BTEX Contamination and Remediation

BTEX -Contamination and Remediation

SEMINAR REPORT BTEX-CONTAMINATION AND REMEDIATION

Submitted MANASY

By

PURUSHOTHAMAN PILLAI

Guided By Ms. ANU CHERIAN DEPARTMENT OF CIVIL ENGINEERING MUSALIAR COLLEGE OF ENGI NEERI NG AND TECHNOLOGY PATHANAMTHITTA-689645 2009-2010


ACKNOWLEDGEMENT

I would like to extend my sincere thank s to Mr. A. Shihabudeen Prof & Head of the Department of Civil Engineering, MCET College of Engineering and Technology, Pathanamthitta for hi s cooperation and encouragement. I express my profound gratitude to Ms. Anu Cherian (Lecturer, department of civil engineering) for her valuable guidance and wholehearted cooperation in preparation of thi s paper ³BTEX- Contamination and remediation´. Without which thi s seminar would not have seen the light of day. I am greatful to Mrs. Sreejakunjamma (Advisor) Lecturer, department of civil engineering . Gracious

gratitude to all the faculty of the Civil department & friend s for their valuable advice . A bove

Engineering

all, I thank the Almighty GOD without who se blessing; I would never have been able to complete thi s work successfully.


ABSTRACT BTEX contamination i s a threat to the mankind a s well as to animals and plant s. Prolonged expo sure to the compound s even in small quantitie s is highly fatal. Due

to ma ssive usage of petroleum product s, BTEX contamination i s considered as one of the major environmental pollution . They are highly toxic and soluble in water and it s presence will be significant hazard for all forms of life on earth. There

are different advanced technique s on detection s and treatment s that have been developed recently . BTEX presence can be alerted to avoid the usage of contaminated water by the public . This paper presents a detailed study on B TEX contamination with effective detection method s like microchip induced la ser fluorescence (LIF). The treatment of B TEX contamination ha s become one of the challenging technique s. The different treatment like in situ chemical oxidation (ISCO) is one of the mo st well developed and widely u sed as it needs only relatively short remediation period compared to other method s.


CONTENTS LIST OF ABBREVIATIONS LIST OF FIGURES LIST OF TABLES 1. INTRODUCTION

1

2. BTEX

3

2.1 COMPONENTS OF BTEX 2.2 BTEX CONTAMINATION 2.3 BTEX HEALTH EFFECTS

3. DETECTION OF BTEX CONTAMINATION

9

3.1 RAMAN DIPSTICK METHOD 3.2 BIOASSAY METHOD 3.3 MICROCHIP INDUCED LASER FLUROSCENCE SENSOR

4. TREATMENT

16

4.1 ORGANOCLAY AND CARBON TREATMENT 4.2 DIRECT PUSH GROUNDWATER CIRCULATION WELLS 4.3 REMEDIATION USING IN SITU CHEMICAL OXIDATION

5. CONCLUSION REFERENCES

23 24


LIST OF ABBREVIATIONS

NO

ABBREVIATION

1.

BTEX

2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

COC

17. 18.

DO DP-GCW EPA GCW

ID ISCO LIF MCL MTBE PAH PMT PPA TDO TOSC TPH

UV

EXPANSION

Benzene, Toluene, Ethylbenzene, and Xylenes Chemical Oxidation Of Carbonate s Dissolved oxygen Direct push groundwater circulation well Environmental Protection Agency Groundwater circulation well Inside diameter In situ chemical oxidation Laser -Induced Fluorescence Maximum Contaminant Level s Methyl tertiary butyl ether Polycyclic aromatic hydrocarbon s Photomultiplier tube s Parts per million Toluene Dioxygena se Coupling Technical Outreach Services for Communities Total petroleum hydrocarbon s Ultra violet


LIST OF FIGURES

Figure

Name

1.1

Sources

of Groundwater Contamination

1

2.1 2.2

Components of BTEX in Gasoline Different pha ses of contamination from a ga s Station Routes Of Pollutant Intake Portable Raman s pectrometer A s implified diagram of a Raman s pectrometer O peration Schematic diagram of experimental apparatu s organoclay and carbon treatment Typical in -well aeration application Typical I SCO Injection Injection System Process Flow Diagram

4

2.3 3.1(a) 3.1(b) 3.2 4.1 4.2 4.3 4.4

Page no

5 6 9 9

12 16 17 19 20


LIST OF TABLE

Table

Name

2.1

MCL set

Page no

by the EPA for each compound compo und in

drinking water

7


1. INTRODUCTION 1.1 GENERAL As

we plunge into the new millennium our environment is being polluted by

different man made activities. One of the major source of water is the groundwater which is considered to be consumable without much treatment.

