Abstract
BackgroundThe enzymatic conversion of lignocellulosic biomass into fermentable sugars is a promising approach for producing renewable fuels and chemicals. However, the cost and efficiency of the fungal enzyme cocktails that are normally employed in these processes remain a significant bottleneck. A potential route to increase hydrolysis yields and thereby reduce the hydrolysis costs would be to supplement the fungal enzymes with their lacking enzymatic activities, such as β-glucosidase. In this context, it is not clear from the literature whether recombinant E. coli could be a cost-effective platform for the production of some of these low-value enzymes, especially in the case of on-site production. Here, we present a conceptual design and techno-economic evaluation of the production of a low-cost industrial enzyme using recombinant E. coli.ResultsIn a simulated baseline scenario for β-glucosidase demand in a hypothetical second-generation ethanol (2G) plant in Brazil, we found that the production cost (316 US$/kg) was higher than what is commonly assumed in the literature for fungal enzymes, owing especially to the facility-dependent costs (45%) and to consumables (23%) and raw materials (25%). Sensitivity analyses of process scale, inoculation volume, and volumetric productivity indicated that optimized conditions may promote a dramatic reduction in enzyme cost and also revealed the most relevant factors affecting production costs.ConclusionsDespite the considerable technical and economic uncertainties that surround 2G ethanol and the large-scale production of low-cost recombinant enzymes, this work sheds light on some relevant questions and supports future studies in this field. In particular, we conclude that process optimization, on many fronts, may strongly reduce the costs of E. coli recombinant enzymes, in the context of tailor-made enzymatic cocktails for 2G ethanol production.
Highlights
The enzymatic conversion of lignocellulosic biomass into fermentable sugars is a promising approach for producing renewable fuels and chemicals
Studies that did delve into the enzyme cost have focused on the economics of the cellulase mixture produced by the filamentous fungus Trichoderma reesei [1,2,3,4,5], which is generally considered to be the most efficient producer of cellulases and, is currently the most prevalent producer of cellulases used in the industry [6, 7]
As described previously (“Methods” section), we considered that the annual production of β-glucosidase proposed here would be sufficient to be used on the hydrolysis of approximately 39% of all the sugarcane bagasse produced annually by a Brazilian sugarcane plant that processes 2 million tons of sugarcane/year
Summary
The enzymatic conversion of lignocellulosic biomass into fermentable sugars is a promising approach for producing renewable fuels and chemicals. A potential route to increase hydrolysis yields and thereby reduce the hydrolysis costs would be to supplement the fungal enzymes with their lacking enzymatic activities, such as β-glucosidase In this context, it is not clear from the literature whether recombinant E. coli could be a cost-effective platform for the production of some of these low-value enzymes, especially in the case of on-site production. Supplementing the fungal cocktail with the enzymes whose activities the cocktail is lacking in is a potential method for process optimization, assuming that the increase in hydrolysis yield outweighs the cost of the supplementary enzymes Producing these supplementary enzymes on-site may be more economical than doing so off-site because the former avoids transportation and formulation costs [2, 12]. Great efforts have been made in the last decade, in Brazil, to make the industrial production of 2G ethanol via enzymatic hydrolysis of sugarcane biomass economically feasible [14,15,16]
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