Study Session 10  Disposal of Solid Wastes

Introduction

So far, in the series of study sessions focusing on solid waste management, you have studied sources and quantities of waste (Study Session 7), ways of reducing, re-using and recycling wastes (the ‘3 Rs’; Study Session 8), and ways of collecting the remaining waste (Study Session 9). Unfortunately, after practising the 3 Rs, we are often still left with a portion of waste to be disposed of. In this study session you will look at the different disposal options and how they can be used in urban areas in Ethiopia. You will also learn more about hazardous waste and how it should be managed.

Learning Outcomes for Study Session 10

When you have studied this session, you should be able to:

10.1 Define correctly all of the key words printed in bold. (SAQs 10.1, 10.2, 10.3 and 10.5)

10.2 List the main options available for solid waste disposal and describe their advantages and disadvantages. (SAQs 10.1, 10.2 and 10.3)

10.3 Describe the key factors to consider when planning a landfill for a small or medium-sized town. (SAQ 10.4)

10.4 Describe how toxic and other hazardous waste can be disposed of safely. (SAQ 10.5)

10.1  Options for waste disposal

Waste disposal processes aim to isolate the waste from people and the environment in a manner that causes no harm. The best option for dealing with any particular waste depends on the nature of the waste itself (its form, composition and quantity), the technologies available in the region, the availability of financial resources, and having enough skilled people to build, operate and maintain the facilities. In Ethiopia, two main waste disposal processes are widely used: landfill, including burial and dumping, and thermal processing, which includes burning and incineration. Different methods of landfill and thermal processing are described in the following sections.

10.2  Landfills

Landfill was defined in Study Session 1 as an area of land set aside for the final disposal of solid waste. Ideally the site is managed to prevent people and animals from entering and the deposited waste is covered with soil to isolate it from the environment. However many informal sites do not cover the waste or have any other control measures. We are using ‘landfill’ here as a general term that applies to any site where solid waste is deposited for final disposal.

There are many different types of landfill, some with greater environmental impact than others. In all of them the waste gradually decomposes by a combination of biological, chemical and physical processes. During these decomposition processes, two major emissions are of primary concern – leachate and landfill gas:

• Leachate is the polluted water that emerges at the base of the landfilled waste. It is formed in two ways. Rainwater landing on the waste slowly flows over and through the waste and soluble substances are dissolved in the water. Also, some of the decomposition reactions taking place in the waste produce liquid that can be acidic. Some substances, such as toxic metals, tend to dissolve more easily in acids, making the final leachate more harmful. If leachate enters a watercourse used to provide human or animal drinking water or for irrigation, people can be exposed to these pollutants.
• Landfill gas is formed in large landfills through degradation of the waste in anaerobic conditions. Landfill gas consists of a mixture of carbon dioxide and methane, which are both greenhouse gases that contribute to global climate change. It is also flammable and will burn if exposed to a flame or other source of ignition. In extreme cases, the gas can build up in a landfill and explode, with the risk of injury and death. Managed landfill sites have vent pipes that allow the gas to get out of the waste and be released to the air or burned in a controlled way.

The different types of landfill can be ranked according to their potential to cause environmental pollution. Starting with the worst, they are:

1. Indiscriminate waste disposal
2. Communal open dumping
3. Burial in pits
4. Controlled landfill
5. Sanitary landfill.

These types of landfill are described in the following sections.

10.2.1  Indiscriminate waste disposal

This is the most unwanted and dangerous practice in solid waste management. It occurs when an individual leaves waste by the roadside, on a piece of disused land, in a field, by the side of a riverbank or in a river (Figure 10.1). This practice is very common in urban areas in Ethiopia and is also known as open dumping.

Figure 10.1  Open dumping on the banks of a river.

10.2.2  Communal open dumping

This method is practised in many small and medium-sized towns in Ethiopia. A convenient area of land near the town is identified, frequently in a valley or a natural depression in the ground. Waste is then deposited at the site and gradually accumulates over time. At their worst, these sites have no barrier to keep out animals, there is no equipment to move or compact the waste, no environmental control measures, and no site staff. (Compacting means reducing the volume occupied by landfilled waste by pressing down on it, usually by driving over it with a tractor or other heavy vehicle.)

