Optimizing peracetic acid pretreatment conditions for improved simultaneous saccharification and co-fermentation (SSCF) of woody biomass to ethanol

The use of biomass for ethanol fuel production has been studied exhaustively in U.S.A. for two decades. Strong environmental legislation has been driving efforts by enterprises, state agencies, and universities to make ethanol from biomass economically viable. Production costs for ethanol from biomass has been decreasing year by year as a consequence of this massive effort. Pretreatment, enzyme recovery, and development or efficient microorganisms an some promising areas of study for reducing process costs. The present paper presents an alternative pretreatment with low energy input where biomass can be treated in a silo type system without need for expensive capitalization. Experimentally, ground hybrid poplar is placed in plastic bags and a peracetic acid solution is added to the woody biomass at concentrations of 0, 6, 9, 15, 21, 30, and 60% w/w of peracetic acid based on oven dried wood. The ratio of solution to wood is 6:1 and a seven day storage period has been used. Tests using hydrolyzing enzymes have been performed to evaluate the pretreatment efficiency. The test using a 60% peracetic acid loading converted most of the cellulose to simple sugars in only 24 hours of enzyme treatment. The lest using 21% peracetic acid loading showed the best performance, considering the reduced amount of peracetic acid, in that 98.3% of the cellulose was converted at the end of the 120 hours of enzyme treatment. The test performed using 15% peracetic acid treated sample had 76.5% of the cellulose converted in 120 hours. Raw wood had a poor conversion of only 6.8% of total cellulose at the end of enzymatic hydrolysis. As an auxiliary method, a series of pre-pretreatments using stoichiometric amounts of sodium hydroxide and ammonium hydroxide based on I-methyl-glucuronic acid and acetate content in the hybrid poplar have been performed before addition of peracetic acid. The basic solutions are: added to woody biomass in a ratio of 1 1 :1 solution to biomass. and mixed for 24 hours at room temperature. The biomass is filtered and washed to a neutral pH before peracetic acid addition. Pn-pretreatment with 6% NaOH prior to 9% peracetic acid resulted in 93.9% cellulose conversion; pre-pretreatment with 14% NH4OH prior to 15% peracetic acid pretreatment resulted in 92.0% cellulose conversion. These results show that peracetic acid is a powerful chemical for improving enzymatic digestibility of hybrid poplar with no need for using high temperatures. Basic pre-pretreatments are helpful in reducing peracetic acid requirements in the pretreatment.