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CURSO INTERNACIONAL SOBRE DISEÑO Y

DISPOSICIÓN FINAL DE RESIDUOS SÓLIDOS

(RELLENOS SANITARIOS)

 

 

 

 

 

 

 

 

 

 

SISTEMA DE CLASIFICACIÓN MEDIANTE EL EMPLEO

DE ESTÁNDARES PARA RELLENOS SANITARIOS

DE CIUDADES EN DESARROLLO

 

 

 

 

 

 

 

Dr. Geoffrey Blight

 

 

 

 

 

 

International Solid Waste Association

ISWA

 

 

PALACIO DE MINERÍA, MÉXICO D.F. 14-19 de Marzo de 1994

 

 

 

 

 

A SYSTEM OF CLASSIFICATION TO ALLOW FOR GRADED

STANDARDS TO BE APPLIED TO LANDFILLS IN DEVELOPING COUNTRIES

G E Blight

University of the Witwatersrand

Johannesburg, South Africa

(Written on behalf of the Working Group on landfilling, International Solid Wastes Association)

Synopsis

In developing countries, the affordability of environmental control measures for sanitary landfilling is a key issue. There is no fundamental reason why standards for landfilling in developing countries should match corresponding standards in developed countries. Also, there is no fundamental reason why standards required for landfills serving large towns and cities should be the same as those required for small villages. This paper explores three factors that can be used to classify landfills, in order to allow graded standards for landfilling to be applied in a rational way. The three factors are

· the type of waste,

· the size of landfill, and

· the climatic conditions at the site.

The classification is suitable for use in a developing country, but could equally well be used in a developed country, particularly one in which conditions vary considerably from one region to another. The classification was originally developed for South Africa, the development being initiated and funded by the State Department of Water Affairs and

Forestry.

lntroduction

If waste treatment and disposal is not carried out by a community to an adequate standard, a severe risk to health can arise, and serious degradation of the environment will usually also result. When considering the disposal of sewage and waste water, the above statement is a self-evident truth to members of all but the least educated of communities. However, while the environmental degradation resulting from inadequate disposal of domestic refuse is evident to all, it is not always plain that inadequate disposal of solid wastes can also pose a serious health hazard. For example, during the politically motivated stayaways and boycotts in South Africa during the 1980's, health workers such as nurses and sewage treatment works operatives were allowed to continue working (Nkosana, 1992). Garbage workers, however, were not regarded as health workers and were forced to stay away from work.

The title refers to "developing countries". What distinguishes a "developing" country from a "developed" one? The usual definition (Campbell, 1993) is that a developing country is one where the gross domestic product is lower than the average for the world. Thus a developing country is one where the people are poor, on average. However, there are many countries for which this definition may be inadequate, because industrialized urban areas in a country may be "developed", while country areas are still "developing". It is rare to find wealth evenly distributed between town and country.

Communities in developing countries, just as in developed countries, can vary in size from a few hundred to several million inhabitants. Whereas developed countries can usually afford to apply the highest standards to refuse disposal, regardless of the size of the community, this does not usually apply in developing countries or developing areas in developed countries. Communities in developing countries are poor, by definition. Large cities in a developing country although poor, may yet have a tax base that is sufficient to enable them to apply adequately high standards to the disposal of their solid waste. However, smaller communities can usually not afford to dispose of their refuse to the standards required in large cities.

There are a number of reasons why it may not be necessary to apply developed-world standards to the developing world:

1. The generation rates and composition for refuse in developed countries -may be very different to those in developing countries:

For example Table 1 (based on Rushbrook and Finnecy, 1988 and Mayet, 1993) shows that the putrescible (vegetable and paper) content of refuse in a developed country may be much the same as in a city in a developing country (Delhi) or it may be vastly different (Wuhan and Soweto). The proportion of dust, ash and other non-putrescible components is usually much higher in a developing country than in a developed country. Although data is not available this point, it appears from personal observation, that the putrescible content of refuse in small developing communities is even lower than that shown in Table 1 for China and South Africa.

