Sustainability 2010, 2, 2070-2083; doi:10.3390/su2072070
OPEN ACCESS
sustainability
ISSN 2071-1050
www.mdpi.com/journal/sustainability
Article
Influence of Handling Practices on Material Recovery from
Residential Solid Waste
Luis F. Marmolejo 1, *, Luis F. Diaz 2, Patricia Torres 1, Mariela García 1, Mary H. Burbano 3,
Carolina Blanco 3, Katherine Erazo 1 and Jairo F. Pereira 1
1
2
3
Facultad de Ingeniería, Universidad del Valle, Calle 13 No. 100-00, Cali, Colombia;
E-Mails: patoloz@univalle.edu.co (P.T.); magarcia@univalle.edu.co (M.G.);
katherineerazo777@hotmail.com (K.E.); jairop045@hotmail.com (J.F.P.)
CalRecovery Inc., 2454 Stanwell Drive Concord, CA 94520-4811, USA;
E-Mail: Ludiaz@Calrecovery.com
Sede Zarzal Universidad del Valle/Calle 14 Carrera 8 Esquina. Zarzal, Valle del Cauca, Colombia;
E-Mails: mahebuce81@hotmail.com (M.H.B.); carolina.blancomoreno@hotmail.com (C.B.)
* Author to whom correspondence should be addressed;
E-Mail: luis.marmolejo@correounivalle.edu.co; Tel.: +57-2-3312175.
Received: 17 June 2010 / Accepted: 29 June 2010 / Published: 9 July 2010
Abstract: Material recovery from municipal solid waste (MSW) is becoming widely
adopted in several developing countries. Residential solid waste is one of the most
important components of MSW and the handling practices of the MSW by the generators
have a major impact on the quality and quantity of the materials for recovery. This article
analyzes the generation and composition of residential solid waste and the handling
practices by users in three municipalities in Colombia that have a solid waste management
plant (SWMP). The findings show that, although there are significant amounts of useful
materials, their handling of the materials as ―garbage‖, the low recognition of recovery
work, and the inadequate storage and source management practices, affect material
recovery and the operation of SWMPs. These results may be taken as a reference for this
type of municipality, because the solid waste management system and the type of operation
of the SWMPs analyzed is similar to all of the SWMPs in the country as well as in other
countries in the region.
Keywords: handling practices; material recovery; municipal solid waste; residential solid
waste; developing countries
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1. Introduction
The management of municipal solid waste (MSW) in Colombia is undergoing a substantial
evolution, changing from a period in which priority was given to collection, transport and final
disposal to a gradual inclusion of material recovery in the solid waste management system [1]. In this
presentation, material recovery is used to mean the segregation and recovery of various types of
materials discarded as wastes. The foregoing is demonstrated by the development and construction of
Solid Waste Management Plants (SWMPs) in several locations in the country. The main objective of
these facilities is the recovery of the largest quantity of materials from the MSW, and the final disposal of
useless and unmarketable fractions. SWMPs have been mainly implemented in small municipalities [2].
Small municipalities happen to be those experiencing the most difficulties in the management of their
solid waste [3], due to factors such as lack of trained personnel, application of inappropriate
technologies, and the use of inadequate methods of finance. These actions demonstrate that the country
is following the outcomes of world events, such as the Rio and Johannesburg Summits, during the last
two decades.
For material recovery and for the proper operation of the SWMPs, handling practices in residential
areas become fundamental due to the fact that residential solid wastes represent the largest portion of
the raw materials (unprocessed garbage) arriving to those facilities. According to the Pan American
Health Organization [4], in Colombia, the average per capita production (pcp) of MSW
is 0.64 kg/person-day and it is equivalent to the residential solid wastes. While in Latin America and
the Caribbean (LAC) municipalities, with populations lower than 50,000 inhabitants, the average pcp
for MSW is 0.62 kg/person-day and the pcp for residential solid wastes is 0.54 kg/person-day.
The quantity and quality of the unprocessed garbage arriving to SWMPs mainly depends upon the
resident or generator practices, who may consider the materials as ―waste‖ (something that may be
used by others) or as ―garbage‖ (that which is thrown away because it is considered useless). Likewise,
he or she decides how, when and where to deliver his or her wastes to the collection and transport
services. At the same time, the knowledge by the users of the existence of the SWMP and the way the
facility operates adequately, may contribute to change their waste management practices at
household level.
