Enhanced Microbial Process in the Sustainable Fuel Production
Authors: Hakalehto Elias 
Published: July 2015

Various biomass sources, such as wood and other plant materials, animal wastes, food and other industry wastes, household wastes, sludge varieties, marine biomass, peat and other carbon‐rich organic reservoirs, offer raw materials for continuous recycling in sustainable bioindustries. The corresponding circulation of matter also maintains the balance in the ecosystems and is powered mainly by the solar energy. A substantial portion of this energy is stored in different forms of biomasses and is liberated by the microbes in “the economy of the nature.” In order to achieve the goals of sustainable development, human agriculture, industries, and other activities should fit into this framework set by the microbial degradation and the reuse of molecules. Those principles are adaptable into the production of energy and chemicals.

Microbes constitute ecosystems of their own, for example, in the intestinal milieu, or in lake sediments. Everywhere, the microbial communities interact with their surroundings. The types of molecular communication in the microscopic level determine the functioning of larger scale ecosystems and also the bioprocesses. In both natural and industrial settings, the ecological principles are alike. Microbes circulate the elements and convert chemical energy into novel formations. If the microbial population is dense and versatile, different species often develop symbiotic forms of action.

Biotechnical processes consist of several steps. In order to achieve optimal biorefining results from a particular process, all these steps require careful consideration. Various biomasses could be combined with each other in order to obtain optimal starting material and conditions in the process. Physicochemical characteristics (dry weight, consistence,pH, etc.) need to be adjusted according to the process needs. Initial steps of sample preparation include homogenization, hydrolysis, and other pretreatments. In most biotechnical procedures, operation temperature plays a significant role. Controlling it becomes more challenging as the biomass volumes increase. Biorefineries could resemble “activity fields” where different substances flow and are then converted further into meaningful direction, adding value into the production process.

Biomass exploitation could be based on the vast potential of biocatalysis in designing processes with positive net energy balance. In microbial fermentations, carbon dioxide is one main product of the biochemical pathways. However, alternative routes for the production of some biochemicals, such as 2,3‐butanediol, with diminished carbon dioxide generation and more substantial recycling of carbon have been found using a testing system for enhanced microbial culturing, the portable microbe enrichment unit (PMEU). For example, in the conversion of food industry wastes, levels of 8–10 g/L/h of 2,3‐butanediol have been observed. Also, enhanced productions of organic acids, ethanol and butanol, as well as methane and hydrogen, have been achieved by this method. The bioconversion approach opens up novel views on producing fuels from waste materials with lower investment costs. Besides the aerobiosis, the microaerobic and anaerobic (low oxygen containing) processes and their enhancement offer alternatives from the point of microbial metabolism.

As a bioreactor system is usually based on the conversion of biomass raw materials, the success of the entire process is dependent on the careful management of these conversions. Organic macromolecules are degraded to smaller molecules by physical, chemical, and biochemical hydrolyzation. They act as a starting point for microbiological metabolic pathways. Speeding up the process often builds up a gradient where joint effects of metabolic regulation and diffusion limitation, as well as overcoming them, play an essential role in the product formation. Microbial strains and their enzymes act as biocatalysts, which can also be circulated in the process or immobilized. Surfaces between different phases create conditions where the accelerated gradient formation improves overall performances of a bioreactor. Besides optimized upstream processes, successful production of organic substances by microbes for energy and chemicals requires an integrated downstream processing system. Different aspects for bioprocess design are presented here with respect to increased production efficiency and improved overall sustainability in biofuel production.