Green biofuels and bioproducts: bases for sustainability analysis

Currently, the chemical industry is largely petroleum based and although the number of ongoing large-scale biocatalytic processes is relatively low, a trend in growth is expected and the Organization for Economic Cooperation and Development (OECD) and other agencies aim to have 30% of the total chemical industry based on renewable sources by 2050 (Philp et al., 2013). At present, a good number of bio-based products (bioethanol, acids such as lactic, succinic, itaconic, and others) are derived from corn syrup and other sugar sources (Geiser et al., 2016; Ramos et al., 2016a); however, because of the food v fuel controversy, new trends have been directed towards the production of bioproducts/biofuels from lignocellulosic biomass – the most abundant and important renewable source for alternative petrol derivatives (Ramos et al., 2016b). Lignocellulosic biomass is the stored energy from sunlight in the form of chemical energy, and it refers to plant biomass that is composed of cellulose, hemicellulose and lignin and includes not only the green parts of vegetables, wood and straw, but also manure and the organic fraction of municipal solid wastes (MSW). The term biofuel includes liquid biofuels; i.e. starch-based and cellulose-based ethanol, biogas, renewable thermal energy, renewable electricity and biobased adhesives, among others (Arjona-Antolin et al., 2012a,b,c,d). In turn, the term bioproduct refers to bioplastics, a range of acids (citric, lactic), surfactants resins and biochemicals. In Europe, there is a slight bias towards the development of bioproducts, and in North America, a clear tendency to produce biofuels. A major obstacle for the industrial-scale production of bioproducts/biofuels from lignocellulose by biological means, known as second-generation (2G) products, is the inefficient deconstruction of plant material due to the recalcitrant nature of the substrates (Horn et al., 2012; Cherry and Fidantsef, 2013; Alvarez et al., 2016). The success of 2G technology requires efficient pre-treatment (physical, chemical or physicochemical) of plant material to disorganize the fibres, which will be the target for the action of enzymatic cocktails that breakdown polysaccharides into their monomeric constituents (Alvarez et al., 2016). Enzymatic hydrolysis of lignocellulosic materials yields glucose, xylose and arabinose, and these sugars can be fermented to produce added-value chemicals such as alcohols (ethanol, butanol), acetone, aldehydes, amino acids and other bioproducts. Liquid or gas bioproducts/biofuels, derived from renewable resources, can only replace a fraction of the fossil fuels used in locomotion, as well as a number of chemicals that are currently derived from petroleum. In the field of bioproduct/biofuel production from renewable plant material, the most relevant advances have been reported for 2G bioethanol production (Gnansounun and Dauriat, 2010), for which, globally, there are two commercial plants in operation. Biofuels are gaining increased public acceptance and scientific attention, driven by factors such as oil price spikes, the need for increased energy security and concerns over greenhouse gas (GHG) emissions from fossil fuels (Valdivia et al., 2016). In addition to the lower GHG emissions from using bioproduct/biofuel, petroleum saved for locomotion will allow this valuable resource to be used as ‘reserve’ for the future. Biofuels are used among others for ethyl tert-butyl ether (ETBE) production (gasoline additive), direct blending of ethanol with gasoline or blending of biodiesel with diesel. Being a renewable energy source, biofuels reduce CO2 emissions and contribute to the security and diversification of the energy supply, while reducing the dependency on fossil fuels and helping towards compliance with international Climate Agreements and Protocols. Bioproducts are also gaining interest, and a number chemicals are being synthesized by direct fermentation of 2G sugars, i.e. butanol, acetone, ethanol from corn stover (Wang and Chen, 2011; Geiser et al., 2016). The biomass that is used for biofuel/bioproduct synthesis should be of sustainable origin and deemed to Received 13 June, 2017; accepted 13 June, 2017. *For correspondence. E-mail [email protected]; Tel. +954-937111. Microbial Biotechnology (2017) 10(5),1111–1113 doi:10.1111/1751-7915.12768 Funding Information No funding information provided.