Estudio comparativo del proceso de compostaje a escala industrialAnálisis metagenómico y vinculación con los parámetros críticos de control del proceso

Abstract

The environmental collapse caused by numerous anthropogenic activities has resulted in the massive accumulation of waste in landfills or in the uncontrolled incineration of the same. The suitable management of this type of waste implies adaptation to a circular economy model. This type of model seeks the conservation of natural resources, the maintenance of biodiversity, recycling and reuse of waste, turning them into products. Most of this type of waste, biodegradable waste, can have a second useful life. Among the most successful alternatives for the biotransformation of this type of waste, composting stands out for adapting to current concepts of sustainability and bioeconomy, considering it an ecological process that does not imply high costs.Composting is a process of aerobic biotransformation of organic matter during which various thermal phases follow, characterized mainly by the biotransformation of organic matter thanks to the action of different microbial populations. The result of this process is a stable and mature product, compost, whose main application is made as a humic amendment in agriculture. In Spain, its use is legislated, as well as the basic physical-chemical characteristics for its commercialization. However, despitethe suitability of the process, its control is complicated when it comes to making the leap to an industrial scale. The main problem is that the work volumes, the operational conditions, and the raw materials are not the same in the different companies dedicated to the management of organic waste through composting. Therefore, it is even more difficult to find some type of physical-chemical or biological indicatorsthat allow evaluating the development of processes a prioriso heterogeneous.The work presented in this Doctoral Thesis Memory has been based on the in-depth study of 15 composting processes on an industrial scale, also taking into account the enormous diversity in regard to the original raw materials (Vegetable Residue, Solid Residues Urban, Sewage Sludge, Agro-Food Waste and Alpeorujo). This study was carried out from a physical-chemical point of view, analyzing multiple parameters related to the carbon and nitrogen cycle, as well as from a biological point of view, evaluating various enzymaticand biodiversity indicators. In this case, the metagenomic analysis of the products obtained from the 15 evaluated processes stands out.The resultsrevealed very different physical-chemical and enzymatic profiles, as well as different degrees of humification according to the type of process and source material, which suggested that the transformation pathway of the different carbon and nitrogen fractions could be unique to each process and dependent of raw materials. Even so, some parameters closely related to the carbon cycle, such as lignocellulosic fractions, amylolytic and β-glucosidaseactivity, together with some humification indices (HR and CHA/ CFA) were positioned as good indicators of the optimal evolution of a compostingprocess, as they showedsimilar trends over time. In addition, thanks to the metagenomic analysis carried out, important relationships were established between the Chao1 and Shannon biodiversity indices, and certain parameters related to the maturity, stability and toxicity of the samples, such as nitrification index, humification rate, content of phenolic compounds, germination rate or oxygen consumption.In conclusion, despite the heterogeneity and exclusivity of the composting processes studied, it can be affirmed that microorganisms, through different mechanisms, are capable of carrying out adequate processes of biotransformation of organic matter, obtaining products that comply, in terms general, with agronomic quality standards. The connection established between parametersof a very different nature represents an advance in the microbial knowledge of composting and provides a new perspective for better management and control of the process on an industrial scale.