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BackgroundIn Europe, almost 87.6 million tonnes of food waste are produced. Despite the high biological value of food waste, traditional management solutions do not consider it as a precious resource. Many studies have reported the use of food waste for the production of high added value molecules. Polyhydroxyalkanoates (PHAs) represent a class of interesting bio-polyesters accumulated by different bacterial cells, and has been proposed for production from the organic fraction of municipal solid waste (OFMSW). Nevertheless, until now, no attention has been paid to the entire biological process leading to the transformation of food waste to organic acids (OA) and then to PHA, getting high PHA yield per food waste unit. In particular, the acid-generating process needs to be optimized, maximizing OA production from OFMSW. To do so, a pilot-scale Anaerobic Percolation Biocell Reactor (100 L in volume) was used to produce an OA-rich percolate from OFMSW which was used subsequently to produce PHA.ResultsThe optimized acidogenic process resulted in an OA production of 151 g kg−1 from fresh OFMSW. The subsequent optimization of PHA production from OA gave a PHA production, on average, of 223 ± 28 g kg−1 total OA fed. Total mass balance indicated, for the best case studied, a PHA production per OFMSW weight unit of 33.22 ± 4.2 g kg−1 from fresh OFMSW, corresponding to 114.4 ± 14.5 g kg−1 of total solids from OFMSW. PHA composition revealed a hydroxybutyrate/hydroxyvalerate (%) ratio of 53/47 and Mw of 8∙105 kDa with a low polydispersity index, i.e. 1.4.ConclusionsThis work showed how by optimizing acidic fermentation it could be possible to get a large amount of OA from OFMSW to be then transformed into PHA. This step is important as it greatly affects the total final PHA yield. Data obtained in this work can be useful as the starting point for considering the economic feasibility of PHA production from OFMSW by using mixed culture.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0888-8) contains supplementary material, which is available to authorized users.

The rise of carbon dioxide (CO2) emissions and the accumulation of non-biodegradable plastics in the environment is leading to an environmental crisis.

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Polyhydroxyalkanoates (PHAs) are biodegradable plastics of microbial origin, whose biodegradability and thermochemical properties make them greener alternatives to conventional plastics. Despite their high industrial potential, the PHAs high production costs still hinder their application. Mixed microbial biomass combined with agroindustrial wastes are being used to strategically reduce these costs. However, it is still necessary to optimize the downstream processing, where the extraction process amounts to 30-50 % of the total costs. Conventional processes apply chlorinated solvents to recover PHAs from microbial biomass but cannot be implemented industrially due to environmental regulations. Alternative solvents, with good results of purity and recovery yields, usually have a negative impact on the molecular weight of the final polymer. In this work, the addition of a pre-treatment based on non--114) to extract PHA from mixed microbial biomass selected on fermented agro-industrial wastes was investigated. The best results were obtained with without any prewith chloroform (63%). The extracted polymer was analysed and characterized, revealing a PHA of high purity (>90%) and low molecular weight loss (under 24%). Additionally, a material-focused economic and a carbon footprint analysis were performed and supported the selection of the method as one of the cheapest options and with the lowest carbon footprint.

A highly productive Arundo donax L. clone (Clone AD-20) was produced at full field to give 54.6 Mg total solids biomass Ha–1. Biomass was chemically and enzymatically pretreated, recovering 13.9 Mg Ha–1 of glucose and 3.6 Mg Ha–1 of xylose, i.e., 3.5–4.5 more than yield typically obtained from corn stover or switchgrass. The subsequent fermentation of the liberated sugars to organic acids (OA) by dark fermentation generated yields of 3850 Nm3 Ha–1 of biohydrogen and 14.2 Mg Ha–1 of OAs. OAs were then used as a feed to produce polyhydroxyalkanoates (PHA), with 3-hydroxybutyrate the major monomer present (PHB > 95% PHA), from a biological process using mixed microbial culture producing 5.04 Mg Ha–1 of PHA. An initial economic analysis indicated that this multistage biorefinery approach would result in a net revenue of 10,415 € Ha–1, which is approximately 9-fold greater than that obtained by a traditional biorefinery producing bioethanol.

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