2.1. Blue water footprint (WFblue)
In WWTPs, the blue water footprint accounts for the water that
evaporates during wastewater treatment and the water used for all
processes related to the different WWTP unit operations (chemicals,
energy consumption, residue management, transportation
and sludge treatment) that is incorporated into the final product.
For example, the consumption of chemicals and energy has an
associated blue water footprint due to the water incorporated
during the production of chemicals and energy. However, the lost
return flow, which is considered in the blue water footprint, of
other processes or products will be zero when the treated WWTP
water is discharged into the same catchment. In certain cases, it can
be interesting to consider the route of blue water, particularly in
processes or products from agriculture (distinction of the water
based on if it comes from the surface, groundwater or another
source). Water recycled back to the process or used for other applications
(e.g., WWTPs that have tertiary treatment and produce
reclaimed water) should also be accounted (as avoided water)
because it reduces the blue water footprint.