Microbial and nutrient delivery system

Abstract

The invention relates to a method for producing a microbial and nutrient delivery system encompassing hydrothermal carbonization of a suitable biomass to form a slurry comprising hydrochar and HTC process water, cooling of the slurry, inoculation of the cooled slurry with a microbial inoculant, fermentation of the inoculated slurry and obtaining or recovering the microbial and nutrient delivery system from the fermentation product, wherein the cooling step and the inoculation step are conducted under sterile conditions. The invention further relates to the microbial and nutrient delivery system obtainable by the method, and uses thereof, including agricultural as well as environmental applications.

Description

[0001]MICROBIAL AND NUTRIENT DELIVERY SYSTEM FIELD The invention relates to the valorization of products of a hydrothermal carbonization process. In particular, a production process for a microbial and nutrient delivery system is provided encompassing the integration of a hydrothermal carbonization process and a fermentation process. The invention further relates to the microbial and nutrient delivery system and uses thereof, including agricultural as well as environmental applications. BACKGROUND In view of the growing world population, and the increasing environmental damage caused by ever greater levels of industrialization, there is a need for improved agricultural plants that will enable the food production demands with more environmentally sustainable inputs. Agricultural fertilizers are widely used to promote crop growth and yield and to avoid soil depletion. Generally, fertilizers deliver nutrients to the soil, which allow a crop to better grow and develop in that soil. A wide range of fertilizer formulations are known in the art of agricultural sciences. The most commonly used fertilizers are raw animal manure, and mineral fertilizers that are created through chemical processes, such as nitrogen fertilizers made through the Haber-Bosch process. Both fertilizers are sources of rapidly available nutrients, but have the disadvantage that there is a significant risk of nutrient run-off, which not only leads to economic losses, but also disrupts aquatic ecosystems (water pollution, eutrophication, loss of biodiversity, etc.). Raw manure has another significant disadvantage in that it may contain bacterial pathogens which can cause disease in humans and livestock. Organic fertilizers, that are derived from living organisms, such as compost, and biofertilizers, that contain beneficial microorganisms, have been proposed as more environmentally sustainable solutions, but their use is not yet widespread. The main challenges with the use and development of biofertilizers are reliability, inappropriate formulations, high levels of contamination, low quality, low shelf-life and consistency of the inoculants under field conditions. A suitable formulation can ensure microbial viability during storage and application. Formulations can be broadly divided into those using solid materials as carriers or liquid formulations. A disadvantage of liquid formulations is that the metabolic activity of the beneficial microbes decreases rapidly after manufacturing, and they may have a high contamination risk. Peat is a frequently used solid carrier material, used for both seed coating and soil applications. To prevent contamination, peat must be sterilized before use, which is an energy intensive process. Moreover, since it is a fossil resource, its use in agricultural applications is being phased out. Hydrochar has been proposed as a promising vector for beneficial microorganisms (Thunshirn et al. 2022. Critical Reviews in Environmental Science and Technology 52: 4147-4171). Hydrochar is the solid product of a hydrothermal carbonization (HTC) process of wet biomass, e.g. digestate of an anaerobic digestion process. Its porous structure and high carbon amount offer a suitable microenvironment for beneficial microorganisms. However, hydrochars were found to show some phytotoxicity (Celletti et al.2021 Journal of Environmental Management 280:111635), which might hamper its use as carrier for the formulation of biofertilizers. Furthermore, large quantities of process water are obtained as a by-product of the HTC process that have to be managed and treated. There remains a need in the art for further and / or improved biostimulants such as biofertilizers, which are stable and have an improved shelf-life, which are environmentally sustainable and whose production process has also a minimal impact on the environment. SUMMARY The present invention is at least in part based on the inventors’ discovery that the process water that is produced in a hydrothermal carbonization (HTC) process performs surprisingly well as a growth medium for microorganisms. The hydrochar, together with the (residual) process water, can support and promote growth and amplification of microorganisms and hence, be used as a substrate for fermentation. Accordingly, an aspect of the invention provides a method or a process for producing a microbial and nutrient delivery system, said method comprising: - providing a biomass; - subjecting the biomass to a hydrothermal carbonization process to form a slurry comprising a hydrochar and HTC process water; - cooling the slurry to a temperature suitable for growth of a microbial inoculant; - inoculating the cooled slurry with the microbial inoculant; - subjecting the inoculated slurry to a fermentation process to form a fermentation product; and - obtaining or recovering the microbial and nutrient delivery system from the fermentation product, wherein the inoculation step and the cooling step are conducted under sterile conditions. By combining a HTC process with a fermentation process, the process water of the HTC process is valorized, namely as growth medium for the microorganisms. Moreover, the microorganisms can convert water-soluble nutrients (e.g. biochemical oxygen demand (BOD) nutrients, nitrate / ammonium) in the process water into biomass, thereby improving nutrient recovery from the biomass substrate. The integration of both a HTC process and a fermentation process is advantageous in that no separate cultivation step of the microorganisms is required, which will reduce the operational cost. Also, the HTC process, which takes place under conditions suitable for killing or deactivating microorganisms, eliminates the need for a sterilization step before the fermentation process. The method is also energy-efficient in that at least part of the heat that is required for the HTC process can be recovered from the cooling step before the fermentation step. A further aspect is directed to the microbial and / or nutrient delivery system obtainable by the method of the invention. The microbial and nutrient delivery system provided herein comprises: - a fermented hydrochar; and - microorganisms adhered to surfaces or in pores of the fermented hydrochar. Due to the sterile conditions in at least the cooling and inoculation steps of the method, the microbial and nutrient delivery system is characterized in that it is minimally contaminated by non-desired microorganisms such that the microorganisms of the system substantially consist of microbial species comprised in the microbial inoculant (desired microorganisms). The fermented hydrochar provides nucleation sites for the microorganisms (carrier / vector function). Moreover, the porous structure of the hydrochar protects the desired or beneficial microorganisms against environmental conditions (drought, heavy rain, soil types...) and / or reduces predation e.g. by nematodes and protozoa in the soil. Without wishing to be bound by any theory, adherence and / or pore colonization may be better due to the growth and amplification of the microorganisms on the hydrochar compared to using the hydrochar as a carrier / vector, whereby the microorganisms are dried on the surfaces and / or mixed with the hydrochar. Also advantageously, due to the at least partial fermentation of the hydrochar by the beneficial microorganisms, the hydrochar is more stable (less fermentable material) resulting in a product with an improved shelf-life. Also advantageously, due to the at least partial fermentation of the hydrochar, the growth of undesired and / or pathogenic microorganisms and phytotoxicity may be reduced. Further, certain nutrients in the hydrochar that are less bioavailable (e.g. phosphor) may be solubilized by the beneficial microorganisms, resulting in a product with enhanced supply of nutrients. Further aspects are directed to uses of the microbial and nutrient delivery system of the invention as a biostimulant, in particular as a biofertilizer and / or as a biocontrol agent, as a bioremediation agent, or as a microbial inoculant, e.g. for an anaerobic digester, for a septic system, for a water treatment system or in a method according to the invention. These and further aspects and preferred embodiments of the invention are described in the following sections and in the appended claims. The subject-matter of the appended claims is hereby specifically incorporated in this specification. BRIEF DESCRIPTION OF DRAWINGS The following description of the figures of specific embodiments of the invention is merely exemplary in nature and is not intended to limit the present teachings, their application or uses. Fig.1 shows a schematic view of embodiments of a process according to the invention. Fig.2: Mycelial growth of Trichoderma harzianum after 7 days in fermented peat (A) or fermented hydrochar from pig manure (fermented HC) (B). Fig. 3: Comparison of microbial species growth on nutrient agar (NA) plates in control (non- fermented) (A,B) and fermented (C, D) hydrochar exposed to non-sterile conditions (B, D) or kept sterile (A, C). Fig. 4: Comparison of Trichoderma harzianum growth on yeast mannitol agar (YMA) plates in fermented hydrochar from pig manure (HC-C), with inoculation conducted under sterile (A) or non- sterile (B) conditions. DESCRIPTION OF EMBODIMENTS As used herein, the singular forms “a”, “an”, and “the” include both singular and plural referents unless the context clearly dictates otherwise. The terms “comprising”, “comprises” and “comprised of” as used herein are synonymous with “including”, “includes”, “containing”, or “contains”, and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. The terms also encompass “constituted of”, “consists in”, “consisting of”, and “consists of”, and also the terms “consisting essentially of”, “consisting essentially in” and “consists essentially of”, which enjoy well-established meanings in patent terminology. The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within the respective ranges, as well as the recited endpoints. This applies to numerical ranges irrespective of whether they are introduced by the expression “from… to…” or the expression “between… and…” or another expression. Any numerical range recited herein is intended to include all sub-ranges subsumed therein. The terms “about” or “approximately” as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, are meant to encompass variations of and from the specified value, such as variations of + / -10% or less, preferably + / -5% or less, more preferably + / -1% or less, and still more preferably + / -0.1% or less of and from the specified value, insofar such variations are appropriate to perform in the disclosed invention. It is to be understood that the value to which the modifier “about” or “approximately” refers is itself also specifically, and preferably, disclosed. Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order, unless specified. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. Whereas the terms “one or more” or “at least one”, such as one or more members or at least one member of a group of members, is clear per se, by means of further exemplification, the term encompasses inter alia a reference to any one of said members, or to any two or more of said members, such as, e.g., any ≥3, ≥4, ≥5, ≥6 or ≥7 etc. of said members, and up to all said members. In another example, “one or more” or “at least one” may refer to 1, 2, 3, 4, 5, 6, 7 or more. As used herein, the term “and / or” when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a list is described as comprising group A, B, and / or C, the list can comprise A alone, B alone, C alone, A and B in combination, A and C in combination, B and C in combination, or A, B, and C in combination. The discussion of the background to the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known, or part of the common general knowledge in any country as of the priority date of any of the claims. Throughout this disclosure, various publications, patents and published patent specifications are referenced by an identifying citation. All documents cited in the present specification are hereby incorporated by reference in their entirety. In particular, the teachings or sections of such documents herein specifically referred to are incorporated by reference. Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the invention. When specific terms are defined in connection with a particular aspect of the invention or a particular embodiment of the invention, such connotation or meaning is meant to apply throughout this specification, i.e., also in the context of other aspects or embodiments of the invention, unless otherwise defined. In the following passages, different aspects or embodiments of the invention are defined in more detail. Each aspect or embodiment so defined may be combined with any other aspect(s) or embodiment(s) unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. Reference throughout this specification to “one embodiment”, “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the appended claims, any of the claimed embodiments can be used in any combination. Similarly, it should be appreciated that in the description of illustrative embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. In an aspect, the invention provides for producing a microbial and nutrient delivery system, said method comprising: - providing a biomass; - subjecting the biomass to a hydrothermal carbonization process to form a slurry comprising a hydrochar and HTC process water; - cooling the slurry to a temperature suitable for growth of a microbial inoculant; - inoculating the cooled slurry with the microbial inoculant; - subjecting the inoculated slurry to a fermentation process to form a fermentation product; and - obtaining or recovering the microbial and nutrient delivery system from the fermentation product, wherein the inoculation step and the cooling step are conducted under sterile conditions. Providing a biomass As used herein, the term “biomass” refers to an organic material that is biodegradable. The biomass is not particularly limited and may include, without limitation, products, by-products, and residues (including waste streams) from agriculture, forestry and related industries, as well as industrial (e.g. sewage sludge) and household waste, and mixtures thereof. Non-limiting examples of biomass suitable for use in the method of the invention include food residues, agricultural residues (e.g. straw, bark, woodchips...), animal by-products (e.g. manure, feathers, wool, exoskeletons...), the organic fraction of household waste, organic fractions of industrial wastes and by-products, sewage sludge, digestate from anaerobic digestion, etc. In particular embodiments, the biomass is an animal by-product such as manure. Advantageously, animal by-products may provide a high concentration of nutrients (nitrogen, phosphor, potassium, micronutrients, etc.). The method of the invention is particularly useful for biomass with a high water content because the HTC process uses water as a reaction medium. In comparison to pyrolysis, wet biomass does not need to be dried prior to or during the process, saving a substantial amount of energy. In particular embodiments, the biomass is a wet biomass such as a biomass having a water content of between 5% and 95% by weight, preferably between 10% and 95% by weight, more preferably between 10% and 90% by weight such as between 10% and 80% by weight. Non-limiting examples of suitable wet biomass include manure and a digestate from anaerobic digestion, which inherently contain water. If the biomass is too dry (e.g. a water content of less than 10% or 5% by weight) water may be added before it is used in the method of the invention as a substrate for the HTC process. For the HTC process to be sustainable from an energy point of view, the water content of the substrate is preferably less than 95% by weight, more preferably less than 90% by weight such as less than 80% by weight. The biomass, also referred to herein as feedstock or substrate, can be either a single input (e.g. animal manure) or a mixture of two or more feedstock types. The biomass may be used as such in the HTC process, or may be subjected to one or more pre- treatment steps before it is used as a substrate for the HTC process. The purpose of such pre-treatment may be to mix different feedstock, to liquefy the biomass, to remove undesirable materials such as large items and / or inert, non-biodegradable materials (e.g. plastic, glass) (separation), to reduce the particle size of the biomass (e.g. breaking up lumps, shredding, grinding , milling,...), to add additives (e.g. acids, bases, salts), etc. to allow a more effective HTC process and / or to modulate the characteristics / composition of the final product. A great variety of pre-treatment processes are available, the selection of which being dependent amongst others on the type of biomass. Hydrothermal carbonization As used herein, “hydrothermal carbonization” or “HTC” refers to a wet thermochemical process involving the application of heat and pressure to convert a biodegradable material, in particular a biomass as defined herein, in the presence of water into a carbonaceous hydrochar and aqueous and gaseous by-products. Without wishing to be bound by any theory, a series of hydrolysis, condensation, decarboxylation, dehydration, aromatization and / or polymerization reactions may occur during HTC. A reaction temperature may be applied within a range of about 160°C to about 300°C, preferably between about 180°C and about 250°C, more preferably between about 200°C and about 220°C, and a corresponding pressure to ensure that the water is maintained in the liquid state such as a pressure of between about 10 bar and about 88 bar, preferably between about 10 bar and 50, 40 or 30 bar, more preferably between about 15 bar and about 25 bar. Treatment time may vary between a few minutes to several hours or even a few days, preferably the HTC process is performed for at least 30 minutes such as between 30 minutes and 20, 19, 18, 17, 16, 15, 14 or 13 hours, preferably between about 30 minutes and about 12, 11, 10 or 9 hours or between about 30 minutes and about 8, 7, 6 or 5 hours, more preferably between about 30 minutes and about 4 hours, such as between 2 hours and about 3 hours. The selected conditions of temperature, pressure and time may depend on the biomass substrate and the desired yield and / or characteristics of the hydrochar product. In certain embodiments, the HTC process is performed at a temperature of between about 180°C and about 250°C and a pressure of between about 10 bar and 50 bar for at least 30 minutes. In certain embodiments, the HTC process is conducted at a temperature of between about 200°C and about 220°C at a pressure of between about 15 bar and about 25 bar for between about 2 hours and 3 hours. The term “hydrochar” as used herein refers to the solid, carbon-rich product of a HTC process. It contains most of the organic compounds originally present in the biomass. Its composition and production yield depend on the biomass substrate and the HTC process parameters. As used herein, the terms “process water” or “HTC process water” refer to the liquid or aqueous by- product of a HTC process. Process waters are rich in dissolved organic components and inorganic salts. Like the hydrochar, the yield and composition of process waters are highly dependent on the biomass being processed and the HTC process parameters. The hydrochar together with the process water forms a solid-liquid “slurry”. Due to the thermal treatment, the slurry, including the hydrochar and the process water, are biologically sterilized. As used herein, the expression “subjecting a biomass to a hydrothermal carbonization process to form a slurry comprising hydrochar and a process water” refers to the conversion of the biomass into a slurry comprising hydrochar and process water by a HTC process. Cooling The slurry is typically at a temperature above 160°C such as at a temperature of between about 200°C and about 220°C. To allow inoculation with desired microorganisms for fermentation, the slurry, or the wet hydrochar, needs to be cooled to a temperature suitable for growth of the microbial inoculum such as a temperature of between about 4°C and about 65°C. In embodiments, the slurry, or the wet hydrochar, is cooled to a temperature of between about 20°C and about 50°C, preferably between about 20°C and about 30°C, depending on the microbial inoculum. The cooling step is carried out under sterile conditions. With “sterile conditions” is meant herein conditions preventing microbial contamination of the slurry. Cooling or sterile cooling of the slurry, or the wet hydrochar, may be achieved by means of a heat exchanger. Advantageously, the heat that is released during the cooling step may be used for the HTC process. The cooling can be conducted in one or more phases. For example, the slurry may be partially cooled to a temperature of between about 80°C and about 120 °C, and the partially cooled slurry can then be further cooled to a temperature suitable for growth of the microbial inoculum such as a temperature of between about 4°C and about 65°C.In embodiments comprising a solid-liquid separation step, the slurry is preferably first cooled before subjecting it to a solid-liquid separation. Alternatively, the slurry may be subjected to a solid-liquid separation to form a wet hydrochar and the wet hydrochar may be cooled, or the slurry may be partially cooled (preferably to a temperature below 100°C) and subjected to a solid-liquid separation, and the wet hydrochar may be further cooled to a temperature suitable for growth of the microbial inoculum. Solid-liquid separation In certain embodiments, the process water content of the slurry is reduced, or the slurry is at least partially dewatered or dried, preferably by means of a solid-liquid separation technique, thereby forming a wet hydrochar. As used herein, a “wet hydrochar” refers to solid hydrochar containing some residual process water. In embodiments, the process water content of the wet hydrochar is below 90% by weight, preferably below 80% by weight or below 70% by weight, more preferably below 60% by weight. In embodiments, the wet hydrochar has a process water content of between about 40% by weight and about 60% by weight such as of between about 50% by weight and about 55% by weight. Solid-liquid separation techniques are known to the skilled person and include, without limitation, gravimetric decanting, centrifugation (various types disc-stack, basket, decanter centrifuge, ...) and filtration (filter press, tangential flow filtration, belt filter, screw press, …). In preferred embodiments, said step of reducing the HTC process water content of the slurry or said dewatering step is conducted under sterile conditions. When subjecting the slurry to a solid-liquid separation, the wet hydrochar may be washed with (sterile) water. Accordingly, in embodiments, the method may further comprise a washing step of the wet hydrochar. This may be particularly advantageous when the process water contains water- soluble compounds that would inhibit the beneficial microorganisms. The solid-liquid separation step also allows to easily add nutrients (e.g. salts and / or a carbon source) and / or acids or bases (to modulate the pH) to the wet hydrochar e.g. to promote growth of the beneficial microorganisms. Further, it also permits to add the microbial inoculum to the wet hydrochar in a convenient way. Inoculation with a microbial inoculant After cooling down, the slurry or the wet hydrochar is inoculated with a microbial inoculant. A “microbial inoculant” refers to a composition or a concentrate of specific microorganisms. As used herein, it refers to a composition or a concentrate of specific microorganisms to be added to a slurry or a wet hydrochar for fermenting the hydrochar. A microbial inoculant may comprise one or a combination of various kinds of live microorganisms. A microbial inoculant may comprise between 106 and 1012 cfu / g or cfu / ml, preferably between 108 and 1012 cfu / g or cfu / ml. The composition or the concentrate can be in solid form, liquid form, or other form (e.g. suspension) or a mix thereof. As used herein, a “colony forming unit” or “CFU” refers to a measure of viable microorganisms in a sample. A CFU is an individual viable cell capable of forming on a solid medium a visible colony whose individual cells are derived by cell division from one parental cell. The phrases “CFU”, “CFU / ml”, and “CFU / g” also encompass the reference to “spores”, “spores / ml” or “spores / g”, respectively, in case the microorganism lends itself to being administered in the form of spores. As used throughout the present specification, the term “microorganism” or “microbe” refers to any strain, any species or taxon of microorganism, including, but not limited to, archaea, bacteria, microalgae, fungi (including mold and yeast species), mycoplasmas, microspores, nanobacteria, oomycetes, and protozoa. In some embodiments, a microbe or microorganism is a bacterial strain. In some embodiments, a microbe or microorganism is a fungal strain such as a yeast strain or a filamentous fungal strain. In some embodiments, a microbe or microorganism encompasses individual cells (e.g., unicellular microorganisms) or more than one cell (e.g., multi-cellular microorganism). As used herein, the term “bacterium”, “bacteria”, or “bacterial” refers in general to any prokaryotic organism, and may refer to an organism from either Kingdom Eubacteria (Bacteria), Kingdom Archaebacteria (Archaea), or both. In some cases, bacterial genera have been reassigned due to various reasons (such as, but not limited to, the evolving field of whole genome sequencing), and it is understood that such nomenclature reassignments are within the scope of any claimed genus. The terms “fungi”, “fungus” or “fungal” broadly refer to a wide variety of nucleated (eukaryotic) spore-bearing organisms that are devoid of chlorophyll (i.e., fungi do not photosynthesize, and are heterotrophs). These organisms are classified in the kingdom Fungi, separately from other eukaryotic kingdoms. Examples of fungi include multicellular filamentous fungi and unicellular fungi. Examples of fungi include yeasts, molds, mildews, rusts, smuts, and mushrooms. Many fungi are free-living in soil or water; others form parasitic or symbiotic relationships with plants or animals. The term “fungal cell” includes any cell of a fungal organism at any stage of the organism’s life cycle, and for example encompasses fungal cells of any ploidy, such as haploid, diploid, and polyploid fungal cells; and encompasses vegetative cells as well as fungal spores. The term “microalga” as used herein refers to microscopic alga(e). “Microalgae” encompass, without limitation, organisms within (i) several eukaryotic phyla, including the Rhodophyta (red algae), Chlorophyta (green algae), Dinoflagellata, Haptophyta, (ii) several classes from the eukaryotic phylum Heterokontophyta which includes, without limitation, the classes Bacillariophycea (diatoms), Eustigmatophycea, Phaeophyceae (brown algae), Xanthophyceae (yellow-green algae) and Chrysophyceae (golden algae), and (iii) the prokaryotic phylum Cyanobacteria (blue-green algae). The term "microalgae" includes for example genera selected from: Achnanthes, Amphora, Anabaena, Anikstrodesmis, Arachnoidiscusm, Aster, Botryococcus, Chaetoceros, Chlamydomonas, Chlorella, Chlorococcum, Chorethron, Cocconeis, Coscinodiscus, Crypthecodinium, Cyclotella, Cylindrotheca, Desmodesmus, Dunaliella, Emiliana, Euglena, Fistulifera, Fragilariopsis, Gyrosigma, Hematococcus, Isochrysis, Lampriscus, Monochrysis, Monoraphidium, Nannochloris, Nannochloropsis, Navicula, Neochloris, Nephrochloris, Nephroselmis, Nitzschia, Nodularia, Nostoc, Odontella, Oochromonas, Oocystis, Oscillartoria, Pavlova, Phaeodactylum, Playtmonas, Pleurochrysis, Porhyra, Pseudoanabaena, Pyramimonas, Scenedesmus, Schyzochitrium, Stichococcus, Synechococcus, Synechocystis, Tetraselmis, Thalassiosira, and Trichodesmium. The term “strain” (such as for example in the phrases “fungal strain” and “bacterial strain”) as a basic operational unit of microbial taxonomy, such as fungal or bacterial taxonomy, is frequently used to denote a population made up of the descendants of a single isolation in pure culture, usually made up of a succession of cultures ultimately derived from an initial single fungal or bacterial colony. Where a species encompasses two or more distinct isolates, the term “strain” may be used to refer to an isolate or group of isolates that can be distinguished from other isolates of the same genus and species by phenotypic characteristics or genotypic characteristics or both. In embodiments, the microbial inoculant may comprise one or more bacterial strains, yeast strains and / or filamentous fungal strains, preferably bacterial strains and / or filamentous fungal strains. The microorganisms may be genetically modified or not. For example, one or several microorganisms of the below listed genera can be used in the invention. Bacteria