UNIT V

Part A(2 Marks)

1. List out the various methods of disposal of solid waste. [N/D-16,N/D-14] • Sanitary landfill

• Composting

• Incineration

• Gasification

• Pyrolysis

2. List the effects of improper disposal of solid waste. [N/D-16,A/M-14] • Acute respiratory tract infections

• Diarrhea

• Viral Hepatitis A

• Typhoid fever

• Cholera

3.How is designate sanitary landfill? [A/M-17,N/D-14] Sanitary landfills are sites where waste is isolated from the environment until it is safe. It is considered when it has completely degraded biologically, chemically and physically. In high-income countries, the level of isolation achieved may be high.

4.What is landfill gas? What are its advantages? [A/M-17]

Landfill gas is a complex mix of different gases created by the action of microorganisms within a landfill. Landfill gas is

approximately forty to sixty percent methane, with the remainder being mostly carbon dioxide. Trace amounts of other

volatile organic compounds comprise the remainder (<1%).

5. What are the factors which affect production of leachate and landfill gas in the landfill? [N/D-11]

1. The amount of runoff, infiltration and percolation will determine the amount of leachate generation.

2. The precipitation less runoff, transpiration and evaporation will determine the amount of infiltration of

leachate.

3. The runoff depends on rainfall intensity and duration over the landfill, permeability of the cover soil, surface

slope (4%, not greater than 30% for side slopes), condition of the soli and its moisture content, and the

amount and type of vegetative cover. Evapotranspiration during the growing season for grasses and grains

may be 20 to 50 inches.

6. What is Variation in gas production with time? [N/D-11,A/M-14]

7. Define -Leachate. [N/D-12]

The generation of leachate is caused principally by precipitation percolating through waste deposited in a

landfill. Once in contact with decomposing solid waste, the percolating water becomes contaminated and if it then

flows out of the waste material it is termed leachate.

8. What do you mean by pyrolysis? [N/D-12]

Most organic substances are thermally unstable and upon heating in an oxygen-free environment can be split

through a combination of thermal cracking and condensation reactions into gaseous, liquid and solid fraction.

Pyrolysis is the chemical decomposition of a condensed substance by heating. Pyrolysis is a special case of

thermolysis, and is most commonly used for organic materials. It occurs spontaneously at high temperatures (ie above

300 °C for wood, it varies for other material), for example in wildfires or when vegetation comes into contact with lava

in volcanic eruptions. It does not involve reactions with oxygen or any other reagents but can take place in their

presence. Extreme pyrolysis, which leaves only carbon as the residue, is called carbonization and is also related to the

chemical process of charring.

9. Brief the treatment mechanism of a sanitary land filling? [A/M-13]

Sanitary landfilling is an operation in which solid wastes are buried into the ground in various layers, each layer being compacted and covered with a layer of soil (daily cover and final cover) in order to provide for moisture and nutrients to the microbes. Initially, the bacterial decomposition occurs under aerobic conditions because a certain amount of air is trapped within the landfill. However, the oxygen in the trapped air is soon exhausted, and the long-term decomposition occurs under anaerobic conditions with the evolution of gases (CH4& CO2) and liquids (leachate).

10.What is the advantage of segregated solid waste disposal by sanitary land filling? [A/M-13] 1. The segregated solid waste will separate biodegradable fraction from the rest and send it to the sanitary landfill for

disposal. This rejects solid waste that may not undergo bacterial decomposition inside a landfill.(e.g) The recyclable fraction like paper, plastic, glass e.t.c can be segregated and sent to the respective industries for recycling. The combustible fraction can be segregated and sent to incinerator for heat recovery. Finally only the biodegradable fraction can be segregated and sent to sanitary landfilling for bacterial decomposition.

2. Since the segregated solid waste sent to sanitary landfills are mostly of biodegradable origin, the bacterial

decomposition will take place at a faster rate and the sanitary landfill will mature in short time. (e.g) Maturation of a sanitary landfill is a stage wherein the bacterial decomposition has exhausted all the organic matter present in the waste and the bacterial reaction has almost ceased. At this stage the sanitary landfill is said to be mature and its surface can be used for other purposes like playground or golf course etc.

Part B (16 Marks)

1. What is leachate? Mention the various methods of treatment of leachate and disposal (16) [N/D-16,A/M-14]

The generation of leachate is caused principally by precipitation percolating through waste deposited in a landfill. Once in contact with decomposing solid waste, the percolating water becomes contaminated and if it then flows out of the waste material it is termed leachate. Additional leachate volume is produced during this decomposition of carbonaceous material producing a wide range of other materials including methane, carbon dioxide and a complex mixture of organic acids, aldehydes, alcohols and simple sugars. The risks of leachate generation can be mitigated by properly designed and engineered landfill sites, such as

sites that are constructed on geologically impermeable materials or sites that use impermeable liners made of

geotextiles or engineered clay. The use of linings is now mandatory within both the United States and the

European Union except where the waste is deemed inert. In addition, most toxic and difficult materials are now

specifically excluded from landfilling. However despite much stricter statutory controls leachates from modern

sites are found to contain a range of contaminants that may either be associated with some level of illegal activity

or may reflect the ubiquitous use of a range of difficult materials in household and domestic products which enter

the waste stream legally.

