3.2. Potential effects on human toxicity and smog creation from
collection system
The collection system was investigated according to two additional
environmental impacts beside GHG. These indicators support
the deep examining the potential impacts being important in urban area such as the human toxicity (analysed by human toxicity
potential/HTP/indicator of CML-IA) and the smog creation potential
(investigated by the photochemical ozone creation potential/POCP/
CML-IA).
The results of HTP showed a familiar distribution as it was found
in the case for GHG, although larger differences could be observed
between the different collection systems (cf Fig. 3 and Table 3). The
lowest impact was caused by the kerbside bag system with approx.
0.009e0.05 kg DCB-equiv./1000 L packed volume (5th columngroup
on Fig. 3.). It was followed by the deposit-refund system
and by the kerbside bin system with values from 0.02 up to 0.7 kg
DCB-equiv./1000 L packed volume. The thermopress method
seemed to be the worst collecting option for plastic bottles with a
human toxicity impact in the range of 0.06 and 0.23 kg DCB-equiv./
1000 L packed volume depending on the specific weight of PETbottle.
Around 64% of HTP originated in direct emissions of transport at
kerbside bag and kerbside bin. Lower ratio of impact could be
identified from direct transport emissions in cases of depositrefund
(31e40%) and sub-systems using thermopress (4e10%).
Significant shifting of HTP between direct and indirect sources was
found in specific cases, in which the processes were using electricity
such as the thermal or mechanical compression of plastic
bottles.
Kerbside bag system showed less beneficial results for POCP in
contrast to the GHG emission and HTP (cf. Figs. 3 and 4 and Table 4).
It originates in the solely diesel fuelled transportation. Best indicator
results were found at collection of PET-bottles in depositrefund
system, but for Al-cans the kerbside bag remained the
best solution in this impact category, as well (cf. Figs. 3. and 4).
Using kerbside bins or employing the thermopress process led to
significant increase of POCP (see Fig. 4.).
Relation of transport direct emissions to external processes of
home take back and collection point found to be around 50:50,
while deposit-refund collection exhibited a proportion by 74e76%
and 26e24% for transport and external processes, respectively. It
was based on of the less effective transport of passenger cars from
the consumers to supermarkets. The relation was changed in case
of thermopress to 2e5% participation of transport and 95e98% of
external process, due to the extreme high electricity demand of
thermo-compression (see Table S4).
To make an easier interpretation of results an external normalisation
depicts the dimensionless outcomes in the Table S5/aec
and Fig. S1. The advantage of lightweight materials like carton or
aluminium leaves no doubt. The effect of bottle volume can be also
observed, bigger the volume smaller the potential environmental
effects of collection, although this reduction after the PET 1.5
seemed to be plateauing. It may be an effect of compressibility
assumed in the model.
At thewaste collection, the density ofwaste becomes important,
for example the PET-bottles and carton show the significance of the
balancing between weight and volume, namely the effective
compression in the case of bigger PET-bottles or cartons might lead
lower impacts in smog creation category (cf. Fig. 4 or Fig. S1 POCP of
thermopress and coll. point PET 2.0).