30 Solid waste disposal, open dumping and landfills

Dr. Yogalakshmi K. N

 

Objectives:

1.      To define waste disposal

2.      To understand the waste disposal of options

3.      To understand the problems of open dumping

4.      To define the process of controlled dumping (i.e) landfills

5.      To study the different types of landfill

6.      To understand the various criteria in selecting a site for a landfill operation

Solid waste

Waste is defined as any unwanted or unusable substance that is discarded after primary use. Wastes are normally generated as a result of human and animal activities. Urbanization and rapid advancements in industrialization has led to an increase in the production and consumption processes resulting in the generation of wastes from various sectors that include agricultural, commercial, domestic, industrial, institutional, social and from community activities. Over time, these waste accumulate and can have real impacts on the health and the environment. Waste management is intended to reduce adverse effects of waste on health, the environment or aesthetics.

Solid wastes are any discarded or abandoned materials that is of no use. that can be solid, liquid, semi-solid or containerized gaseous material discarded by the human society. According to the source of generation and type they are classified as urban wastes, agricultural wastes, biomedical wastes, bulky waste, open area waste, radioactive wastes, e wastes and many more. The term refuse is also used for solid wastes. Examples of solid wastes include waste tires, septage, scrap metal, latex paints, furniture and toys, garbage, appliances and vehicles, oil and anti-freeze, empty aerosol cans, paint cans and compressed gas cylinders, construction and demolition debris, asbestos, plastics, styrofoam containers, bottles etc.

Disposal of solid waste

The solid waste must be properly managed to avoid environmental and health hazards. The waste management involves various steps namely waste collection, segregation, transport, processing, treatment and disposal. Disposal is the final step in the waste management. Ultimately all solid waste ends in disposal site either directly or after some processing and treatment it ends in disposal sites. Most of the developing and under developed countries, dispose or dump the solid waste in an open land without any protection or environmental control. Such dumping is not safe and is called as open dumps or open dumping. Solid waste is also disposed off in water bodies eg. Sea, ocean, lake, river etc. Sometimes they are also burned in open areas, the phenomenon termed as open burning. Developed countries are practicing a system of safe or controlled dumping called the landfill. Landfill is an engineered structure where the waste is safely disposed and contained.

Uncontrolled or open dumping

It is the most common method of waste disposal. Open dumping is practiced in many parts of the world especially the under developed and developing countries. In this method, wastes are dumped at a designated site or land without any environmental protection or control. The waste disposed in these open areas remain there for a long period of time and affects the environment and health of the individual Due the problems associated with the open dumping they are not considered as a safe option. The problems of open dumping are discussed below.

Problems of open dumping

Waste when dumped in open areas causes a lot of problems thereby affecting the different environmental matrices namely water, soil, air and noise. It also disturbs the ecosystem and the population of the earth. Also, open dumping leads to a lot of health hazards which even possess lethal and fatal effects.

The problems associated with open dumping of solid waste includes

• It causes contamination to soil, water and air
• During uncontrolled dumping the leachate (a watery liquid that oozes out from the waste) percolates into the soil and contaminates it with various toxic pollutants
• It also affects the microbial diversity of the soil and vegetation of the area
• Through the soil medium the leachate can percolate into the ground water and contaminate them
• During precipitation, the rain water can mix with leachate and be carried off as surface run. Through this they also pollute the water bodies
• It acts as a source of non point pollution It affects the biodiversity of the location
• Open dumps serve as a breeding ground for many of the disease causing vectors (e.g., flies, mosquitoes and rodents). Even the stray animals eg, dogs, pigs, cows and many more act as a carrier of diseases.
• Since the waste dumped in the open area does not have a cover, the waste is carried off by wind thereby creating a menace. Sometimes they fly and stick on to the traffic signals and vehicles creating danger to the individuals
• To recover the valuable metals in the waste dump, the rag pickers set fire to the waste resulting in emission of particulate matter and other gaseous emissions leading to air pollution.
• Smoke is also a major problem of open dump.
• Air pollution is also caused by emission of gaseous pollutants eg. Carbon dioxide, methane, VOCs etc. produced during waste degradation
• The emission of green house gases results in global warming
• Dioxins, a carcinogen is released during the burning of plastics.
• The land where the waste is dumped undergoes degradation and gets deteriorated The waste dumped in open dumps create unpleasant odor
• The aesthetics of the area is affected when waste is dumped in open areas
• The waste dumps or piles attract lot of insect, rodent, birds and animals. The contaminates are toxic and affect these species. Sometimes they also kill the insects, birds and animals
• The toxic contaminants enter the food chain though the birds and animals that visit the open dumps for food.
• Sometimes these open dumps act as breeding grounds for migratory birds as they stop at these open dumps in search of food