Composition of leachate

When water percolates through the waste, it promotes and assists process of decomposition by bacteria and

fungi. These processes in turn release by-products of decomposition and rapidly use up any available oxygen

creating an anoxic environment. In actively decomposing waste the temperature rises and the pH falls rapidly and

many metal ions which are relatively insoluble at neutral pH can become dissolved in the developing leachate.

The decomposition processes themselves release further water which adds to the volume of leachate. Leachate

also reacts with materials that are not themselves prone to decomposition such as fire ash and cement based

building materials changing the chemical composition. In sites with large volumes of building waste, especially

those containing gypsum plaster, the reaction of leachate with the gypsum can generate large volumes of

hydrogen sulfide which may be released in the leachate and may also form a large component of the landfill gas.

In a landfill that receives a mixture of municipal, commercial, and mixed industrial waste, but excludes significant

amounts of concentrated specific chemical waste, landfill leachate may be characterized as a water-based

solution of four groups of contaminants ; dissolved organic matter (alcohols, acids, aldehydes, short chain sugars

etc.), inorganic macro components (common cations and anions including sulfate, chloride, Iron, aluminium, zinc

and ammonia), heavy metals (Pb, Ni, Cu, Hg, , and xenobiotic organic compounds such as halogenated

organics, (PCBs, dioxins etc.). [3].

The physical appearance of leachate when it emerges from a typical landfill site is a strongly-odoured yellow- or

orange-coloured cloudy liquid. The smell is acidic and offensive and may be very pervasive because of hydrogen,

nitrogen and sulfur rich organic species such as mercaptans.

Leachate management

In older landfills and those with no membrane between the waste and the underlying geology, leachate is free to

egress the waste directly into the groundwater. In such cases high concentrations of leachate are often found in

nearby springs and flushes. As leachate first emerges it can be black in colour, anoxic and may be effervescent

with dissolved and entrained gases. As it becomes oxygenated it tends to turn brown or yellow because of the

presence of Iron salts in solution and in suspension. It also quickly develops a bacterial flora often comprising

substantial growths of Sphaerotilus.

2. Describe in detail the different methods of landfilling and the operations involve with neat Sketches. [N/D-16,N/D-13]

Landfills are facilities for the final controlled disposal of waste in or onto land.

Under the Resource Management Act 1991 (RMA), landfills must have consent conditions which are appropriate to the material they accept.

Types of landfill

Municipal solid waste landfills Landfills that accept household waste as well as other wastes.

Managed landfills Landfills composed mainly of cleanfill, but also construction and demolition waste with light contaminants.

Construction and demolition landfills

Landfills where contruction and demolition materials such as wood products, asphalt, plasterboard, insulation and others are disposed to land.

Cleanfills

Landfills where cleanfill material is disposed to land. Cleanfill material is material that when buried will have no adverse effect on people or the environment. It includes virgin natural materials such as clay, soil and rock, and other inert materials such as concrete or brick that are free of: combustible, putrescible, degradable or leachable components hazardous substances products or materials derived from hazardous waste treatment,

hazardous waste stabilisation or hazardous waste disposal practices materials that may present a risk to human or animal health such as

medical and veterinary waste, asbestos or radioactive substances liquid waste.

Industrial landfills Landfills that accepts specified industrial wastes. In most cases industrial waste landfills are monofills associated with a specific industry or facility.

3. Discuss the solid waste disposal options. (16) [A/M-17,N/D-13] Landfill Disposing of waste in a landfill involves burying the waste, and this remains a common practice in most countries.

Landfills were often established in abandoned or unused quarries, mining voids or borrow pits. A properly-

designed and well-managed landfill can be a hygienic and relatively inexpensive method of disposing of waste

materials. Older, poorly-designed or poorly-managed landfills can create a number of adverse environmental

impactssuch as wind-blown litter, attraction of vermin, and generation of liquid leachate. Another common

byproduct of landfills is gas (mostly composed of methane and carbon dioxide), which is produced as organic

waste breaks down anaerobically. This gas can create odor problems, kill surface vegetation, and is a

greenhouse gas.

