Sustainable Solutions for Environmental Pollution. Группа авторов

Sustainable Solutions for Environmental Pollution - Группа авторов


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in oil than water) and increased the mass transfer efficiency, yielding higher production of bioplastics. However, utilizing oil may not be environmental-friendly and the high costs triggered by the aeration requirement and feedstock must still be considered (Liu et al., 2020a).

      1.3.7 L-lysine

      The market of amino acid, which is known to be a key sector of industrial biotechnology, has been rapidly growing recently (Vassilev et al., 2018; Xafenias et al., 2017). Specifically, such a high production rate for L-lysine, an amino acid (e.g., 2.2 million tons per year with 7% increase per year) has been reported due to the growing demand for meat because the L-lysine was extensively used as an additive in animal nutrition (Ajinomoto Co., 2013; Eggeling and Bott, 2015; Xafenias et al., 2017). Over the decades, various industrial biotechnologies, based on Gram-positive soil bacteria (e.g., Corynebacterium glutamicum), have been utilized for the production of lysine due to their advantages (e.g., a safe production host) (Eggeling and Bott, 2005; Tatsumi and Inui, 2012; Vassilev et al., 2018; Wittmann and Becker, 2007). To begin with, using C. glutamicum in aerobic bioreactors (e.g., using oxygen as a terminal electron acceptor) was the initial attempt to produce L-lysine, but low product yields via substrate loss and oxygen mass transfer were the limitations for further development and scaling-up (Gill et al., 2008; Hannon et al., 2007; Takeno et al., 2007). In fact, aerobic bioreactors will result in higher capital costs compared to anaerobic systems (Garcia-Ochoa and Gomez, 2009). Alternatively, a study in 2004 revealed that C. glutamicum was capable of performing fermentation of glucose to organic acids, such as lactate and acetate under oxygen deprivation conditions (Inui et al., 2004), which demonstrated another pathway for L-lysine production. Despite the advantages of the anaerobic process (e.g., low cost), due to the low yield, efforts (e.g., the introduction of nitrate, anoxic condition) have been made to promote the growth of C. glutamicum, but the growth was inhibited due to the production of toxicants (e.g., nitrite) in the bioreactor (Takeno et al., 2007).

      1.3.8 1,3-propanediol

      1,3-propanediol is an important industrial chemical widely used as a monomer to synthesize various commercial products, including cosmetics, plastics, foods, and medicines (Yang et al., 2018). The global market size for1,3-propanediol is expected to reach ~690 million USD by the year 2025 (www.marketsandmarkets.com). Although 1,3-propanediol can be produced chemically through two methods (hydroformylation of ethylene and the hydration of acrolein), these traditional chemical synthesis methods are not considered sustainable due to high energy consumption, the requirement of expensive catalysts, and the generation of hazardous intermediates (Yang et al., 2018). Therefore, the biological production of 1,3-propanediol from waste biomass (e.g., glycerol waste from the biodiesel production process) is considered as a greener and safer approach (Vivek et al., 2017; Yang et al., 2018). Particularly, microbial conversion of glycerol with various fermentative bacteria (e.g., Citrobacter, Klebsiella, Lactobacillus, Enterobacter, and Clostridium) has been extensively investigated (Drozdzynska et al., 2011; Vivek et al., 2017; Yang et al., 2018). Crude glycerol, a major by-product from biodiesel production process can serve as a feedstock for 1,3-propanediol synthesis via fermentation. Typically, 1 L of crude glycerol is generated per 10 L of biodiesel production via transesterification of triglycerides (vegetable oil or animal fats), in the presence of primary alcohol (e.g., methanol) and a catalyst (Sarma et al., 2012). However, low yield, product inhibition, etc., have been identified as the major bottlenecks in the fermentation of glycerol to 1,3-propanediol (Vivek et al., 2017; Yang et al., 2018).


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