Controlled dumping or landfills

Landfills are the largest route of disposal. Landfill is an engineered structure (Figure 1) for disposal or containment of solid waste. It is considered to be the safe method of waste disposal. Landfills are designed and operated according to acceptable standards. It is designed in a way to protect the environment and health of people. Landfills are not homogeneous. They are usually made up of cells in which a discrete volume of waste is kept isolated from adjacent waste cells by a suitable barrier. This landfill option of waste disposal is suitable only when the land is available at an affordable price, availability of adequate workforce, availability of technical resources to operate and manage the site. Landfill helps in protecting the environment from various effects. The main purpose of designing a landfill is to contain the waste and protect the environment through a geological barrier and liner system at the base, sides and on top named the cap of the system landfill. The requirement and type of the barrier system depends on the nature of waste being loaded in the landfill. The barrier system is selected based on few criteria. They are

• prevent the pollution of soil, groundwater or surface water

• ensure efficient collection of the leachate

The barrier used are both natural and synthetic. Natural or geological barrier used for a particular landfill is selected based on the geological and hydrogeological conditions below the landfill and availability of material in the vicinity of the landfill site.

The landfills are composed of three main components. They are

• A liner system – used at the bottom to protect the soil and ground water.

• Waste emplacement cells – pattern by which waste is loaded into the landfill

• Cover or capping – It is the top most protection layer that prevents the entry of water or other animals into the waste pile

• Leachate collection system

• Groundwater monitoring system

• Methane gas monitoring system

Leachate collection, ground water and gas monitoring are used for monitoring the performance of landfills and failure of liner or cover system

Figure 1 Landfill structure

Landfill site selection and assessment

The selection of a site for a waste landfill depends on certain criteria. They are

• the proximity of the site to the source of waste generation – Distances from the boundary of the site to residential areas, agricultural or urban sites. The site should not be close to any residential or industrial area.

• Accessibility and suitability of access roads – transport infra-structure: The connectivity to the site should be good so that transport of waste can be facilitated.

•Impact on the local environment of site operations: The impact of the landfills on the local environment should be studied.

• The geological and hydrogeological stability of the site should be assessed.

• The site should not be located in disaster prone zones. The risks of hazards such as flooding, landslides and even avalanches should be taken care off. Such zones should be avoided.

• The assessment of soil and bedrock grain sizes, mineralogy and permeabilities should be done. This will help us determine the movement of leachate and how vulnerable is the site to contamination.

• Hydrological isolation – Ground water levels, Distances from the boundary of the site to waterways should be measured to avoid contamination of the water bodies

• Meteorological data – rainfall, wind speed and direction should be collected to prevent the waste from rainfall so that leachate production is minimized and further contamination is avoided. Likewise wind speed is also essential to avoid wind blown litter.

• A topographical survey is undertaken to calculate the available void space and therefore the waste capacity of the site.

• Background levels of water and air quality to assess the impact of the site in the long-term.

• Assessment of the direct and indirect effects of the project on human beings, fauna, flora, soil, water, air, climate and landscape, material assets and the cultural heritage.

• The site should not be close to UNESCO heritage site, national parks, wildlife sanctuaries, monuments and places of significant importance

• Land with agricultural productivity should not be chosen

Considerations of landfill

A waste landfill is major design and engineering project and requires a number of consideration. The following considerations are very important

• Site capacity: The capacity of the site is a key factor in design of a landfill. The capacity is decided based on

• amount of waste generated

• waste density

• Amount of intermediate and daily cover

• Thickness of capping system

• Amount of settlement

• Waste density: The density of the waste within the landfill depends

• on the degree of pre-compaction of the waste before emplacement

• the variation of components within the waste

• the extent of biodegradation

• the amount of daily and intermediate cover and

• the mass of overlying waste.

