Improving ethanol production from alfalfa stems via ambient-temperature acid pretreatment and washing

• On-farm ensiling of alfalfa stems is a strategy for storage prior to biorefining.
• Pretreatment with dilute sulfuric acid prior to ensiling improves subsequent SSF.
• Washing after ensiling to remove ash further improves ethanol production by SSF.
• Acid pretreatment alters plant cell wall structure, and washing removes inhibitors.

The concept of co-production of liquid fuel (ethanol) along with animal feed on farm was proposed, and the strategy of using ambient-temperature acid pretreatment, ensiling and washing to improve ethanol production from alfalfa stems was investigated. Alfalfa stems were separated and pretreated with sulfuric acid at ambient-temperature after harvest, and following ensiling, after which the ensiled stems were subjected to simultaneous saccharification and fermentation (SSF) for ethanol production. Ethanol yield was improved by ambient-temperature sulfuric acid pretreatment before ensiling, and by washing before SSF. It was theorized that the acid pretreatment at ambient temperature partially degraded hemicellulose, and altered cell wall structure, resulted in improved cellulose accessibility, whereas washing removed soluble ash in substrates which could inhibit the SSF. The pH of stored alfalfa stems can be used to predict the ethanol yield, with a correlation coefficient of +0.83 for washed alfalfa stems.