Environmental Engineering Reference
In-Depth Information
was discussed in Chapter 8, in the section titled, “Air Cycle Refrigeration.” The idea has been
known for more than a century, but the compressors capable of running this cycle were just
developed in the last few decades.
In the food-processing arena, several technologies are promising in terms of reduction
of environmental impact and reduction of emissions. Few examples of these technologies are
pulsed electric fields, high hydrostatic pressure, supercritical/subcritical fluids, and membrane
separation systems.
Application of pulsed electric fields is a technique that works alone or in combination with
other processing technologies. When cells are exposed to a pulsing electric field of enough
intensity, the field induces the formation of pores in the cell walls, which produces microbial
inactivation and can be a pretreatment for drying, disintegration, and extraction. The reader
with interest in this topic may consult Toepfl et al. (2006).
Supercritical fluids, particularly carbon dioxide, have been used for an extensive period of
time in applications such as decaffeination of coffee. Other uses, such as the extraction of
vegetable oils from oils seeds, have been studied at laboratory scale extensively, but up to now,
no industrial systems are in place. The extraction of vegetable oils with supercritical carbon
dioxide would reduce furtive emissions of hexane, a petroleum-derived solvent with concerns
in human health, and likely reduce the total emissions of carbon dioxide.
When water is heated under pressure above its boiling point and below its critical point
(374°C and 218 atm), it is in subcritical state. In the subcritical range, water properties change
as the temperature increases and approach the critical point. The dielectric constant and den-
sity decrease to the point of resemblance of nonpolar solvents. Water maintained in subcritical
state can be used as a solvent for extractions or to conduct chemical reactions (e.g., hydrolysis
of protein or carbohydrates).
Separation with membranes is not a new technology, but still there is room for innovative
applications. For the purpose of illustrating the idea, an example will be presented about the
combination of reverse osmosis and evaporation in the sugar industry. The production of cane
sugar relies heavily on evaporation to concentrate the sugar content. Juice extracted from the
cane contains around 15 percent of sugars and is concentrated in multiple effect evaporators
to around 60 percent where it is further processed. Madaeni and Zereshki (2008) have reported
that a preconcentration using reverse osmosis performed before evaporation could produce
energy savings of 33 percent and consequently less energy consumed and less direct emissions
of carbon dioxide to run the evaporators.
In the packaging arena, new advances, such as active packaging, will not only improve
the quality and safety of food products but also extend their shelf life. More stable products
translate into less waste and as a result a contribution to more sustainable practices. (See
Chapter 12 for more on sustainable packaging alternatives.)
LOW CARBON AND NEUTRAL CARBON ENERGY
Buying “green power”
Green power is a term used to identify energy, especially electricity, which has been produced
from renewable resources, such as wind, solar, geothermal, low-impact hydro, biomass, and
geothermal sources (Fig. 11.7). There are other sources of renewable energy, for instance,
large hydroelectric power, that are not included in the subset of green power.
Green power is offered in many parts of the world including North America, Europe,
Australia, and Japan; and it can be purchased at a premium from utility companies or other