Most, if not all studies of the decomposition of refuse and the composition of leachate (e.g. Christensen, Cossu and Stegmann, 1992) have, however, been carried out on refuse from developed countries. It is very likely that low-putrescible content refuse in a developing country will produce a less concentrated leachate than high-putrescible content refuse in developed countries, and therefore will have a lesser pollution potential. The lesser concentration of the leachate would be enhanced by the fact that the field capacity of a low-putrescible content refuse would be lower than that of a high-putrescible refuse.

 

TABLE 1

Composition of Municipal Refuse in

Developed and Developing Countries

Composition in % by Mass

Developed Countries

Developing Countries

USA

UK

India

(Delhi)

China

(Wuhan)

South Africa

(Soweto)

Vegetable

22

25

47

16

9

Paper

34

29

6

2

9

Metals

13

8

1

0.5

3

Glass

9

10

0.6

0.6

12

Textiles

4

3

-

0.6

1

Plastics

10

7

0.9

0.5

3

Wood

4

-

-

1.8

63

Dust. Ash. other unidentified

4

18

44.5

78

Refuse Density kg/m3 (uncompacted)

100+

150

420

600

(estimated)

400

Refuse Generation Rate Ton (1000kg)/Person/year

0.65

0.65

0.14

0.20

0.15

2. As Table 1 shows, refuse generation rates in poor developing countries are smaller by a factor of 3 or 4 than in developed countries:

Thus a community of a certain size in a developing country will produce far less refuse than in a corresponding community in a developed country. Because less refuse is produced, landfills will be smaller, or have a longer life, and will therefore represent a smaller source of potential pollution.

3. The climate in many developing countries is humid and the potential for leachate production high. However, there are also developing countries that have arid climates with little potential for producing leachate:

Whereas in developed countries, the same standards can be applied to landfilling regardless of climate, in developing countries, standards may be relaxed if little or no leachate is likely to be generated in landfills. This relaxation can make landfilling more affordable without compromising protection of the environment.

The purpose of this paper is to set out a method for classifying landfills that will enable graded standards to be applied, without compromising environmental protection. The scheme is suitable for either developed or developing countries, but will probably be more attractive in developing countries, where affordability is always a key issue.

The paper will deal only with landfills for domestic and commercial refuse and dry-non- hazardous industrial wastes. The disposal of hazardous wastes will not be considered.

Components of the Classification System

The classification depends on an assessment of three components:

1. the waste type,

2. the landfill size, and

3. the climatic characteristics.

The components of the overall classification relating to these three factors will now be described:

1.- Waste Type: For the purpose of the system, waste is classified according to its putrescible (vegetable and animal matter and paper) content. If the content of putrescible material exceeds 20% by dry mass the waste is classified as "P" or high-putrescible waste. If the putrescible content is less that 20%, it is classified as "p", or low-putrescible waste. While this is unproved at present, it appears reasonable to relax standards required for P refuse, as compared with these required for P refuse. The dividing point of 20% of putrescible material between p and P wastes is tentative at present, and must be refined by future research.

2. Landfill Size: All landfills grow in size with the passing of time. The one characteristic that has the biggest influence on the operation of the landfill, and therefore, the need for facilities, plan and operating skills, is the rate of deposition of refuse. A landfill with a small final volume, but a large rate of deposition, should, if standards are to be maintained, be operated in exactly the same way, and to the same standards as a landfill with a large final volume and a large rate of deposition. Vice-versa, a landfill where the rate of deposition is small, can be properly operated with lesser skills, plant and facilities, even if it has a long life and, therefore, will ultimately occupy a large volume. The classification is based an the Maximum Rate of Deposition (MRD) in tons of refuse deposited per year. The MRD is the projected rate of deposition at the end of the life of the landfill, and is calculated from the Initial Rate of Deposition (IRD) and the estimated annual growth rate or development rate for the community that the landfill is intended to serve. The IRD can be estimated by the amount of refuse entering the site at present, or in the case of a new site, from the current rate of deposition at the site or sites it is intended to replace. Failing this, a suitable generation rate (such as those tabulated in Table 1) multiplied by the number of people presently in the community can be used to estimate the IRD. Care should be taken to estimate the IRD for an appropriate working year. This is usually 260 days (52 weeks x 5 days) if the landfill is operated on 5 days of the week.

