Mi ¼ MGDP;i ai bi ci di ð Þ; ð4Þ
where
Mi is the flux of MSW in scenario i (kg·person−1 day−1).
MGDP,i is the flux of MSW in scenario i calculated as
a function of GDP in scenario i.
ai is the parameter considering the relation
between the amount of people living in the urban
area and that in the rural area of MRS in scenario i,
in comparison to scenario BAU (urbanization
process).
bi is the parameter considering the change of
household size between scenario i and BAU.
ci is the parameter considering the change of
household income between scenario i and BAU.
di is the parameter considering the change of years
of schooling between scenario i and BAU.
The MGDP to be used in Equation 4 is calculated as
follows:
MGDP;i ¼ 0:0294 GDP0:367
i
þ 2:6473 105
GDPi 0:1908; ð5Þ
where GDP again is the gross domestic product in scenario
i.
Urbanization processes (factor ai): in several
studies [28-30], a positive correlation between the
degree of urbanization and waste generation was
found, whereas more densely populated areas
(urban areas) are producing more waste per capita
than rural areas and that MSW production in
cities can be twice as high as that in rural areas.
The degree of urbanization also affects indirectly
waste generation due to a change in consumption
patterns. For this study, it was assumed that a
doubling of the share of people living in urban areas
(compared to the BAU scenario) would lead to an
increase in the production of MSW per capita
by 30%.
Household size: larger households produce less
waste per capita than smaller ones [28,30-33]. It is
assumed that a doubling in the household size
(compared to the BAU scenario) would lead to a
decrease in the production of MSW per capita
by 60%.
Household income: more affluent households are
more likely to produce larger quantities of waste
than the less affluent ones [28-31,33-36].
Additionally, income and MSW production are
linked to some extent, but at a certain level of
income, they become delinked. The turning point
occurs at very high levels of value added per capita
[33]. It is assumed that a doubling in household
income (compared to the BAU scenario) would lead
to an increase of 80% in the production of MSW
per capita.
Years spent in education: households with only
primary education produce more waste than those
belonging to professional levels [33]. However, not
much research has been conducted in this area. For
this reason, it was assumed that a doubling in the
years spent in education (compared to the BAU
scenario) would decrease MSW production per
capita by 20%.
For the calculation of parameters ai to di, (named as
gi), a linear correlation was used:
gi ¼ 100% þ ΔgBAUi CFg ; ð6Þ
where
gi are the parameters a to d, for scenario i.
ΔgBAU-i is the variation between the BAU scenario
and scenario i, for parameters g.
CFg is the correction factor for parameters g.
Table 2 summarizes the results of Equation 6 for each
parameter a to d. The correction factor (CF) is directly
taken from the overall framework scenarios, developed
by the Risk Habitat Megacity Project [18].
Selection of MSW management technologies for the
different scenarios
Each scenario is defined by storylines and specific framework
conditions. Based on these, it was possible to develop
a general waste mass flow defining the different
waste treatment options to be applied in each scenario;
however, for each of these treatment options, different
technologies exist.
The choice of which technology can be applied depends
on the specific scenario because each technology
was evaluated and compared by means of variables, including
technical, environmental, and economic aspects,
but the weight importance given to each aspect differs in
each scenario, as shown in Table 3.
Variables used in the evaluation include:
1. Technical aspects
(a) Quantity of residual waste sent to landfill after
treatment
(b) Quantity of compost produced
(c) Quantity of metals recovered
(d) Quantity of energy recovered