Landfills are a regular occurrence all over the world, owing to the rising volume of trash generated by our homes, schools, offices, hospitals, and markets. The rising number of landfills around the world is largely due to increased urbanisation and population growth rates.
As the world’s population and cities develop, so does the need for goods and commodities. Consequently, the amount of solid trash produced also increases. They eventually reach landfills. In this blog, let’s go on a trip to a landfill and understand its operation, lifecycle and impacts
Let me begin with the definition of landfills.
What are Landfills?
Landfills are places where we dispose of trash, garbage, and other solid wastes. They have traditionally been the most frequent method of disposing of solid garbage. In the landfills, the waste is either buried or piled in heaps. The garbage in these heaps is a combination of residential and commercial waste.
Landfills commonly use either of the following techniques for waste disposal:
- Landraising – This technique involves depositing trash directly on the ground.
- Landfilling – This technique involves filling a hole in the ground with the rubbish.
Causes of Landfills
With the rise in land utilization and pollution, landfills also saw a rise in the number. Let’s see the causes of land pollution. Before jumping into the next section make sure that you go through Land Pollution Causes -Top 6 causes explained.
Wood, paper, plastic, broken furniture, glass, grounded cars, old electronic items, and hospital and market garbage are examples of solid waste materials. Because most of these waste materials are non-biodegradable, they heap in the landfills where they stay for years.
Agricultural wastes comprise waste products such as animal dung, crop residue, and agricultural garbage. Solid wastes such as animal manure and other agricultural wastes are collected and disposed of in landfills.
Now, let’s try to understand how landfills operate.
- On arrival waste collection vehicles move to a scale or weighbridge to weigh their loads.
- Workers inspect loads for wastes that do not meet the landfill’s waste-acceptance standards.
- The garbage collecting vans next travel to the tipping face or working front and drop their contents.
- Compactors or bulldozers redistribute and compact the garbage on the working face.
- The vans may pass through a wheel-cleaning facility before leaving the landfill’s borders. If necessary, they return to the weighbridge without any load for re-weighing.
Sanitary landfills life cycle
A sanitary landfill is a pit with a sealed bottom where rubbish is buried and compacted in layers to make it more solid. In sanitary landfills, waste decomposition is a complex process involving the sequential and/or simultaneous occurrence of a variety of chemical and biological reactions. These reactions result in the breakdown of the waste materials. The organic fractions of MSW break down quickly, resulting in landfill gases and liquids.
The amount of biodegradable organic matter present in the waste, the availability of moisture and nutrients required for biodegradation, and final landfill closure measures all influence the duration of individual phases, as well as the nature and quantity of various landfill gases generated during each phase.
Over the lifetime of a sanitary landfill, five successive phases can be distinguished based on the formation of major landfill gases and physicochemical conditions. Let’s have a closer look at each of the phases.
Phase 1 – Initial adjustment
- The first phase of a sanitary landfill’s life cycle.
- During this phase, the organic constituents easily biodegrade organic compounds in Municipal Solid Waste undergo microbial breakdown, typically under aerobic circumstances, soon after dumping them in the landfill.
- This phase usually lasts a short time from the moment of waste dumping until around a week.
- The oxygen-rich air trapped within the landfill promotes aerobic reactions.
- Microorganisms are the primary agents in biodegradation. The soil that is utilised for daily cover serves as the primary source of microbes.
- Sludge from wastewater treatment plants is sometimes recirculated. Leachate also serves as a source of the microbial population.
Phase 2 – Transition Phase
- The landfill undergoes a transition from an aerobic to an anaerobic state in this phase.
- Because of the high consumption of oxygen during Phase I, and its subsequent depletion, the situation is mainly anaerobic. The oxidation/reduction potential of the waste helps to track the change from aerobic to anaerobic conditions.
- In the absence of oxygen, the terminal electron acceptors are nitrate and sulphate in the chemical reactions that occur. Hence the landfill gas consists mainly of nitrogen and hydrogen sulphide.
- Due to the formation of organic acids and higher CO2 concentrations within the landfill, any leachate created during the transition period is often acidic.
