Introduction 

Solid waste disposal is the process of collecting and treating solid waste. It is the movement of solid waste to a place designated for its disposal so that it cannot impact the environment. It is also the process of recovering items from waste that can be recycled and repurposed. The indiscriminate disposal of solid wastes creates unhygienic conditions. This affects human health and leads to environmental pollution. The safe disposal of solid waste is a complex task. There are a variety of economic, social, and administrative problems associated with solid waste disposal that must be addressed. 

Disposal in Landfills

All human activities generate waste. The generation of waste cannot be stopped. All waste that is not recycled must go somewhere, and it often ends up in a landfill. A landfill is an area of land that receives household and municipal waste. It may also receive non-hazardous, industrial, or commercial waste. Though the term ‘landfill’ is the more common one, some sites practice ‘land raising.’ Land raising is when waste is dumped directly on the ground, whereas landfilling is when a hole in the ground is filled with waste. 

A lot of material disposed of today in landfills is from commercial and construction businesses. The waste consists of soil, brick, rubble, concrete, etc. These wastes are known as ‘inert’ since they are safe to be disposed of and do not react with other wastes in a landfill.  

Landfills are designed and monitored to protect human health and to stop contaminants from polluting the environment. They should be situated away from ecologically sensitive zones. 

After a landfill reaches its maximum capacity, it is capped with a layer of clay and vegetation. This forms a sort of barrier, keeping in the bad odours. 

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Secure Landfills and Landfill Bioreactors

A secure landfill is one that usually receives hazardous waste. It is engineered in a way that prevents interaction between wastes and groundwater. It also prevents rainwater from seeping into the landfill. A secure landfill is so named because it is completely secured from contaminating the surrounding environment by completely isolating the landfill from the surrounding elements. A secure landfill has been designed with preventive measures such as:

1. Dust control
2. Bad odour
3. Wind-blown litter
4. Pests and rats
5. Fire hazard
6. Slope instability
7. Bird menace
8. Greenhouse gas emissions 

As can be seen from the above points, a secure landfill allows for the completely safe disposal of waste. It ensures that the waste buried is safely contained. It also allows the safe degradation of waste over time until it becomes a part of nature again. 

The essential components of a secure landfill are:

1. The lining of the base and sides of the landfill with appropriate material to prevent the migration of leachate and gas. 
2. A facility for the collection and storage of leachate. 
3. A facility for the collection and control of gas.
4. A system that monitors the waste disposed of in the landfill.

In a bioreactor landfill, some liquids are added to wastes to help bacteria degrade them faster. The addition of liquid enhances microbial activity that helps in waste degradation. There are three types of bioreactor landfills:

1. Aerobic

An Aerobic landfill has systems that remove leachate from the bottom, store it in storage tanks, and introduce them back into the landfill in a controlled manner. Air is also made to circulate in the landfill through vertical or horizontal wells. This promotes aerobic microbial activity.

2. Anaerobic

In an anaerobic landfill, wastes biodegrade in the absence of oxygen. Leachate that drains off is collected and reintroduced back into the landfill. The recirculation of leachate adds moisture to the biodegradation process. The anaerobic biodegradation of wastes produces landfill gas. Gas released from landfills is composed largely of methane. There are systems in landfills that collect this methane. The collection of methane allows it to be used for sustainable energy projects. The collection of methane also ensures that its release into the atmosphere is prevented.

3. Hybrid (aerobic-anaerobic)

A hybrid landfill uses the method of aerobic and anaerobic degradation in an alternate manner. Organic matter is made to biodegrade in the upper section of the landfill while the lower section collects the gas produced. 

Leachate and Landfill Gas Management 

Leachate is the liquid that drains from a landfill after water percolates through it and leaches away components of the wastes. Its composition is widely variable and depends upon the type of waste and the age of the landfill. It contains harmful dissolved substances. Leachate cannot be further used in industrial processes. Leachate from landfills must be properly controlled so that it does not affect the environment and surrounding infrastructure. The control of leachate is especially important in landfills that contain industrial waste. 

In most cases, leachate is drained into a collection system. From here, it is transferred to a holding pond onsite. In landfills that don’t have holding ponds, leachate is transported to an offsite treatment plant for safe disposal. 

Landfill gas (LFG) is gas emitted as a natural byproduct of the breakdown of organic wastes in a landfill. LFG is composed of approximately 50% methane and 50% carbon dioxide. Methane is much more potent than carbon dioxide at trapping heat in the atmosphere. Therefore, its careful management is critical to the health of our planet. 

Through the use of proper equipment and planning, LFG can be collected and used as a renewable form of energy. Controlling LFG helps in preventing the spread of bad odours from a landfill. It also prevents methane from being released into the atmosphere, which would otherwise further enhance global climate change. 

LFG can be drawn out from landfills using wells or a vacuum. It is then collected, stored, and treated. Its treatment depends on its ultimate use. The gas is then transported to be used in a renewable energy project. The energy projects can include the generation of electricity and renewable natural gas. 

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Rehabilitation of Open Dumps

Developing countries severely suffer from inadequate funding for engineered solid waste disposal sites. A phased approach to the rehabilitation of open dumps is the only way these countries can improve their waste disposal practices.

1. Controlled Dumps

A controlled dump is the first step in the rehabilitation of open dumps. Controlled dumps consist of authorized individuals that monitor incoming wastes. There is also regular inspection of the compaction of waste and the application of soil cover once the dump has reached its capacity.

2. Engineered Landfills

Engineered landfills are those in which technological measures are incorporated to control their basic functions. These landfills have systems to control greenhouse gas emissions, collect and treat leachate, and provide a daily cover of soil on waste.

3. Sustainable Landfills

This is the final step in the rehabilitation of landfills. The functioning of such a landfill does not negatively impact the environment in any way. A sustainable landfill has a perfect balance between incoming waste, biodegradation of earlier wastes, moisture levels, and microorganisms. The management of a sustainable landfill largely depends on society’s perception, generation, and minimisation of waste. 

Landfill Remediation

Every human generates waste equal to 1.97 kg every day. This waste most often ends up in a landfill. Landfills are a sight for sore eyes. Not only are they a threat to the environment, but they also take up valuable land. With a booming population, many cities lack land for residential spaces and recreational activities. Cities are also starting to experience the environmental impacts of open landfills. The impacts include water contamination, land degradation, and air pollution. It has already been discussed earlier how landfills emit greenhouse gases that contribute to a warming planet. Remediating a landfill that has reached its capacity provides extra land and generates revenue that contributes to a region’s economy while also taking care of the environment. Below are some common remediation methods.

1. Excavation/mining

Landfills can be mined to recover waste that can be recycled or combusted to free up space. The quantity of material recovered heavily depends on the chemical and physical properties of the waste. Landfill mining is an effective method of remediation only after waste is fully decomposed or processed by a bioreactor.

2. Capping

Landfill capping involves adding a layer of soil and vegetation over the landfill after it has been sealed by synthetics. The sealed layer prevents bad odours from being emitted by the underlying waste. It also isolates the wastes and prevents them from interacting with the environment.

3. Redevelopment

After a landfill has been sealed, the space can be used for economic development. Businesses can be established, or parks can be developed in the new free space. This method provides an opportunity for people and communities to come together.