A landfill compaction vehicle in action. Design characteristics of a modern landfill include methods to contain leachate such as clay or plastic lining material. Deposited waste is normally compacted to increase its density and stability, and covered to prevent attracting vermin (such as mice or rats). Many landfills also have landfill gas extraction systems installed to extract the landfill gas. Gas is pumped out of the landfill using perforated pipes and flared off or burnt in a gas engine to generate electricity Incineration Incineration is a disposal method that involves combustion of waste material. Incineration and other high temperature waste treatment systems are sometimes described as "thermal treatment". Incinerators convert waste materials into heat, gas, steam, and ash. Incineration is carried out both on a small scale by individuals and on a large scale by industry. It is used to

dispose of solid, liquid and gaseous waste. It is recognized as a practical method of disposing of certain

hazardous waste materials (such as biological medical waste). Incineration is a controversial method of waste

disposal, due to issues such as emission of Incineration is common in countries such as Japan where land is

more scarce, as these facilities generally do not require as much area as landfills. Waste-to-energy (WtE) or

energy-from-waste (EfW) are broad terms for facilities that burn waste in a furnace or boiler to generate heat,

steam and/or electricity. Combustion in an incinerator is not always perfect and there have been concerns about

micro-pollutants in gaseous emissions from incinerator stacks. Particular concern has focused on some very

persistent organics such as dioxins which may be created within the incinerator and which may have serious

environmental consequences in the area immediately around the incinerator. On the other hand this method

produces heat that can be used as energy.

Recycling methods

PVC, LDPE, PP, and PS are also recyclable, although these are not as commonly collected. These items are

usually composed of a single type of material, making them relatively easy to recycle into new products. The

recycling of complex products (such as computers and electronic equipment) is more difficult, due to the

additional dismantling and separation required..

Biological reprocessing

Waste materials that are organic in nature, such as plant material, food scraps, and paper products, can be

recycled using biological composting and digestion processes to decompose the organic matter. The resulting

organic material is then recycled as mulch or compost for agricultural or landscaping purposes. In addition, waste

gas from the process (such as methane) can be captured and used for generating electricity. The intention of

biological processing in waste management is to control and accelerate the natural process of decomposition of

organic matter.

There are a large variety of composting and digestion methods and technologies varying in complexity from

simple home compost heaps, to industrial-scale enclosed-vessel digestion of mixed domestic waste (see

Mechanical biological treatment). Methods of biological decomposition are differentiated as being aerobic or

anaerobic methods, though hybrids of the two methods also exist.

An example of waste management through composting is the Green Bin Program in Toronto, Canada, where

household organic waste (such as kitchen scraps and plant cuttings) are collected in a dedicated container and

then composted.

Energy recovery

Anaerobic digestion component

The energy content of waste products can be harnessed directly by using them as a direct combustion fuel, or

indirectly by processing them into another type of fuel. Recycling through thermal treatment ranges from using

waste as a fuel source for cooking or heating, to fuel for boilers to generate steam and electricity in a turbine.

Pyrolysis and gasification are two related forms of thermal treatment where waste materials are heated to high

temperatures with limited oxygen availability. The process typically occurs in a sealed vessel under high

pressure. Pyrolysis of solid waste converts the material into solid, liquid and gas products. The liquid and gas can

be burnt to produce energy or refined into other products. The solid residue (char) can be further refined into

products such as activated carbon. Gasification and advanced Plasma arc gasification are used to convert

organic materials directly into a synthetic gas (syngas) composed of carbon monoxide and hydrogen. The gas is

then burnt to produce electricity and steam.

Avoidance and reduction methods

An important method of waste management is the prevention of waste material being created, also known as

waste reduction. Methods of avoidance include reuse of second-hand products, repairing broken items instead of

buying new, designing products to be refillable or reusable (such as cotton instead of plastic shopping bags),

encouraging consumers to avoid using disposable products (such as disposable cutlery), removing any

food/liquid remains from cans, packaging, and designing products that use less material to achieve the same

purpose (for example, light weighting of beverage cans .

4.What are the requirements of a landfill layout? Write a note on sanitary land filling. (16) [A/M-17,N/D-12,A/M-10] The construction of a landfill requires a staged approach. Landfill designers are primarily concerned with the

viability of a site. To be commercially and environmentally viable a landfill must be constructed in accord with

specific requirements, which are related to:

Location

Easy access to transport by road

Transfer stations if rail network is preferred

Land value (price)

Cost of meeting government requirements

Location of community served

Type of construction (more than one may be used at single site)

• Pit - filling existing holes in the ground, typically left behind by mining

• Canyon - filling in naturally occurring valleys or canyons

• Mound - piling the waste up above the ground

Stability

Underlying geology

Nearby earthquake faults

Water table

Location of nearby rivers, streams, and flood plains Capacity

The available voidspace must be calculated by comparison of the landform with a proposed restoration profile.

