trichoderma spp. solid-state fermentation (SSF) to produce a potentially ameliorated fertilizer combined with fungal biomass as a value-added bioproduct. Plant-growth-promoting Trichoderma atroviride Ta13, T. reesei RUT-C30, T. asperellum R, and T. harzianum T-22 were tested on different SSF substrates: whole digestate (WD), digestate dried up with wood sawdust (SSF1), and digestate enriched with food waste and dried up with wood sawdust (SSF2). The fungal biomass was quantified by using a qPCR assay. The growth of the four Trichoderma spp. was only observed on the SSF2 substrate. The highest quantity of mycelium was produced by T. reesei RUT-30 (689.80 ± 80.53 mg/g substrate), followed by T. atroviride Ta13, and T. asperellum R (584.24 ± 13.36 and 444.79 ± 91.02 mg/g substrate). The germination of Lepidium sativum seeds was evaluated in order to assess the phytoxicity of the Trichoderma-enriched substrate. The treatments with 7.5% SSF2-R, 3.75% SSF2-T-22, and 1.8% SSF2-Ta13 equally enhanced the root elongation in comparison to the non-fermented SSF-2. This study demonstrated that digestate, mixed with agro-food waste, was able to support the cultivation of Trichoderma spp., paving the way to the valorization of fermented digestate as a proper biofertilizer.
Highlights
Introduction and Camilla Maria BragugliaOne hundred and eighty million tonnes of digestate are produced in the 28 countries of the European Union (EU-28) per year, as residue remaining after biogas production through anaerobic digestion
This study demonstrated that digestate, mixed with agro-food waste, was able to support the cultivation of Trichoderma spp., paving the way to the valorization of fermented digestate as a proper biofertilizer
Trichoderma asperellum, T. atroviridae, T. harzianum, and T. reseei strains did not show any growth on the whole digestate (Figure 1, substrate WD) as well as on the sole digestate added with the wood sawdust (Figure 1, substrate SSF1)
Summary
One hundred and eighty million tonnes of digestate are produced in the 28 countries of the European Union (EU-28) per year, as residue remaining after biogas production through anaerobic digestion. This process has been increasing steadily in recent years. More than 65% of this residue product is ascribable to agricultural digestate, typically a mix of manure and plants [2], whose current management is land application as fertilizer (Regulation (EU) 2019/1009) [3]. Agricultural digestate has a high content of organic matter in comparison to mineral fertilizer and could improve the health and structure of soil, besides being rich in nutrients [4,5,6]. Several potential drawbacks in digestate management still exist, namely the transportation issue (mainly linked to ammonia emissions during storage), the different land application techniques (ammonia emissions and nitrate leaching risks) [7], the highly variable composition [8], and the presence of high metal concentrations [9]
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