If D is the annual development rate estimated for a landfill, then the MRD can be calculated from the IRD by:

(MRD) - (IRD) (1 + D)T (1)

where T is the estimated life of the landfill site in years.

MT, the mass of refuse deposited after T years of operation is then:

MT – (IRD) [(1 + D)T_1] (2)

D

As an example : A site is required having a life of about 15 years, and (IRD) = 350 Tons/day. D is expected to be 3% per year. What will be (MRD) and MT?

(IRD) = 550 Tons/day - 350 x 260 = 91 000 Tons/year

(MRD) = 91 000 (1 +0.03)15 = 142 000 Tons/year

MT = 91 000 [(1.03)15-1] = 1 692 500 Tons

0.03

The required total deposition volume, or air space can then be estimated by dividing the tonnage MT, by an assumed compacted unit mass or density. If a unit mass of 0.75 Ton/m3 is chosen, the deposition volume required for the compacted refuse will be:

VT (net) = 1 692 500 =2 257 000 m3

0.75

Allowing for a ratio of compacted refuse to cover material of 1 to 6, the total air-space required will be

VT(gross) = 1 1 x 2 257 000 = 2 633 000 m3

6

The complete size classification is illustrated by Table 2.

Table 2

Size Classification for Landfills

LANDFILL

SIZE CLASSIFICATION

MAXIMUM RATE

OF DEPOSITION (MRD)

(Tons per year)

Communal C

Less than 250

Small S

up to 5000

Medium M

up to 150 000

Large L

over 150 000

In this classification, a "Communal" landfill would be one serving a village, typically of

1000 to 1500 persons. A "Small" landfill would serve a town of up to 30 000 inhabitants, while "Medium" and "Large" landfills would serve cities and large towns of over 30 000 inhabitants.

3. Climate : it has been well established (e.g. Christensen, Cossu and Stegmann, 1992) that the quantity of leachate generated in a landfill depends on the climate in which the landfill is situated. The effects of climate can be quantified by the water balance for a landfill. The water balance compares the quantities of water entering the landfill as part of the refuse and as infiltrating rain and snow-melt, with the quantity of water stored in the landfilled refuse, and leaving the landfill as evaporation or evapotranspiration. The difference between the net water input and the water stored in the refuse will be available to form leachate.

In humid climates, the difference between net water input and water stored will be positive over a year or season. In arid climates the difference will be negative, whether over the complete year, or seasonally. In other words, in arid climates, landfills will either not produce any leachate at all, or will only produce leachate seasonally.

In cases where no leachate is ever produced, it is possible to reduce the standards required for the design of a landfill, by omitting the leachate collection system and underliner.

However, even in an arid climate, there are occasional wet years or wetter than normal wet seasons. When extreme weather conditions occur, some leachate may be generated. If there is no leachate collection system, this leachate will be available to seep into the soil underlying the landfill. Provided that this does not occur more frequently than (say) once in 5 years, the consequences of such an escape will not be serious and can be ignored.

The classification system uses a "climatic water balance" as a means of deciding on whether or not a landfill will generate significant quantities of leachate and therefore whether or not a leachate collection system and underliner should be provided. The climatic water balance is expressed as

B = R - E

Where R is the rainfall in mm of water

E is the evaporation from the landfill cover surface.

E is taken as 0.7 x A-pan evaporation or 0.9 x S-pan evaporation.

To allow for seasonal influences and variable weather patterns, B is calculated for the wet season of the wettest year on record. (The wet season would usually be taken as the wettest six month period in a year, based on long-term averages). If the value of B is positive the indication is that the landfill will generate leachate in a wet year. Vice- versa, if B is negative the indication is that the landfill will not generate leachate even in a wet year.

As the rainfall and evaporation in any one -year do not necessarily correlate, B is re- calculated for successively drier years to establish if

(i) B is positive in less than one year in 5 for which data is available, or

(ii) B is positive in more than one year in 5. (If (i) applies, the site is classified as B and a leachate collection system and underliner can safely be omitted from the landfill. If (ii) applies, the site is classified as B. In this case, regular generation of leachate can be expected, and a leachate collection system and underliner would need to be provided.