• The degree of pre-compaction influences the amount of waste to be loaded into the landfill and amount of waste settlement in landfill. The waste densities range from 0.65 to 0.85 tonnes/m3. It can also go upto 0.4 tonnes/m3 or 1.23 tonnes/m3 depending on the biodegradable and inert waste. Inert waste have higher densities, typically about 1.5 tonnes/m3

• Settlement: Settlement of the waste in the landfill occurs due to physical rearrangement of the waste soon after loading. Later settlement also occurs due to biological, physical and chemical degradation processes. It occurs due to overburden pressure due to compaction by weight of the overlying waste. Municipal solid waste over long-term results in 15-20% reduction of waste. Around 90% settlement takes place in first five years. Settlement take place over periods of 50 years. However, inert waste shows low settlement. settlement occurs in three ways.

• Initial compression – it is instantaneous and occurs due to compaction of void space and particles caused by the compression of the overlying waste and the compaction vehicles

• Primary compression – occurs due to the dissipation of pore water and gases from the void space and usually takes around 30 days

• Secondary compression – it takes years and occurs due to biodegradation of waste. Leachate and landfill gas reduces mass and volume.

The amount and rate of landfill settlement depends on different factors such as void space in the waste, compaction of the waste and thickness of the waste. According to studies, deeper landfills exhibit faster rates of settlement.

• Material requirement: Landfill construction requires lot of materials Eg. natural fill material such clay, sand, gravel and soil – used as lining material. Clay provides an additional low permeability and is used as liner and capping material. Likewise gravel for drainage of leachate. The availability of such materials on site reduce cost and increases the ease of operation. Material is also required for daily cover to control wind blown litter, scavengers, fires and odours. The daily cover material can be soil, garden waste or alternative materials such as re-usable blanket material and inert wastes. Daily cover uses valuable void space and reduces the operating life time of the site.

• Drainage: It is another important factor that needs consideration during construction of a landfill. The excessive water that is received from rainfall and runoff from surrounding areas should not be allowed to infiltrate into the site. Cut-off drains both around and inside the site should be constructed to keep the waste from becoming too wet thereby increasing the leachate generation. Capping acts as a barrier system and reduce the excessive water falling on the site from entering the mass of waste.

• Operation practice: During landfill construction and operation, daily operation of the landfill including traffic movement, cover material storage and laying, security should be considered. A landfill site should have a secured fence with access routes for the waste transport vehicle.

Types of landfill

Landfills are of three types. They are

• Waste landfills for hazardous waste or secured landfill – This type of landfill is used for containment of hazardous waste that possess great potential in causing health and environmental effects. Hazardous waste is defined as waste which is a threat or dangerous to store, treat or dispose off. Hazardous waste possess either one or more properties like corrosive, toxic, reactive, ignitability. Certain hazardous waste are not permitted into landfill egs. liquid waste, flammable waste, explosive or oxidising wastes, infectious waste, clinical or hospital waste and used tyres. These landfills have high specification containment barrier liner system to contain the derived leachate and landfill gas.

• Waste landfills for non-hazardous waste or sanitary landfill – This type of landfill is generally used for municipal solid waste that does not cause dangerous effects on environment and living beings. Stable, non-reactive hazardous wastes that are solidified or vitrified, are also permitted to be deposited into non-hazardous waste landfills, provided that their leaching behaviour is equivalent to the general category of non-hazardous waste can also be dumped in sanitary landfill.

• Waste landfills for inert waste – Used mainly for wastes that does not react and remains inert. Inert waste is defined as that does not undergo any significant physical, chemical or biological transformations. They also do not dissolve, burn, biodegrade or react physically or chemically. They do not give rise to environment pollution or harm human health. Egs of inert wastes include bricks, glass, tiles and ceramic materials, concrete, stones, etc.

Summary

To summarize, in this module we have discussed about

• Solid waste disposal Open dumping
• Problems of open dumping
• Controlled dumping and landfills
• Site selection for landfill construction Considerations for landfills
• Types of landfill

References

• Williams, Paul T. (2013) Waste treatment and disposal, John Wiley Publishers.