Development of a pilot scale process for polyhydroxyalkanoates production from food waste

The focus of this thesis was on investigation of culture selection step for PHA production by using food waste as no-cost feedstock with mixed microbial cultures (MMC). PHAs (polyhydroxyalkanoates) are biologically synthesized polymers that can be produced from renewable resources and are completely biodegradable. Because at the present times the demand of alternatives to replace conventional plastics is rapidly growing due to environmental issues, the possibility to produce PHAs on a large scale by using waste materials as carbon source is considered to be very attractive both from an environmental and economic point of view. The experimental work was developed during a traineeship carried out at the Laboratory of Biochemical and Chemical Engineering of NOVA School of Science and Technology. The selection step was conducted through the employment of a sequential batch reactor (SBR) at pilot scale and had the main goal of getting a high performance process while ensuring a satisfying reactor stability. Operations were performed using fermented food waste provided by ValorSul. ValorSul is a Portuguese company which is responsible for the management of urban solid waste produced in five municipalities in the area of Lisbon. In particular, the aim was to assess selection step outcomes while operating with a high OLR (organic loading rate). Few studies on MMC culture selection step conducted applying high OLR values are currently reported in literature. Two different SBR operating conditions were investigated and compared in this thesis work: HRT (hydraulic retention time) equal to 1 day in a first phase and HRT equal to 0.66 day in a second phase. After several cycles, a PHA-rich culture was selected from the SBR and it was inoculated in fed-batch lab scale reactors during accumulation tests with the main aim of evaluating the maximum reachable PHA content and PHA productivity for both two operating conditions configurations.