Biorefineries using waste – production of energy and chemicals from biomasses by micro-organisms - Biomass as Energy Source: Resources, Systems and Applications - page 242

of the most considerable stores for the solar energy in chemically bonded form. In practice, its
exploitation is restricted by the lignin fraction of the biomasses in wood and other plant-derived
sources (Gressel and Zilberstein, 2007).
In a novel application, direct conversion of lignin into liquid bio-oil is achieved with a very low
oxygen content of the product (Kleinert and Barth, 2008). In this liquefaction process, formic
acid serves both as a hydrogen donor and a pyrolysis/solvolysis reaction medium. It has been
stated that “Conversion of biomass to chemicals and energy is imperative to sustain our way of
life as known to today” (Amidon et al. , 2008). A biorefinery plant is “a catch and release” way of
using carbon that is beneficial to the environment being also feasible from the point of view of
the global economy. In this context, it is important to emphasize that this label of environmentally
friendly technologies has to include the recycling of wood-derived products, improved care of the
liquid and gaseous disposals, and protection of global forest ecosystems as a diverse reservoir
of plants and animals. The multiple uses of forests for recreation, as sources for medicinal plant
species and molecules, berries and fruits, mushrooms and other species of relevance for humanity,
as well as a valuable “respiratory” organ for the earth, should be taken into account when designing
the exploitation of forests or forest ground. It should also be clear that combustion is a wasting
process for the wood rawmaterials. Therefore, improved strategies and methods need to be further
developed.
Sugar maple woodchips were subjected to hot water extraction at 160 ◦ C for two hours (Amidon
et al. , 2008). In an extraction pretreatment, the wood material can yield 15% of the mass recov-
ered as wood sugars (2/3) and as acetic acid and other extractives (1/3) (Amidon, 2006). These
extraction products have the value being one-half of the value of the wood. Therefore, it could be
considered as highly feasible to extract wood or other cellulose-containing biomasses. These rev-
enues could then be further increased by producing valuable chemicals from these materials. The
most widely used pulping technology, theKraft process, is removing about 20%of thewoodweight
as hemicellulose during cooking. The resulting black liquor has a heating value (13.6MJ/kg)
about 50% that of lignin (25MJ/kg) (Gullichsen and Fogelblom, 2000). Consequently, it could
be more feasible to extract the hemicelluloses prior to pulping. This approach could then
lead to such higher value-added products as ethanol, butanol and 2,3-butanediol, or various
polymers.
Besides the industrially disposed materials, the municipal waste fractions contain high amounts
of carbohydrates, such as paper wastes, mixed wastes, fibrous packing materials, biowaste, and
parts of the construction wastes, which could be treated in a biorefinery type of processes (Rättö
et al. , 2009). Theoretically, the mixed wastes dumped into landslides in Finland could produce
annually 260.000 tonnes of ethanol from these materials. For example, in the UK there has been
developing a strong interest in producing fuels frommunicipal wastes instead of combusting them
directly (www.engineerlive.com). Critical water (250-300 ◦ C under elevated pressure) has been
suggested for extractions and separations. When the pressure is then lowered, the water returns
to its normal properties. In addition, gas-expanded liquids such as methanol with CO 2 provide a
flexible solvent whose properties can be adjusted by changing the pressure. The cellulose polymers
can also be decomposed by using supercritical water or methanol extraction methods (Ehara and
Saka, 2005; Ishikawa and Saka, 2001). For instance, supercritical methanol treatment at 350 ◦ C
with 43MPa for 7 minutes, for instance, converted microcrystalline cellulose (Avicel) to the
methanol-soluble form. These types of reactions could potentially be used also as pretreatments
for industrial microbiology processes.
In our laboratory in Finland, we have established the use of the PMEUmethod for the microbial
monitoring of the process waters (Mentu et al. , 2009). The ecology of the processes and products
thereof has a decisive role for the characteristics of the products. Similarly, the bioprocesses
originating from wood could be monitored by the PMEU system. This kind of laboratory inves-
tigation has revealed a balanced action of common enterobacterial intestinal strains (Hakalehto
et al. , 2008). These bacteria, which occur also in the wood industry fluids, are forming symbiotic
co-cultures. Such interactions are providing huge potential for industrial microbiology processes.
For example, we have studied the conversion of cellulose plant wastewaters into bulk chemicals,