Polyhydroxyalkanoates production from salted food waste using mixed microbial cultures.

Plastic is an essential asset for the modern lifestyle, given its superiority as a material from the points of view of cost, processability and functional properties. However, plastic-related environmental pollution has become nowadays a very significant problem that can no longer be overlooked. For this reason, in recent decades, the research for new materials that could replace fossil fuel-based plastics has been focused on biopolymers with similar physicochemical properties to fossil fuel-based plastics, such as Polyhydroxyalkanoates (PHA). PHAs are a family of biodegradable polyesters synthesized by many microorganisms as carbon and energy reserves. PHA appears as a good candidate to substitute conventional petroleum-based plastics since it has similar properties, but with the advantage of being biobased and biodegradable, and has a wide range of applications (e.g., packaging). However, the PHA production cost is almost four times higher (€5/kg) than conventional plastic manufacturing. The PHA production by mixed microbial cultures (MMC) allows to reduce production costs as it does not require aseptic conditions and it enables the use of inexpensive by-products or waste streams as these cultures are more amenable to deal with complex feedstocks. Saline wastewaters (WWs), generated by several industries such as seafood, leather and dairy, are often rich in organic compounds and, due to a strong salt inhibition, the biological treatments are inefficient, and their disposal is expensive. These saline WWs are a potential feedstock for PHA production, as they are an inexpensive raw material. Moreover, saline WWs could allow the utilization of seawater in the process as dilution and cleaning agent, further decreasing the operational costs and the environmental burden of the process. The main goal of the current project is to assess and optimize the PHA production from a mixture of food waste and brine wastewater from the fishery industry by MMC.

Microfluidic microbial fuel cell fabrication and rapid screening of electrochemically microbes

The demand for novel renewable energy sources, together with the new findings on bacterial electron transport mechanisms and the progress in microbial fuel cell design, have raised a noticeable interest in microbial power generation. Microbial fuel cell (MFC) is an electrochemical device that converts organic substrates into electricity via catalytic conversion by microorganism. It has represented a continuously growing research field during the past few years. The great advantage of this device is the direct conversion of the substrate into electricity and in the future, MFC may be linked to municipal waste streams or sources of agricultural and animal waste, providing a sustainable system for waste treatment and energy production. However, these novel green technologies have not yet been used for practical applications due to their low power outputs and challenges associated with scale-up, so in-depth studies are highly necessary to significantly improve and optimize the device working conditions. For the time being, the micro-scale MFCs show great potential in the rapid screening of electrochemically active microbes. This thesis presents how it will be possible to optimize the properties and design of the micro-size microbial fuel cell for maximum efficiency by understanding the MFC system. So it will involve designing, building and testing a miniature microbial fuel cell using a new species of microorganisms that promises high efficiency and long lifetime. The new device offer unique advantages of fast start-up, high sensitivity and superior microfluidic control over the measured microenvironment, which makes them good candidates for rapid screening of electrode materials, bacterial strains and growth media. It will be made in the Centre of Hybrid Biodevices (Faculty of Physical Sciences and Engineering, University of Southampton) from polymer materials like PDMS. The eventual aim is to develop a system with the optimum combination of microorganism, ion exchange membrane and growth medium. After fabricating the cell, different bacteria and plankton species will be grown in the device and the microbial fuel cell characterized for open circuit voltage and power. It will also use photo-sensitive organisms and characterize the power produced by the device in response to optical illumination.

Assessing the impact of ammonia content in VFA-rich streams on the PHA-storing MMC acclimatization and the PHA production stage

The use of environmentally friendly products increased the interest in renewable resources as alternatives to petrochemical products. Polyhydroxyalkanoates (PHAs) are examples of such promising products, as they are biodegradable polymers with numerous potential applications. PHA production approach consists of using an open mixed microbial culture (MMC) and inexpensive feedstocks (waste or industry byproducts feedstock). The PHA process generally comprises three stages: (1) acidogenic fermentation (AF) stage (conversion of organic carbon into fermentation products); (2) culture selection stage (enrichment in PHA-storing organisms by applying Feast and Famine regime); and (3) PHA production stage (PHA accumulation up to the culture’s maximum capacity). AF of protein-rich residues results in ammonia-rich fermented streams, which can be presented as a challenge for the PHA production stage. The presence of ammonia during this stage may induce organisms to grow instead of producing PHAs. For this reason, the assessment of the effect of a high content of ammonia on PHA production it is the utmost importance. The main goal of the current project is to select a MMC enriched in PHA-accumulating organisms in conditions of high ammonia content and to evaluate the effects of ammonia presence during PHA accumulation. The culture was selected applying the Feast & Famine strategy, and fed, firstly, using a synthetic mixture of VFAs and later using a fermented stream obtained from the fermentation of protein-rich raw materials. The selected culture could accumulate up to 24% PHA per VSS with the synthetic mixture of VFAs and up to 29% for the real fermented stream. The PHA accumulation resulted in different production in the presence and absence of ammonia. Regarding to the synthetic feed, 59%wt. PHA (VSS basis) in the absence of ammonia, and 55%wt. (VSS basis) in the presence, were obtained. For the real feed, the PHA content was about 40%wt. (VSS basis) in both reactors.