From collection to myco-reactor: filamentous fungi for bioremediation

Despite the water is present on Earth planet in a large amount, only a small fraction of it can beexploited by living organisms. Mankind use much more water than other living beings because, inaddition to its survival, it is used for agriculture, breeding, industry and as an energy source. Research on new and different water purification techniques is currently one of the unsolved points to reducethe human environmental footprint. In general, water or any polluted matrix can be purified with different methods (chemical, physical, biological), but none of them fully satisfies the efficiency andsustainability criteria. In the last thirty years, the research in the field of eco-friendly technologies is increasing: among thevarious purification processes, bioremediation is giving excellent results. This system aims to reducepollutants in the various environmental matrices, exploiting the metabolic capabilities of livingorganisms, such as bacteria, fungi and plants, to degrade them into simple products without usingchemical substances or expensive and complex treatment plants. The bioremediation that uses fungi for the treatment of polluted environmental matrices is called mycoremediation. Fungi are organisms suitable to be used in bioremediation processes because their metabolism allows them to grow andsurvive in the presence of toxic substances and in extreme conditions that are not tolerated by mostof the other organisms. One of the advantages of using fungi in bioremediation processes is the possibility of using them evenwhen the concentration and bioavailability of the pollutants is very low in the substrates, as in thecase of drugs for human and veterinary use dispersed in wastewater. Another advantage related to filamentous fungi - on which this thesis will focus - is their hyphal structure which greatly increasestheir distribution and colonization capacities. Several filamentous fungi are able to act on recalcitrantorganic pollutants: from chlorophenols to dioxins, from toluene to hydrocarbons. They are not alwaysable to completely degrade them, but they can at least transform them into less toxic compounds. Theability to metabolize organic compounds that are very different from each other in chemical structureis due to the low specificity of many fungal enzymes. The characteristics of the fungi are not only species specific, but often strains specific, which is why the research and identification of new strains is fundamental for mycoremediation. It is precisely fromthe experiments carried out on the strains kept in the collections and isolated from different environments such as extreme ones that new treatments can be developed. Nowadays, theenvironments that can be defined as extreme are no longer just the sea depths or Arctic glaciers, but also the production and wastewater treatment plants. Although they are ideal environments for theselection of new fungal strains, research continues to focus only on bacterial communities, leaving the fungal component practically unexplored. Another unexplored field is the application of fungal strains with known metabolic abilities in treatment plants at laboratory scale and, above all, at industrial level. A type of plant that may be suitable for filamentous fungi, of which very few examples are found in literature today, is that of aerated membrane bioreactors (MABR). This is a promising technology for the treatment of recalcitrant substances in an aqueous environment, based on the transfer of a gas (e.g. air or oxygen, but in principle also other gases can be used) across a membrane to a biofilm in contact with a liquid phase containing the substrates to be metabolized. The use of filamentous fungi in MABR is currently limited mainly to biotransformation and industrial processes for the production of enzymes and bioproducts. Thanks to the multidisciplinary research approach, carried out between the mycology laboratory (DiSTAV - Department of Earth, Environmental and Life Sciences) and that of industrial chemistry (DCCI - Department of Chemistry and Industrial Chemistry) of the University of Genoa, it was possible to study the filamentous fungi isolated from extreme environments and to apply the strains present in the mycological collection of the laboratory (ColD - Collection of DiSTAV) for the development of this type of implant. In summary, the purpose of the work was to develop, expand and test protocols in the field of mycoremediation such as MABR, with particular attention to the isolation, conservation and use of fungal strains suitable for the treatment of polluted matrices. The thesis is structured in five chapters. In the first chapter the techniques used by the mycology laboratories to isolate and identify the filamentous fungi found in extreme or polluted environments are discussed. In the second and third chapters two case studies concerning isolation and identification of filamentous fungi from landfill leachate and from different ripening stages of a composting plant are discussed, as a starting point for future applications of native strains to treat complex wastewater. In the fourth chapter the plants and the diversity of aerobic biological treatments are presented, with particular attention to the methods for supplying oxygen and substrate. The chapter concludes with the types of bioreactor developed with filamentous fungi. The last chapter describes the development of an aerated membrane bioreactor with a model filamentous fungus for future use in wastewater treatment.