The Complete Classification System

Table 3 illustrates the complete landfill classification system. Examples of the application of the classification are as follows:

l. A landfill receives waste having a putrescible content of 53%. (MRD) is 300 000 Tons/year and the landfill is situated in a climate where B is positive in 4 years out of five. The landfill would be classified as

PLB+

and would have to be constructed and operated to the highest standards.

2. A landfill receives waste having a putrescible content of 18% (MRD) is 190 Tons/year and the landfill is situated in a climate where B is positive once in 11 years. The landfill would be classified as

pCB

and could be constructed and operated to lesser standards without risks to health or the environment.

Application of the Classification System

The detailed application of the classification system would depend on the requirements and conditions in the country in which it would be applied. For example, the climate in a country may be such that the entire country would be classified as B+. In such a case the climatic consideration could be omitted, as it would be the same for all sites. A study of the types of waste might indicate that all waste would be classified as "High Putrescible" or P. In such a case the right hand half of Table 3 could be omitted.

Once the classification has been carried out, the graded requirements can be set under each of the headings of:

site selection

site investigation

environmental impact assessment

landfill design

site preparation and commissioning

operation and operational monitoring

rehabilitation, closure and end-use

post-closure monitoring

Table 4, for example shows some of the minimum requirements under the heading of "Landfill Design" for a hypothetical country that does not differentiate between P and p waste, but which has both B+ and B climatic zones.

TABLE 3

LANDFILL CLASSIFICATION SYSTEM

 

TABLE 4

Example of Graded Standards Applied to the

Design of a Landfill Receiving Only One Type of Waste

R = Requirement

NR = Not a requirement

F = Flat: special consideration to be

given by expert

C

Communal

Landfill

S

Small

Landfill

M

Medium

Landfill

L

Large

Landfill

B

B+

B

B+

B

B+

B

B+

Conceptual design:

               

Estimate unsaturated zone thickness after cover excavation

NR

NR

NR

R

R

R

R

R

Assess cover volume

NR

NR

R

R

R

R

R

R

Determine available airspace

NR

NR

R

R

R

R

R

R

Estimate airspace utilization

NR

NR

R

R

R

R

R

R

Estimate site life

NR

R

R

R

R

R

R

R

Confirm site classification

R

R

R

R

R

R

R

R

Surface hydrology design

R

R

R

R

R

R

R

R

Development Plan

R

R

R

R

R

R

R

R

Rehabilitation Plan

R

R

R

R

R

R

R

R

Design of leachate management system

NR

NR

NR

R

NR

R

NR

R

Ground water monitoring system design

NR

NR

NR

R

R

R

R

R

End-use and Closure Plan

NR

NR

R

R

R

R

R

R

Testing of soils and materials

NR

NR

NR

NR

F

F

F

F

Technical design:

               

Validation of Surface hydrology

NR

NR

NR

NR

R

R

R

R

Lining system

NR

NR

NR

R

NR

R

NR

R

Leachate management system

NR

NR

NR

R

NR

R

NR

R

Gas Management system

NR

NR

NR

NR

F

F

F

F

Final cover design

NR

NR

NR

NR

R

R

R

R

 

Conclusions

Although it is usual to set standards for solid waste landfilling practice that are uniform for all sizes of landfill end all climatic conditions (as with the 1993 U.S. EPA Subtitle D Municipal Waste Regulations), (Daniel et al, 1993), there are good reasons why standards should be graded depending on the type of waste, the size of the landfill and the climatic conditions in which the landfill is situated. There is a particularly good case for applying graded landfill standards in developing countries, where affordability to the community is an important, and may be an over-riding consideration.

The classification scheme outlined in this paper provides a way of grading standards in a scientifically sound manner that need not compromise standards for environmental protection.

Acknowledgements

This paper is based on an earlier paper (Ball, Blight and Bredenhann, 1993) that deals with the intention to introduce graded standards for landfilling in South Africa.

References

Ball, J.M., Blight, G.E. and Bredenhann, L. (1 993). "Minimum requirements for landfills in South Africa. Proceedings, 4th International Landfill Symposium, Cagliari, Italy (Sardinia '93) vol II, pp 1931-1940.

Campbell, D.J.V. (1993). Waste management needs in developing countries. Proceedings, 4th International Landfill Symposium, Cagliari, Italy (Sardinia '93) vol II, pp 1851-1866.

