More efficient conversion of potato waste to ethanol

Researchers from Pennsylvania State University have developed a novel approach to more efficiently convert potato waste into ethanol — a process that may lead to reduced production costs for biofuel in the future and add extra value for potato chip manufacturers. Their research has been published in the journal Fuel.

More efficient bioethanol production is needed to meet the demand for renewable energy and reduce the negative environmental impacts of petroleum fuel, noted study co-author Ali Demirci. To make ethanol production cost-competitive, inexpensive and easily available, feedstocks such as potato mash are needed, as well as improved processing technologies with higher productivities.

Using potato mash made from the peelings and potato residuals from a Pennsylvania food processor, Demirci and his colleague Gulten Izmirlioglu triggered simultaneous saccharification — the process of breaking down the complex carbohydrate starch into simple sugars — as well as fermentation — the process in which sugars are converted to ethanol by yeasts or other microorganisms in bioreactors. The addition to the bioreactor of mould and yeast — Aspergillus niger and Saccharomyces cerevisiae, respectively — meanwhile catalysed the conversion of potato waste to bioethanol.

The bioreactor had plastic composite supports to encourage and enhance biofilm formation and to increase the microbial population. Biofilms are a natural way of immobilising microbial cells on a solid support material. In a biofilm environment, microbial cells are abundant and more resistant to environmental stress causing higher productivities. In this application, these benefits were especially important because mould enzyme activity required higher temperature and the yeast had to tolerate this.

The researchers evaluated the effects of temperature, pH and aeration rates in biofilm reactors, with the optimal conditions found to be 35°C and a pH of 5.8 with no aeration. After 72 hours, the researchers achieved the maximum ethanol concentration of 37.93 g/L. The yield was 0.41 g of ethanol per gram of starch.

“These results are promising, because the co-culture biofilm reactor provided similar ethanol production — 37.93 g/L — compared to the conventional ethanol production — 37.05 g/L — which required pretreatment with added commercial enzymes at a higher temperature,” Demirci said. “Therefore, eliminating the externally added enzyme and energy costs will certainly reduce the cost of bioethanol production.”

The researchers also evaluated biofilm formation of co-culture on the plastic composite supports using a scanning electron microscope, said Izmirlioglu, who revealed, “Scanning electron microscope images revealed that when mould and yeast are allowed to form a biofilm, hyphae (filaments) of the mould provide surface area for the yeasts’ attachment. That’s a good thing.”

Izmirlioglu believes the results are significant for industry, with the research proving that bioethanol production from starchy industrial wastes can be “improved with application of biofilm reactors, while the production cost is reduced with integrations of the simultaneous saccharification and fermentation process and co-culturing”.

“This research is of great interest to Keystone Potato Products in Hegins, Pennsylvania, a subsidiary of Sterman Masser Inc,” added Demirci. “The company is paying attention to this project, hoping this novel approach may help it add more value to its waste potato mash. Industrial food wastes are potentially a great substrate in production of value-added products to reduce the cost, while managing the waste economically and environmentally.”

Image credit: ©iStockphoto.com/Tobias Helbig