Journal of Environmental Protection, 2010, 1, 105-110
doi:10.4236/jep.2010.12013 Published Online June 2010 (http://www.SciRP.org/journal/jep)
Systemic Analysis of Supermarket Solid Waste
Generation in Mexicali, Mexico
Aurora Fierro Ochoa, Moisés Galindo Duarte, Lorenzo A. Sánchez Bueno, Benjamín Valdez Salas,
Gisela Montero Alpírez, Michael Schorr Wiener
Engineering Institute, Autonomous University of Baja California, Mexicali, Mexico.
uabc.mx, ,
Received March 20th, 2010; revised April 16th, 2010; accepted April 20th, 2010.
ABSTRACT
The common practice of managing solid waste (SW) generated by supermarkets in Mexicali, Mexico, consists of mixing
all kinds of SW without any separation process. The concern of these actions is that does not involve some of these
products to be reused or sold for recycling. The company ceases to receive an income of $ 3,881 Mexican pesos as an
additional benefit by the generation of approximately 5,869 kg of SW than can be recovered in only one of its eleven
branches in the city. However, the only two products that are valued by the supermarkets are wax boxes for fruits and
vegetables which are sold to a company that subsequently resell them to fruit shops for reuse, and the cardboard boxes,
whose weekly generation in one branch is 5,375 kg. They are separated from the waxed boxes and placed in a compac-
tor to form bales from 300 to 400 kg each and then are collected for sale to a recycling company. As for the generation
of different types of plastics that can be recycled, a branch generates weekly 339 kg. The model to simulate the genera-
tion of SW in supermarkets was performed using “system dynamics” as a tool for modeling and simulation in order to
make better decisions to reduce generation of waste.
Keywords: Solid Waste, Supermarket, Model, System Dynamics
1. Introduction
Mexican Law defines “waste” any material or product
that is solid or semisolid, which was discarded in con-
tainers or tanks and can be capable of being valued or
require treatment [1].
Mexican environmental policy promotes integrated
waste management through waste minimization, reuse,
recycling, source separation, and recovery of materials
and energy [2].
Some wastes have value for the company and are used
for their benefit [3] reducing the environmental impact
[4]. Disposal of these wastes in the form of garbage im-
plies a high cost to society [5] because the places where
waste can be deposited with the proper conditions of
health and safety must be enabled [6].
Mexico produced 36.8 million tons of SW in 2007 and
only 3.8% was recovered for recycling purposes. For
2009, the estimated SW generation was 38.3 million
tonnes of which only 68% were disposed in landfills or
controlled sites [7]. The separation of re-usable materials
from landfills is a common economic activity developed
by people working in low economic conditions. Cur-
rently, the separation takes place mainly in the informal
sector of scavengers that separate the material before
harvesting or before final disposal [8].
In 2007 in Mexicali were collected 773 tons of non-
hazardous SW, and in 2008 were generated 850 tons.
Due to the increase in municipal and commercial SW
Mexicali opened about 54 thousand m3 of landfill cell in
the Ejido Benito Juárez. This increased the capacity of
solid waste landfill and impacted positively on the qual-
ity of life for Mexicali residents [9]. An unknown
amount of SW was generated by the supermarket sector,
including 35 stores [10], which are considered commer-
cial establishments [11].
The supermarket is a commercial establishment [11],
of retail [12] with a wide range of self-service products
[13] designed to meet the needs of food and household
products of consumers [14] with an area between 501 to
4.500 m2 [15]. Every day, tons of waste are generated in
the form of packaging, plastics, nonferrous metals, or-
ganic, and others that are not managed for reuse or recy-
cling [8].
The main issues for consideration by the supermarket
sector in the recycling of materials includes: identify the

