Biofuels from waste materials with wild type bacteria

Jan 2017

Fossil fuel production and use contribute to air, water and soil pollution and global warming. According to Enerdata Global Energy Statistical Yearbook 2016, more than 31,000 megatons of CO2 was emitted globally in 2015. It is generally agreed that reduction of fossil fuel uses requires alternative, economical energy sources that are less carbon-intensive. One such alternative source is biofuels, or fuels derived from contemporary biological processes, such as plant or microbial growth processes. These processes takes in CO2 from the atmosphere and converts the carbon into potential fuels.

The two most common types of biofuels in use today are ethanol and biodiesel. Biodiesel can only be burnt in diesel engines. Ethanol is mostly used as blending agent with gasoline to increase octane and cut down carbon monoxide and other smog-causing emissions. It cannot be burnt directly in the vast majority of car engines today. Even specially modified vehicles, called Flexible Fuel Vehicles, can only run on E85, an alternative fuel with 85% ethanol content. In addition, ethanol has about half the energy per mass of gasoline. Butanol is considered better than ethanol because butanol’s energy content is close to gasoline, and can run in any car that uses gasoline without the need for modification to engine components.

First vs. second generation biofuels

First generation biofuels refers to fuels that have been derived from sources like starch, sugar, fats and vegetable oil, found commonly in arable crops. The fuel is obtained using the conventional techniques of production. Research has shown that energy must be invested into producing crops and converting them into biofuels before any energy is obtained. A 2005 study from Cornell University found that producing ethanol from corn used almost 30% more energy than it produced. In other words, invested energy is lost in creating them in the first place, breaking even is impossible according to the 2nd law of thermodynamics.

In contrast, second generation biofuels are made from lignocellulosic biomass or woody crops, agricultural residues or other waste materials. It is more difficult to extract the required fuel from waste than from virgin materials because more processing steps are required to break down the lignocellulose or woody waste matter.

However, current research into second generation biofuels production has achieved several breakthroughs. At the NUS Environmental Research Institute (NERI), the work of several research groups such as those of A/Prof He Jianzhong has been successful in butanol production via fermenting biomass.

According to Prof He, the secret lies in the successful cultivation of a wild-type solventogenic Clostridium species, which could utilize lignocellulosic waste such as its feedstock. This Clostridium directly converts biomass (such as sugarcane bagasse, food waste, horticultural waste hydrolysate) into butanol.  This bacterium possesses hydrolysis enzymes (e.g., amylase, hemicellulase, etc) which could efficiently hydrolyze these organics into monosugars for following on fermentation

Other advantages

There are other advantages of this new Clostridium strain, according to Prof He.

  • High amount of butanol generated in the fermentation broth.
    After process optimization such as applying two-state batch fermentation, butanol can be produced up to 19 g/L in the fermentation broth by this Clostridium with glucose or cassava starch as a substrate, reaching the industrial economical demand level.
  • Co-production of riboflavin improves the economic value in the fermentations process.  This strain could synthesize riboflavin when using glucose or xylose as the substrate.  The high amount of riboflavin (~120mg/L) produced in the fermentation broth makes the fermentation process more economically competitive with the sole butanol production.
  • Elimination of carbon catabolic repression during the fermentation process. 
  • This strain is capable of simultaneous utilization of glucose and xylose usually co-existing in the lignocellulosic hydrolysate, leading to elimination of carbon catabolic repression and having great impact on direct utilization of lignocellulosic materials.
Conversion from waste substrates through Clostriduim to butanol for fuel.

Prof He added that wild type microbes have advantages over genetically modified microbes in that they are more resilient to invading species in the open environment, and can replicate and sustain its populations over many generations. This has implications for scale-up production of butanol in large reactors, which are basically open systems that operate continuously. Under these industrial settings, wild type organisms might survive better and have greater practical uses.

Therefore, the approach of identifying wild type organisms and optimising their biofuel production potential, such as butanol, might be one of the ways to combating many environmental challenges, including climate change.

This work has been published in the following:

  1. Yan Y, A. Basu, T. Li, and J. He. 2016. Direct conversion of xylan to butanol by a wild-type Clostridium species strain G117. Biotechnol. Bioeng., 113: 1702-1710.
  2. Xin F, A. Basu, K-L. Yang, and J. He. 2016. Strategies for production of butanol and butyl-butyrate through lipase-catalyzed esterification.  Bioresource Technol., 202: 214-219
  3.  Xin, F., A. Basu, M. C. Weng, K-L Yang, and J. He. 2016. Production of 2,3-Butanediol from Sucrose by a Klebsiella Species.  Bioenerg. Res. 9: 15-22
  4.  Li, T., Y. Yan, and J. He. 2015. Enhanced direct fermentation of cassava to butanol by Clostridium species strain BOH3 in cofactors-mediated medium. Biotechnol. Biofuels.  8: 166
  5. Wu, Y-R., and J. He. 2015.  Characterization of a xylanase-producing Cellvibrio mixtus strain J3-8 and its genome analysis.  Sci. Rep. 5:10521.
  6. Wang, S., K. R. Chng, A. Wilm, S. Zhao, K.-L. Yang, N. Nagarajan, and J He. 2014. Genomic characterization of three unique Dehalococcoides that respire on persistent polychlorinated biphenyls. Proceedings of the National Academy of Sciences of the United States of America (PANS), 111:12103-12108.