Christensen, T.H., Cossu, R. and Stegmann, R. (Eds) (1992). Landfilling of waste leachate. Elsevier Applied Science, London, ISBN 185 166 7334.

Daniel, D.E. (Introducer) (1993) Series of papers on U.S. EPA Subtitle D on Municipal Waste Regulations. Geotechnical News, USA, Vol II, no 3. pp 36-52.

Mayet, M.A.G. (1993). Domestic waste generation in the urban core of the Durban functional region. MSc (Eng) Thesis, University of Natal, Durban, South Africa.

Nikosana, M.J. (1992). The effects of unrest, situations on solid waste management in the late eighties and early nineties. Institute for Waste Management, South Africa, 1lth Congress, Johannesburg, pp 249-257.

Rushbrook, P.E. and Finnecy, E.E. (1988). Planning for future waste management operations in developing countries. Waste Management and Research, vol.6., pp 1-21.

DESCRIPCION DEL CURSO ISWA Y DE LOS MATERIALES INSTRUCCIONALES SOBRE LA DISPOSICIÓN FINAL DE RESIDUOS SOLIDOS (RELLENOS SANITARIOS)

 

El propósito de las notas del curso es el de proporcionar material de apoyo a las conferencias que se dictarán como parte del curso ISWA sobre disposición final de residuos sólidos, para los países en desarrollo. En ellas se define a los rellenos sanitarios y su práctica para diferentes niveles de calidad y protección ambiental. Por razones claras, la práctica de disposición de residuos sólidos en los países en desarrollo debe ser económica y reflejar las condiciones de la localidad. Conforme a ello, las notas están orientadas hacia una práctica de disposición de residuos implementable bajo una variedad de situaciones, muchas de las cuales implican una severa carencia de equipo o recursos financieros y quizás falta de interés público en relación a la calidad del relleno sanitario.

El concepto general del relleno sanitario abarca una amplia gama, básicamente desde un tiradero abierto, en el cual hay muy poco insumo de ingeniería, hasta el más riguroso de los diseños, como los requeridos bajo algunas de las regulaciones ambientales actuales más avanzadas del mundo.

Propiamente, el término relleno sanitario no debería usarse para describir las operaciones más rudimentarias, pues por definición, un relleno sanitario requiere el control de todas las emisiones e impactos estéticos a niveles aceptables. Los requerimientos para una práctica aceptable pueden cambiar de acuerdo al tamaño del relleno, los tipos de residuos y la práctica local en relación a su aceptabilidad ambiental y estética. En este sentido, el curso considera la práctica del relleno sanitario aplicable a la situación predominante y no sólo los requerimientos del relleno sanitario clásico.

El tamaño del relleno sanitario deber ser tal que sirva para alojar la cantidad de desperdicios generados por las personas para un periodo de, al menos, 5 a 10 años. Los desechos sólidos a ser manejados deben conocerse o proyectarse en relación a su cantidad y composición, de tal manera que el volumen a llenar con los desperdicios sea suficiente, así como el material para su cobertura, el equipo y los procedimientos de manejo. La geología y localización del sitio son factores importantes. El espectro de la geología puede variar desde suelos muy porosos que pueden permitir el flujo de gran cantidad de gas y lixiviado proveniente del relleno sanitario, y no proporcionar virtualmente ninguna protección ambiental el agua subterránea, o a las áreas circundantes, hasta suelos relativamente impermeables tales como arcillas, las cuales limitan el flujo de gas y lixiviado y de esa manera permitir que éstos sean manejados en el lugar. El sitio debe estar localizado apropiadamente con respecto al agua de la superficie y áreas inundables, de manera tal que el agua superficial no resulte afectada por ninguna contaminación que surja de las operaciones del relleno sanitario.