There

are numerous chemicals

associated with federal, commercial, industrial, and agricultural operations that are considered hazardous to humans, animals, plants, and the ecological environment. Groundwater

becomes contaminated when hazardous chemicals leak into the ground and

drain through the soil matrix into aquifer s. s.

Once

they reach the aquifer, chemicals either

float or sink depending on their s pecific gravity (i.e., whether they are lighter or heavier than water).

Gradually,

the chemicals dissolve into groundwater and flow down gradient

to impact additional aquifer s, water reservoir s, land, and sea, expanding the risk to human health and the environment.

Fig1.1 Sources of Groundwater Contamination

BTEX -Contamination and Remediation Petroleum has been recognized as a potential environmental contaminant since shortly

after the beginning of the Twentieth Century. Organic compounds can be a major

pollution problem in groundwater . Their presence in water create hazard to public health and the environment.

The

term BTEX reflects that benzene, toluene, ethylbenzene and

xylenes are often found together at contaminated sites. Because they are all highly toxic and soluble in water, they represent a significant hazard for humans.The main source of BTEX contamination is the leakage of gasoline from faulty and poorly maintained underground

storage

tank s. s.

They

are considered one of the major causes of

environmental pollution because of wides pread occurrences of leakage from underground petroleum storage tank s and s pills at petroleum production wells, refineries, pipelines, and distribution terminals.


2. BTEX 2.1 GENERAL

Benzene,

Toluene, Ethyl

Benzene and

Xylene

(BTEX) are the volatile

components commonly associated with petroleum products. Benzene, toluene and xylenes are found naturally in petroleum products like crude oil, die sel fuel and gasoline. Ethylbenzene is

a gasoline and aviation fuel additive. Because of the high concentration

of B TEX compounds in petroleum and the massive use of petroleum products as energy source,

as solvents and in the production of other organic chemicals, their presence in

water creates a hazard to public health and the environment. Contamination of groundwater with the BTEX compounds is difficult to remedy because these compounds are relatively soluble in water and can diffuse rapidly once introduced into an aquifer .

2.2 COMPONENTS OF BTEX

BTEX is the abbreviation used for four compounds found in petroleum products. The

compounds are benzene, toluene, ethylbenzene and xylenes. These organic chemicals

make up a significant percentage of petroleum products like crude oil, diesel, gasoline etc. Ethylbenzene is a ga soline and aviation fuel additive. They are also u sed extensively in manufacturing processes. Benzene is used in the production of synthetic materials and consumer products, such as synthetic rubber, plastics, nylon, insecticides and paints. Toluene is used as a solvent for paints, coatings, gums, oils and resins. Ethylbenzene

may be present in consumer products such as paints, ink s, plastics and pesticides. Xylenes are used as a solvent in printing, rubber and leather industries.

BTEX -Contamination and Remediation The

BTEX chemicals are present in a standard gasoline blend in approximately

18%(w/w), and the group is considered to be the largest one that is related to any health hazards.

Fig. 2.1 Components of BTEX in Gasoline (Source: Publication of hazardous substance research centers, TOSC publications) Naphthalenes

make up only 1%(w/w) of gasoline. Benzene, which is recognized

as the most toxic compound among BTEX, represents 11%, toluene represents 26%, ethylbenzene 11% and xylene 52% of the total BTEX fraction in gasoline.

2.3 BTEX CONTAMINATION

BTEX contamination of soil and groundwater can occur by the accidental s pill of gasoline, diesel fuel and leakage from underground storage tank s in pumping stations. Once

released to the environment, BTEX can volatilize, dissolve, attach to soil particles

or degrade biologically. Volatilization occur s when chemicals evaporate, allowing them to move from a liquid into the air . Volatilization of the BTEX components of gasoline commonly occur s when you pump gasoline into your car, and is res ponsible for the characteristic odour . soils.

