Systemic Analysis of Supermarket Solid Waste Generation in Mexicali, Mexico

doi:10.4236/jep.2010.12013

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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.

Email: [email protected], [email protected], [email protected], [email protected].

uabc.mx, [email protected], [email protected]

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

200

400

600

800

1000

1200

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

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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