Notes of Environment and Ecology for 2nd Sessional (1)

8/10/2019 Notes of Environment and Ecology for 2nd Sessional (1)

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SAMPLING

Some tests require the measurement to be conducted at the site because

the process of obtaining a sample may change the measurement. For

example, to measure the dissolved oxygen in a stream or lake, either the

measurement should be conducted at the site or the sample must beextracted with great care to ensure that there has been no loss or addition

of oxygen as the sample is exposed to the air. Similarly, it is better to

measure pH at the site if you are sampling water that is poorly buffered

from pH changes (see discussion on alkalinity).

Most tests may be performed on a water sample taken from the stream.

The process, by which the sample is obtained, however, may greatly

influence the result. The three basic types of samples are grab samples,

composite samples, and flow-weighted composite samples.

Dissolved Oxygen (DO):

Oxygen dissolved in water is vital for aquatic life. The optimum

value for dissolved oxygen in a good quality water is 4-8mg/L. It is

consumed by oxidation of organic matter/ reducing agent etc. present in

water.Water which has DO value less than 4 mg/L is termed as polluted

and is unfit for human or aquatic animal consumptions.

Chemical Oxygen Demand (COD):

It is an index of the organic content of water, since the most

common substance oxidized by the dissolved oxygen in water is organic

matter, which has a biological origin, such as dead plants etc. The COD

of a water sample is determined by the chemical oxidation of the organic

matter by K2Cr

2O

7in 50% H

2SO

4. This method includes other reducible

inorganic species that may be present in water such as,., and hence thismethod does not truly reflect the organic content in water. However

since this method is rapid, it is widely used. - 2 NO2- 2 3 S O 2- S

Biological Oxygen Demand (BOD):

The capacity of the organic matter in the sample of natural water to

consume oxygen is called its BOD. It is determined experimentally by


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determining the dissolved oxygen (DO) at the beginning and at the end

of a 5-day period in a sealed sample. The BOD gives the measure of

oxygen utilized or consumed in the period as a result of oxidation of

dissolved organic matter present in the water sample.

Threshold limit value (TLV):

This value indicates the permissible level of a toxic pollutant in

atmosphere to which a healthy industrial worker can be exposed during

an eight-hour day without any adverse effect. TLV of a pollutant is

found by experimentation on animals, medical knowledge and

experience and environmental studies.

Now let us discuss the various segments of our environment in detailone by one. In the first instance let us discuss about the atmosphere and

atmospheric chemistry.

Measurement of total organic carbon (TOC):

Both BOD and COD give indications of the oxidisability and oxygen

demand of water samples. Neither, however, measures the total organic

content of water. When this is required a determination of total organic

carbon (TOC) is made. This is done by quantitatively oxidising all theorganic matter in the sample to carbon-di-oxide soon after acidification

to remove interference from carbonates or bicarbonates. Oxidation in a

gas stream passing through a heated tube or wet oxidation with

potassium peroxodisulphate have both been used. The latter is less

convenient, but more sensitive and can be used at low levels below 1

mgdm-3

. The carbondioxide produced is measured either by

conductivity after absorption in solution or by catalytic conversion to

methane which is then passed to a flame ionisation detector as used ingas chromatography.

The TOC test can be performed in a relatively short period of time (few

minutes) compared to BOD and COD measurements and, hence offers a

valuable supplement to BOD and COD estimations.


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TURBIDITYWater that is not clear but is dirty, in the sense that light transmission

is inhibited, is known as turbid water. Many materials can causeturbidity, including clays and other tiny inorganic particles, algae, and

organic matter. In the drinking water treatment process, turbidity is of

great importance, partly because turbid water is aesthetically

displeasing, and also because the presence of tiny colloidal particles

makes it more difficult to remove or inactivate pathogenic organisms.

