Abstract
In the coming years, the world will grapple with significant societal challenges primarily stemming from the consequences of climate change and the inefficient exploitation of natural resources. Furthermore, we are witnessing exponential population growth. This upward trajectory underscores the urgent necessity for more efficient management of our natural resources, encompassing the valorization of waste products and the substantial reduction of both agri-food losses and waste. The reduction of waste presents substantial environmental and economic advantages. One of the most promising approaches in this regard is the conversion of agri-food by-products and waste into edible and reusable materials. However, it is crucial to recognize that these types of by-products and treated waste may contain and interact with emerging contaminants such as antibiotics, microplastics, or potential pathogens, which pose health risks to consumers. Therefore, ensuring the quality and safety of these products is paramount to fully realize the benefits of this valorization strategy. While there is a substantial body of work focused on the exploitation of agri-food by-products, it is important to note that safety assessments, including microbiological evaluations and the determination of toxic contaminants, have been conducted in only a limited number of studies. A highly promising area of research, facilitated by newly available methodologies, is the utilization of total bacterial communities as indicators of environmental stress and pollution. Despite the global use of various bioindicators, the application of bacteria in this context remains relatively limited, primarily due to various theoretical and conceptual constraints that need to be addressed. In this context, guided by the One Health perspective, this thesis encompasses several interconnected studies. To begin, the primary focus was the examination of the relationships between the use of treated food-agricultural products and emerging contaminants, such as plastic pollutants, antibiotics, and heavy metals in the environment following irrigation, amendment, and fertilization practices, all viewed through the lens of the One Health approach. In a perspective-style review, we synthesized the existing knowledge on this subject and proposed a more effective One Health policy to address the challenges explored (Paper I). Subsequently, a comparative microbial analysis was conducted between a traditional wastewater treatment system and a microalgal consortium-based system using shotgun metagenomics. The new method demonstrated enhanced removal of microbial pathogens, an increased presence of photosynthetic and denitrifying microorganisms, and a reduced likelihood of gas emissions. Additionally, the discovery of anammox and nitrification bacteria highlighted alternative pathways for nitrogen treatment in the consortium-based system (Paper II). The third study involved monitoring the structure and dynamics of bacterial communities in a full-scale two-stage anaerobic digestion (AD) plant. This monitoring occurred as the plant transitioned from utilizing energy crops as feedstock to agricultural waste. Throughout the feedstock change, the process remained stable, resulting in shifts in bacterial populations associated with various functional groups. These shifts exhibited distinctive adaptation patterns in the two separate stages of the plant (Paper III). Next, a study was conducted with the primary objective of assessing the feasibility of using treated wastewater in the Southern Italy and investigating the presence of soil microorganisms capable of withstanding and potentially degrading emerging micropollutants, such as antibiotics (including ciprofloxacin, vancomycin, and cefotaxime). The study demonstrated the persistence of these pollutants in the environment even after treatment. Isolation, Minimum Inhibitory Concentrations (MICs), and taxonomic identification through sequencing revealed the presence of resilient strains for all the tested contaminants (Paper IV). To address future scientific perspectives in the field, a three-year project was undertaken to explore the connections between plastic pollutants and antibiotic resistance in laboratory-scale microcosms composed of agricultural products, specifically the same treated wastewater/sediments for irrigation purposes as characterized in the previous study, vermicompost, and manure. Functional, metabolic, and taxonomic changes in the microbiota were assessed using a metagenomic approach (Paper V).