This article analyzes the generation and composition of residential solid waste and handling
practices by residential users of the urban area of three Colombian municipalities, located in the
northern portion of the Department of Valle del Cauca: Bolívar, La Victoria and Versalles. These
municipalities were the first to implement SWMPs in this Department. Table 1 shows general
information about the three localities.
In the three cases, the public cleaning service includes the collection of all residential, commercial
as well as non-hazardous institutional solid waste. Ninety percent or more of the users are residential;
wastes are transported to SWMP, where materials are segregated manually.
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Table 1. General information about the three Colombian municipality localities.
Information
Population (inhabitants)
Annual population growth rate (%)
Masculinity index
Average number of inhabitants per home [8].
Bolívar
3,632 [5].
–1.5 [5].
1 [5].
Alphabetization rate (%)
Inhabitants with Unsatisfied Basic Needs (%)
Human Development Index
per-capita GDP (Col $ 2005)
Altitude [9].
Local average temperature (ºC) [9].
76.3 [5].
13.2 [5].
0.75 [5].
7.126.579 [5].
976
23
Less or equal to 3.5
La Victoria
9,550 [6].
–1.4 [6].
1 [6].
Between 3.6 and
3.7
86.3 [6].
14.6 [6].
0.78 [6].
8.643.431 [6].
915
26
Versalles
3,831 [7].
–1.4 [7].
1.1 [7].
Less or equal to
3.5
82.8 [7].
11.1 [7].
0.78 [7].
9.232.364 [7].
1860
18
The analysis shows the impact of variables such as: acknowledgement of the existence of the
SWMP, the utilization and storage of the materials at home and the manner of putting out the wastes
for the waste collector and the material recovery carried out at the SWMP. These results may be taken
as reference for this type of municipalities, because the type of operation of the SWMPs analyzed is
similar to all of the SWMPs in the country [2] as well as in other countries in the region.
2. Methodology
This investigation was developed during 2008 and 2009, and included direct contact with the citizens of
all three municipalities, through visits to randomly selected homes, surveys, interviews and workshops.
Maps containing all of the homes in each locality were used as sampling frames. These maps were
supplied by the Public Service Company of each municipality. Homes to be surveyed were selected by
using a random sampling method with a systematic selection. This method aimed to achieve a
representative sample of the population. The availability of a resident older than 15 years old was
established as basic criterion to carry out the survey. Most of the survey participants were adult women,
generally mothers and/or housekeepers.
Sample sizes were determined taking into account the availability of local logistic resources.
Equation (1) was used to estimate each sample size:
(1)
Where:
n: sample size
z: z value of standard Normal Distribution (e.g., 1.96 for 95% confidence level)
p: proportion picking a choice, expressed as decimal
ME: margin of error
N: size of the population
Table 2 shows data on the number of homes surveyed in each locality.
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Table 2. Surveyed homes.
Location
Bolívar
La Victoria
Versalles
Total number
of homes
1,080
2,788
1,045
Number of
homes surveyed
340
53
108
Sampling
error (%)
5
12
10
Confidence
level (%)
95
90
95
Response
rate (%)
80
80
80
Handling practices were evaluated in the framework of the research projects developed by the
Universidad del Valle [10,11]. Similarly, the most recent residential solid waste characterization
studies carried out in Bolívar [12], and in La Victoria and Versalles were taken into consideration
(generation and composition) [10].
For the cases of La Victoria and Versalles, each home was surveyed with a survey instrument consisting
of four elements: 1) General information about the home, 2) Family group characterization, 3) Handling of
solid waste at home and 4) The perception of both the waste collection system and the operation of the
SWMP. The answers to the survey were complemented with in situ observations of the solid waste
handling. In addition, in Bolívar, the surveyors consulted the users about the meaning of the terms
―solid waste‖ and ―garbage‖. The information collected was complemented with structured and semi
structured interviews as well as with the observations of the service providers of collection and
transport, and the operators of the SWMP.
3. Results and Discussion
3.1. Generation and Composition Analysis of Residential Solid Waste
The data in Table 3 present information pertinent to waste generation (pcp) and
physical composition of solid waste generated at the three localities. As can be seen, the pcp is lower
than the average indicated by [4] for LAC with populations having less than 15,000
inhabitants (0.59 kg/inhabitant-day). This situation may be associated with the practice of an old
custom of waste recovery at home combined with the low purchasing power of those populations.
All cases show a relatively high concentration of bio-wastes (food and garden wastes), which is in
agreement with the indicators given in several sources [4], for developing countries [13]. The
agricultural and cattle raising activities of the northern portion of the Department del Valle del Cauca,
offers a potential market for the compost that could be produced using those materials.