Turbidity is measured using a turbidimeter. Turbidimeters are

photometers that measure the intensity of scattered light. Opaque

particles scatter light, so scattered light measured at right angles to abeam of incident light is proportional to the turbidity. Formazin polymer

is currently used as the primary standard for calibrating turbidimeters,

and the results are reported as nephelometric turbidity units (NTU).

COLOR,TASTE, AND ODOR

Color, taste, and odor are important measurements for determining

drinking water quality. Along with turbidity, color, taste, and odor are

important from the standpoint of aesthetics. If water looks colored,

smells bad, or tastes swampy, people will instinctively avoid using it,

even though it might be perfectly safe from the public health aspect.

Color, taste, and odor problems in drinking water are often caused by

organic substances such as algae or humic compounds, or by dissolved

compounds such as iron. Color can be measured visually by comparison

with potassium chloroplatinate standards or by scanning at different

spectrophotometric wavelengths. Turbidity interferes with color

determinations, so the samples are filtered or centrifuged to removesuspended material. Odor is measured by successive dilutions of the

sample with odor free water until the odor is no longer detectable.

(Odor-free water is prepared by passing distilled, deionized water

through an activated charcoal filter.) This test is obviously subjective

and depends entirely on the olfactory senses of the tester. Panels of


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testers are used to compensate for variations in individual perceptions of

odor.

Taste is evaluated using three methods: the flavor threshold test (FIT),

the flavor rating assessment (FRA), and the flavor profile analysis

(FPA). For the FIT, water samples are diluted with increasing amountsof reference water until a panel of taste testers concludes that there is no

perceptible flavor. In the FRA, a panel of testers is asked to rate the

flavor from very favorable to very unfavorable. The oldest, and most

useful, of the taste tests is the FPA, which measures both taste and odor

of a water sample in comparison to taste and odor reference standards.

The intensity of specific tastes and odors are described on a 12-point,

ranging from no taste or odor (0) to taste or odor (12).

pHThe pH of a solution is a measure of hydrogen (H+)io n concentration,

which is, in turn, a measure of acidity. Pure water dissociates slightly

into equal concentrations of hydrogen and hydroxyl (OH-) ions:

The measurement of pH is now almost universally done using electronic

pH meters. A typical pH meter consists of a potentiometer, a glass

electrode and a reference electrode (or a single, combination

electrode), and a temperature-compensating device. The glass electrode

is sensitive to H+ activity and converts the signal to electric current,

which can be read as electrode potential (mV) or pH.

The pH of an effluent or water sample is important in almost all phases

of drinking water and wastewater treatment. In water treatment as well

as in disinfection and corrosion control, pH is important in ensuring

proper chemical treatment. Aquatic organisms are sensitive to pH

changes, as well as to the actual pH of the water. Few aquatic organisms

tolerate waters with a pH less than 4 or greater than 10. Acid mine

drainage, unregulated acids or bases in industrial effluents, oratmospheric acid deposition may alter the pH of a water body

substantially and have detrimental effects on aquatic life.

pH, Acidity and Alkalinity:


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The pH of a water sample measures its hydrogen ion concentration and

indicates whether the sample is acidic, neutral or basic. The pH may be

measured accurately using a pH meter. The pH meter must be calibrated

before making pH measurements. For calibration standard buffers of pH

4.00, 7.00 and 10.00 are used.

Table.2 pH ranges for

environmental waters

Type of water

pH range

Soft water 5.3-7.4

Hard water 7.6-8.8

Sea water 8.2-9.2

Water affected by acidic

pollutants

2.2-4.8

pH of water in equilibrium

with atmosphere

5.6

It should be noted that the unpolluted rain water is slightly acidic due to

the presence of dissolved carbon dioxide (pH=5.6). The range of pH

values of hard and soft water samples are also shown in Table.2.

H2O CO2(gas) H2O.CO2(solution) H HCO3 2H CO3Hard water is

slightly alkaline. The hardness is due to the presence ofpolyvalent metal

ion, e.g. Calcium and magnesium arising from dissolution ofminerals.