Acetobacter, Achromobacter, Acinetocacter, Actinomyces, Actinoplanes, Actinomadura, Aerococcus, Aeromonas, Alcaligenes, Alcanivorax, Alloiococcus, Alteromonas, Amycolatopsis, Anabaena, Arthrobacter, Arthrospira, Atopobium, Azoarcus, Azobacter, Azorhizobium, Azospirillum, Azotobacter, Bacillus, Beijerinckia, Bifidobacterium, Bradyrhizobium, Brevibacterium, Brevundimonas, Carnobacterium, Catenisphaera, Cellulomonas, Chryseobacterium, Citrobacter, Clostridium, Corynebacterium, Cyanobacteria, Dermatophilus, Desulfotomaculum, Dietzia, Enterobacter, Enterococcus, Escherichia, Frankia, Flavobacterium, Geobacillus, Gluconacetobacter, Gluconobacter, Gordonia, Herbaspirillum, Humicola, Janthinobacterium, Lactobacillus, Lactococcus, Leuconostoc, Klebsiella, Marinobacter, Microbacterium, Micromonospora, Microtetraspora, Moraxella, Mycobacterium, Mycococcus, Micrococcus, Nocardia, Oenococcus, Paenibacillus, Pediococcus, Phormidium, Phyllobacterium, Propionibacterium, Pseudomonas, Raoultella, Rastonia, Rhizobia, Rhizobium, Rhodococcus, Saccharopolyspora, Serratia, Shigella, Sinorhizobium, Sphingomonas, Staphylococcus, Streptococcus, Streptomyces, Symbiobacterium, Synechococcus, Synechocystis, Tetragenococcus, Thermoactinomyces, Thermomonospora, Vagococcuswhich, Vibrio, Weissella, Xanthomonas. Preferably, the microbial inoculant comprises one or more bacterial strains which belong to a genus selected from the group consisting of Achromobacter, Aeromonas, Azospirillum, Bacillus, Bradyrhizobium, Enterobacter, Gluconacetobacter, Klebsiella, Pseudomonas, Rhizobia, Rhizobium and Streptomyces or the group consisting of Achromobacter, Aeromonas, Azospirillum, Azotobacter, Bacillus, Bradyrhizobium, Enterobacter, Gluconacetobacter, Klebsiella, Pseudomonas, Rhizobia, Rhizobium and Streptomyces, more preferably a genus selected from the group consisting of Streptomyces, Bacillus, Azospirillum and Bradyrhizobium or the group consisting of Azotobacter, Streptomyces, Bacillus, Azospirillum and Bradyrhizobium. Yeasts Arxula, Aureobasidum, Blastobotrys, Brettanomyces (its perfect stage, Dekkera), Candida, Citeromyces, Cryptococcus, Cystofilobasidium, Debaryomyces, Endomycopsis, Filobasidiella, Galactomyces, Geotrichum, Glaciozyma, Guehomyces, Hansenula, Hanseniaspora (its asexual counterpart Kloeckera), Hyphopichia, Kluyveromyces, Kodamaea, Komagataella, Lachancea, Lipomyces, Metschnikowia, Meyerozyma, Moniella, Mrakia, Ogataea, Pichia, Phaffia, Pseudozyma, Rhodotorula, Rhodosporidium, Starmerella, Saccharomyces, Saccharomycodes, Saccharomycopsis, Scheffersomyces, Schizosaccharomyces, Schwanniomyces, Torulopsis, Torulaspora, Trichosporon, Trigonopsis, Yarrowia, Xanthophyllomyces and Zygosaccharomyces. Filamentous fungi Acremonium, Agaricus, Agrocybe, Akanthomyces, Alternaria, Ampelomyces, Amylosporus, Antrodia, Armillaria, Ashbya, Aspergillus, Atkinsonella, Aureobasidium, Auricularia, Balansia, Balansiopsis, Beauveria, Bispora, Bjerkandera, Boletus, Cantharellus, Catenaria, Cephalosporium, Chaetomium, Chrysonilia, Cladosporium, Claviceps, Clitocybe, Clitopilus, Colletotrichum, Collybia, Coniochaeta, Coprinus, Cordyceps, Coriolus, Cunninghamella, Cyathus, Cyclocybe, Cylindrocarpon, Cylinrocarpum, Cytonaema, Cytospora, Daldinia, Dentipellis, Doratomyces, Echinodothis, Emericella, Emericellopsis, Entoloma, Epichloe, Epicoccum, Exophiala, Favolaschia, Flammulina, Fomes, Fomitopsis, Fusarium, Ganoderma, Giberella, Gliocladium, Grifola, Gymnoascus, Hericium, Hohenbuehelia, Hormonema, Humicola, Hydropus, Hypomontagnella, Hypomyces, Hypoxylon, Hypsizigus, Inocutis, Inocybe, Inonotus, Isaria, Kuehneromyces, Lactarius, Laetiporus, Laxitextum, Lecanicillium, Lentinula, Lentinus, Lepista, Leptoshaeria, Lignosus, Lycoperdon, Lyophyllum, Martierella, Metarhizium, Monascus, Monilia, Monocillium, Morchella, Mortierella, Mucor, Mycelia, Myriogenospora, Neurospora, Nigrospora, Omphalotus, Ophiocordyceps, Oudemansiella, Paecilomyces, Panellus, Panus, Paraconiothyrium, Paraepichloe, Penicillium, Peniophora, Periconia, Pestalotiopsis, Phellinus, Phlebia, Pholiota, Phoma, Phomopsis, Piptoporus, Pleurotus, Pochonia, Polyporus, Preussia, Pycnoporus, Ramaria, Rhizoctonia, Rhizopus, Rhodotorula, Rhodotus, Sarcodon, Schizophyllum, Scytalidium, Scytalidium, Scytinostroma, Sparassis, Sphaerodes, Spicaria, Stachybotrys, Steccherinum, Stropharia, Suillus, Talaromyces, Thermoascus, Thermomyces, Tolypocladium, Torula, Trametes, Tremella, Trichoderma, Tricholoma, Tuber, Verticillium, Volvariella, Wolfiporia, Wrightoporia, Xylaria. Preferably, the microbial inoculant comprises one or more filamentous fungal strains which belong to a genus selected from the group consisting of Alternaria, Aspergillus, Chaetomium, Exophiala, Fusarium, Penicillium, Phoma, Talaromyces and Trichoderma or the group consisting of Alternaria, Aspergillus, Beauveria, Chaetomium, Exophiala, Fusarium, Penicillium, Phoma, Talaromyces and Trichoderma, more preferably a genus selected from the group consisting of Trichoderma and Penicillium or the group consisting of Beauveria, Thrichoderma and Penicillium. Selection of the microorganism comprised in the microbial inoculant may depend among other parameters on the desired final product, on its ability to develop in one or many type(s) of a given substrate, on its availability and price, etc. By means of an illustration and without limitation, plant- beneficial microorganisms that may be comprised in the microbial inoculant may include fungi belonging to the divisions Ascomycota (e.g. fungi of the genus Ampelomyces), Basidiomycota, and Zygomycota, bacteria of the family Rhizobiaceae, bacteria of the genera Frankia, Azotobacter, Azospirillum, Acetobacter, Azoarcus, Burkholderia, Herbaspirillum, Pseudomonas (e.g., Pseudomonas fluorescens, P. putida, P. gladioli), Bacillus (Bacillus subtilis, B. cereus, B. circulans), further bacteria such as Serratia marcescens, Flavobacterium spp., Alcaligenes sp., Agrobacterium radiobacter, and others. For example and without limitation, biocontrol micoorganisms that may be comprised in the microbial inoculant may include bacteria of the genus Agrobacterium, Pseudomonas, Streptomyces or Bacillus, and / or fungi of the genus Gliocladium, Trichoderma, Ampelomyces, Candida or Coniothyrium. In particular embodiments, the microbial inoculant comprises a bacterium selected from Streptomyces spp. (e.g. Streptomyces griseoviridis), Bacillus spp. (e.g. Bacillus subtilis), Azospirillum spp. (e.g. Azospirillum brasilense), or Bradyrhizobium spp. (e.g. Bradyrhizobium japonicum), or a filamentous fungus selected from Trichoderma spp. (e.g. Trichoderma harzianum) or Penicillium spp. (e.g. Penicillium bilaiae), or any combination thereof. In particular embodiments, the microbial inoculant comprises a bacterium selected from Azotobacter spp. (e.g. Azotobacter chroococcum), Pseudomonas spp. (e.g. Pseudomonas fluorescens), Streptomyces spp. (e.g. Streptomyces griseoviridis), Bacillus spp. (e.g. Bacillus subtilis), Azospirillum spp. (e.g. Azospirillum brasilense), or Bradyrhizobium spp. (e.g. Bradyrhizobium japonicum), or a filamentous fungus selected from Beauveria spp. (e.g. Beauveria bassiana), Trichoderma spp. (e.g. Trichoderma harzianum) or Penicillium spp. (e.g. Penicillium bilaiae), or any combination thereof. Inoculation of the slurry with a microbial inoculant may comprise adding the microbial inoculant to the slurry and optionally mixing the slurry. Mixing may be performed using a mixing device, by pumping e.g. gas through the slurry, or by shaking. Inoculation of the wet hydrochar with a microbial inoculant may comprise optionally mixing the microbial inoculant and a liquid (e.g. water), adding the inoculant and optionally the liquid to the wet hydrochar and optionally mixing the inoculant throughout the wet hydrochar to ensure exposure to the various surfaces of the hydrochar and adherence thereto. The inoculation step is conducted under sterile conditions. With “inoculation under sterile conditions” is meant herein conditions that prevent the contamination of the slurry or the wet hydrochar with microorganisms other than the microorganisms contained in the microbial inoculant. Fermentation The method further comprises fermenting the inoculated slurry or wet hydrochar. Said fermentation comprises storing the inoculated slurry or wet hydrochar under conditions to promote the growth and amplification of the microbial inoculant and degradation of the hydrochar by the microorganisms during a sufficient time. A time sufficient for a fermentation of the hydrochar varies amongst others with the composition of the biomass, the microbial inoculant and the fermentation conditions. The fermentation may not be completed but at least a part of the content of the hydrochar should be fermented. A time sufficient for a fermentation of the hydrochar can be, for example, at least one day, at least 5 days, at least 10 days, at least 15 days, or at least 20 days. A time sufficient for a fermentation of the hydrochar can be for example at most 60 days, at most 50 days, at most 40 days, at most 30 days, or at most 20 days. In embodiments, the inoculated slurry or wet hydrochar may be fermented for between about 2 days and about 14 days. Preferably, the fermentation conditions are controlled during the fermentation step. For example, the temperature may be controlled. In certain embodiments, the fermentation is conducted at a temperature below 85°C, preferably below 75°C, more preferably at a temperature between 15°C and 70°C or between 15°C and 65°C or between 15°C and 60°C. Fermentation typically occurs at temperatures of between 15 °C and 65 °C, depending on the microorganisms involved, and the biomass. Other parameters that may be controlled include hygrometry, oxygen and CO2 levels. For example, the humidity may be maintained above 35%, preferably above 45%, more preferably above 50%, even more preferably above 60%, for example above 65%. CO2levels can be maintained between 600 and 1200 ppm, preferably 800 and 1000 ppm. The fermentation may be conducted under aerobic (i.e. in the presence of oxygen) or anaerobic (i.e. in the absence of oxygen) conditions, depending e.g. on the microorganisms involved. For aerobic fermentation, oxygen may be fed as air to the slurry. However, it is also possible to feed pure oxygen to the slurry and / or air enriched with oxygen and / or air and oxygen in separate feeds. For aerobic solid-state fermentation, the wet hydrochar may be exposed to the air. In preferred embodiments, the fermentation is conducted under sterile conditions. As used herein, “fermentation under sterile conditions” or “sterile fermentation” means in the absence of undesirable microorganisms or with minimal such as preferably without contamination by microorganisms other than the microbial species contained in the microbial inoculant. Techniques for sterile fermentation are known to the skilled person, and include, for example, sterilizing the fermenter before inoculation with the microbial inoculant, use of a sterile fermentation broth, use of sterile (e.g. filtered) air or oxygen, etc. and any combination thereof. The fermentation may be conducted in one, single stage, or in two or more stages (i.e. multi-stage fermentation) such as a two-stage fermentation. In embodiments, the fermentation process may comprise fermenting the inoculated slurry to form a first fermentation product, followed by inoculating a second slurry formed in the HTC process with said first fermentation product and fermenting the inoculated second slurry to form the (second) fermentation product. In further embodiments, the fermentation of the (first) slurry inoculated with the microbial inoculant is conducted in sterile conditions. In further embodiments, the fermentation of the (second) slurry inoculated with the first fermentation product is conducted in non-sterile or sterile conditions. In further particular embodiments, the fermentation of the (first) slurry inoculated with the microbial inoculant is conducted in sterile conditions and the fermentation of the (second) slurry inoculated with the first fermentation product is conducted in non-sterile conditions. In certain embodiments, the fermentation process is a submerged fermentation. The term “submerged fermentation” generally refers to the process of fermenting microorganisms that are submerged in a liquid medium providing nutrients for the microorganisms. As used herein, “submerged fermentation” may refer to fermentation of the hydrochar wherein the microbial inoculant is inoculated to the slurry of the HTC process or a partially dewatered slurry. In certain embodiments, the fermentation is a solid-state fermentation. The term “solid-state fermentation” generally refers to the process of fermenting microorganisms on a solid medium or substrate that provides anchorage points and nutrients for the microorganisms. As used herein, “solid- state fermentation” may refer to fermentation of the hydrochar wherein the microbial inoculant is inoculated to a wet hydrochar. The expression "fermentation product" as used herein, refers to products generated during a fermentation step according to the invention. A fermentation product can correspond to fermented substrate, in particular fermented hydrochar, spore, biomass such as bacteria, yeasts or filamentous fungi, molecules, or any mixture thereof. As used herein, “fermented hydrochar” refers to hydrochar that has been at least partially degraded in a fermentation process. The term fermented hydrochar encompasses “partially fermented hydrochar”, which comprises a portion fermented hydrochar and a portion fermentable hydrochar, and “completely fermented hydrochar”. Recovery of the microbial and nutrient delivery system The fermentation product may be used as such as a microbial or nutrient delivery system, or the fermentation product may be subjected to one or more processing steps to obtain a microbial and nutrient delivery system. Recovering a microbial and nutrient delivery system from the fermentation product may encompass one or more processing steps selected from a solid-liquid separation step, a drying step, grinding, milling, pelletizing, a micro-granulation process, extruding, etc. In certain embodiments, recovering a microbial and nutrient delivery from the fermentation product comprises separating the fermentation product in a solid-rich fraction and a liquid fraction (or subjecting the fermentation product to a solid-liquid separation), wherein the microbial and nutrient delivery system is obtained or recovered from the solid-rich fraction. The solid-liquid separation techniques as described elsewhere herein for solid-liquid separation of the slurry may be used. In certain embodiments, recovering a microbial and nutrient delivery from the fermentation product comprises drying the fermentation product or a solid-rich fraction of the fermentation product. Different drying techniques may be used, including, without limitation, freeze drying, spray drying, fluid bed drying, vacuum tray drying, etc., depending on the type of micro-organisms in the microbial inoculant (sensitive micro-organisms may require more gentle drying techniques). In certain embodiments, recovering a microbial and nutrient delivery from the fermentation product comprises extruding the fermentation product e.g. pelletizing the fermentation product. The step of “extruding” the fermentation product can be