- The pH during this phase is normally between 6 and 7.
- This phase can last between 1 to 6 months.
Phase 3 – Acid Formation Phase
- In the acid formation phase, the biodegradable component of the solid waste begins to hydrolyze. As a result, there is a rapid accumulation of volatile fatty acids (VFAs) in the leachate.
- The increasing organic acid concentration lowers the pH of the leachate from 7.5 to 5.6.
- The leachate has the potential to dissolve many inorganic elements, including heavy metals, due to the decreased pH, making it very poisonous.
- This phase lasts anything from 3 months to 3 years on average.
- The further breakdown of intermediate chemicals, such as VFAs, generate a significant amount of chemical oxygen demand during this phase.
- High VFA concentrations raise both the biochemical oxygen demand (BOD) and VOA levels. This triggers H2 generation by fermentative bacteria and promotes the growth of H2-oxidizing bacteria.
- Acetic acid (C2H4O2), CO2, and hydrogen gas are produced from long-chain volatile organic acids (VOAs) towards the end of this phase.
Phase 4 – Methane Fermentation
- Methanogenic bacteria convert the intermediary products of the acid formation phase such as acetic, propionic, and butyric acids to CH4 and CO2.
- As methanogens continue to digest the VFAs, the pH of the landfill water returns to neutrality.
- The organic strength of the leachate, expressed in terms of COD, drops rapidly as the rate of CH4 and CO2 gas generation rises.
- This is the most time-consuming part of the breakdown process. The typical duration of this phase is approximately 8 to 40 years,
Phase 5 – Final maturation and stabilization
- This is the final stage of a sanitary landfill’s life cycle.
- Once the microorganisms finish consuming easily biodegradable organic materials they begin digesting other difficult to biodegrade materials.
- As the amount of available biodegradable organic matter considerably decreases during the maturation phase, the rate of landfill gas generation drops dramatically from prior phases.
- This phase’s leachate frequently contains humic and fulvic acids. The main gases produced at this period are CH4 and CO2.
Impacts of Landfills
Landfills all over the world have social, economic and environmental impacts. Below mentioned are a few of them:
When rain falls on open landfills, the water percolates through the waste, becoming contaminated with suspended and dissolved material. This creates leachate. All modern landfills use a combination of impermeable liners several metres thick, geologically stable sites, and collection systems to collect and contain the leachate. Most landfills use clay as the liner material, but geosynthetic membrane liners also find wide application in sanitary landfills.
Also read: Geosynthetics- Types and Benefits Full Guide
Following that, it can be treated and evaporated. Once a landfill is full, authorities seal it to prevent precipitation intrusion and the development of new leachate. Any landfill liner would eventually leak. This leads to the contamination of groundwater in the long run.
Rotting food and other decomposing organic waste produce gases particularly CO2 and CH4 through aerobic and anaerobic decomposition, respectively. Both processes take place at the same time in separate regions of a landfill. The fraction of gas constituents will vary based on the age of the landfill, the type of waste, moisture level, and available O2.
On average, CH4 accounts for roughly half of the volumetric concentration of landfills gas, with CO2 accounting for slightly less than half. About 5% molecular nitrogen (N2), less than 1% hydrogen sulphide (H2S), and a modest quantity of non-methane organic chemicals (NMOC), about 2700 ppmv, are also present in the gas.
Due to the high percentage of methane in the landfills gas, some countries utilize it as a fuel.
Landfills serve as a breeding ground for mosquitoes, flies and rats. Because vectors such as rodents and flies can spread dangerous diseases, poorly managed landfills can become a nuisance. The application of daily cover can help to reduce the occurrence of such vectors.
Modern landfills that adhere to all standards governing site selection, design, building, and operation ensure not only a clean and safe facility but also a potential source of energy that helps reduce greenhouse gas emissions. Proper management of landfill gases and leachate help in avoiding environmental pollution. Sanitary landfills are still the most cost-effective way to dispose of MSW if they are properly planned and managed.
In case of any queries feel free to ask in the comments section. Happy Learning.