Valorisation of crude glycerol through biological conversion into bioplastics and biofuels in the frame of an FP7 project

Intro: In recent years, the exponential growth of biodiesel production has led to a glycerol glut and thus crude glycerol represents a suitable, abundant and low-priced feedstock for fermentation technologies. The EU is the largest biodiesel producer in the world, and the total EU27 production for 2011 was over 8.6
million metric tons, but to date an effective use for the glycerol derived from biodiesel production does not exist on the market. In fact, even though high purity glycerol can be used in the cosmetic and pharmaceutical industry, crude glycerol derived from biodiesel production has a very low value, due to the impurities and contaminants, and the purification of glycerol is not a viable option for the biodiesel industry anymore. In fact, crude glycerol is usually contaminated with water, methanol, soap, oil, and other compounds deriving
from the transesterification process. Therefore, the purification cost is high when converting crude glycerol by traditional chemistry methods. Setting up of biorefineries, that co-produce high-value compounds, has been considered a concrete solution to enhance economic viability of biodiesel production.
The project: the overall aim is the valorisation of glycerol streams generated during the biodiesel production process, using microbial mixed culture (MMC) technology. The use of bioconversion into high-value products represents a promising route to achieve economic viability in the biofuel industry. Until now there have been several studies on microbial processes to convert glycerol, but still too little has been reported with crude glycerol and MMC technology, which really reduces the production costs. Most of the studies dealing with crude glycerol have been focusing on the conversion into 1,3 propanediol, while almost nothing has been done for the conversion in biofuels (ethanol and hydrogen), and even less for bioplastics (PHA and PHB).
- Bioplastics: enrichment and selection of PHA-accumulating organisms, grown on pre-fermented crude glycerol, will be performed using fed-batch or sequence batch mode with aerobic/aerobic carbon limitation conditions (feast and famine). The distribution of metabolic products during the pre-fermentation phase will
be thoroughly investigated. The basic assumptions and structure of the IWA-ADM1 will be the basis for the development of a kinetic model with variable stoichiometry of metabolic products, depending on the operating conditions. Predictions of the model will be compared to the results obtained by statistical
optimization. The milestone set for PHA production is to reach a PHA yield higher than 80 wt. %.
- Biofuels: process intensification of an already developed (and patented) process, for the joint production of hydrogen and ethanol, will be investigated. Application of microaerophilic conditions for further enhancement of ethanol production (which is expected to enhance biomass and thus substrate degradation efficiency, without the need of yeast extract or other nutrient supplements) in continuous mode will be tested and kinetics of the process will be studied. Moreover, scale-up to a larger bioreactor will be performed using
an Applikon 20 L pilot plant bioreactor. The milestone is to reach an ethanol concentration of at least 40g/L and a hydrogen production of at least 3.5 L H2/L/d.
European dimension: The large accumulation of glycerol (by European biodiesel industries) is a European problem and it requires a European dimension. This study will be part of a larger FP7 KBBE Cooperation project that involves 15 partners from 10 different countries (called “GRAIL” - Glycerol Biorefinery
Approach for the Production of High Quality Products of Industrial Value), with the aim to identify at least 15 commodity products and generate a prototype biorefinery for integral use of glycerol as a feedstock for the production of economically value-added chemicals and biofuels.
The presented research will thus be part of a broader European strategy, in good synergy with other on-going FP7 projects, which can contribute to achieve new solutions for a knowledge-based economy, increasing the economic viability of the biodiesel industry, and developing new international collaborations.