This calculation of capacity is based on:

Density of the wastes

Amount of intermediate and daily cover

Amount of settlement that the waste will undergo following tipping

Thickness of capping

Construction of lining and drainage layers

SANITARY LANDFILLS

Sanitary landfills are sites where waste is isolated from the environment until it is safe. It is considered when it has completely degraded biologically, chemically and physically. In high-income countries, the level of isolation achieved may be high. However, such an expensive high level of isolation may not be technically necessary to protect public health. Four basic conditions should be met before a site can be regarded as a sanitary landfill (see following.) The ways of doing this should be adapted to local conditions. The immediate goal is to meet, to the best extent possible, the four stated basic sanitary landfill conditions, with a longer term goal to meet them eventually in full.

Small incremental improvements in landfill design and operation over several years are more likely to succeed than attempts to make a single, large leap in engineering expectations. Large landfills will require more investment to improve standards than smaller sites. However, the unit cost of these improvements (measured per tonne of waste landfilled or per head of population served) will decrease with increasing site size. There are financial and other benefits to sites with long operating lifetimes (ten years or more). Large regional sites serving two or more cities could be economically beneficial, providing waste transport costs are not too high.

Basic requirements As a minimum, four basic conditions should be met by any site design and operation before it can be regarded as a sanitary landfill:

• Full or partial hydrogeological isolation: if a site cannot be located on land which naturally contains leachate security, additional lining materials should be brought to the site to reduce leakage from the base of the site (leachate) and help reduce contamination of groundwater and surrounding soil. If a liner - soil or synthetic - is provided without a system of leachate collection, all leachate will eventually reach the surrounding environment. Leachate collection and treatment must be stressed as a basic requirement. • Formal engineering preparations: designs should be developed from local geological and hydrogeological investigations. A waste disposal plan and a final restoration plan should also be developed. • Permanent control: trained staff should be based at the landfill to supervise site preparation and construction, the depositing of waste and the regular operation and maintenance. • Planned waste emplacement and covering: waste should be spread in layers and compacted. A small working area which is covered daily helps make the waste less accessible to pests and vermin.

5.Explain the various phases of municipal solid waste decomposition in a closed landfill?

[N/D/11,A/M-12,N/D-14]

6. Identify the adverse effects of landfill leachate and list appropriate control measures?

[N/D/11,A/M-11]

Adverse effects of landfill leachate:

1. The nature of landfill leachate is the function of waste type, solubility, the state of decomposition and

degradation. Rainfall input can serve to dilute and flush contaminants in addition to assisting the degradation

process by wetting the wastes. A wide range of substances may be present in leachate, some of which are

potentially harmful to human health.

2. The major potential environmental impacts related to landfill leachate are pollution of groundwater and surface

water. The risk of groundwater pollution is probably the most severe environmental impact from landfill because

historically most landfills were built without engineered liners and leachate collection systems in the past. Most

recent regulations in many countries have required the installation of liners and leachate collection systems. The

pollution impact of leachate plumes downgradient of landfills is vital as it could contaminate the ground water.

Surface water pollution caused by leachate have also been observed in certain cases wherein the goundwater

comes to the surface during rainy seasons thus affecting the flora and fauna of nearby streams, lakes and rivers.

3. Most landfills containing organic material will produce methane, some of which dissolves in the leachate. This

could in theory be released in weakly ventilated areas in the treatment plant. This may result in explosion risk and

the zone should be identified to prevent future accidents. The most important requirement is the prevention of

discharge of dissolved methane from untreated leachate when it is discharged into public sewers, and most

sewage treatment authorities limit the permissible discharge concentration of dissolved methane to 0.14 mg/l, or

1/10 of the lower explosive limit. This entails methane stripping from the leachate.

4. Leachate streams running directly into the aquatic environment have both an acute and chronic impact on the

environment which may be very severe and can severely diminish bio-diversity and greatly reduce populations of

sensitive species. Where toxic metals and organics are present this can lead to chronic toxin accumulation in

both local and far distant populations. Rivers impacted by leachate are often yellow in appearance and often

support severe overgrowths of sewage fungusand ammonia toxicity.

5. The greatest environmental risks occur in the discharges from older sites constructed before modern

engineering standards became mandatory and also from sites in the developing world where modern standards

have not been applied. There are also substantial risks from illegal sites and ad-hoc sites used by criminal gangs

to dispose of waste materials.

6. Leachate stored or treated at a landfill site can become low in oxygen, resulting in generation of odorous

compounds such as sulphides. This can result in odour from tanks used to store leachate. This is likely to

contribute to odour complaints asociated with landfill sites.

7. Toxic Metal concentrations in leachate could become poisonous to all living beings including flora and fauna of

waterbodies.

8. Lastly leachate could contain organo-nitogenated substances, organo-halogenated compounds and toxic

metals and any form of mixing into public water supply system underground due to leakage could be disastrous.

9. Since nitrogenous compounds are abundant in leachate, its overflowing from storage tanks in rainy season

could spark off sporadic algal blooms in lakes, thus killing off fishes and biodiversity being seriously disturbed.

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