When the estimated specific energy
was converted to indirect carbon footprints
(i.e. 0.9 kg CO2
-e/kWh), the indirect
GHG emission was estimated to be in
the range of 0.20 kg CO2
-e/kL (H2
O2
/UV
treatment process) to 10.73 kg CO2
-e/kL
(O3
treatment process) (see Figure 4) (Hall
et al., 2009). It is apparent, however, from
Figure 2 that a comprehensive sustainability
assessment cannot be made, as these
estimations were not validated through
energy system monitoring, as well as the
fugitive GHG emissions which add up to
the overall carbon footprint for sustainability
assessment of different AOTs. Further
inventory data sets from different pilot or
full-scale AOT plants are needed to allow
for a more accurate and comprehensive
multi-criteria assessment of AOTs for
decentralised wastewater applications.
However, the costs estimated in this study
still present a useful guide on the selection
of AOTs based on technical, economical
and environmental criteria.