For instance, the dissolution of limestone involves the following

equilibria:


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In general, hard waters originate in areas where top soil is thick

and lime stone formations are present. Soft waters originate in areas

where the top soil is thin and lime stone formations are sparse or absent.

Analysis is normally performed by complexometric titration using

the disodium salt of ethylene diamine tetra acetic acid (EDTA).

Advanced Waste Water Treatment

Different waste water treatment processes

Removal Of Suspended SolidsMicrostraining

Coagulation and flocculation

Filtration

Removal of dissolved solids

Ion exchange

Reverse osmosis

Electrodialysis

Removal of nitrogen

Phosphate removal (chemical treatment)

Phosphate removal (biological treatment)Removal of dissolved organic compounds

Adsorption

Sludge treatment and disposal

The effluent from a typical secondary treatment plant still contains

20-40 mg/L BOD which may be objectionable in some streams.

Suspended solids, in addition to contributing to BOD, may settle on thestream bed and inhibit certain forms of aquatic life. The BOD if

discharged into a stream with low flow can cause damage to aquatic life

by reducing the dissolved oxygen content. In addition the secondary

effluent contains significant amounts of plant nutrients and dissolved


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solids. If the waste water is of industrial origin, it may also containtraces of organic chemicals, heavy metals and other contaminants.

Different methods are used in advanced waste treatment to satisfy any of

the several specific goals, which include the removal of (1) suspendedsolids (2) BOD (3) plant nutrients (4) dissolved solids and (5) toxic

substances. These methods may be introduced at any stage of the total

treatment process as in the case of industrial waterways or may be used

for complete removal of pollutants after secondary treatment.

Removal of Suspended Solids:

This treatment implies the removal of those materials that have been

carried over from a secondary treatment settler. Many methods wereproposed of which two methods were commonly used. The two methods

are microstaining and chemical coagulation followed by settling and

mixed media filtration.

Microstraining:

It is a special type of filtration procedure which makes use of

filters oven from stainless steel wires with opening only 60-70 m

across to remove very small particles. High flow rates and low backpressures are normally achieved.

Coagulation and flocculation:

Key Difference:Coagulation means to curdle; it basically refers to a chemical

process in which the destabilization of non-settleable particles takes place. These

particles form clumps with the help of a coagulant. On the other hand, flocculation

means to form flocs. It can be described as a physical or a mechanical process in

which the coagulated clumps or flocs are joined together to form masses as a

cloud and then a precipitate.


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In coagulation, the forces responsible for keeping the particles apart after

they contact, are reduced. Flocculation brings the de-established

colloidal particles together and they form large aggregates. Both these

techniques are employed in the treatment of water. Thus, we canunderstand the process of coagulation and flocculation with the help of

examples derived from water treatment techniques.

Water may contain colloidal solids like non-settleable organic matter,

clay particles, bacteria, plankton, small particles of decayed plant

material, etc. Thus, coagulation and flocculation techniques are

employed for separating these impurities from water.

Coagulation is achieved by neutralizing the particles and thus, therepelling force between the particles is greatly reduced. After employing

the flocculation process, the coagulated particles form a large

agglomeration, which is also known as floc.


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Coagulation can be easily achieved with the help of a coagulant. In raw

water, inorganic salts of aluminum or iron can be added, these salts

neutralizes the charge on the particles that are responsible for the raw

water turbidity. These salts also hydrolyze to form insoluble precipitatesentrapping the particles. Some of the common inorganic coagulants are

aluminum sulphate, alum, ferric sulfate and aluminum chloride.

In flocculation, these agglomerations of destabilized particles take the

form of large particles. This can also be achieved by adding high

molecular weight, water soluble organic polymers. Due to these

polymers, the size of the floc increases and then the particles settle

down. It is very important to gently mix the flocculating agent at a slowspeed so that small flocs can easily agglomerate into large particles, and

finally settle down.

For water treatment, coagulation is generally followed by flocculation.

Thus, in terms of water treatment, both can be differentiated easily.