The generation of recyclable materials such as paper, cardboard, plastic, glass and metals, reaches
approximately 11.7; 16.8 and 5.1 tons per month for Bolívar, La Victoria and Versalles, respectively.
These amounts, together with those generated by the commercial and institutional sectors, also have
market possibilities in the region, as all three municipalities are located less than 30 km from at least
one intermediate city where all of the recovered materials could be marketed. On the other hand, the
operators of the municipal waste collection service have a high interest in improving the material
recovery process, due to the reduction of the useful life span of the disposal sites and the difficulty of
citing new landfills, as the population exhibits a strong resistance to the implementation of new
disposal sites in their vicinity. This situation may lead to the use of existing regional sanitary landfills,
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which would lead to significant increase in the tariffs for the service due to the increase in transport
and waste disposal costs.
Table 3. Generation (pcp) and physical composition of residential solid waste in the
locations under study. * Includes garden wastes **Included in others.
pcp (kg/person-day)
Food
Bolívar1
La
Victoria2
Versalles
0.31
0.43
0.27
51.3*
64.48
64.5
5.22
1.0
Garden
Physical
Composition (%)
Hygienic
wastes
4.4
8.93
9.0
Paper
9.7
3.08
3.2
Carton
2.8
1.24
1.4
Plastic
17.1
7.20
8.7
Glass
3.9
1.15
2.0
Metals
Rubber
leather
1.4
1.01
1.1
0.2
0.72
**
Textile
3.0
2.99
3.2
Wood
**
0.45
**
Ceramic
**
1.77
0.5
Bones
0.1
0.38
0.8
Others
6.0
1.36
4.6
and
Sources 1 [12], 2 [10]
3.2. Evaluation of Waste Handling Practices
3.2.1. Concept of solid waste and garbage
Terms like ―take out‖ or ―throw out the garbage‖, ―garbage collection truck‖, ―garbage collecting‖
referring to the method of storage, collection and transport of the wastes, are common in the localities.
The survey at the municipality of Bolívar, allowed the identification of the concepts used by the users
with respect to the terms ―solid waste‖ and ―garbage‖. Regarding the term ―solid waste‖ (Figure 2),
most of the population (32%) ignored the meaning or did not answer the question, 20% thought it was
―garbage‖ and only one-tenth of those surveyed associated it with ―reusable‖. In so far as the term
―garbage‖ is concerned (Figure 3), 57% of those surveyed defined it as ―useless materials‖ or as
―trash‖, with a closer definition to that established by the Colombian norm regulating solid waste
management (Decree 1713, 2002 [14]). It should be kept in mind that the standardization of the terms
―solid waste‖ and ―garbage‖ may have an influence on handling practices, because to list materials as
garbage, makes it unnecessary to store or deliver them separately, thus reducing the possibilities
of recovery.
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Figure 2. Definition of solid waste by users in Bolívar.
Figure 3. Definition of garbage by users in Bolívar.
Another factor reinforcing the concept and material handling such as garbage is the collection
service of mixed wastes in the different locations. Barr et al. [15] indicate that the largest influences in
performance of recycling by the people are those factors such as norm acceptance, available logistics
for recycling and the convenience and knowledge of recycling. Similarly, a study carried out by
Brixworth [16] showed that positive attitudes of users with respect to recycling were associated with
their knowledge of the issue and the availability of an adequate and well-publicized collection scheme.
Keeping in mind the reports from these authors, the concept of garbage may have been stimulated
by the solid waste management tendencies established in the country before the nineties. According
to [1], between the sixties and the nineties, most municipalities began the task of providing and
improving their collection and transport systems and designing and operating final disposal systems
(open dumping). This concept used the notion of ―throwing out or rejecting‖, associated to what needs
to be done with ―that which is useless‖. Few cases contemplate actions like reduction, recovery or
waste treatment.
3.2.2. Acknowledgment of the existence of a local SWMP
Although in all three locations the survey showed that more than 77% of users showed satisfaction
with the municipal waste collection service, Versalles was the only locality where there was a high
recognition of the existence of a SWMP, as seen in Figure 4. This is due to the active development of
continuous awareness by the waste collection service company. In Bolívar and La Victoria, awareness
activities were only carried out during start up of the systems.
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Figure 4. Acknowledgment of the existence of SWMP in the localities.
