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.
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)
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.
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:
The different types of landfill can be ranked according to their potential to cause environmental pollution. Starting with the worst, they are:
These types of landfill are described in the following sections.
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.
Why do we discourage open dumping?
Open dumping is discouraged for a number of reasons. It:
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:
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.
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:
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.
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.
For the largest cities, the ideal sanitary landfill would also have:
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.
According to the data in Study Session 7, typical waste generation rates in Ethiopia are between 0.3 kg and 0.5 kg per person per day. If you assume a rate of 0.3 kg, how big a population would a city need for it to operate a sanitary landfill?
To be cost-effective, a sanitary landfill needs to take at least 150 metric tons of waste a day, which is 150,000 kg. If all this waste came from residential sources, this would need:
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.
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:
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:
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:
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:
If the site were rectangular, a space of 100 m by 140 m would be suitable.
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:
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.
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.
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.
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:
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:
All of these waste materials, apart from food waste, should be considered hazardous.
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.
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).
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:
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.
In Study Session 10, you have learned that:
Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering these questions.
Which of the following waste disposal methods would you consider to be the safest to public and environmental health? Explain the reasons for your choice and why the other two options are less desirable.
Option (c), sanitary landfill, is the safest option.
If a community wanted to transform its open dump site into a controlled landfill, what measures would it have to take?
Measures to transform an open dump site into a controlled landfill should include:
Explain how incineration differs from open burning.
Incineration is burning that is enclosed and controlled. Open burning is uncontrolled. Incineration produces less smoke; the ash is contained and can be removed for burial; it is safer because the burning waste cannot be blown around and spread fire. A higher temperature can be maintained in an incinerator which ensures more of the waste is consumed, leaving little residue.
What are the key factors to be considered when planning a new landfill in small and medium-sized towns? List at least four factors.
Key factors to consider when planning a landfill in small and medium-sized towns include:
|Type of waste||Type of hazard|
|Old batteries from wrecked cars and lorries||Corrosive|
|Firecrackers that were thrown away because they got damp||Explosive or flammable|
|Empty pesticide can||Toxic|
|Bloody bandages from a health centre||Infectious|
|Liquid waste from a factory with pH 13||Corrosive|
|Used solvent from cleaning paint brushes||Ignitable and flammable|