This

phenomenon can also occur within the air pockets present in

BTEX can also dissolve into water, allowing it to move in the groundwater .

BTEX -Contamination and Remediation Since

BTEX can "stick" to soil particles, these chemicals move slower than the

groundwater . BTEX can also dissolve into water, allowing it to move in the ground water . Because of their polarity and very soluble characteristics, BTEX will be able to enter the soil and groundwater systems and cause serious pollution problems. If oxygen is present in sufficient quantities, BTEX can also degrade biologically, though very slowly.

Fig. 2.2 Different phases of contamination from a gas station (Source: Publication of hazardous substance research centers, TOSC publications)

BTEX -Contamination and Remediation 2.4 BTEX HEALTH EFFECTS

Exposure skin.

to BTEX can occur by ingestion, inhalation or absorption through the

Inhalation of BTEX can occur while pumping gasoline or while showering or

bathing with contaminated water . A bsorption of these chemicals can occur by s pilling gasoline onto one's skin or by bathing in contaminated water .

Acute

exposures to high

levels of gasoline and its BTEX components have been associated with skin and sensory irritation, central nervous system depression and effects on the res piratory system.

Fig 2.3 Routes Of Pollutant Intake (Source: Publication of hazardous substance research centers, TOSC publications)

These

levels are not likely to be achievable from drinking contaminated water, but

are more likely from occupational exposures. Prolonged exposure to these compounds causes the kidney, liver and blood systems disorder . According to the U.S. Environmental Protection studies

Agency

(U.S.

EPA),

there is sufficient evidence from both human and animal

to believe that benzene is a human carcinogen. Worker s exposed to high levels of

benzene in occupational settings were found to have an increase incidence in leukaemia.

2.5 BTEX REGULATIONS


The

U.S.

EP A

has established permissible levels for chemical contaminants in

drinking water supplied by public water systems. Contaminant Levels (MCLs).

To

derive these

T hese

MCLs,

levels are called Maximum

the US

EPA

uses a number of

conservative assumptions, thereby ensuring adequate protection of the public. is set so that a lifetime expo sure to the contaminant at the

MCL

The MCL

concentration would

result in no more than 1 to 100 (depending on the chemical) excess cases of cancer per million million people peo ple exposed.

Table2.1 MCL set by the EPA for each compound in drinking water

Chemical

MCL (mg/liter or ppm) benzene

.005

toluene

1

ethylbenzene

0.7

xylene (total)

10

0

(Source: Publication of hazardous substance research center s, TOSC publications)


2.6 REDUCING EXPOSURE TO BTEX

The

minimized.

To

U.S.

EPA

recommends that exposure to BTEX be

avoid or reduce exposure to BTEX, people should use water supplies

having concentrations of these compounds that are below the MCL the MCL or apply appropriate water treatment or filtration systems. If necessary, short-term reductions in exposure may be accomplished by using bottled water for food and beverage preparation and avoiding bathing or showering with the contaminated water . With in-home treatment processes, such

as activated charcoal filtration, it is usually possible to remove sufficient BTEX

from water to meet the

MCL

and thereby minimize health risk s. s. If benzene is present

above the MCL, treatment should be applied to all household water because of inhalation hazards.


3. DETECTION OF BTEX CONTAMINATION Since sensitive

the BTEX compounds are very toxic to humans and aquatic life, their

and rapid determination is of critical importance.

There

are many established

methods for determining BTEX contaminants in water, namely liquid-liquid extraction, solid

phase extraction, gas chromatography, air stripping etc. But these methods exhibit

high levels of sensitivity and selectivity. successful

operation. If a

small

So

they require well-trained per sonnel for its

error occur s during

sampling,

obtained using the best instrument will be inevitably wrong.

Most

the analytical result existing methods for

detecting BTEX are time-consuming, complicated and very expensive for routine screening. Also

these methods require skill for it s operation.

There

has been a lot of

development in this area recently and many advanced techniques for the detection of BTEX contaminations have been developed.

The

use of laser s and optic fiber s are some

among them.