broadly described as a step of forcing the fermentation product through an opening. During the step of extruding, generally involving at least one screw and a die, high pressure can build up at the end of the screw and the die. In particular, it can be considered that this extrusion step combines various unit operations into one system: transport, particle size reduction, particle size alteration, shape alteration, moisture alteration (increase or decrease), mixing, extraction, washing, cooling and / or heating, steaming, compression and / or expansion of the material. The step of extruding the fermentation product can be followed by a drying of the extruded fermentation product. In certain embodiments, recovering a microbial and nutrient delivery from the fermentation product comprises grinding or milling the fermentation product or a solid-rich fraction thereof, optionally after a drying step. In certain embodiments, recovering a microbial and nutrient delivery from the fermentation product comprises a micro-granulation process. In certain embodiments, in particular, embodiments wherein the microbial inoculant comprises spore-forming micro-organisms, the fermentation product may be subjected to a spore separation step, wherein the spores are separated from the fermentation product. Both, the separated spores and the residual fermentation product can be used as microbial and nutrient delivery system as described herein. The separation of spores can be done in a variety of ways as known to the skilled person, including, without limitation, sieving, filtration, centrifugation, cyclonic separation, and any combination thereof System Also disclosed herein is a system for producing a microbial and nutrient delivery system. In particular, the system for producing a microbial and nutrient delivery system can be used to perform a method for producing a microbial and nutrient delivery system according to the invention. The system may comprise a unit for conducting a HTC process (e.g. e.g. a pressurized reactor equipped with a thermocouple; Ingelia S.L. HTC plant), a cooling unit (e.g. a heat exchanger) and a fermentation unit (e.g. a fermenter, an open container). Suitable equipment for carrying out a HTC process or a fermentation process according to embodiments of the invention, as well as cooling equipment is known to any person skilled in the art and can be appropriately selected by the skilled person. For example, submerged fermentation may be conducted in a (stirred) tank. Non-limiting examples of suitable solid state fermenters include tray-type bioreactors, stirred tank bioreactors, rotary drum bioreactors, fluidized bed bioreactors, etc. as known to the skilled person. The system may further comprise one or more of a liquid-solid separator (e.g. a centrifuge), a dryer, a grinding machine, a milling machine and an extruder for recovering the microbial and nutrient delivery system from the fermentation product. Microbial and nutrient delivery system A further aspect is directed to a microbial and nutrient delivery system obtainable by the method of the invention. In particular, a microbial and nutrient delivery system is provided comprising: - a fermented hydrochar; and - microorganisms adhered to surfaces or in pores of the fermented hydrochar. As used herein, a “microbial and nutrient delivery system” denotes a system or composition comprising microorganisms and nutrients. The term “nutrient” broadly refers to substances used by organisms such as microorganisms and plants to survive, grow, and reproduce. The term nutrient encompasses macronutrients and micronutrients and includes, without limitation, carbon, oxygen, nitrogen, phosphorus, minerals (e.g. calcium, sodium, potassium, magnesium, chloride), etc. The nutrients may be present in the system in any form, e.g. as ions, as salts, as chemical compounds (e.g. carbohydrates), etc. The microbial and nutrient delivery system may comprise nutrients for the microorganisms present in the system, as well as for other organisms such as plants, depending on the application. Advantageously, the microorganisms in the system may convert certain nutrients into a form so that it becomes bioavailable for other organisms (e.g. plants). The microbial and nutrient delivery system according to the invention comprises a fermented hydrochar, microorganisms and optionally spores. The microbial and nutrient delivery system may further comprise (residual) process water. The microorganisms are adhered to surfaces or in pores of the fermented hydrochar. Without wishing to be bound by any theory, due to the fermentation step said adherence may be stronger and / or colonization of the pores may be better compared to the use of a non-fermented hydrochar as microbial carrier. Due to the sterile conditions applied in at least the cooling and inoculation steps of the method of the invention, the microbial and nutrient delivery system according to the invention is characterized in that it is minimally contaminated by non-desired micro-organisms or microbial species not comprised in the microbial inoculant. The microbial and nutrient delivery system of the invention is characterized in that the micro-organisms essentially consist of microbial species comprised in the microbial inoculant. In embodiments, at least 50%, preferably at least 55%, 60%, 65%, 70% or 75%, more preferably at least 80%, 82%, 85%, 86%, 88% or 90% such as at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% of the microorganisms in the microbial and nutrient delivery system consist of microbial species comprised in the microbial inoculant.As noted before, the fermented hydrochar may be partially fermented hydrochar or completely fermented hydrochar. Completely fermented hydrochar may be preferred because the absence of fermentable substrate makes it less attractive for non-desired and / or pathogenic microorganisms. Due to the fermentation of the hydrochar, the microbial and nutrient delivery system is more stable and has an improved shelf-life compared to systems wherein non-fermented hydrochar is used as a microbial carrier. In particular embodiments, such as wherein the microbial and nutrient delivery system is obtainable by a method according to the invention comprising a spore separating step, the microorganisms essentially consist of spores, preferably spores of microbial species comprised in the microbial inoculant. The microbial and nutrient delivery system may further comprise one or more auxiliary agents. The terms “auxiliary”, “auxiliary agent”, “additive”, or “adjuvant” may be used interchangeably herein. The auxiliaries may be natural or synthetic organic or inorganic materials, preferably natural materials, which facilitate the administration of the microbial and nutrient delivery system to e.g. plants, plant parts, seeds, plant growth loci, or environmental loci. The auxiliaries may be one or more of a solvent, a carrier, a binder, a surfactant, a sticker, a tackifier, an antifreeze agent, a thickener, a buffering agent, an antifoaming agent, an antioxidant, a preservative, a stabilizer, an aroma, a colorant, etc. Suitable auxiliary agents are known in the art and are commercially available. In general, the microbial and nutrient delivery system can be combined with any solid, semi-solid or liquid additive customarily used for formulation purposes. A carrier is to be understood as meaning a natural or synthetic, organic or inorganic substance which is mixed or combined with the microbial and nutrient delivery system for better applicability, such as for application to plants or plant parts such as seeds. The carrier, which may be solid, semi-solid, or liquid, is generally inert and suitable for use in agriculture or horticulture. For instance, liquid carriers may include water, organic solvents, and mineral oils and vegetable oils. Suitable liquefied gaseous extenders or carriers are liquids which are gaseous at ambient temperature and under atmospheric pressure, for example aerosol propellants, such as butane, propane, nitrogen and carbon dioxide. A sticker is to be understood as meaning an additive or adjuvant to improve adhesive properties of the composition to the plant or part thereof. Suitable surfactants are emulsifiers, dispersants or wetting agents having ionic or nonionic properties, or mixtures of these surfactants. It is possible to use colorants such as inorganic pigments, for example iron oxide, titanium oxide, Prussian blue, and organic dyes, such as alizarin dyes, azo dyes and metal phthalocyanine dyes, and trace nutrients, such as salts of iron, manganese, boron, copper, cobalt, molybdenum and zinc. Stabilizers, such as low-temperature stabilizers, preservatives, antioxidants, light stabilizers or other agents which improve chemical and / or physical stability may also be present. For certain applications, the auxiliaries that are added to the microbial and nutrient delivery system are preferably agriculturally acceptable auxiliaries. The terms “agriculturally acceptable” or “agriculturally compatible” are consistent with the art and mean not deleterious to the recipient plant, such as not producing, having or causing any adverse effects when applied to a plant or a plant part, or adverse effects to the plant grown from that plant part. In certain embodiments, the microbial and nutrient delivery system comprises one or more further active ingredient such as nutrients and / or microorganisms. The terms “active ingredient” or “active component” can be used interchangeably and broadly refer to a material, such as an element, molecule, substance, and / or microorganism, which, when provided in an effective amount, achieves a desired outcome, such as achieves one or more effects on one or more plant growth features or achieves one or more effects on bioremediation. Typically, an active ingredient as intended herein may achieve such outcome(s) through interacting with and / or modulating the plant, part thereof, a seed for growing the plant, the locus of the plant (e.g. the soil), or the environmental locus (e.g. a contaminated soil). For example, microorganisms may be added, which together with the microorganisms of the microbial and nutrient delivery system, form a microbial consortium suitable for bioremediation applications, but which are less or not compatible with the microorganisms of the microbial and nutrient delivery system for fermenting the slurry or wet hydrochar (e.g. different fermentation conditions). Further non-limiting examples of active ingredients that can be added to the microbial and nutrient delivery system include fertilizers (e.g. chemical fertilizers), pesticides (e.g. chemical pesticides, chitosan), biostimulants (e.g. microbial biostimulants, plant extracts, (plant) hormones, (bio)chemicals), or any combination thereof. A microbial and nutrient delivery system or composition as taught herein may be liquid, semi-solid, or solid, and may include solutions or dispersions. Non-limiting examples of the compositions as taught herein may be (soluble) powders, (soluble) granules, wettable granules, pellets, tablet formulations, dry flowables, aqueous flowables, wettable dispersible granules, oil dispersions, suspension concentrates, dispersible concentrates, emulsifiable concentrates, aqueous suspensions, fertilizer granules, sprayables, and the like. The term “powder” refers to a dry, bulk solid composed of many very fine particles that may flow freely when shaken or tilted. Uses Further aspects are directed to applications of the microbial and nutrient delivery system of the invention. The microbial and nutrient delivery system of the invention is useful as agricultural biological, in particular as a biostimulant, more particularly as a biofertilizer and / or a biocontrol agent. Accordingly, in as aspect the invention relates to use of a microbial and nutrient delivery system according to the invention as a biostimulant. As used herein, a "biostimulant" refers to a substance or microorganism that, when applied to a plant, a part thereof (e.g., roots), a seed for growing the plant, or a locus of the plant (e.g., to soil or plant growth medium surrounding the plant), stimulates natural processes to improve a plant growth feature. The term “plant growth feature” is intended to broadly encompass any feature that relates in some way to plant growth. The feature may relate to or be observable with respect to an individual plant or to a population of plants. Examples of such features include, without limitation, plant wet or dry biomass, plant height, plant size, emergence %, emergence date, canopy cover, flowering status, seed yield, grain yield, fruit yield, number of tillers per plant, shoot length, root length, root architecture, seed weight, senescence, stay-green, number of mature plant reproductive elements per plant, visual appearance, etc. The reference to an improvement encompasses any qualitative or quantitative change or modification in a plant growth feature that is industrially beneficial, in particular in the context of agriculture. To the extent a plant growth feature is quantifiable, an improvement may be synonymous to an increase or a reduction in that quantity, depending on the nature of the plant growth feature. By means of an example and without limitation, an increase may be desired in quantifiable features such as plant wet or dry biomass, plant height, plant size, canopy cover, seed yield, grain yield, fruit yield, number of tillers per plant, shoot length, root length, seed weight, etc. By means of an illustration, a biostimulant may be capable of increasing nutrient uptake and / or nutrient use efficiency of a treated plant as compared to an untreated plant, increasing the nitrogen fixating capacities or phosphorus uptake of a treated plant as compared to an untreated plant, increasing the amount of biomass of a treated plant as compared to an untreated plant, increasing the number of tillers per plant of a treated plant as compared to an untreated plant, increasing growth and / or yield of a treated plant as compared to an untreated plant, and / or helping a treated plant overcome stress conditions, such as nutrient stress or abiotic stress (e.g., drought, heat, and saline soils), compared to an untreated plant; and the like. Further plant growth features that can be improved by a biostimulant may include disease resistance, drought tolerance, heat tolerance, cold tolerance, salinity tolerance, metal tolerance, herbicide tolerance, chemical tolerance, improved water use efficiency, improved phosphorus solubilization, improved phosphorus mobilization, improved nitrogen utilization, improved nitrogen fixation, pest resistance, herbivore resistance, pathogen resistance, increase in yield, increase in yield under water-limited conditions, health enhancement, vigor improvement, growth improvement, improved plant emergence, photosynthetic capability improvement, nutrition enhancement, altered protein content, altered oil content, increase in biomass, increase in number of tillers per plant, increase in shoot length, increase in root length, improved root architecture, increase in