Inherent Safe and Sustainable Process Design applied to Polyhydroxyalkanoates Bioproduction from Wastes

Nowadays, the environmental impact deriving from plastic waste represents a global challenge due to its persistence in natural ecosystems, directly associated to its difficulty in disposal. These issues heightened the urgency to find sustainable alternatives to conventional plastics. Polyhydroxyalkanoates offer a promising solution as biodegradable biopolymers, but their large-scale introduction is hindered by high production costs, primarily due to the use of food-based carbon sources such as glucose, which account for around 50% of the total expenses. This issue can be addressed through the use of alternative carbon substrates like agro-food wastes, which are able to lower the overall production costs and reduce the waste accumulation, becoming powerful resources and introducing polyhydroxyalkanoates production within the biorefinery concept. With these regards, the present work focused on the development of an inherent safe and economically sustainable design of polyhydroxyalkanoates, basing on preliminary results obtained at a laboratory scale. Indeed, during the first step of this research, the polyhydroxyalkanoates bioproduction in Cupriavidus necator DSM 545, through the use of spent coffee grounds oil as alternative carbon substrate, was investigated. Sequential spent coffee grounds pre-treatments were initially performed demonstrating the potential of this residue, allowing, at the same time, the extraction of oil and the recovery of commercially valuable compounds like caffeine and polyphenols, addressed to several applications, including food and pharmaceuticals sectors. The obtained results, along with those achieved for the spent coffee grounds powder characterization in terms of flammability and explosivity properties, allowed to perform an early-stage inherent safety design and economic analysis of the process. Even if conventional carbon substrates like fructose represent inherently safer solutions than biomass wastes since they do not comprise additional pre-treatment steps, the latter present the potentialities to obtain both appreciable polyhydroxyalkanoates yields and high-added value subproducts, minimizing the overall biopolymer production costs. Furthermore, considering a trade-off between technical feasibility, safety, and economical sustainability at the basis of the technological transfer of a chemical process, the economic viability of the polyhydroxyalkanoates production in the case spent coffee grounds were used as carbon substrate was verified. In summary, the topics addressed by this thesis work are organized and subdivided into the following chapters: Chapter 1 – State of the art. This section was dedicated to a literature review about the main existing inherent safety tools and methodologies, with a focus on the index-based approaches. A second part was dedicated to review the main polyhydroxyalkanoates production processes and conditions starting from wastes as carbon substrates. Chapter 2 – Polyhydroxyalkanoates production from spent coffee grounds: an experimental study. This section focused on an experimental feasibility study concerning the polyhydroxyalkanoates production from spent coffee grounds, properly pre-treated by sequential extraction steps. Chapter 3 – Study of the flammability and explosiveness properties of spent coffee grounds. This section concerned the flammability and explosiveness characterization of spent coffee grounds powders, both as such and pre-treated by sequential extraction steps. Chapter 4 – Inherent safety development applied to polyhydroxyalkanoates production from spent coffee grounds. This section was addressed to an inherent safety design of each polyhydroxyalkanoates production step: bacterium and carbon source selection, pre-treatment of the carbon source, and downstream processing. Chapter 5 – Polyhydroxyalkanoates production from spent coffee grounds and glucose: an economic comparison. This section focused on an economic comparison between two polyhydroxyalkanoates process routes options, based on the use of spent coffee grounds or glucose as carbon feedstocks.