Page 32 - Chemical Technology

water treatment
◦ including decisions regarding the inclusion of labour
and transport which have to made.
The decisions made during this step assist in forming
the assumptions that will be used in the water account-
ing calculation.
Water Footprint accounting
During this step a water balance is performed. Beyond
this, the water footprint concept distinguishes and
separates water by type, resource and quality. The water
footprint consumption is classified as blue water, green
water and grey water. A water footprint is the sum of blue,
green and grey water.
Water Footprint = Blue Water + Green Water + Grey Water
Green Water=Green Water Evaporation+Green Water
Incorporation
Grey Water
Grey water is the volume of water required to assimilate
the waste stream, to ensure that the ambient water qual-
ity of the water system is not disturbed. The grey water
footprint can be calculated using the following equation:
GreyWater L
C Cmax natural
=
where:
L is the pollutant load (mass/time)
Cmax is the ambient water quality standard for the
pollutant (mass/volume)
Cnatural is the natural concentration in the receiving
water body (mass/volume)
Water Footprint sustainability assessment
The calculated water footprint is assessed during this
step to determine the effect the business operation or
process has on the local environment and society.
Water Footprint response formulation
Recommendations are made in this last step of the
Water Footprint Assessment on how to reduce the impact
that the process has on the local water scarcity and pol-
lution. Methods, a time frame and a responsible person
are specified.
Some Water Footprinting examples
Water Footprint of SAB Miller
SAB Miller in partnership with WWF conducted a water
footprint assessment study for beer produced in two
different countries, the Czech Republic and South Africa.
This was a total water footprint assessment study cover-
ing both the direct and indirect water consumption of
producing a product measured across the whole supply
chain. This means for direct water use, it covered the
water consumption in manufacturing processes in mak-
ing the product, and for indirect water use, it covered the
water consumption for growing, transporting, consum-
ing and disposing of the product (Hoekstra, 2003). The
purpose of the assessment study was to (Hastings and
Pegram, 2012):
• Understand and compare the water consumption in
the beer supply chain in the two countries; and,
• Understand how the company can use the Water
Footprint Assessment to help make decisions.
The study covered the whole supply chain of the beer-
making process, from crop cultivation, crop processing,
brewing, distribution to disposal and recycling. The find-
ings were that agricultural cultivation was the largest con-
tributor to the water footprint, accounting for about 90%
of water consumption in both the Czech Republic and
South Africa. The water footprint of beer in South Africa
was 155 litres of water per litre of beer and 45 litres of
Hoekstra (2011) defines ‘consumption’ as a decrease,
reduction or loss of water through different mechanisms
that are available from a defined space, such as river
basins, catchment areas or production processes.
Examples of consumption include:
• Evaporation of water;
• Incorporation of water into a product;
• Spatial considerations (water is taken from one
specific area and returned to a different area); and
• Temporal considerations (water is withdrawn in winter
and returned in summer).
Blue Water
Blue water is the amount of water removed from ground
and surface water sources during the production of a
product that is not returned to the same source or during
the same time. The blue water footprint for a process
step is calculated using the following equation:
BlueWater=BlueWater Evaporation+BlueWater
Incorporation+Lost Return flow
Lost return flow refers to the water that is returned to
another source or at another time.
Green Water
Green water is the amount of rain water used during the
production process that could have been stored in the
soil or temporarily on top of the soil. The green water for
a process step is calculated using the following equation:
Figure 2: Water Footprint consumption
30 Chemical Technology • January 2013