Acknowledgement of the existence of a SWMP and its operating benefits could be an important
factor to stimulate source separation and storage practices of the materials to be delivered to the
municipal waste collection service. In addition to the sanitary and environmental benefits associated to
material recovery, this can have a positive impact on service tariffs (paid by the users) due to the cost
reduction in collection, transport and final disposal. A good understanding of these aspects may
encourage the user to deliver the waste in such a way that it would facilitate its recovery.
3.2.3. Recovery by the residential sector
As shown in Figure 5, more than 30% of residential users keep waste fractions for recovery or final
disposal, keeping at home items such as food waste, paper, cardboard, plastic, glass, metal and
hygienic wastes. The first six are mainly used for internal recovery purposes or delivery to waste
pickers and hygienic wastes normally are disposed internally.
Regarding the handling of food waste, as shown in Figure 6, whereas La Victoria and Versalles
predominate in the delivery of material to the collection vehicle; in Bolívar it is common to use the
material as animal food as well as the production of what people call ―fertilizer‖, reaching significant
percentages when compared to other locations. The practice of recovering materials at the household
level positively impacts the operation of the SWMP in Bolívar; as the recovery materials received at
the SWMP show a lower degree of mixture and moisture, the facility is free of unpleasant odors or the
presence of birds scavenging for food.
Paper, cardboard, plastic, glass and metals are recoverable materials that many users do not
completely deliver to the municipal collection service. The data in Table 4 show the use given to the
various components of the waste stream in each location. This practice is related to the marketing
possibilities with local and external purchasers who, due to their geographical location, are higher in
number in Bolívar and in La Victoria municipalities, or with the existence of local waste pickers, also
found more frequently in those municipalities.
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Figure 5. Percentage of homes that keep waste fractions for internal recovery or
final disposition.
Figure 6. Uses given to bio-wastes by the householders.
Since marketing of these materials is one of the most significant sources of income for the SWMPs,
in Versalles the collection company is implementing a strategy known as ―the recycling store‖, through
which they purchase recovered materials from the users or waste pickers at competitive prices with
those offered by external purchasers. The value of the waste is discounted from the payment of the
tariff, stimulating the prompt payment for the service and higher volume marketing of the waste, at
better selling prices. Table 4 also shows that reuse is not a popular practice and is only reported
in Bolívar.
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Table 4. Use given to recoverable materials in each of the municipalities under study.
Use given to recoverable waste (%)
Type of Waste Municipality
Paper
Cardboard
Glass
Plastic
Metal
Bolívar
Versalles
La Victoria
Bolívar
Versalles
La Victoria
Bolívar
Versalles
La Victoria
Bolívar
Versalles
La Victoria
Bolívar
Versalles
La Victoria
Sells it
Gives it away Reuses
5.6
1.9
1.9
6.2
4.6
1.9
5.3
3.7
0.0
2.9
0.9
1.9
13.8
3.7
5.7
5.0
0.9
11.3
9.4
1.9
17.0
2.1
0.9
3.8
1.8
1.9
11.3
3.5
0.9
3.8
2.1
0.0
0.0
1.5
0.0
0.0
0.9
0.0
0.0
1.5
0.0
0.0
1.8
0.0
0.0
Deliveries to the
municipal collection
service
73.5
96.3
81.1
70.0
92.6
77.4
73.8
95.4
96.2
80.9
96.3
81.1
61.8
95.4
90.6
Other
13.8
0.9
5.7
13
0.9
3.8
18
0.0
0.0
13
0.9
5.7
19.2
0.0
0.0
3.2.4. Storage and putting the waste out
The research in the field showed that these activities normally are the responsibility of adult women
who determine the basic aspects such as location and cleanliness of the container. As shown in
Figure 7, delivery to the collection vehicle in only one container is the predominant practice. Mixed
collection results in mixing the materials and leading to a deterioration in their quality and decreased
possibilities of recovery [17]. Waste mixing enhances cross contamination. In the case of Versalles, the
significant proportion of users using three or more containers is attributed to factors such as the
implementation of campaigns stimulating separation at the source, led by the Municipal Collection
Company and by the educational sector, and also to the high level of acknowledgment of existence of
the SWMP and positive evaluation by the users of the municipal collection service.