seed weight, altered seed carbohydrate composition, altered seed oil composition, increase in radical length, delayed senescence, stay-green, altered seed protein composition, increase in dry weight of mature plant reproductive elements, increase in fresh weight of mature plant reproductive elements, increase in number of mature plant reproductive elements per plant, increase in chlorophyll content, reduced number of wilted leaves per plant, reduced number of severely wilted leaves per plant, increase in number of non-wilted leaves per plant, and / or improved plant visual appearance, and the like. In embodiments, the invention relates to use of a microbial and nutrient delivery system as a biofertilizer. As used herein, the term "biofertilizer” refers to a substance which contains one or more nutrients (e.g., nitrogen, phosphorus, and / or potassium) and living microorganisms, which, when applied to a plant, a part thereof (e.g., roots), a seed for growing the plant, or a locus of the plant (e.g., to soil or plant growth medium surrounding the plant), colonize the locus of the plant or the plant structure and promote growth by increasing the availability of nutrients to the plant. In embodiments, the invention relates to use of a microbial and nutrient delivery system as a biocontrol agent. As used herein, the term “biocontrol agent” refers to a substance containing microorganisms or a microorganism with the capacity to reduce the population of a possible pathogenic agent or to avoid its effects. A biocontrol agent, when applied to a plant, a part thereof (e.g., roots), a seed for growing the plant, or a locus of the plant (e.g., to soil or plant growth medium surrounding the plant), greatly reduces plant disease incidence and severity. The mode of action may be because the biocontrol out- competes the pathogen for an ecological niche, because the biocontrol secretes or contains a substance that is toxic to the pathogen, because of parasitism of the biocontrol on the pathogen, or some combination of these or other effects. The uses may entail administering or applying a microbial and nutrient delivery system according to the invention to the plant, the part thereof (e.g., roots), the seed for growing the plant, or the locus of the plant (e.g., to soil or plant growth medium surrounding the plant). The reference to plants includes any plants. The plants may include wild plants and domesticated varieties. In certain embodiments, the plants may be agricultural plants. The terms “agricultural plants” or “crops” include plants that are cultivated by humans for but not limited to food, feed, fiber, fuel, gardening, and / or industrial purposes. The phrases “part of a plant” or “plant part” as used herein refer to any one or more portions of a plant, such as to any one or more of the seeds, shoots, stems, leaves, roots (including tubers), flowers, etc. In addition, a “plant part” is intended to generically refer to any part of a plant that is able to initiate other plants via either sexual or asexual reproduction of that plant, for example but not limited to: seed, seedling, root, shoot, cutting, scion, graft, stolon, bulb, tuber, corm, keikis, or bud. In certain embodiments, the microbial and nutrient delivery system is applied to the seeds. The plant parts, when treated with the microbial and nutrient delivery system according to the invention, may be attached to (e.g., growing on) the whole plant, or may be detached from (e.g., not growing on) the whole plant. For instance, seeds may be detached from (e.g., not growing on) the whole plant when treated with the microbial and nutrient delivery system of the invention. The phrases “locus of a plant” or “locus of growth of a plant” as used herein refers to an area in close proximity of a plant (including parts thereof such as a seed). For instance, the locus of a plant may be a circular area around the plant, e.g., around a seed, such as a circular area having a diameter of at most 1 meter, for instance at most 50 centimeters (cm), at most 40 cm, at most 30 cm, at most 20 cm, at most 10 cm, or at most 5 cm, around the plant, e.g., around a seed. The locus of growth may include the growth medium (e.g., soil, hydroponic medium, or hydroculture medium) for cultivating the plant. The phrase “administering” generally refers to man- and / or machine-driven or effected disposing, applying, delivering, or providing of a recited object, such as microbial and nutrient delivery system, to a recipient entity, such as the plant, a part thereof, a seed for growing the plant, or locus of the plant. The microbial and nutrient delivery system as taught herein may be administered by any known method wherein all or part of the plant is treated, such as by root or seed inoculation. For example, the administration can be to the roots of the plant, to the seed of the plant prior to planting the seed in soil, or to the soil or plant growth medium surrounding the plant or plant seed. Application methods such as spraying, coating, covering, contacting, and / or immersion can be adopted. In certain embodiments, application may be to a surface, such as to the surface of growth medium (such as soil), plant, plant part, seeds, harvested plants or plant parts (e.g. harvested roots, bulbs or tubers). In certain embodiments, the administration may be to the plant, part thereof, or locus of the plant, present on the field or the farmland. In certain embodiments, the microbial and nutrient delivery system as taught herein may be administered to the locus of the plant, such as by inoculating the soil or growth medium. Hence, in certain embodiments, the method comprises inoculating soil or a plant growth medium with the microbial and nutrient delivery system and growing the plant in said soil or medium. The terms “growth medium” or “plant growth medium” as used herein refer to a substrate or medium for culturing plants. The growth medium may be soil, compost, peat, coco-coir, wood fibers, a soil- mimicking substrate such as mineral lava or basalt substrate, textile, or a soil-less substrate. For example, the growth medium may be sand, gravel, polysaccharide, mulch, peat moss, straw, logs, clay, or a combination thereof. The plant growth medium may also include a hydroculture system or an in vitro culture system. The plant growth medium may also be a hydroponic medium or a hydroculture medium. The skilled person understands that different types of growth media may be used for growing different types of plants. Inoculating a plant growth medium can be performed, by way of example using a liquid, a powder, a granule, a pellet. For example, aquatic plants may be grown in granules or pellets of the microbial and nutrient delivery system as described herein. The inoculation of the plant growth medium with the microbial and nutrient delivery system as taught herien may be performed before, during and / or after sowing or before, during and / or after the start of the plant growth cycle in case of hydroculture or in vitro culture. The inoculation can be performed once or multiple times during the plant growth cycle. In certain embodiments, sprayable liquids may be applied by spraying the plant, part thereof, or locus of the plant, preferably the locus of the plant, by conventional spraying equipment as known in the art, such as airplanes, backpack sprayers, tractor mounted boom sprayers etc. In certain embodiments, application of the microbial and nutrient delivery system as taught herein to the plant, part thereof, or locus of growth of the plant may be carried out directly or by action on their surroundings or habitat using customary treatment methods, for example by dipping, drenching, spraying, coating, atomizing, irrigating, evaporating, dusting, fogging, broadcasting, foaming, painting, spreading-on, watering (drenching) or drip irrigating. For example, the application may comprise spraying, sprinkling, showering, spritzing, spreading in droplets, spattering; dispersing, diffusing, or douching the plant, part thereof, or locus of growth of the plant with the microbial and nutrient delivery system. Further disclosed herein are uses of the microbial and nutrient delivery system for environmental applications, e.g. as a bioremediation agent. Accordingly, a further aspect is directed to use of a microbial and nutrient delivery system as taught herein as a bioremediation agent. “Bioremediation” generally refers to remediation of contaminated soils utilizing the ability of certain microbes to transform harmful substances in to nontoxic compounds. Main requirements for effective bioremediation are: a biodegradable organic substrate, an appropriate active microbial community (consortium) and bioavailability of contaminants. Bioremediation may further require nutrients for the microorganisms. According to the present invention, a slurry or wet hydrochar from a HTC process is inoculated with the appropriate microbes or microbial blend, and the inoculated slurry or wet hydrochar is fermented allowing the adherence of the microbes to the fermented hydrochar and colonization of its pores. The fermentation product, optionally after some processing steps as taught elsewhere herein, can be applied to the contaminated soil. The hydrochar acts as a source of nutrients for growth and proliferation of the microbes in the system, and provides protection against predation by protozoan. Moreover, due to the fermentation of the hydrochar, competition with native-born microorganisms in the soil may be reduced. In further aspects, the invention relates to uses of the microbial and nutrient delivery system as a microbial inoculant, e.g. for an anaerobic digester, for a septic system, for a water treatment system, etc. Depending on the specific application, the skilled person can select appropriate microorganisms for the microbial inoculant. In certain embodiments, the microbial and nutrient delivery system may be (re-)used as a microbial inoculant in the method of the invention. The present invention is explained in more detail with reference to the accompanying Figure 1 which provides a schematic diagram illustrating embodiments for implementing a process according to the invention, without restricting the invention to the special steps and parameters represented. In the method, biomass (101) is subjected to a hydrothermal carbonization process (10) to form a slurry (103) comprising a hydrochar and a process water. The slurry is cooled (20) to a temperature suitable for growth of a microbial inoculant. The cooled slurry (105) may be inoculated with a microbial inoculant (109) and subsequently subjected to a fermentation process (40), in particular a submerged fermentation. Optionally, the cooled slurry (105) may be first subjected to a solid-liquid separation (30) before the inoculation step. The solid-liquid separation reduces the process water content of the slurry to obtain a wet hydrochar (106). The process water (107) that is separated from the wet hydrochar (106) may be recirculated to the HTC process (10). The solid-liquid separation step also allows to easily add additional ingredients (110) to the wet hydrochar and it permits to add the microbial inoculum (109) to the wet hydrochar in a convenient way. The fermentation (40) of the wet hydrochar (106) may be a solid state fermentation. Additional ingredients (110) such as nutrients to promote growth of the beneficial microorganims or to adjust the composition of the microbial and nutrient delivery system, may be added in various steps of the process, e.g. before the HTC process (10), during the solid-liquid separation (30), before fermentation (40), etc. The fermentation product (111) comprising fermented hydrochar can be used as such as a microbial and nutrient delivery system. Alternatively, the fermentation product (111) may be subjected to one or more processing steps (50), such as from a solid-liquid separation step, a drying step, grinding, milling, pelletizing, etc., and / or formulated (50), optionally together with one or more co-formulants (112), to provide a formulated microbial and nutrient delivery system (113). Statements. In these statements, the wording “The [subject] according to Statement [number], wherein…” or “The [subject] according to any one of Statements [numbers], wherein…” also discloses and may be replaced by the simple wording “In certain embodiments…”. Statement 1. A method for producing a microbial and nutrient delivery system (113), said method comprising: - providing a biomass (101); - subjecting the biomass (101) to a hydrothermal carbonization process (10) to form a slurry (103) comprising a hydrochar and a process water, in particular HTC process water; - cooling (20) the slurry (103) to a temperature suitable for growth of a microbial inoculant; - inoculating the cooled slurry (105) with the microbial inoculant (109); - subjecting the inoculated slurry to a fermentation process (40) to form a fermentation product (111); and - obtaining or recovering (50) the microbial and nutrient delivery system (113) from the fermentation product. Statement 2. The method according to Statement 1, further comprising a step of reducing (30) the process water, in particular HTC process water, content of the slurry (103, 105) to form a wet hydrochar (106) before inoculation with the microbial inoculant. Statement 3. The method according to Statement 1 or 2, wherein the cooling step (20) and the inoculation step are conducted under sterile conditions. Statement 4. The method according to Statement 2 or 3, wherein the cooling step (20), the inoculation step and the step of reducing (30) the process water, in particular HTC process water, content of the slurry are conducted under sterile conditions. Statement 5. The method according to any one of Statements 2 to 4, wherein the process water, in particular HTC process water, content of the slurry is reduced (30) by a mechanical process, preferably a solid-liquid separation such as a decantation, a centrifugation or a filtration. Statement 6. The method according to any one of Statements 1 to 5, wherein said fermentation process (40) is a solid-state fermentation. Statement 7. The method according to any one of Statements 1 to 5, wherein said fermentation process (40) is a submerged fermentation. Statement 8. The method according to any one of Statements 1 to 7, wherein the fermentation process is a single-stage fermentation. Statement 9. The method according to Statement 8, wherein the fermentation is conducted under sterile conditions. Statement 10. The method according to any one of Statements 1 to 7, wherein the fermentation process is a multi-stage fermentation such as a two-stage fermentation wherein the fermentation process comprises fermenting the inoculated slurry to form a first fermentation product, followed by inoculating a second slurry formed in the HTC process with said first fermentation product and fermenting the inoculated second slurry to form the (second) fermentation product. Statement 11. The method according to Statement 10, wherein the fermentation of the (first) slurry inoculated with the microbial inoculant is