US researchers create biofuel from potato waste
Researchers at Penn State’s College of Agricultural Sciences have developed a method of converting potato waste into the biofuel ethanol, which is more cost effective than current methods and achieves a slightly greater yield. Using potato waste from Pennsylvania crisp factories, the team triggered the simultaneous processes of saccharification and fermentation, while mould and yeast were added as catalysts to the bioreactor.

Researchers evaluated the effects of temperature, pH and aeration rates in biofilm reactors, and the optimal conditions were found to be 95 degrees Fahrenheit and a pH of 5.8 with no aeration. After 72 hours, the researchers achieved the maximum ethanol concentration of 37.93 grams per liter. The yield was 0.41 grams or ethanol per gram of starch.

"These results are promising, because the co-culture biofilm reactor provided similar ethanol production — 37.93 grams per leader — compared to the conventional ethanol production — 37.05 grams per liter — which required pre-treatment with added commercial enzymes at a higher temperature," Demirci explained. "Therefore, eliminating the externally added enzyme and energy costs will certainly reduce the cost of bioethanol production."

Researchers also evaluated biofilm formation of co-culture on the plastic composite supports using a scanning electron microscope, said researcher Gulten Izmirlioglu, a doctoral student in agricultural and biological engineering when the study was conducted. "Scanning electron microscope images revealed that when mold and yeast are allowed to form a biofilm, hyphae (filaments) of the mold provide surface area for the yeasts' attachment," she said. "That's a good thing."

The research findings, which demonstrated that plastic composite supports can be used for simultaneous saccharification and fermentation processes in biofilm reactors with co-cultures when producing ethanol, were published in Fuel. Izmirlioglu believes the results are significant for industry.

"Overall, 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," she said.

More efficient bioethanol production is needed to meet the demand for renewable energy and reduce the negative environmental impacts of petroleum fuel, Demirci noted. 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.

"This research is of great interest to Keystone Potato Products in Hegins, Pennsylvania, a subsidiary of Sterman Masser Inc.," said 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."

Also contributing to the research was John Cantolina in the Microscopy and Cytometry Facility at the Huck Institutes of the Life Sciences, Penn State.

The Turkish Ministry of Education, by providing a scholarship to Izmirlioglu and the Pennsylvania Agricultural Experiment Station supported this work.