Open dumping can be an effective way of isolating waste from people, but adverse effects can emerge in the long run, such as:

• There is no barrier between the waste and the ground below so leachate can contaminate groundwater and surface waters.
• The areas selected for such sites are often some distance from the community and not accessible to carts and other wheeled transport. This means that the waste must be carried to the site, which is time-consuming. Some people will be tempted to dispose of waste indiscriminately rather than walk all the way to the site.
• Unless the site is well looked after (which is unlikely), waste can be blown off the surface by the wind and the exposed waste may attract flies, rodents, dogs, hyenas and birds.
• Finally, if the waste is deposited in a normally dry valley, flooding can occur in the event of unexpected heavy rain. The rainwater will become contaminated with leachate and with waste items such as plastics.

10.2.3  Burial in a pit

This is practised mainly in the yards of individual households. It can be an effective way of dealing with waste, especially when the waste is covered by earth every day. But care must be taken in choosing where to position the pit so that there is no danger of leachate contaminating groundwater or surface water. Another disadvantage is that these pits cannot accommodate a huge volume of solid waste, so a household could run out of disposal space. An example of a burial pit, which is fenced to keep out animals and children, is shown in Figure 10.2.

Figure 10.2  Waste pit for a small community.

10.2.4  Controlled landfill

For urban waste disposal, a controlled landfill is a significant improvement on the communal open dump. The area is fenced to control access and the waste is covered with soil at the end of each day. This prevents the waste being blown around, stops flies breeding on the waste, makes it less accessible to scavenging animals and prevents the waste catching fire. A controlled landfill site is staffed, and some machinery (such as a tractor) is available to spread, compact and cover the waste with soil.

The national Urban Solid Waste Handling and Disposal Strategy (MUDHC, 2015) includes standards for waste disposal areas of different categories of town and city. The standard for smaller cities and towns requires that the site should:

• accommodate up to 50 metric tons of waste daily
• have an inlet road, which is kept repaired
• make sure that dumped waste is covered with soil
• have procedures for controlling the waste coming to the site
• have light machinery, such as tractors, regularly on site
• have an additional 15% land area for operating space and site services
• forbid the disposal of rubber products, industrial wastes, medical and hazardous wastes, and keep construction waste separate from general waste.

Note that the standard specifically mentions the problem of rubber products, which generally refers to vehicle tyres. Tyres should not be added to landfill for several reasons: they cannot be compacted; they may collect water which creates a breeding site for mosquitoes; and, if they catch fire, they can burn for many weeks or even months.

Following these standards is good practice in small and medium-sized towns, but continuous staffing is needed to control how and where the waste is deposited and to prevent the site from becoming an open dump. Furthermore, there is no control of leachate being formed or contaminating ground and surface waters.

10.2.5  Sanitary landfill

A sanitary landfill is an engineered facility for the disposal of waste from larger towns and cities (Figure 10.3). To be cost-effective there needs to be more than around 150 metric tons of waste deposited in a day. The site is designed and operated to minimise public health and environmental impacts. The additional environmental control measures should include a system to collect and treat leachate, better gas venting systems and good amenities for site staff. In Figure 10.3 you can see the drainage channels for leachate that have been prepared before the waste is added to the area in the foreground. Larger sites should be divided into ‘cells’ separated by earth banks. Adding waste to one cell at a time allows each part of the site to be filled and covered more quickly.

Figure 10.3  A sanitary landfill.

For the largest cities, the ideal sanitary landfill would also have:

• an active system to pump out landfill gas and burn it, ideally making use of the heat generated
• a liner made of compacted clay or a synthetic membrane sheet that separates the waste from the ground below and prevents leachate leaking from the site and into the surrounding ground.

These types of landfill sites are uncommon in African countries, but efforts are being made to convert the Repi landfill in Addis Ababa into a sanitary landfill.

10.3  Planning controlled landfills for small and medium-sized towns

If small and medium-sized towns wish to reduce open dumping, a dedicated controlled landfill site needs to be identified and developed. To plan for a new site, two key factors to consider are the area of land required and the choice of the best location.

10.3.1  Estimation of the required land area

As an example, think of a town with a population of 25,000 people that produces around 4000 metric tons of waste a year (residential, commercial and industrial). The town intends to construct a controlled landfill that will last for five years.

The first stage is to estimate the volume of space that this waste will occupy. From previous experience, it is known that one cubic metre (1 m³) of waste weighs about 600 kg when landfilled; in other words the density of waste is 600 kg per m³. So one year’s worth of waste (4,000,000 kg) will occupy:

 m³

Therefore five years’ waste will need m³.

