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Causal Loop Analysis
From the observed waste flow the
cause and effect relationships of the variables
were analyzed. This relationship is shown in
Figure 6. Household population, number of
commercial establishments, institutions and
market were factors affecting the rate of solid
waste generation. As these sources of waste
increased, so do the volume of generated
waste as affected by waste generation rate.
The total amount of waste is reduced through
composting, recycling, and collection activities.
Waste collection activities increase the
stock of waste in the dumpsite. Uncollected
wastes in residential areas were treated
traditionally through backyard burning by the
residents. These burning activities reduced the
quantity of unmanaged waste.
Of all the elements in Figure 5, per
capita waste generation and population are
the strongest factors influencing total waste
generation.
Identifying Stocks, Rates, and Auxiliary
Variables
The stocks are the elements of the
solid waste flow that accumulate or decrease
over time, the rates are the factors that control
the increase or decrease of the stocks over
time and the auxiliary variables are the factors
that quantify the rate variables.
Based on the causal loop, the identified
stocks were the generated wastes from the
households, commercial establishments,
institutions and the market, total solid waste
generated, compostable solid waste, recyclable
solid waste, collected solid waste, and littered
solid waste.
The rate variables quantify the increased
or decreased of the stocks. The increase in
household waste is a function of the average
annual growth rate of the populations, the
increase in commercial establishments,
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institutions, and the markets wastes is a
function of the average annual growth rate of
their generated waste. The increase in total
waste generated is a function of the rate of
waste generation by the four sources.
Linking Stocks, Rates and Auxiliary Variables
The stocks, the rates and the auxiliary variables
of the model were linked as shown in Figure 6.
This was developed using Stella software. The
rectangles are the stock variables, the valves
are the rate variables, while the circles are the
auxiliary variables. The red arrows show the
flow of information as one variable affect other
variables. The bigger blue arrows show the
flow of wastes as they moved from one stock
to the other.
Information on the sources of wastes
such as the population data, average annual
population growth rate, per capita generation
rate, and growth rate of waste generated from
commercial establishments, institutions and
market were used to parameterized the model.
Information on the rate of generation linked the
sources to the stock of waste they generate.
The stock of total waste generated
was then broken down into several stocks
such as compostable, recyclable, collected,
and unmanaged waste. The stock of total
waste generated was linked to the stock of
compostable waste using data on the percent of
compostable waste, percent rate of segregating
waste and total waste generated in the area.
The stock of total waste generated was linked to
the stock of recyclable waste using information
on the percent of recyclable waste, percent
rate of recycling and the total recyclable waste
in the area. The stock of total waste generated
was linked to the stock of collected waste using
information on the capacity of garbage trucks.
The stock of total waste generated was linked
to the unmanaged waste using information on
the volume of uncollected waste.
The stock of compostable was linked to
the stock of compost using information on the
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