Page 132 - Sustainability in the Process Industry Integration and Optimization

Ma s s I n t e g r a t i o n 109

represents the total rainwater evaporation from the fields during a
crop’s growing period. The virtual blue water content of a product is
the volume of surface water or groundwater that evaporates as a
result of production—for example, the evaporation of irrigation water
from fields, irrigation canals, and storage reservoirs. The virtual grey
water content of a product is the volume of water required to dilute
pollutants in order to meet water quality standards for reuse or
discharge to the environment. A water footprint can be calculated for
any product or activity that has a well-defined group of producers
and consumers. The water footprint is a geographically and
temporally explicit indicator: it reflects not only volumes of water
consumption and pollution but also the type of water use as well as
where and when the water was used.
The idea of water life-cycle assessment has gained more interest
since the concept of a water footprint was introduced (Hoekstra and
Chapagain, 2007; Hoekstra, 2008). In food supply chains, the actual
water content of the final product is usually negligible when
compared with the virtual water content, which is the total fresh
water used during the various steps of supply and production. Aside
from the water that appears as an ingredient in prepared foods, most
water use in the food industry consists of the virtual water described
in the previous paragraph (Casani, Rouhany, and Knøchel, 2005).
The most common water-using operations are as follows:

• Heating: Boilers, heat exchangers, etc.
• Process water: Cooling towers
• Potable uses: Offices, canteens, etc.
• Washing: Equipment, bottles, floors, vehicles, etc.
• Rinsing: Equipment, bottles, food materials, final products
• Firefighting
• Transport medium

The food industry consumes a large amount of water: its
3
consumption was estimated to be 347.2 Mm in Canada (Dupont and
3
Renzetti, 1998) and 455 Mm in Germany (Fahnich, Mavrov, and
Chmiel, 1998). Other studies (Hoekstra and Chapagain, 2007; Water
Footprint Network, 2009) have reported figures for use of virtual water
in the production of some common food products; see Table 5.1.
Just as in the case of heat recovery, for water recovery it is best to
start with simple measures based on efficient management (e.g., good
housekeeping) before moving on to more advanced methodologies
(e.g., Process Integration techniques). Industrial operations are not
always run in continuous mode, since they depend to a great extent
on the availability of feed stock and the need to control quality. As
mentioned before, sugar, fruit juices, and cereal are typically
processed intermittently, and breweries operate continuously. These