Some

advanced techniques of detection of BTEX contamination are:

1. Raman Dipstick method 2. Bioassay method 3.

Detection

using Microchip Induced Fluorescence Sensor


3.1 RAMAN DIPSTICK METHOD

Raman dipstick method is the detection of BTEX contamination using long path length fiber optic Raman dipstick .

Determination

of BTEX components via optical

remote sensing is attractive because eliminates many of the problems in other established methods. Samples are interrogated through the long- path length µdip-stick¶. It is directly inserted into the liquid of interest or an extension hose is attached to the end of the µdipstick¶,

providing a low profil pro filee and more flexible means of sample interrogation.

Fig3.1 (a) Portable Raman spectrometer

Fig3.1 (b) A simplified diagram of a Raman

spectrometer¶s operation


Fiber -optic s pectro scopic

techniques used for detection include visible

absorption, infrared absorption, fluorescence and Raman s pectro scopy.

Of

these

techniques, Raman s pectro scopy is particularly better method for detecting BTEX analytes in water because it offer s a high degree of selectivity and is compatible with aqueous matrices.

Even

though this method is very simple and cheaper, practically a lot

of problems are there. Turbidity of the sample could block collection of Raman scattering from the sample. sensitivity.

Also

the presence of interfering compounds can lead to diminished

If the interfering compounds are fluorescent it will mask Raman signals.

3.2 BIOASSAY METHOD

Bioassays are typically conducted to measure the effects of a substance on a living organism. Bioassays may be qualitative or quantitative. bioassay using Pseudomonas putida

F1,

Toluene Dioxygenase

a quantitative

which has been well characterized genetically

and possesses a diver se metabolism of aromatic compounds. compounds using

This is

Detection

of BTEX

peroxide coupling reaction is called bioassay

method. It is simple, sensitive, whole-cell- based bioassay system for detection of bioavailable BTEX compounds based on a method developed for screening of oxygenase activity. Pseudomonas putida

F1

is known to express

TDO

capable of oxidizing

compounds i.e., it is involved in the conver sion of aromatic compounds to their corres ponding catechols. s.

As

pseudomonas putida is capable of both monooxygenation

and Dioxygenase reactions a screening of oxygenase is provided using whole cell system. This

bioassay system requires no sophisticated instruments and exquisite techniques. The

bioassay has long term storage stability so that it can be used for field monitoring of BTEX compounds and it s tracking in contaminated water . The convenience of multiple sample-handling

makes this whole cell assay an attractive method to be developed as a

field diagnostic method for on-site BTEX contamination.

The

main disadvantage of this

method is that pseudomonas putida doesn¶t oxidize xylene and ethylbenzene.


3.3 DETECTION USING MICROCHIP INDUCED FLUORESCENCE SENSOR

Most

radiation.

organic molecules when excited with ultra rays re emit le ss energetic optical

This

emitted radiation is known as fluorescence and is characterized by its

intensity as a function of both time and wavelength.

Since

this information is linked to

the physical characteristics of an individual molecular s pecies, it provides a powerful means to perform chemical analyses. By the observation of wavelength and time we can detect, identify and quantify the chemical s pecies within an aqueous solution.

The

Laser -Induced

Fluorescence

(LIF) takes advantage of both time and

wavelength information to investigate the contamination of BTX compounds in soil and water .

The

device provides excitation using a passively Q-switched microlaser pumped

by fiber -coupled near -infrared diode laser and generates short pulses of 2 66nm radiation at a repetition rate near 10 k Hz. system

The

microchip laser focusing optics and collection

are very compact and the entire assembly can be placed in a monitoring well or

contained within the shaft of a cone penetrometer .

Thus

the UV radiation necessary to

excite fluorescence in environmental pollutants such as gasoline is generated at the point of contamination while the infrared diode pump laser remains above the ground.

This

configuration takes advantage of the excellent transmission of infrared energy through fiber optics cable and minimizes the ultraviolet attenuation.


3.3.1 EXPERIMENTAL APPARATUS

The

includes

experimental apparatus used to evaluate the performance of the LIF probe

s pectro scopic

hardware, a test cell and a data acquisition

Fig. 3.2 Schematic diagram of experimental apparatus (Source: Sinfield. J.V .et.al, 200 7)

system.