But we also need to allow for the soil that is used to cover the waste. Again, from experience, it is known that this will add about 10% to the space required. In this case we will need:

m³

We now need to calculate the land area. If we assume that the depth of the waste and soil cover in the site will be 3 m, the site area required will be:

m²

Although this is the requirement for the land used for disposal, additional land is required to give space for vehicles to move, for the cover soil to be stored and for an amenity building. From Section 10.2.4, this will account for a further 15%, so the site area becomes:

m²

If the site were rectangular, a space of 100 m by 140 m would be suitable.

10.3.2 Finding a suitable location

Once the area of land is known, the next step would be to find a suitable location. The main factors in deciding if a site is suitable are as follows:

• How far is the site from the centre of the population? On the one hand, if the site is too close, the people may be bothered by odours. However, if the site is more than about 3 km from the town, a transfer station (see Study Session 9) will be needed to transfer the waste from the collection vehicles to a lorry that then takes the waste to the site.
• Is the site near a watercourse? Generally speaking it is better to avoid an area close to flowing water because there is always a risk that leachate will leak from the site. It may be tempting to use a dry valley but this may not be dry during the rainy season and running water could carry the landfilled waste over a large area. For this reason, valleys are best avoided.
• Is there any groundwater under the site? It is important to take specialist advice about this because of the risk of contamination.
• What is the local soil type? Water and leachate flows through different soils at different speeds. Sandy soils tend to be very permeable and leachate will flow through them quickly and for a long distance. Clay soils tend to be less permeable so leachate travels slowly and for shorter distances through them.
• What do the local community think about it? Some areas of land are considered to be sacred by one or more religious groups and should never be considered for landfill. Using such land would be deeply offensive to the people concerned.

10.4  Thermal processing methods

Thermal processing of waste means heating waste so that it burns. During the burning (also known as combustion) process, the combustible material is converted into gases (mainly carbon dioxide and water vapour) and an ash residue. Thermal processing leads to a large reduction in the volume of solid material left over for landfill disposal and destroys pathogens, so it may look like an attractive option. However, unless the combustion takes place under tightly controlled conditions using equipment designed to prevent and capture any pollutants produced, the process will emit a large amount of smoke and other invisible air pollutants that can cause serious health problems.

There are two main thermal processes you may come across: open burning; and incineration. There are other more advanced thermal processing methods but these are not currently used in Ethiopia.

10.4.1  Open burning

Many individual householders practise open burning in their yards, where waste is burned in a pile in the open air and the remaining ash is buried or spread on the ground. This may be easier for the householder than taking their waste to a collection point or a landfill, but the smoke is an annoyance to the neighbours and can be a health hazard (Figure 10.4). You should always discourage open burning unless it really is the only option for dealing with the waste.

Figure 10.4 Open burning produces a lot of smoke and can be dangerous.

10.4.2  Incineration

Incineration, as opposed to open burning, is the combustion of waste material in an enclosed container with an air supply and ideally fitted with a chimney. The combustion process can be controlled to some extent so less pollution is produced and a chimney helps to reduce the impact by sending product gases upwards into the atmosphere. An incinerator of the type that may be used in large schools or hospitals is shown in Figure 10.5(a). Smaller, lower-cost incinerators may be built from bricks (Figure 10.5(b)). These can be built locally and are the type you are most likely to see.

Figure 10.5  (a) A metal incinerator with a chimney. (b) A brick incinerator is simpler and cheaper to build.

Incinerators are mostly used in Ethiopia to treat healthcare waste or waste in other institutions such as schools. They are preferable to open burning but they still generate smoke and other pollutants. They need to be operated with care to make sure they function correctly and to minimise possible pollution. Good practices in managing small incinerators include the following:

• Make sure there is a sufficient air supply to the container where the burning takes place. Usually the air flows upwards through the chamber, so the bars that the burning waste sits on should not be blocked.
• Most pollution is formed when the incinerator is heating up, so use firewood or clean, dry waste at the start.
• Waste should be added to the incinerator regularly so that the temperature does not fall and cause smoke to be formed. Generally, wet waste should be added in small amounts and ideally mixed with dry waste.
• The ash should be removed when cold and then buried. Care must be taken to avoid light ash blowing away in the wind.
• The incinerator should be in a fenced-off area – when operating, the external surfaces will become very hot.
• The incinerator operators should be trained adequately. They should wear protective clothing (gloves, face masks, etc.), especially when burning healthcare waste. They should have access to and use handwashing facilities at the end of each shift and before meal breaks.

