The production of biofuels from carbonated beverages

Commonly sold carbonated beverages typically contain 110g/L of sugar. Consequently, this study evaluated the use of four products, including two colas, one diet cola and one lemon–lime flavored beverage from two large distributors world-wide and one local distributor, as fermentative sugar sources. Zymomonas mobilis ZM4 cultures were able to ferment the sugars present, which included sucrose, fructose and glucose, consuming all three completely within about 10h after addition. The results from each of the beverages tested were similar, except for the diet beverage, with a final ethanol concentrations of around 25g/L, an average productivity of approximately 2g*L−1h−1 and average yields of 0.43g ethanol/g glucose. Using a diet beverage with a fructose–glucose mixture added extraneously, we demonstrated that the beverages were not inhibitory or toxic to the cultures. Subsequent experiments with three clostridial strains showed that these beverages can also be used within fermentative processes to generate butanol and butyric acid. As with Z. mobilis ZM4, Clostridium acetobutylicum ATCC 824 and Clostridium beijerinckii NCIMB 8052 were capable of fermenting all three sugars and had final butanol concentrations of 5.3 and 8.7g/L, respectively. In contrast, Clostridium tyrobutyricum ATCC 25755 is unable to utilize sucrose as a carbon source. Although limited to only the monosaccharides fructose and glucose, the butyric acid concentration was 15.4g/L and had a yield of 0.43g butyrate/g glucose, which is only slightly below the theoretical maximum of 0.47. This study illustrates the potential of using wasted or expired carbonated beverages in the biofuels industry.