Systemic Analysis of Supermarket Solid Waste Generation in Mexicali, Mexico
106
materials are diverted from the waste stream, the reuse
and recycling and the specifications of the buyers of re-
covered materials [16].
2. Methodology
The research methodology includes, characterization of
SW generated in the supermarket, conceptual model de-
sign, development of a quantitative model, and simula-
tion of the generation of SW at supermarket. The results
were analyzed in an Excel spreadsheet from Microsoft
and to develop and simulate the system dynamics models
were used Vensim and Stella programs.
2.1 Characterization of Solid Waste Generated in
the Supermarket
The operations manager of a regional supermarket chain
located in Mexicali was interviewed in order to request
permission to perform the characterization of solid waste
generated. The characterization was performed in only
one branch of that chain in the supermarket it was not
possible to apply the sampling technique under the quar-
tering using Standard NMX-AA-015-1985 since to ho-
mogenize the waste was difficult to obtain a uniform
sample [17]. For this reason, it was decided to sample in
situ adapting Standard NMX-AA-019-1985 to obtain the
weight of waste in kg rather than the volumetric weight
(kg/m3) [18]. The decision reflects the fact that super-
market managers did not agree to compact the waste and
not to wait to fill a container of known volume. For this
reason, the garbage was placed in the container as they
would be generated.
For the waste characterization it was necessary to use a
scale at the temporary disposal site within each super-
market where each head of department maintained the
waste generated before being deposited in the container.
The residues were separated by-product and placed on
the scales and subtracting the tare. The results were re-
corded in a log sheet following the registration form
by-products of the Standard NMX-AA-022-1985 [19].
The adequacy of the format was evaluated according to
the predominance of the type of waste found and that
some of the items listed in record format of the standard
were absent or the amounts found were minimal [20].
Thus, all waste generated in a day of activities within the
supermarket was characterized.
2.2 Design the Conceptual Model
The elements of the system and their relationship were
determined based on the objective. These were classi-
fied according to their specific role in the structure of
the system and the relations between components that
generate the dynamics of the system were also identi-
fied [21].
Finally, it was drawing up the formal outline of the
conceptual model using the symbology of “System Dy-
namics” [22]. The data used to feed the model are the
initial value of solid waste in the container and cardboard
in the area of receipt, the packaging for recycling fraction,
the fraction of waste packages for the weekly flow of
cardboard and paper, plastics, construction waste, wood,
glass, garbage, organic waste, nonferrous metals, and
shrinkage.
2.3 Development of the Quantitative Mode
In the analysis, the quantitative model of the system un-
der study was developed using the conceptual model as a
basis, and thus set the rules governing the flow of mate-
rial into the system using mathematical representations.
2.4 Simulation of the Generation of SW
Several runs were made of the proposed models by
comparing the system behavior under different condi-
tions of interest.
3. Results
The regional supermarket generated 5,375 kg of carton
(Figure 1). This material was compacted into bales of
0
200
400
600
800
1000
1200
0
2
4
6
8
10
12
14
SundayMondayTuesdayWednesday ThursdayFridaySaturday
Cardboard (kg/week)
paper types (kg/week)
Day
Office paper
Tetrabrick
Egg carton
Paper deals
Fruit wrapping
paper
Cardboard
Figure 1. Quantity of cardboard and paper in kilograms per week generated in a regional supermarket located
in Mexicali, B. C. Source: characterization performed in summer 2008

Systemic Analysis of Supermarket Solid Waste Generation in Mexicali, Mexico107
0
2
4
6
8
10
12
14
16
18
20
SundayMondayTuesdayWednesday ThursdayFridaySaturday
kg/week
Day
PET bottles
Plastic film
Wrap producs
Grocery bags
Plastic display case
Plastic food packaging
Plastic buckets
Container cleaning
Figure 2. Quantity in kilograms per day of the week of plastics generated in a regional supermarket, located in
Mexicali, Mexico. Source: characterization implemented in summer 2008
350 kg, and then sold to a recycling company getting an
income of $ 2,956 pesos per week [10].
During the week 339 kg of plastic, with plastic film
were generated in larger quantities (Figure 2).
Causal models in Figures 3-6 show the interaction in
the management of various types of SW generated in a
regional supermar.
Figure 3. Causal model for paper and cardboard
Figure 4. Causal model for plastic and glass
Figure 7 shows a general outline of the model of “sys-
tem dynamics” for the management of waste generated
by-product. The model represents the internal destination
of the waste generated. First, the cardboard is separated
for sale and only a small amount is pulled into the con-
tainer because it lacks the characteristics required to be
sold to a recycler. The remaining waste is indiscrimi-
Figure 5. Causal model for waste, expired products and
organic residue
Figure 6. Causal model for wood, metal and construction
waste

Systemic Analysis of Supermarket Solid Waste Generation in Mexicali, Mexico
108
Figure 7. System dynamics model of the products of waste generated in a regional supermarket chain
Figure 8. Simulation results for different types of generated paper

Systemic Analysis of Supermarket Solid Waste Generation in Mexicali, Mexico 109
Figure 9. Simulation results for generated plastics
Figure 10. Simulation results for generated plastics
nately thrown into the container, instead of being sepa-
rated from the source for further appreciation.
Figures 8, 9 and 10 show the simulation results using
the “Stella” and can observe the dynamics of the various
types of waste generated during one week. These results
can be compared with those in Figures 1 and 2 obtained
from the characterization in situ.
4. Conclusions and Discussion
Supermarkets should classify the types and quantities
of solid waste being generated and also the tools that
are available to separate at source, that is, they must
carry out a sustainable management of waste generated
as this concept is based on identification of the possible

Systemic Analysis of Supermarket Solid Waste Generation in Mexicali, Mexico
110
uses of each of the materials contained in a product, to
provide from the conceptual stage the future handling
of the material itself is important and appropriate
choice of those providers committed to the environ-
ment [2]. Proper management of solid waste allows the
company to earn additional income to cover some of
their expenses.
The supermarket sector must be able to assess the en-
vironmental conflict that is generated by improper man-
agement of their waste and take part in the settlement
through their involvement. They should not wait for the
authorities verification, resulting in penalties and a poor
image for the company. Moreover, it is the responsibility
of the authorities to encourage the creation of companies
engaged in the collection and recycling of packaging [7].
Using “dynamic systems” as a tool, it is possible to
model and simulate the generation of solid waste in su-
permarkets, which allows observing the operation and
behavior of each product generated. It is also possible to
include additional variables that allow better decisions to
reduce generation of waste.
5. Acknowledgements
The authors gratefully acknowledge the financial support
of Consejo Nacional de Ciencia y Tecnología (CONA-
CYT), Mexico.
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