10.5  Types of hazardous waste

Hazardous waste was defined in Study Session 7 as any discarded material that may pose a substantial or potential threat to public health or the environment. Hazardous waste, whether liquid or solid, must be kept separate from non-hazardous waste and requires special handling and treatment. Hazardous wastes may be:

• Toxic – these are wastes that are capable of causing acute or chronic health problems. Examples include asbestos, arsenic, heavy metals and synthetic pesticides.
• Ignitable – ignitable wastes will catch alight very easily when exposed to a flame or spark. Ignitable wastes are also highly flammable meaning they burn easily. Examples are organic solvents, oils and paint wastes.
• Corrosive – corrosive substances that are strongly acidic (pH less than 2) or strongly alkaline (pH higher than 12.5), and can readily dissolve standard container materials or damage living tissue. Examples include acids, alkalis, cleaning agents and discarded batteries or battery manufacturing residues.
• Reactive – reactive wastes are dangerous because of their vigorous reaction with air and water, or because they can explode and generate toxic fumes. Examples are obsolete munitions, wastes from manufacturing dynamite or firecrackers, and some chemical wastes.
• Infectious – any waste that contains micro-organisms that can harm humans. Much of the waste produced by hospitals, health centres and dentists may well be infectious. This type of waste may also be referred to as a biohazard.

How do you know whether a waste is hazardous? Many hazardous products are found in Ethiopia but people do not always know how to identify them. It is important that anyone who comes in contact with hazardous materials understands their nature so they can protect themselves and handle the specific product or waste with care to avoid damage to skin, clothes or even property and life. There is an internationally agreed set of hazard symbols, shown in Figure 10.6.

Maximise

Figure 10.6  Hazardous waste symbols.

10.5.1 Household hazardous waste

You may think that hazardous waste is only produced in factories and hospitals, but you should be aware of household hazardous wastes. These are wastes produced in normal households that have any of the hazardous properties listed above. This could include bleaches and some cleaning products, batteries, paints, pesticides, and pharmaceuticals (Figure 10.7).

Figure 10.7 Some harmful chemicals that can be found in our homes.

10.6  Management of hazardous waste

When it comes to treating hazardous wastes, the principle of the 3 Rs should be followed where possible. Alongside reduction, replacement should also be practised as the first stage in the waste hierarchy. This means replacing hazardous substances with non-hazardous ones in manufacturing processes and avoiding processes that produce hazardous by-products. Applying the 3 Rs to hazardous waste is highly specialised and would normally be the responsibility of the industries concerned.

There are a number of options for treating hazardous waste, based on transforming it to a non-hazardous form or isolating it from people and the environment. The options are:

• Secure landfill, where the waste is completely isolated from the environment. This is generally the safest method, but sites that are designed to take hazardous waste are uncommon in Africa.
• Treating the hazardous waste chemically to transform it into a non-hazardous waste. For example, acid waste can be neutralised by the addition of the correct amount of an alkali.
• Treating organic hazardous wastes (oils, for example) with micro-organisms to break them down into non-hazardous materials.
• Controlled high-temperature incineration of flammable wastes (oils and chemicals) and medical wastes. However, the process needs to be very carefully controlled and carried out in a purpose-designed incinerator.

In reality, much of Ethiopia’s hazardous waste, along with other wastes, is disposed of in landfill sites. This does give some isolation from people and the environment in the short term, but you must be aware that this means that all landfills should be treated as containing hazardous waste and all possible steps should be taken to keep people away from these sites.

Summary of Study Session 10

In Study Session 10, you have learned that:

1. Solid waste that cannot be recycled can be treated or disposed of by landfill or thermal processing.
2. The two main environmental problems from landfill are leachate, which can contaminate water sources, and landfill gas, which is a greenhouse gas and is flammable.
3. Landfills range from uncontrolled open dumps to sanitary landfills, where leachate and landfill gas are managed and controlled.
4. Factors to be considered when selecting a new landfill site include the area of land required, distance from the town, potential for pollution of water sources, soil type and local culture and beliefs.
5. The open burning and open dumping of solid waste, which is a common practice in many urban centres in Ethiopia, is dangerous to human health and safety and to the wider environment.
6. Incineration reduces the volume of waste for disposal, but the remaining ash still needs to be landfilled.
7. It is important to know the nature and characteristics of solid waste, to recognise hazardous waste, and to appreciate how it should be handled and treated.

Self-Assessment Questions (SAQs) for Study Session 10

Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering these questions.