Potential Enzyme Cost Reduction with the Addition of Surfactant during the Hydrolysis of Pretreated Softwood

The potential economic benefits of surfactants addition on enzymatic hydrolysis of steam-exploded lodgepole pine (SELP) and ethanol-pretreated lodgepole pine (EPLP) were investigated in this study. Free cellulase readsorption on fresh substrate was used to recover and recycle cellulase enzymes during the hydrolysis of SELP and EPLP substrate. Supplementing Tween 80 during the hydrolysis could facilitate enzyme recycling for EPLP substrate. A logarithmic correlation was established between surfactant concentration and free cellulase content after lignocellulosic hydrolysis, which was used to compute enzyme cost savings over various Tween 80 concentrations. A simple economic analysis of enzyme cost savings versus the cost of surfactant was undertaken. The results indicated that the addition of Tween 80 (priced at US $0.25/kg) during the hydrolysis of the EPLP substrate could save 60% of the total enzyme cost at concentrations in the 0.025% to 0.2% range. The addition of Tween for the hydrolysis of the SELP substrate significantly reduced the material cost by 24% per 1 gal of ethanol produced, and the ethanol production cost could be reduced by 8.6% with the addition of Tween and enzymes recycle for the hydrolysis of SELP substrate. A schematic concept of recycling enzyme and surfactant was also presented with a recirculation of process streams during hydrolysis. Further analysis indicated a 66% reduction in total enzyme cost could potentially be achieved under the concept.