Titolo della tesi: Optimisation of biotechnological processes for polyhydroxyalkanoates production from food industry by-products
This thesis is part of the European Horizon 2020 project, entitled “USABLE Packaging” (Unlocking the potential of Sustainable BiodegredabLe Packaging, BBI JU-Project ID: 836884). The aim of this project was to develop plastic materials that are biodegradable and bio-based, and that does not compete with the food chain or cause land use problems, thus implementing a correct circular economy in the plastics sector.
To date, the continuous impoverishment of the land, the increase in atmospheric emissions and, in general, the increase in pollution in all environmental sectors, has generated the interest of the scientific, social and political world in finding increasingly green and eco-sustainable solutions. Among the solutions proposed by the new circular economy model is undoubtedly the replacement of some non-recyclable and non-biodegradable materials with more eco-friendly alternatives. One of the most widely used materials in the world is plastic, a material that is as useful and versatile as it is harmful to the environment and human health if not disposal correctly at the end-of-life. Therefore, replacing fuel-based plastics with bio-based and biodegradable products would be beneficial on several fronts. Indeed, this would reduce the volume of waste dumped into the environment, the amount of greenhouse gases released into the atmosphere and all the environmental risks associated with these issues. Thus, biopolymers have emerged as a great alternative, as they come from renewable sources and can be biodegradable. Among the others, polyhydroxyalkanoates (PHAs) are one of the most promising bioplastics, as they are synthesised by microbial fermentation of renewable resources such as agro-industrial and urban waste, are biodegradable, biocompatible, non-toxic, with properties comparable to their petroleum-based counterparts. Thanks to its characteristics, PHA can be used for a wide range of applications, but above all it can overcome the problems caused especially by non-biodegradable packaging.
In this context, the general objective of this PhD thesis was:
The optimisation of the PHA production process by means of mixed microbial cultures and purple bacteria, testing different operating conditions to obtain a polymer while valorizing food industry by-products.
To achieve this goal, specific objectives had to be realized:
1 Implementing sustainable production of volatile fatty acids as precursors in the production of PHA from MMC.
1.1 Evaluation of fermentation degree of food industry by-products through acidogenic
fermentation process. Study performed through batch tests and semi-continuous stirred tank reactor.
2 Management of a sequencing batch reactor for the PHA-MMC production.
2.2 Study of the Influence of the Organic Loading Rate applied and of the cycle length using a synthetic acids mixture as substrate in the PHA-MMC production through a sequencing batch reactor in laboratory scale.
2.3 Influence of real feed, obtained from the acidogenic fermentation semi-continuous test, on selected biomass at different OLRs during the accumulation tests.
2.4 PHA-MMC production operated under different feeding conditions.
3 PHA production from photosynthetic micro culture and from phototrophic purple bacteria.
3.2 Study of permanent Feast regime, through a laboratory scale SBR, using real feed as a substrate in purple bacteria-PHA production.