conducted under sterile conditions. Statement 12. The method according to Statement 10 or 11, wherein the fermentation of the (second) slurry inoculated with the first fermentation product is conducted under non-sterile conditions. Statement 13. The method according to any one of Statements 1 to 12, wherein the fermentation is conducted at a temperature below 85°C, preferably below 75°C, more preferably at a temperature between 15°C and 70°C or between 15°C and 65°C or between 15°C and 60°C. Statement 14. The method according to any one of Statements 1 to 13, wherein the slurry (103) or the wet hydrochar is cooled (20) to a temperature of between about 4°C to about 65°C, preferably between about 20°C to about 50°C, more preferably between about 20°C and about 30°C. Statement 15. The method according to any one of Statements 1 to 14, wherein the cooling (20) is performed by means of a heat exchanger. Statement 16. The method according to any one of Statements 1 to 15, wherein heat released during the cooling step (20) is used for the hydrothermal carbonization process (10) . Statement 17. The method according to any one of Statements 1 to 16, wherein one or more nutrients (110) such as a carbon source are added to the slurry or the wet hydrochar before the fermentation process and / or wherein the pH of the slurry or the wet hydrochar is adjusted to a pH suitable for growth of the microbial inoculant before the fermentation process. Statement 18. The method according to any one of Statements 1 to 17, wherein the hydrothermal carbonization process (10) is performed at a temperature of between about 180°C and about 250°C, preferably between about 200°C and about 220°C. Statement 19. The method according to any one of Statements 1 to 18, wherein the hydrothermal carbonization process (10) is performed at a pressure of between about 10 bar and about 50 bar, preferably between about 15 bar and about 25 bar. Statement 20. The method according to any one of Statements 1 to 19, wherein the hydrothermal carbonization process (10) is performed for a period of at least 30 min, preferably between about 30 minutes and about 8 hours, more preferably between about 30 minutes and about 4 hours, even more preferably between about 2 hours and about 3 hours. Statement 21. The method according to any one of Statements 1 to 20, wherein the hydrothermal carbonization process (10) is performed at a temperature of between about 180°C and about 250°C and a pressure of between about 10 bar and 50 bar for at least 30 minutes. Statement 22. The method according to any one of Statements 1 to 21, wherein the hydrothermal carbonization process (10) is performed at a temperature of between about 200°C and about 220°C at a pressure of between about 15 bar and about 25 bar for between about 2 hours and 3 hours. Statement 23. The method according to any one of Statements 1 to 22, wherein the biomass (101) is a wet biomass having a water content of between 10% and 95% by weight, preferably between 10% and 90% by weight. Statement 24. The method according to any one of Statements 1 to 23, wherein the biomass (101) is selected from a food residue, an agricultural residue, an animal by-product, or any combination thereof. Statement 25. The method according to any one of Statements 1 to 24, wherein the biomass (101) comprises an animal by-product such as manure. Statement 26. The method according to any one of Statements 1 to 25, wherein the microbial inoculant (109) comprises one or more bacteria which belong to a genus selected from the group consisting of Achromobacter, Aeromonas, Azospirillum, Bacillus, Bradyrhizobium, Enterobacter, Gluconacetobacter, Klebsiella, Pseudomonas, Rhizobia, Rhizobium and Streptomyces or the group consisting of Achromobacter, Aeromonas, Azospirillum, Azotobacter, Bacillus, Bradyrhizobium, Enterobacter, Gluconacetobacter, Klebsiella, Pseudomonas, Rhizobia, Rhizobium and Streptomyces, such as a genus selected from the group consisting of Streptomyces, Bacillus, Azospirillum and Bradyrhizobium or the group consisting of Azotobacter, Streptomyces, Bacillus, Azospirillum and Bradyrhizobium. Statement 27. The method according to any one of Statements 1 to 26, wherein the microbial inoculant (109) comprises one or more filamentous fungi which belong to a genus selected from the group consisting of Alternaria, Aspergillus, Chaetomium, Exophiala, Fusarium, Penicillium, Phoma, Talaromyces and Trichoderma or the group consisting of Alternaria, Aspergillus, Beauveria, Chaetomium, Exophiala, Fusarium, Penicillium, Phoma, Talaromyces and Trichoderma, such as a genus selected from the group consisting of Trichoderma and Penicillium or the group consisting of Beauveria, Thrichoderma and Penicillium. Statement 28. The method according to any one of Statements 1 to 27, wherein the recovery step (50) comprises separating the fermentation product in a solid-rich fraction and a liquid fraction. Statement 29. The method according to any one of Statements 1 to 28, wherein the recovery step (50) comprises drying the fermentation product or a solid-rich fraction of the fermentation product. Statement 30. The method according to any one of Statements 1 to 29, wherein the recovery step (50) comprises a step of separating spores from the fermentation product, wherein the microbial inoculant comprises spore-forming micro-organisms. Statement 31. The method according to any one of Statements 1 to 30, wherein the recovery step (50) comprises a processing step selected from the group consisting of: grinding, milling and pelletizing or wherein the recovery step (50) comprises one or more of grinding, milling, pelletizing, extruding and a micro-granulation process. Statement 32. A microbial and nutrient delivery system obtainable by a method according to any one of Statements 1 to 31, the system comprising: - a fermented hydrochar; and - microorganisms adhered to surfaces or in pores of the fermented hydrochar. Statement 33. The microbial and nutrient delivery system according to Statement 32, wwherein at least 50%, preferably at least 55%, 60%, 65%, 70% or 75%, more preferably at least 80%, 82%, 85%, 86%, 88% or 90% such as at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% of the microorganisms in the microbial and nutrient delivery system consist of microbial species comprised in the microbial inoculant. Statement 34. The microbial and nutrient delivery system according to Statement 32 or 33, further comprising one or more auxiliary agent, such as one or more auxiliary agents selected from a solvent, a carrier, a binder, a surfactant, a sticker, a tackifier, an antifreeze agent, a thickener, a buffering agent, an antifoaming agent, an antioxidant, a preservative, a stabilizer, an aroma and a colorant. Statement 35. Use of a microbial and nutrient delivery system according to any one of Statements 32 to 34 as a biostimulant. Statement 36. Use of a microbial and nutrient delivery system according to any one of Statements 32 to 34 as a biofertilizer. Statement 37. Use of a microbial and nutrient delivery system according to any one of Statements 32 to 34 as a biocontrol agent. Statement 38. Use of a microbial and nutrient delivery system according to any one of Statements 32 to 34 as a bioremediation agent. Statement 39. Use of a microbial and nutrient delivery system according to any one of Statements 32 to 34 as a microbial inoculant such as a microbial inoculant for an anaerobic digester, for a septic system or for a water treatment system. Statement 40. Use of a microbial and nutrient delivery system according to any one of Statements 32 to 34 as a microbial inoculant in a method according to any one of Statements 1 to 31. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as follows in the spirit and scope of the appended claims. The herein disclosed aspects and embodiments of the invention are further supported by the following non-limiting examples. EXAMPLES Example 1: Microbial growth on hydrochar and process water in agar Materials and methods: Hydrochar was produced in an Ingelia S.L. HTC plant (València, Spain). The feedstock used in the production of the hydrochar was pig manure (HC-C). Hydrothermal carbonization was conducted at 210°C and 20-25 bar for 3 to 4 hours. Using gravimetric filtration, the slurry obtained after hydrothermal carbonization was separated into a (wet) hydrochar and a process water fraction. As a reference material, blonde peat moss from Baltic origin (Novabalt) was used. Three types of agar plates were prepared and sterilized by autoclaving (121°C for 15 minutes): ^ PW-Agar: 1,5% w / v agar diluted in process water (adjusted to pH 7 using 1M sodium hydroxide) ^ HC-Agar: 2% w / v of hydrochar HC-C, 1,5% w / v agar diluted in reverse osmosis water. ^ HC+PW-Agar: 2% w / v of hydrochar HC-C, 1,5% w / v agar diluted in process water (adjusted to pH 7 using 1M sodium hydroxide) ^ Peat-Agar: 2% w / v of peat, 1,5% w / v agar diluted in reverse osmosis water. The bacterial strains Streptomyces griseoviridis (LMG19321), Bacillus subtilis (LMG 23370), Azospirillum brasilense (LMG 28319) and Bradyrhizobium japonicum (LMG 4252), and the fungal strains Trichoderma harzianum (MUCL 22194) and Penicillium bilaiae (MUCL 31187) were obtained from the Belgium Coordinated Collections of Microorganisms (BCCM). All strains were revitalized and grown on yeast mannitol agar (YMA) medium at 28°C for the bacterial strains and at 25°C for the fungal strains. Agar for microbiology (900040) and yeast mannitol agar NutriSelect Plus (900050) were obtained from Merck Life Sciences BV (Belgium). The six different strains were inoculated with an inoculation loop by streaking the pure culture from YMA plates onto the four types of custom agar plates in a laminar air flow cabinet. The plates were inoculated under normal atmosphere at 28°C and 25°C for bacterial and fungal strains, respectively. After four days, growth on the medium was scored visually. Results: Table 1: Growth of selected micro-organisms after 4 days on PW-Agar, HC-Agar, HC+PW-Agar and Peat-Agar. Scoring system: 0: No colonies visible; +: Some colonies visible, minimal growth; ++: Good growth, many colonies; +++: Overgrown, colonies spreading; C: Contamination. Micro-organism PW-Agar HC-Agar HC+PW- Peat-Agar Agar Streptomyces griseoviridis 0 +++ + C Bacillus subtilis + + ++ 0 Azospirillum brasilense + ++ + C Bradyrhizobium japonicum 0 + ++ C Trichoderma harzianum + ++ +++ 0 Penicillium bilaiae 0 ++ +++ ++ The results in Table 1 show that all 6 selected microbial strains were able to grow well on HC-Agar and HC+PW agar, indicating that hydrochar optionally in combination with process water provides the necessary nutrients for uninhibited microbial growth. No contamination was observed on PW- Agar, HC-Agar or HC+PW-Agar plates. Only Penicillium bilaiae was able to grow on Peat-Agar. Most Peat-Agar plates showed contamination by spores which were not destroyed during the standard sterilization process at 121°C. The lack of nutrients and risk of contamination indicate inferior performance of Peat as a growing substrate for the selected micro-organisms. Example 2: Microbial growth on hydrochar and process water (without agar) Materials and methods: Hydrochar was produced in an Ingelia S.L. HTC plant (València, Spain). The feedstock used in the production of the hydrochar was cattle manure (HC-A), pig manure (HC-C) or lignocellulosic biomass (HC-BM). Hydrothermal carbonization was conducted at 210°C and 20-25 bar for 3 to 4 hours. Using gravimetric filtration, the obtained slurry after hydrothermal carbonization was separated into a (wet) hydrochar and process water fraction. As a reference material, blonde peat moss from Baltic origin (Novabalt) was used. The same micro-organisms and microbial culture conditions as in Example 1 were used. The three types of hydrochar (containing approximately 50% by weight moisture (process water)) and peat (wetted with reverse osmosis water) were sterilized at 121°C for 15 minutes. The materials were distributed (approximately 1 gram dry matter each) in empty (sterile) petri dishes in a laminar air flow cabinet. The materials were inoculated using an inoculation loop from a microbial culture growing on a YMA agar plate. The plates were taped in parafilm to prevent moisture losses. The materials were incubated at respectively, 28°C and 25°C for bacterial and fungal strains, and a solid state fermentation process was performed. After 7 days, the growth was assessed visually and scored. For the HC-C samples, the growth was quantified by resuspending the dried material in sterile physiological water (0,8% NaCl), and a dilution series from 10-2 to 10-10 was prepared in triplicate. The number of colony forming units (CFU) in the dilution series was determined by plating on YMA plates. Results: Table 2: Growth of selected micro-organisms after 7 days on hydrochar (HC) from cattle manure (HC-A), pig manure (HC-C) or lignocellululosic biomass (HC-B), or peat. Scoring system: 0: No colonies visible; +: Some growth visible; ++: Good growth, clearly visible; +++: Overgrown, colonies spreading; NVC: No visible growth. Micro-organism HC-A HC-C HC-BM Peat Streptomyces griseoviridis ++ ++ ++ ++ Bacillus subtilis NVC NVC NVC NVC Azospirillum brasilense NVC NVC NVC NVC Bradyrhizobium japonicum + ++ ++ + Trichoderma harzianum + ++ ++ 0 Penicillium bilaiae ++ ++ +++ 0 With the exception of Bacillus subtilis and Azospirillum brasilense, which did not produce visual signs of microbial growth, it was possible to grow the selected micro-organisms on three different types of hydrochar, without providing any other nutrients (Table 2). Table 3: Quantification of growth of selected micro-organisms after 7 days on hydrochar from pig manure (HC-C). Micro-organism Average Standard (CFU / g) deviation Streptomyces griseoviridis 3,88E+08 1,06E+08 Bacillus subtilis 1,18E+08 7,10E+07 Azospirillum brasilense 1,81E+07 1,58E+07 Bradyrhizobium japonicum 1,03E+08 5,18E+07 Trichoderma harzianum 1,40E+08 1,09E+08 Penicillium bilaiae 4,23E+07 2,81E+07 CFU count confirmed that each of the selected micro-organism strains could be cultivated on HC-C to industrially relevant concentrations (Table 3), even Bacillus subtilis and Azospirillum brasilense, which did not show visual signs of growth. No contamination was observed on the CFU count agar plates. Example 3: Microbial growth on hydrochar and process water versus peat Materials and methods: Hydrochar was produced from pig manure (HC-C) as described in Examples 1 and 2. Using chamber filter press filtration, the slurry after hydrothermal carbonization was separated into a (wet) hydrochar and process water fraction. As a reference material, blonde peat moss from Baltic origin (Novabalt) was used. The bacterial strain Bradyrhizobium japonicum (LMG 4252) and the fungal strain Trichoderma harzianum (MUCL 22194) from the Belgium Coordinated Collections of Microorganisms (BCCM) were used. All strains were revitalized and grown in yeast mannitol broth (YMB) medium at 25°C in shake flasks, thereby obtaining a liquid inoculum. The concentration of colony forming units in the liquid