The production of biopolymer from wastewater treatment

The growing environmental challenges related to plastic pollution and waterscarcity have prompted the search for sustainable technologies that promoteresource recovery and minimize environmental impact. Plastic pollution,driven by extraordinary growth in plastic production and inadequate wastemanagement practices, contaminates marine ecosystems, freshwater sourcesand the atmosphere. Conventional petroleum-based plastic materials use isfostered by their high resistance properties, which caused their build-up inthe environment and fragmentation into microplastics, related to significantecological and health risks. Simultaneously, water scarcity affects billionsof people worldwide, exacerbated by climate change effects. Addressingthese challenges requires innovative approaches that reduce pollution andpromote efficient use of resources.In this scenario, polyhydroxyalkanoates (PHAs) have emerged as a potentialsolution to plastic pollution. PHAs are biopolymers produced bymicroorganisms as intracellular storage compounds when exposed tonutrient-limited conditions with excess carbon sources. Unlike conventionalplastics, PHAs are biodegradable and biocompatible; hence, they are anenvironment-friendly alternative which can contribute to reduce plasticpollution. Furthermore, PHAs can also be produced from renewablefeedstocks, like organic-rich wastes, which further provide a goodopportunity for their full integration into waste management.At the same time, wastewater treatment plants (WWTPs) have recentlyestablished as a potential solution to water scarcity. The treated wastewaterproduced often meets the legislative requirements for reuse in agriculture,thus fostering the development of efficient technologies aimed at improvingthe effluent water quality. In this context, one of the major drawbacks of wastewater treatment may become the key to facing the two environmentalchallenges in a single process. Waste-activated sludge (WAS) is the surplussludge produced during the wastewater treatment process. Due to theenvironmental hazards related to it, WAS treatment and management are aconsistent part of WWTP operation. However, the spread of the circularbioeconomy approach led to waste valorization into resources, whichallowed to exploit WAS as a substrate to produce PHA. The microorganismswithin the sludge can exploit the organic carbon to produce volatile fattyacids (VFAs) through acidogenic fermentation, which will further be usedto produce PHAs. This approach shaped the WWTPs into water resourcerecovery facilities (WRRFs) where wastewater treatment is a biorefinery tovalorize waste streams. However, compared to other waste feedstocks,WAS is characterized by low VFA production yield because of its complexnature and high stability, which led to its under-exploitation in PHAproduction.The activities related to this thesis were focused on the pilot-scale testingand optimization of different solutions to produce VFAs from WAS and usethem to produce PHA. The experimental activities were carried out in twodemonstration case studies of the EU Horizon 2020 project “Wider Uptakeof water-smart solutions”: the WRRF of the University of Palermo and theMarineo’s WWTP.The activities were focused on testing and optimize several pre-treatmentsto maximize VFAs production during WAS acidogenic fermentation. Theeffect of the pre-treatments on the microorganisms involved has also beentaken into account in view of providing comprehensive insights. Theenrichment of the PHA producers’ microorganisms was tested underdifferent conditions followed by optimization of the PHA accumulation, which led towards establishing a reliable automatic process. The PHAproduced was then extracted by applying a water-based extraction protocol.The insights gained from the optimization of the various steps of the processwere then applied at the pilot scale PHA production plants in the twodemonstration case studies.In view of providing insights towards the implementation of the PHAproduction process in the WRRFs, the five layouts tested at the pilot plantswere operated by monitoring the system’s efficiency in PHA production,removing contaminants, direct greenhouse gas emissions (nitrous oxide) andassessing the overall carbon footprint. Finally, the life cycle assessment wascarried out for the pilot plant layouts tested to evaluate the environmentalimpact and gain insights for future optimization.