Treatment and valorization of brewery waste through polyhydroxyalkanoates production

The integrated treatment and valorisation of organic waste streams with the production of added-value compounds, namely polyhydroxyalkanoates (PHAs), is an important step towards a more sustainable society. In this project, treatment and valorisation of brewery waste through the production of PHA, will be investigated. The brewery industry produces high amounts of waste, namely brewer's spent grain (BSG) (30000 ton/yr) and wastewater (BWW) (2.5 L/ L beer) (Unicer data). A lab scale plant consisting of a 3-stage process will be operated and the impact of operating parameters on PHA production and produced effluent quality will be evaluated. An expanded granular sludge bed reactor will be used for the anaerobic digestion of the feedstock (stage I). With this technology the fermented waste can be directly fed to the PHA production reactors (stage II and III). The use of a particulate feedstock, BSG, will represent an important challenge, as information on the effects of particulate feedstocks on anaerobic granules is scarce. A greener BSG sugar extraction method using sub-critical water will be assessed. The feedstock that will reach the highest acidification will be selected. Stage II, PHA culture selection, will be carried out using a sequencing batch reactor, operated under Feast and Famine regime. PHA maximum production (stage III) will be accomplished in a fed-batch mode using the fermented feedstock (stage I) and the selected biomass (stage II). Greener PHA extraction/purification methods will be investigated. The microbial communities of both, the anaerobic digester and the PHA-storing mixed microbial culture, will be followed using molecular tools, namely high throughput sequencing and fluorescence in situ hybridisation (FISH). The PHA production process is currently operated by measuring offline parameters, such as PHA concentration by gas chromatography. This results in a lengthy time response (1-2 days). In this project, 2D fluorescence spectroscopy will be used for the first time for online monitoring of the process performance. Metabolic models will be developed for the 3-stages of the process and integrated with each other, in order to identify combinations of operational conditions to maximize PHA production rates and conversion efficiencies. The short-term goals are to accomplish the main objectives proposed in this research plan, simultaneous treatment and valorisation of brewery waste, resulting in the production of a PHA based container for Unicer. In a long term basis, it is intended to perform an economical evaluation of the integrated process and implement the process in the industry. The companies Unicer and Logoplaste and Université de Liège are supporting this project, being the right partners for getting this technology to be transferred to industry and its implementation. The outcome of this project will be crucial to assess the potential to convert a WW treatment plant into a biorefinery, promoting circular economy.