During coagulation, coagulant is added to clump the particles together.

On the other hand, during flocculation, the solution is mixed gently, so

that the small clumps formed during coagulation, gather together and

form larger clumps. These large clumps easily settle down and thus can

be separated.The object of coagulation is to alter these particles in such a

way as to allow them to adhere to each other. Most colloids of interest in

water treatment remain suspended in solution because they have a net

negative surface charge that causes the particles to repel each other. The

intended action of the coagulant is to neutralise that charge, allowing the

particles to come together to form larger particles that can be more

easily removed from the raw water.

The usual coagulant is alum [Al2(SO

4)

2 18H

2O ], though FeCl

3,

FeSO4

and other coagulants, such as polyelectrolytes, can be used. Alum

when added to water, the aluminium in this salt hydrolyses by reactions

that consume alkalinity in the water such as:


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The gelatinous hydroxide thus formed carries suspended material with it

as it settles. In addition, however, it is likely that positively chargedhydroxyl-bridged dimers such as

and higher polymers are formed which interact specifically with

colloidal particles, bringing about coagulation. Metal ions in coagulants

also react with virus proteins and destroy upto 99% of the virus in water.

Anhydrous ion (III) sulphate can also act as effective coagulant similar

to aluminium sulfate. An advantage with iron (III) sulfate it that it works

over a wide range of pH.

Reverse osmosis:In the reverse osmosis process, demineralisation water is produced by

forcing water through semipermeable membranes at high pressure. In

ordinary osmosis, if a vessel is divided by a semipermeable membrane

(one that is permeable to water but not the dissolved material), and one

compartment is filled with water and other with concentrated salt

solution, water diffused through the membrane towards the compartment

containing salt solution until the difference in water levels on the twosides of the membrane creates a sufficient pressure to counteract the

original water flow. The difference in levels represents the osmotic

pressure of the solution (fig.1a).


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The process can be reversed by applying sufficient pressure to the

concentrated solution to overcome the osmotic pressure force the net

flow of water through the membrane towards the dilute phase. The

solute concentration (impurity) builds up on one side of the membrane

while relatively pure water passes through the membrane. In order to

obtain adequate solvent (water) flux through the membrane, pressures of

the order of 4000 to 7000 kN/m2

are required. Fig.1b represents the

principle of operation of the reverse osmosis unit.


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- -

Electrodialysis:

Electrodialysis uses ion-selective membranes and an electricalpotential difference to separate anions and cations in solution.


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In the past electrodialysis was most often used for purifying

brackish water, but it is now finding a role in hazardous waste treatment.

Metal salts from plating rinses are sometimes removed in this way.

Fig.2 shows a simple dialysis cell in which waste water may be

deionised. As shown in the figure two types of membranes (anionic and

cationic) are arranged alternatively to form many compartments betweenthe electrodes placed at the two ends. When the voltage is applied across

the cell containing mineralised water, the anions migrate to the positive

electrode and the cations migrate to the negative electrode. This causes

solution in alternate compartments to become more concentrated while

that in the remaining becomes more dilute. The electric power

requirement is proportional to the number of ions removed from the

water.

In the electrodialysis process, organic molecules are not removed andthey can collect on and clog the membranes. Another disadvantage of

this method is that it still leaves concentrated waste water to be disposed

of by some appropriate scheme. The process does not require any


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chemical additives and has low energy requirements and as such it can

be an economically feasible means of demineralisation.

Disinfection:

Disinfection, using chemical and physical methods is the final step in

drinking water purification. The finished water is disinfected often with

chlorine. It kills the remaining microorganisms in the water, some of

which will be pathogenic. It is a very efficient oxidising, bleaching anddisinfecting agent. In water chlorine reacts as follows:

The hypochlorous acid (HOCl) is the prime disinfecting agent. Its

dissociation in pH dependent yielding less effective hypochlorite ions

(OCl-

) at higher pH values:

Together, HOCl and OCl-

are called the free available chlorine.