inoculum was quantified through a CFU count. In a laminar air flow cabinet, one mL of the liquid inoculum was diluted to 50 mL in sterile saline solution (0,8% NaCl). Wet hydrochar (HC-C; 100 g dry matter) and peat (100 g dry matter) were inoculated with the diluted inoculum to ensure good distribution of inoculum throughout the material. All materials were adjusted to a moisture content of 40% with reverse osmosis water. The materials were aerobically incubated in a sterile environment, to perform a solid state fermentation process. After 7 days the microbial growth was quantified by resuspending the fermented hydrochar and peat in sterile physiological water (0,8% NaCl), and a dilution series from 10-4 to 10-10 was prepared in triplicate. The number of colony forming units (CFU) in the dilution series was determined by plating on YMA plates. Results: Table 4: Quantification of growth of B.japonicum and T.harzianum after 7 days on hydrochar from pig manure (HC-C) or peat. Micro-organism Substrate Average Standard (CFU / g) deviation Bradyrhizobium japonicum HC-C 1,32E+08 3.06E+07 Bradyrhizobium japonicum Peat NVC Trichoderma harzianum HC-C 1,36E+09 6,47E+08 Trichoderma harzianum Peat 9,42E+05 3,3E+05 The comparative analysis of microbial growth, measured in CFU / g, revealed a significantly higher concentration of microbial activity on fermented HC-C compared to fermented peat (Table 4 and Figure 2). There was an absence of growth on peat for Bradyrhizobium japonicum. These results indicate the potential of HC-C as a nutrient source for a broader spectrum of microorganisms as opposed to peat. Example 4: Shelf-life of fermented hydrochar Materials and methods: Hydrochar is produced from pig manure (HC-C) as described in Examples 1 and 2. Using chamber filter press filtration, the slurry after hydrothermal carbonization is separated into a (wet) hydrochar and process water fraction. A liquid inoculum of the bacterial strain Azospirillum brasilense (LMG 28319) and the fungal strain Trichoderma harzianum (BCCM: MUCL 22194) was prepared as described in Example 3. In a laminar airflow cabinet, one mL of the liquid inoculum was diluted to 50mL in sterile saline solution (0,8% NaCl). The diluted liquid inoculum was mixed with the wet hydrochar (HC-C; 100g dry matter) in duplicate. All samples were adjusted to a moisture content of 40% with reverse osmosis water. The samples were aerobically incubated in a sterile environment for 7 days to perform a solid state fermentation process (fermented hydrochar). After the drying, the material was distributed over a number of aluminium foil lined packages, which were split and stored at 4°C or 25°C to assess the shelf life. A commercially available reference of the fungal strain Trichoderma harzianum formulated on a mineral clay was included as reference. After 0, 1, 714, 28, 42 and 56 days of storage, the CFU count was measured by resuspending the fermented hydrochar and the reference in sterile physiological water (0,8% NaCl), and dilution series from 10-1 to 10-7 were prepared in triplicate. The number of colony forming units (CFU) in the dilution series is determined by plating on YMA plates. Results: Table 5: Quantification of growth of Trichoderma harzianum on fermented hydrochar (HC-C) and formulated with mineral clay (reference) at different storage temperatures. Time (Days) Sample / Storage 0 7 14 28 42 56 Temperature Colony forming units (CFU / g) T.harzianum (SSF-HC) / 4°C 3,28E+08 6,62E+08 5,73E+08 3,63E+08 1,53E+08 2,51E+08 Reference / 4°C5,26E+07 3,51E+07 4,95E+07 2,70E+08 4,18E+07 5,44E+07 T.harzianum in SSF (HC) / 3,28E+08 2,93E+08 2,83E+08 1,12E+08 1,37E+08 4,68E+07 25°C Reference / 25°C5,26E+07 1,05E+07 1,63E+07 1,79E+07 3,37E+07 2,63E+06 Table 5 shows that T.harzianum fermented on hydrochar had an improved shelf-life, resulting in a higher CFU count after storage, compared to the commercial reference of a formulation with mineral clay, at different storage temperatures. Table 6: Quantification of growth of Azospirillum brasilense on fermented hydrochar (HC-C) at different storage temperatures. Time (Days) Sample / Storage 0 7 14 28 42 56 Temperature Colony forming units (CFU / g) A.brasilense (SSF-HC) / 1,03E+08 1,08E+08 9,41E+07 4,44E+07 5,75E+07 8,40E+07 4°C A.brasilense (SSF-HC) / 1,03E+08 1,86E+08 4,46E+07 1,52E+08 3,02E+07 6,03E+07 25°C Table 6 shows that the population of A. brasilense in fermented hydrochar exhibits an enhanced shelf life, leading to a higher CFU count after storage at both 4°C and 25°C, in comparison to formulating A. brasilense with PBS, wherein respectively, 5.5E+07 CFU / mL and 1.77E+05 CFU / mL were counted after 60 days of storage at 4°C and 28°C (Fig.2A and 2C in Cortés-Patiño and Bonilla (2015) African Journal of Biotechnology 14:2547-2553). Example 5: Resistance of fermented hydrochar against desiccation and oxidative stress Materials and methods: Hydrochar is produced from pig manure (HC-C) as described in Examples 1 and 2. Using chamber filter press filtration, the slurry after hydrothermal carbonization is separated into a (wet) hydrochar and process water fraction. A liquid inoculum of the bacterial strain Bacillus subtilis (BCCM: LMG 23370) and the fungal strain Trichoderma harzianum (BCCM: MUCL 22194) is prepared as described in Example 3. One mL of the liquid inoculum is diluted to 50mL in sterile saline solution (0,8% NaCl). The diluted liquid inoculum is mixed with wet hydrochar (HC-C; 100g dry matter) in duplicate. All materials are adjusted to a moisture content of 40% with reverse osmosis water. One sample is immediately placed in a desiccator and allowed to air dry at 25°C (micro-organism formulated on hydrochar). The other is aerobically incubated in a sterile environment for 7 days, to perform a solid state fermentation process (fermented hydrochar). After the drying (micro-organism formulated on hydrochar) or the solid state fermentation (fermented hydrochar) the material is distributed over a number of air and water permeable packages, which are stored at 25°C, to assess the shelf-life under desiccation and oxidative stress. After 0, 1, 714, 28 and 56 days of storage, the CFU count is measured by resuspending the fermented hydrochar and the micro-organism formulated with hydrochar in sterile physiological water (0,8% NaCl), and a dilution series from 10-4 to 10-10 is prepared in triplicate. The number of colony forming units (CFU) in the dilution series is determined by plating on YMA plates. Results: A higher CFU count in fermented hydrochar is obtained after environmental stress during storage. Example 6: Resistance of contamination of fermented hydrochar Materials and methods: Hydrocharwas produced from pig manure (HC-C) as described in Examples 1 and 2. Using chamber filter press filtration, the slurry after hydrothermal carbonization was separated into a (wet) hydrochar and process water fraction. A liquid inoculum of the fungal strain Trichoderma harzianum (BCCM: MUCL 22194) was prepared as described in Example 3. In a laminar air flow cabinet, one mL of the liquid inoculum was diluted to 50mL in sterile saline solution (0,8% NaCl). The diluted liquid inoculum was mixed with wet hydrochar (HC-C; 100g dry matter). The material was adjusted to a moisture content of 40% with reverse osmosis water, and aerobically incubated in a sterile environment for 7 days, to perform a solid state fermentation process (fermented hydrochar). The other (control) sample was wet hydrochar (HC-C; 100g dry matter), which was not inoculated or fermented with microorganisms, and adjusted to a moisture content of 40% with reverse osmosis water (control). The non-sterile samples, both the fermented hydrochar and control were exposed to the outside air for 2 hours, to allow for contamination by micro-organisms. After two hours, both materials were again incubated for 7 days at 25°C in a sterile environment. Microbial growth was visually observed and quantified, by resuspending the fermented hydrochar and the wet hydrochar (control) in sterile physiological water (0,8% NaCl), and a dilution series from 10-1 to 10-7 was prepared in triplicate. The number of colony forming units (CFU) in the dilution series was determined by plating on nutrient agar (NA) plates. Results: There was a significant decrease in the growth of contaminating micro-organisms on the fermented hydrochar compared to the control hydrochar (Fig.3). Our analysis revealed that the only microbial species in the fermented hydrochar, both when it was exposed to the outside air (non-sterile) or not (sterile) prior to fermentation, was Trichoderma harzianum (Table 7 and Figure 3). These observations suggests the effectiveness of the fermentation process by the desired microorganism in creating an environment less conducive to the growth of undesired microorganisms. Table 7: Quantification of growth of T.harzianum after 7 days on control and fermented hydrochar from pig manure (HC-C). % of Sample Average Standard T.harzianum (CFU / g) deviation in the samples Control HC 0 0 Non-sterile Control HC 0 0 Fermented HC 1,65E+09 5,85E+08 100 Non-sterile Fermented HC 2,65E+08 1,36E+08 100 Example 7: Submerged fermentation on hydrochar Materials and methods: Hydrochar was produced from pig manure (HC-C) as described in Examples 1 and 2. A liquid inoculum of the bacterial strain Azospirillum brasilense (LMG 28319) and the fungal strain Trichoderma harzianum (BCCM: MUCL 22194) was prepared as described in Example 3. Four different liquid fermentation media were prepared and sterilized by autoclaving (121°C for 15 minutes): ^ 50 g HC-C (dried at 105°C) diluted to 1L with saline solution (0,8% NaCl) (HC-C) ^ 50 g Process water diluted to 1L with diluted to 1L with saline solution (0,8% NaCl) (PW) ` ^ 50 g HC-C (dried at 105°C) and 50 g process water diluted to 1L with saline solution (0,8% NaCl) (HC-C + PW) ^ 1L saline solution (0,8% NaCl) – (control) 100 mL of the fermentation media was distributed in 250 mL shake flasks in triplicate. The shake flasks were inoculated with 1mL of the liquid inoculum and incubated in a shaker-incubator at 25°C for 3 days at 150 rpm. A. brasilense growth was quantified by preforming a CFU count (diluted in saline water and plated on YMA medium) for each of the shake flasks. For T. harzianum, the growth in each liquid fermentation condition was quantified by measuring the dry mass of its mycelium, which is typically produced in liquid media fermentation. The mycelial mat was filtered on filter paper (e.g., Whatman No.1) and dried at 50°C overnight. Results: Table 8: Quantification of growth of A.brasilense (CFU) in the different liquid fermentation media tested. Liquid Average Standard deviation fermentation media (CFU / g) Control 7,40E+05 1,22E+05 HC-C 2,28E+07 1,28E+07 PW 4,30E+07 1,43E+07 HC-C+PW 1,49E+08 3,87E+07 Table 8 shows that the highest population of A.brasilense was in the liquid fermentation that includes HC-C and PW as nutrient sources for the microorganism. Table 9: Mycelium dry mass of T.harzianum growth in the different liquid fermentation media tested. Liquid Dry mass fermentation media (g) Control 0,023 HC-C 0,093 PW 0,459 HC-C+PW 0,878 Table 9 illustrates that the most abundant population of T. harzianum was observed in the liquid fermentation incorporating HC-C and PW as nutritional sources for the microorganism. Example 8: Microbial growth on hydrochar and process water (without agar) Materials and methods: Hydrochar was produced from pig manure (HC-C) as described in Examples 1 and 2. The bacterial strains Azotobacter chroococcum (LMG 3852) and Pseudomonas fluorescens (LMG 1244), and the fungal strain Beauveria bassiana (IHEM 3558) were obtained from the Belgium Coordinated Collections of Microorganisms (BCCM). The HC-C (containing approximately 50% by weight moisture (process water)) was distributed in microbox containers (50 g of dry matter each). These microboxes were sterilized at 121°C for 15 minutes. Within a laminar airflow cabinet, an inoculation loop retrieved from a microbial culture thriving on a YMA agar plate was diluted in 50 mL of process water (PW) and subsequently introduced into the materials. The microboxes with the inoculated HC-C were incubated at respectively, 28°C and 25°C for bacterial and fungal strains, and a solid state fermentation process was performed. After 7 days, the growth was assessed visually and scored. For the HC-C samples, the growth was quantified by resuspending the dried material in sterile physiological water (0,8% NaCl), and dilution series from 10-1 to 10-7 were prepared in triplicate. The number of colony forming units (CFU) in the dilution series was determined by plating on YMA plates. Results: Table 10: Quantification of growth of selected micro-organisms after 7 days on hydrochar from pig manure (HC-C). Micro-organism Average Standard (CFU / g) deviation Azotobacter chroococcum 1,10E+07 1,91E+06 Pseudomonas fluorescens 9,52E+08 5,52E+07 Beauveria bassiana 3,33E+08 7,7E+07 The CFU quantification validated the successful cultivation of Azotobacter chroococcum, Pseudomonas fluorescens and Beauveria bassiana on HC-C, with concentrations reaching industrial relevance (Table 10). Notably, no instances of contamination were observed on the CFU count agar plates. Example 9: Importance of maintaining sterile workflow Materials and methods: Hydrochar was produced from pig manure (HC-C) as described in Examples 1 and 2. Using chamber filter press filtration, the slurry after hydrothermal carbonization was separated into a (wet) hydrochar and process water fraction. A liquid inoculum of the fungal strain Trichoderma harzianum (BCCM: MUCL 22194) was prepared as described in Example 3. In a laminar air flow cabinet, one mL of the liquid inoculum was diluted to 50mL in sterile saline solution (0,8% NaCl). The diluted liquid inoculum was mixed with wet hydrochar (HC-C; 100g dry matter). The material was adjusted to a moisture content of 40% with reverse osmosis water. The other (control) sample contained the same composition but the steps were performed in non-sterile conditions, outside the laminar air flow cabinet. Both samples were aerobically incubated in a sterile environment for 7 days to perform a solid state fermentation process (fermented hydrochar). Microbial growth was visually observed and quantified, by resuspending both samples in sterile physiological water (0,8% NaCl), and a dilution series from 10-1 to 10-7 was prepared in triplicate. The number of colony forming units (CFU) in the dilution series was determined by plating YMA plates. Results: Table 11: Measurement of the growth of Trichoderma harzianum conducted after 7 days on fermented hydrochar from pig manure (HC-C), with assessments performed under sterile or non- sterile conditions. Average per % of Workflow condition sample of Standard T.harzianum T.harzianum deviation in the (CFU / g) samples Sterile 1,36E+09 6,47E+08 100 Non-sterile 5,16E+06 3,66E+06 5 T. harzianum was detectable in the sample processed outside the laminar airflow cabinet, although in a lower population, due to the growth of undesired, contaminant micro-organisms (Figure 4).