The effects of segregation practices are significant in recovery processes such as in compost
products [18]. A pilot scale evaluation of composting bio-wastes was done. It used both materials
separated at the source and mixed residential wastes of La Victoria. Waste separated at the source
exhibited parameter values like Carbon/Nitrogen and ash content, offering better conditions for the
process. This waste reflected a higher degree of degradation, lower stabilization times, and a higher
microbiological quality of the product [10]. In the case of recyclable waste recovery such as paper,
cardboard and plastic, recovered from mixed sources, the costs and requirements of resources such as
water for the cleaning processes of the recovered materials are significant, and the recovered materials
have significantly lower prices than those separated at the source.
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Figure 7. Number of containers delivered to the municipal collection service.
Figure 8 shows the type of containers used for delivery of the solid waste, indicating a higher use of
plastic bags with sufficient capacity to store the amounts of waste generated and easily handled by the
collectors. However, because plastic bags are normally manufactured using Low Density Polyethylene
(LDP) and because the LDP is contaminated with waste, generally their recovery and
commercialization at the SWMP is difficult, culminating in significant amounts at the final disposal
sites. Due to the fact that wastes put out in trash cans and in burlap bags should be emptied directly
into the collection vehicle (because the containers have to be returned), their use helps mixing of the
materials in the vehicle and consequently affects the recovery of high quality materials.
Figure 8. Type of containers delivered to the municipal collection service.
Waste containers are normally set out in front of the residence (Figure 9) from where they are
picked up by the operator of the municipal collection service; users and waste collector are satisfied
with this situation, and in general, they establish good cooperation to facilitate the collection. With
respect to the delivery of waste containers to the collection vehicle at la Victoria and Versalles
(Figure 10), although there are significant percentages of users that do it at the moment the vehicle
passes through, the proportion of users that do it one or more hours ahead of time is also high. At
La Victoria, normally informal pickers are observed removing materials from the waste containers,
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before or during the collection process. According to the operators of the SWMP, this situation is
reflected in a significant reduction of materials received at the facility.
Figure 9. Place of delivery of solid waste to the municipal collection service.
Figure 10. Time ahead of delivery of solid waste to the municipal collection service.
According to [19], a recovery system of recyclable waste acting to advance in the direction of social
and environmental sustainability requires the combination of at least two factors: generator’s
responsibility regarding production and the integration of waste pickers into the process. Given the
existence of SWMPs in the cases under study, it becomes necessary to establish agreements between
the operators of the public cleaning service, users and waste pickers to facilitate planning of the
operation regarding quantity and quality of waste to be processed.
4. Conclusions
Recovery of waste at the household level considerably influences the waste production (pcp) at the
locations studied. In all cases, the pcp is lower than 0.59 kg/person-day, the average value indicated
in [4] for municipalities with a population of less than 15,000 inhabitants. The foregoing appears to be
related to a tradition of recovery at home, as well as with the relatively low purchasing power of
the population.
The physical composition of residential solid waste shows that in all cases proportions of bio-wastes
and recyclable materials such as cardboard, paper, plastic and glass reach proportions, is higher
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than 78.7%. These values, together with the existence of markets for the materials, show the
importance of strengthening recovery of some components in the solid waste management in the
localities. Therefore, these municipalities can get benefits from material recovery, especially because
they show limitations for final disposal in situ.
A high proportion of residential users mix their waste in the storage containers. This situation
affects not only the amount but the quality of materials and therefore, their recovery. For this reason, it
is necessary that projects for the development of infrastructure for SWMPs be accompanied with
awareness programs stimulating and committing the users to handling the materials under conditions
favoring their recovery. The fundamental elements to structure awareness programs are the perceptions
and practices of adult women who generally are responsible for the handling of the material at home.
Cultural practices such as the recovery of bio-wastes at home, favor the conservation of the quality
of the recovered materials in non source separation recovery systems. Similarly, the resulting reduction
in moisture content eases the operating conditions and maintenance at the SWMP.
The impact of practices such as: segregation of materials at the source, relatively quick delivery of
the waste to the municipal collection service and the tariffs paid by the users may be very useful tools
to stimulate their participation. These strategies form a good starting point to promote separation at the
source. Additionally, users must be stimulated to be aware of the sanitary and environmental benefits
of the material recovery, as well as of the development of jobs at local levels, instead of only
indicating economic benefits. It is also necessary to promote a decrease in consumption patterns and
reuse of materials.
Handling practices have a high influence on the quality and quantity of materials to be recovered in
the studied localities. Such practices affect both the efficiency of public cleaning services as well as the
operation and sustainability of the SWMP; for these reasons it is imperative to strengthen the
relationship between the users, the local governments and the operators of the public cleaning service,
recognizing the benefits of material recovery from municipal solid waste.
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1
2
3
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5
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