A principal advantage of chlorination over other forms of disinfection is

that a chlorine residual is created that can protect the treated water after

leaving the treatment plant. This is guard against possible contamination

that might occur in water distribution system. To increase the lifetime of

the residual, some systems add ammonia to the treated water, forming

chloramines.


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Chloramines, although they are less effective as oxidants than

HOCl, are more persistent. Residual chlorine that exists as chloramine is

referred to as combined available chlorine.

Chlorine may have adverse secondary effects. It has the potential

to combine with trace amounts of organic substances to form

trihalomethanes (THMs) such as the carcinogen chloroform. Some

studies have shown an association between bladder and rectal cancer andconsumption of chlorinated drinking water. One approach to reducing

THMs is to remove more of the organics before any chlorination takesplace, which can be accomplished by adsorption on activated carbon.

The problem faced with the formation of THMs has spurred

interest in alternatives to chlorination as the preferred method of

disinfection. Alternative disinfectants include chlorine dioxide andozone. Chlorine dioxide (ClO

2) is a potent bactericide and viricide and it

does not form a residual capable of protecting water in the distributionsystem. However, there is concern for certain toxic chlorate and chlorite

substances that it may create, and it is a very costly method of

disinfection. Ozonation involves the passage of ozone (O3) through

water.

Ozone is a very powerful disinfectant that is even more effective against

cysts and viruses than chlorine, and it has the added advantage of having

no taste or odour problems. Unfortunately, the disinfective power ofozone is limited by its relatively low solubility in water.


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Trickling Filter Process for waste water treatment

In the biological-film system also known as trickling filters, the waste

water is brought into contact with a mixed microbial population in the

form of a film of slime attached to the surface of a solid support medium

whereas in the activated sludge system the waste water is brought in

contact with a diverse group of microorganisms in the form of a

flocculants suspension in an aerated tank. In both cases the organic

matter is metabolized to more stable inorganic forms. The most popular

means of treating domestic sewage has been the biological film system

because of its ease of operation. However the activated sludge process

can be more reliably be handled when handling large volumes of waste

water, and a high degree of treatment is achieved.

Conventional trickling filters normally consist of a rock bed, 1 to 3

meters in depth, with enough opening between the rocks to allow air to

circulate easily. The influent is sprinkled over a bed of packing which is

coatedwith a biological slime. As the liquid trickles over the packing, oxygen

and the dissolved organic matter diffuse into the film to be metabolized

by the microorganisms in the slime layer. End products such as CO2, ,

etc., diffuse back, out of the film and appear in the filter effluent. Milk

processing, paper mills and pharmaceuticals wastes are among those

treated by trickling filters. Like all biological units trickling filters are

affected by temperature; therefore cold weather slows down thebiological activity in the filter.


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Range for Drinking water:

NO. PARAM

ETERS

UNITS DRINKING

WATER

WHO Standard

Expe

ental

Value

(Rang

HDL MPL

1 Temperature

0C --- ----- 22-30

2 Turbidity NTU 5 10 18-47

3 pH value - 6.5 to 8.5 No

relaxatio

8.4- 8


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n

4 Total

hardness

(asCaCO3)

mg/l 300 600 122-2

5 Iron mg/l 0.3 1.0 0.2-0.

6 Chloride

s

mg/l 250 1000 7-26

7 Dissolve

d Solids

mg/l 500 2000 256-5

8 Calcium mg/l 75 200 28-48

9 Sulphate mg/l 200 400 50-91

10 Nitrate mg/l 50 No

relaxatio

n

0-1.77

11 Fluoride mg/l 1.0 1.5 0-0.4

12 Total

Alkalinity

mg/l 200 600 13-24

13 Magnesi

um

mg/l 30 150 9.23-

26.24

14 Oxygen

Observed from

KMnO4

at 370Cin 3 hrs.

mg/l 3.0 No

relaxation

2.4-7.