Claims

CLAIMS 1. A method for producing a microbial and nutrient delivery system (113), said method comprising: - providing a biomass (101); - subjecting the biomass (101) to a hydrothermal carbonization process (HTC) (10) to form a slurry (103) comprising a hydrochar and HTC process water; - cooling (20) the slurry (103) to a temperature suitable for growth of a microbial inoculant; - inoculating the cooled slurry (105) with the microbial inoculant (109); - subjecting the inoculated slurry to a fermentation process (40) to form a fermentation product (111); and - obtaining or recovering (50) the microbial and nutrient delivery system (113) from the fermentation product (111), wherein the cooling step and the inoculation step are conducted under sterile conditions.

2. The method according to claim 1, further comprising a step of reducing (30) the HTC process water content of the slurry (103, 105) to form a wet hydrochar (106) before inoculation with the microbial inoculant, wherein said step of reducing (30) the HTC process water content of the slurry (103, 105) is conducted under sterile conditions.

3. The method according to claim 2, wherein the process water content of the slurry is reduced by a mechanical process (30), preferably a solid-liquid separation such as a decantation, a centrifugation or a filtration.

4. The method according to any one of claims 1 to 3, wherein the fermentation is conducted at a temperature below 85°C, preferably below 75°C, more preferably at a temperature between 15°C and 70°C or between 15°C and 65°C or between 15°C and 60°C.

5. The method according to any one of claims 1 to 4, wherein the fermentation process (40) is a submerged fermentation.

6. The method according to any one of claims 2 to 4, wherein the fermentation process (40) is a solid- state fermentation.

7. The method according to any one of claims 1 to 6, wherein the fermentation process is a single- stage fermentation.

8. The method according to claim 7, wherein the fermentation is conducted under sterile conditions.

9. The method according to any one of claims 1 to 6, wherein the fermentation process is a multi- stage fermentation such as a two-step fermentation wherein the fermentation process comprises fermenting the inoculated slurry to form a first fermentation product, followed by inoculating asecond slurry formed in the HTC process with said first fermentation product and fermenting the inoculated second slurry to form the (second) fermentation product.

10. The method according to claim 9, wherein the fermentation of the (first) slurry inoculated with the microbial inoculant is conducted under sterile conditions.

11. The method according to any one of claims 1 to 10, wherein the hydrothermal carbonization process (10) is performed at a temperature of between about 180°C and about 250°C and a pressure of between about 10 bar and 50 bar for at least 30 minutes.

12. The method according to any one of claims 1 to 11, wherein heat released during the cooling step (20) is used for the hydrothermal carbonization process (10).

13. The method according to any one of claims 1 to 12, wherein the biomass (101) is a wet biomass having a water content of between 10% and 95% by weight, preferably between 10% and 90% by weight.

14. The method according to any one of claims 1 to 13, wherein the biomass (101) is selected from a food residue, an agricultural residue, an animal by-product, or any combination thereof, preferably an animal by-product such as manure.

15. The method according to any one of claims 1 to 14, wherein the recovery step (50) comprises any one or more of: -separating the fermentation product in a solid-rich fraction and a liquid fraction; - drying the fermentation product or a solid-rich fraction of the fermentation product; and - a processing step selected from the group consisting of: grinding, milling, pelletizing, extruding and a micro-granulation process.

16. The method according to any one of claims 1 to 15, wherein the recovery step (50) comprises a step of separating spores from the fermentation product, wherein the microbial inoculant comprises spore-forming micro-organisms.

17. The method according to any one of claims 1 to 16, wherein the microbial inoculant (109) comprises one or more bacteria which belong to a genus selected from the group consisting of Azotobacter, Streptomyces, Bacillus, Azospirillum and Bradyrhizobium and / or one or more filamentous fungi which belong to a genus selected from the group consisting of Beauveria, Trichoderma and Penicillium.

18. A microbial and nutrient delivery system obtainable by a method according to any one of claims 1 to 17, the system comprising: - a fermented hydrochar; - microorganisms adhered to surfaces or in pores of the fermented hydrochar; and- optionally one or more auxiliary agents selected from a solvent, a carrier, a binder, a surfactant, a sticker, a tackifier, an antifreeze agent, a thickener, a buffering agent, an antifoaming agent, an antioxidant, a preservative, a stabilizer, an aroma and a colorant.

19. Use of a microbial and nutrient delivery system according to claim 18 as a biostimulant, preferably as a biofertilizer or a biocontrol agent.

20. Use of a microbial and nutrient delivery system according to claim 18 as a bioremediation agent.

21. Use of a microbial and nutrient delivery system according to claim 18 as a microbial inoculant such as a microbial inoculant for an anaerobic digester, for a septic system or for a water treatment system, or a microbial inoculant in a method according to any one of claims 1 to 17.

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