Cellulosic Ethanol Production From Warm-Season Perennial Grasses.

Warm-season (C₄) perennial grasses are able to produce large quantities of biomass, and will play a key role in bioenergy production, particularly in areas with long warm growing seasons.  Several different grass species have been studied as candidate bioenergy crops for the Southeast USA, and each has advantages and challenges.  It is likely that several species will be needed for a robust bioenergy industry, and strategies to maximize productivity while minimizing inputs need to be developed as well.  A study was established at Midville, GA to compare irrigation and harvest timing on production of cellulosic ethanol from multiple species of warm season grasses. Half of the test plots were irrigated, and half were rainfed only.  The test consisted of two thick-stemmed tropical grasses, napiergrass (Pennisetum purpureum Schum) and energycane (Saccharum hyb.), and two senescent grasses, switchgrass (Panicum virgatum L.) and Miscanthus × giganteus.  These grasses were harvested at monthly intervals over two winters.  Bermudagrass (Cynodon sp.), a summer-harvested forage crop, was also included in the test, and was harvested three times, twice, or only once during the summer growing season, also for two years.  The grasses were compared for changes in biomass yields, nutrient composition, and fiber properties over the varying harvest and irrigation systems.  Conversion of the biomass to ethanol was measured directly using a bench-scale dilute acid pretreatment and simultaneous saccharification and fermentation (SSF) protocol.  Nutrient concentrations tended to decrease with age of the standing biomass.  Conversion to ethanol also varied with harvest timing, particularly for energycane, likely due to loss of fermentable free sugars.