En el diseño de un relleno sanitario se debe tener en consideración el tipo de suelo disponible, la cantidad y características de los residuos, la geología del lugar, su accesibilidad, y otros factores que permitan la disposición de desechos, libre de molestias, y de una manera lógica y continua. Esto se logra por medio de la adecuada ubicación del relleno sanitario en relación a las carreteras, cuerpos de agua superficiales, colinas, estratos rocosos, aguas subterráneas y los tipos de suelo del lugar, a fin de aprovechar al máximo las propiedades únicas de cada lugar. De la misma manera, algunos sitios pueden ser tan inadecuados por cualquiera de las consideraciones mencionadas, que sencillamente no deberían usarse a menos que fuera absolutamente necesario. En este curso se describirán las condiciones de ubicación y métodos empleados para minimizar problemas.

El sitio debe funcionar y ha de proporcionarse también el equipo y el personal necesario a fin de que se dé la operación diaria bajo todo tipo de condiciones cismáticas y para manejar el flujo de desechos. Muy a menudo se cree que son necesarios grandes equipos para tener un buen relleno sanitario. Esto no es necesariamente el caso, pues con frecuencia el uso óptimo del equipo disponible puede proporcionar una buena operación del relleno sanitario.

Se presenta en el curso la manera de determinar las cantidades y la composición del gas y el lixiviado, incluyendo los principales factores para su control. Los sistemas para cubrir el relleno son especialmente importantes a este respecto. En algunos casos se requerirán controles de gas y lixiviado. El primer método para controlar el gas y la migración de lixiviados del relleno sanitario y que se discutirá, es a través de sistemas de revestimiento (liners).

Los revestimientos pueden hacer uso de suelos del lugar o suelos importados para minimizar el flujo de emisiones y gas provenientes del relleno. Los sistemas de revestimiento se discutirán en relación a su necesidad, y se presentarán diferentes diseños de acuerdo a las condiciones locales. Una vez que se retarda el flujo de lixiviados a través de los sistemas de revestimiento o por el uso de los materiales disponibles naturalmente, se tiene que controlar el lixiviado, lo cual típicamente implica su recolección y tratamiento. De manera similar si el flujo de gas se retarda, tendrá que proporcionarse un control de éste en el lugar, el cual puede incluir la ventilación del gas a la atmósfera o aún el uso del gas como una fuente de energía.

Es necesario diseñar el relleno para su cierre como parte del diseño inicial. Debe determinarse asimismo el uso final del relleno y su diseño debe cumplir con los requerimientos para ese uso, incluyendo la topografía o forma. Los recursos financieros y de suelos deben estar disponibles a la clausura de tal manera que el lugar pueda cubrirse y reforestarse apropiadamente. El hecho de que ya no se trasladen los residuos y el relleno sanitario haya sido tapado con la cubierta final no libera de responsabilidad al operador, por lo que no puede abandonar el lugar. Se debe proporcionar un cuidado a largo plazo que de cuenta, tanto del monitoreo, como de las reparaciones de cualquier erosión, asentamiento, agua estancada u otros problemas que pudieran desarrollarse al paso del tiempo en un relleno sanitario cerrado. El monitoreo debe empezar antes de la construcción del relleno, para establecer la calidad presente del agua subterránea y del gas. El monitoreo continúa a lo largo de las operaciones del relleno y sobre un largo periodo después del cierre para estar al tanto de cualquier impacto significativo que pudiera afectar el uso del agua subterránea, la calidad del agua superficial o usos potenciales del área. El monitoreo continúa hasta que es claro que el lugar se ha estabilizado y no presenta peligro.

Finalmente, debe disponerse tanto de un financiamiento apropiado como de una voluntad política para asegurar que el relleno sanitario pueda continuar operando a lo largo de toda su vida útil, desde su concepción y diseño, hasta su operación, clausura y cuidado de largo alcance. Esto significa que el público debe apoyar el sitio y el sitio debe estar apoyado políticamente y por las necesarias organizaciones, para estar seguros que el lugar cuenta con un adecuado respaldo financiero.

Por lo anterior puede verse que el diseño, operación, clausura y cuidado de larga duración no son tareas simples. Para la gente es rutinario subestimar las demandas para minimizar los efectos adversos de la eliminación de los residuos.

En resumen, este curso y los materiales que lo acompañan, están dirigidos a interpretar las condiciones locales y recursos en la medida en que se puedan diseñar el mejor relleno sanitario posible y pueda ser operado para minimizar los efectos adversos tanto de la gente de los alrededores como del medio ambiente.

 

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