Environmental Engineering Reference
In-Depth Information
exploit nature's own means for circulating matter. The corresponding technologies represent
sustainable industries in their purest form. Their usage includes also circulating the waters. In
addition, the carbon-containing gases like CO and CO
2
are being effectively collected in the
biorefinery solutions. All the waste materials become useful substrates for the future industries.
13.2 SUSTAINABLE PRODUCTION OF FUELS AND CHEMICALS FROMWASTES
AND OTHER BIOMASSES
13.2.1
Circulation of matter and chemical energy in microbiological processes
In biorefinery industries, wastes are not wastes, but they form another raw material source.
Establishing biorefinery “fields” instead of landslides, for example, we are able to fully exploit
the circulation of matter described above. During these times of critical oil price fluctuation and
risks of inadequate supply, the biomass alternative could offer a replacement and new backbone
for our modern societies. This sustainable alternative is based on the enormous potential of
microscopic cells and their enzymes in the production of fuels, plastic, textiles, bulk chemicals
and other commodities.
The cell theory was established in 1839, and the reproduction of cells by division was affirmed
as a basis of biological life in 1858 (Graham, 1982). All metabolic activities of the cells require
exchange of substrates with the surroundings. Small bacterial cells have more surface area in
proportion to the cell volume than the larger eukaryotic cells. This partially explains the relatively
high speed of their metabolic action. The basis of this exchange of substances is the diffusion
of gases. In aerobic bioprocesses on optimal substrate availability oxygen is usually forming the
rate-limiting step.
The smaller the cells are, the quicker the nutrient molecules are diffused and metabolized
inside the cells. The pace of the metabolic events is determining the rate of the production of the
biochemical (of course taking the cell's regulatory mechanisms into account). Thus, the overall
productivity of the biotechnical reaction is largely depending on the diffusion conditions. The
gases are freely diffused into and out of the cells, whereas larger molecules, such as glucose, need
facilitated diffusion across themembranes with carrier molecules. Undoubtedly, the concentration
gradient is contributing to the rate of transport. The active transport requires energy in the form
of the ATP. Naturally, the diffusion moves substances from higher concentrations toward the
lower ones. Therefore, exploitation of the diffusion and overcoming it on the other hand play a
key role in the cell metabolic efficiency. These principles are offering new grounds for modern
biotechnology era.
Waste is a heterogeneous energy source and different types of wastes can be converted into
different energy products or bulk chemicals in different conversion processes (Thorin
et al.
, 2011).
In all reaction sequences, the convertible source of chemical energy is derived from solar energy
bound on the plant material and into the nutritional chains. Microbes carry out the degradation
and circulate the matter in nature. This approach has been adopted by the industrial microbiology
discipline.
13.3 REPLACING FOSSIL FUELS BY THE BIOMASSES AS RAW MATERIALS
The term “feedstock” refers to raw materials used in biorefinery (Cherubini, 2010). The biomass
is synthesized via the photosynthetic process that converts atmospheric carbon dioxide and water
into sugars. In a photosynthetic organism, such as an algae or a plant, the cells utilize the sugar
molecules to synthesize
via
the biosynthesis the complex materials that are generically named
biomass. Then the so-called heterotrophic organisms use the organic biomass as raw materials for
their catabolic and anabolic reactions. These further conversions from one entity to another one
are establishing also new classes of substrates. As the raw material supply is an important stage
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