Industrial composting of low carbon/nitrogen ratio mixtures of agri-food waste and impact on compost quality.

The agri-food waste (AW) require amendments for composting to adjust nutritional and physicochemical deficiencies. The theoretical mixtures formulation is difficult to reach on an industrial scale. The main objective of this work was to evaluate to what extent the composition of AW-based mixtures determines the quality of the final compost produced at the industrial scale. Raw materials having the same AW share characteristics, irrespectively of the amendments added, but their compost were different. All the materials were biological stable at the cooling phase, and mature enough at the end, although the degree of humification did not match with the absence of phytotoxicity. The final compost had sufficient quality even though the AW-based raw materials have a low C/N ratio (<20) and other characteristics such as high electrical conductivity (13 mS·cm-1) and pH (<8.5) that are unfavorable for composting. The management operations during industrial composting correct the deficiencies of raw materials.

Integral approach using bacterial microbiome to stabilize municipal solid waste.

Biological transformation of municipal solid waste is an environment-friendly management strategy against recalcitrant residues. The bacterial biome that inhabit said residues are responsible of decomposing both simple and complex materials. For this reason, processes such as composting, which favor the acceleration of the transformation of organic matter, can contribute to the degradation of municipal solid waste. Not only as mere fertilizer for crops, but also as methods for the recovery of solid waste. However, the control of the conditions necessary to achieve an optimal process on an industrial scale is a great concern. Thus, the aim of this work focuses on the characterization of the bacterial microbiome on three municipal solid waste facilities in order to deepen the role of microorganisms in the state of the final product obtained. For it, an intensive metagenomic analysis as well as a battery of physicochemical determinations were carried out. The lack of adequate thermophilic phases was decisive in finding certain bacterial genera, such as Lactobacillus, which was significant through these processes. Biodiversity did not follow a common pattern in the three processes, neither in abundance nor in richness but, in general, it was greater during the bio-oxidative stage. Despite the different trend in terms of the degradation of carbon fractions in these wastes, at the end of the biodegradation treatments, a sufficient degree of bioestabilization of the organic matter was reached. The results offer the opportunity to obtain a level of detail unprecedented of the structure, dynamics and function of the bacterial community in real conditions, without the control offered by laboratory conditions or pilot plants.