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15 Suspend

ed Solids

mg/l 20 150 70-28

Electrostatic Precipitator:

An electrostatic precipitator (ESP) is a particulate collection device that

removes particles from a flowing gaseous stream (such as air) using the

force of an induced electrostatic charge.

ESP can be operated at high temperature and pressures, and its power

requirement is low.

For these reasons the electrostatic precipitation is often the preferred

method of collection where high efficiency is required with smallparticles.

Steps in Electrostatic Precipitation

1.Generation of Electric field high voltage Direct current 20-80kv.

2.Generation of electric charges

3.Transfer of electric charge to a dust particle.

4.Movement of the charge dust particle in an electric field to the

collection electrodes.

5.

Adhesion of the charge dust particle to the surface of the collectionelectrode.

6.Dislodging of dust layer from collection electrode

7.Collection of dust layer in a hopper

8.

Removal of the dust from the hopper.


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PRINCIPLE OF ESP

Principle of ESP has four distinct phases as follows:

(I) Ionization or corona generation: When the potential difference

between the wire and electrode increases, a voltage is reached where an

electrical breakdown of the gas occurs near the wire. This electrical

break down or ion discharge is known as corona formation and therebygas is transformed from insulating to conducting state.

Two types of corona discharge can be generated which are:

(a) Negative corona: In negative corona, discharge electrode is of

negative polarity and the process of electron generation occurs at narrow

region


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(b) Positive corona: When positive voltage is applied to discharge

electrodes in the same way as negative corona, large number of free

electron and positive ions are generated. Or large number of positive

ions produced move towards collecting electrode and thus transfer

charge to dust particles upon collision.Negative coronas are more commonly used in industrial application,

while for cleaning air in inhabited space positive coronas are used. Due

to ozone generation in negative corona itsapplication for air cleaning in

inhabited area is avoided.

(II) Charging of Particles: Particle charging takes place in region

between the boundary of corona glow and the collection electrode,

where particles are subjected to the rain of negative ions from the corona

process. Mainly two mechanisms are responsible for particle charging.Each mechanism becomes significant according to particle size ranges.

For particles having diameter greater than 1m, field charging is

dominant force; and for particle size less than 0.2m diffusion charging

predominates.

(III) Migration and precipitation of particle:

(IV) Removal of deposited dust: Once collected, particle can be

removed by coalescing and draining, in the case of liquid aerosols and

by periodic impact or rapping, in case of solid material. In case of solid

material, a sufficiently thick layer of dust must be collected so that it

falls into the hopper or bin in coherent masses to prevent excessive re-

entrainment of the material into the gas system


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STANDARD PROCESSES FOR MANAGING MUNICIPAL WASTE

[7]

Incineration: Energy is stored in chemical form in all MSW materialsthat contain organic compounds i.e. which can be used to generate

electricity and steam. It is being done by a few major hospital for managing

clinical wastes.

Composting: The natural organic components of MSW (Food and plant

wastes, paper, etc.) can be composted aerobically to carbon dioxide, water,

and a compost product that can be used as soil conditioner. Anaerobic

digestion or fermentation produces methane, alcohol and a compost

product. Recovery/recycling: Recovered paper, plastic, metal, and glass can be re-

used. 18. In the absence of formalized waste segregation practices,

recycling has emerged only as an informal sector using outdated

technology, which causes serious health problems to wastepickers [9].

Land filling: MSW materials that cannot be subjected to any of the above

three method, plus any residuals from these processes (e.g. ash from

combustion) must be disposed in properly designed landfills.

Almost all categories of waste may be disposed to better managed landfills

directly. However, those types of wastes which will destroy the

microbiological degradation processes within the landfill are unwelcome

i.e. the non-biodegradable wastes. Management of these could include:

incineration, recycling and reusing

Sanitary Landfill:

Basic requirementsAs 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 o


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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 fromlocal 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


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Documents

Notes of Environment and Ecology for 2nd Sessional (1)