Pretreatment of Reed Canary Grass
Among the pretreatment methods tested on reed canary grass are liquid hot water [178], dilute ammonia [178], ammonia fiber expansion [179], dilute acid pretreatment [180, 175, 181], and calcium hydroxide [181].
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Table 3.17 Average composition of reed canary grass [177].
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In a comparison study by Digman and coworkers on the effects of different pretreatment methods on reed canary grass and switch — grass, dry powdered grass samples were pretreated at ambient temperature and pressure with sulfuric acid and calcium hydroxide in separate experiments [181]. In these experiments chemical loadings from 0 to 100 g/kg of dry matter, and durations of anaerobic storage from 0 to 180 days were investigated by way of a central composite design at two moisture contents (40% or 60% w/w). Then, pretreated and untreated samples were fermented to ethanol by Saccharomyces cerevisiae D5A in the presence of a commercially available cellulase (Celluclast 1.5 L) and в-glucosidase (Novozymes 188). Xylose levels were also measured following fermentation, because xylose is not metabolized by S. cerevisiae. After sulfuric acid pretreatment and anaerobic storage, conversion of cell wall glucose to ethanol for reed canary grass ranged from 22% to 83%, whereas switchgrass conversions ranged from 16% to 46%. They found that, pretreatment duration had a positive effect on conversion, but was mitigated with increased chemical loadings. Grass samples subjected calcium hydroxide pretreatment and anaerobic storage produced glucose to ethanol conversions in the range from 21% to 55% and 18% to 54% for reed canary grass and switchgrass, respectively [181].
Dien and coworkers at the USDA have also evaluated different pretreatment strategies on reed canary grass, where liquid hot water and dilute ammonia pretreatments were used prior to fermentation [178]. The resulting hydrolyzates were then evaluated for production of ethanol, xylose and soluble xylans. According to their experiments, dilute ammonia gave higher yield efficiencies than liquid hot water. The optimal condition for dilute ammonia (4% w/v) pretreatment was 170°C for 20 min. Hydrolyzates were converted to ethanol using Saccharomyces in the presence of a blend of commercial cellulases and additional carbohydrases. The final ethanol conversion efficiency was 84% based upon total hexosans, with 72% of the xylan converted to soluble xylan oligomers [178].