Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2009
Publication Date: 3/1/2010
Citation: Widmer, W., Zhou, W., Grohmann, K. 2010. Pretreatment effects on orange processing waste for making ethanol by simultaneous saccharification and fermentation. Bioresource Technology. 101:5242-5249. Interpretive Summary: In Florida over 80% of the citrus crop is processed into juice generating 3.5 to 5 million tons of peel processing waste annually which is a disposal problem. The processors currently process the peel in to cattle feed for a no or a marginal profit. They would like alternative value added products from the processing waste and ethanol is one potential product. This laboratory is optimizing a process to ferment citrus peel sugars into ethanol which was facilitated by pretreatment of the peel waste using acid. Pretreatments using base did not facilitate the pretreatment process to produce ethanol. owever, the benefits of acid pretreatment of the peel may be offset by increased equipment costs.
Technical Abstract: Pretreatment of orange processing waste (CPW) by steam explosion under various conditions (pretreatment time, pH and temperatures) was investigated. Pretreatments longer than 4 min with steam purging resulted in CPW containing less than 0.1% limonene, an inhibitor for fermentation. Steam pretreatments for 2-6 min at 160 ºC with rapid decompression (steam explosion) broke down peel tissues, solubilized 90% of the hemicelluloses and 70% of the pectin in natural CPW. Addition of 0.6% phosphoric acid to pretreat CPW at pH 2.8 increased pectin solubility to better than 80%, but did not significantly increase the total dissolved solids until pretreatment times exceeded 6 min. Pretreatments at 160 ºC with addition of sodium carbonate to increase CPW initial pH to 6.8 and 8.2 destroyed 50% of the pectin and galacturonic acid after just 2 min, had significantly lower dissolved solids, and resulted in excessively viscous products. Total sugars fermentable by Saccharomyces cerevisiae were not changed after pretreatments at 160 ºC for up to 8 min on CPW between pH 2.2-8.2. Ethanol yields following 48 hr simultaneous saccharification and fermentations (SSF) ranged from 76 to 94%. Ethanol yields were slightly lower but not statistically significant in base modified pretreatments.