BTEX -Contamination and Remediation A

diode laser pump attached to the microchip laser, mounted in the probe

is pumped by a 1W continuous wave at 808nm.

The

UV thus generated is focused onto

probe¶s sapphire window through the excitation fiber . UV radiation to the s pecimen in the test cell.

The sapphire

Molecular

window focuses the

fluorescence excited by the UV

microchip laser is imaged through probe¶s sapphire window onto the tip of the return fiber . The

output fiber is focused on the entrance slit of a 1/8m scanning

monochromator . Silica beam s plitter mounted within the monochromator to direct a small fraction of light as trigger signal to the trigger P MT and the rest is directed on to the detector PMT. The fast photomultiplier tubes used to detect the intensitie s of the light are operated approximately at 800V. Both the PMTs are connected to a 1.5 storage

GHz

digital

oscilloscope. It is used as an analog-to digital converter to acquire fluorescence

signals. The

PMT output signal is measured across a 50

load.

A

per sonal computer is

used to control the monochromator grating and the oscilloscope. A series

of tests were performed to determine the sensor¶s sensitivity to

BTX compounds and it s time-res ponse. fluorescence s pectrum (from 275 to

Each

350nm)

test involved recording the time-dependent

of one of the BTX compounds at a particular

concentration in water . Using this, profile was plotted and the s pectra from each test were analyzed to determine: 1.

The

total fluorescence signal gathered from the test medium- by time and

wavelength integration 2.

The

fluorescence lifetime of the compound in solution- by time and emission

wavelength integration 3.

The

wavelength of the peak fluorescence emission-the highest intensity at any

wavelength 4.

The

peak fluorescence intensity-the volume under wavelength-time-intensity

profile The

LIF sensor can accurately measure fluorescence lifetime lifetimes as short as 2.5 ns.


3.3.2 ADVANTAGES AND DISADVANTAGES

3.3.2.1 Advantages

1. It is a very compact collection system. So it can be placed in a monitoring well or within a cone penetrometer . 2. LIF can be used for the detection of contamination both in water as well as in soil. 3.

The

intensity of fluorescence is a function of wavelength and time, which is

linked to the physical characteristics of an individual molecular s pecies, provides a powerful means to detect the contaminants. 4.

It has the ability to detect the presence of a compound in solution or recognize a change in state, relative to background conditions. So it help s in finding leak s in landfill systems or indicates the presence of harmful agents in water .

5.

Since

it is possible to detect, identify and quantify the contamination, it is easy to

select

the type and extent of treatment to be given.

3.3.2.2 Disadvantages

1. It is very difficult to detect the presence of Benzene in water . cannot be detected at all. 2.

The

entire system is costly as it has sophisticated instruments.

Also Ethylbenzene


4. TREATMENT OF BTEX CONTAMINANTS

The

field of ³Remediation´ was developed to address the growing and ongoing

problem of subsurface contamination of land and water by hazardous chemicals.

An

interdisciplinary approach is employed during the remedial process involving various branches of science, such as geology and hydrology, chemistry, and sound engineering methods. The remedial process typically involves:

 Site

investigations to characterize the site geology and hydrology, geochemical

conditions, and nature and extent of contamination.



Laboratory testing to identify potential applicable remedial methods.



Pilot-scale testing onsite to verify effectiveness of chosen remedial methods and identify optimal conditions for full-scale implementation.

 Full-scale

remediation.

Remediation methods can generally be divided into ex sit u (i.e., contamination is extracted and treated aboveground) and in sit u (i .e., treatment in place, below ground) methods with the latter having evolved and developed extensively over the past decade to provide more effective and efficient e fficient solutions.

The

methods of treatment of BTEX contaminants are: 1.

Organoclay

and carbon treatment method

2.

Direct

3.

Remediation of groundwater using in situ chemical oxidation

push groundwater circulation well method


4.1 ORGANOCLAY AND CARBON TREATMENT

Organoclays

differ from naturally occurring clay minerals in two basic

characteristics: (1) the s pace between the layer s (i.e., basal s pace) is increased producing additional s pace for the adsorption of large molecular petroleum compounds and (2) their nature is changed from a hydrophilic to an organophilic state due to their functional group among the quaternary ammonium cations.

Different

types of organoclay employed

are organically modified bentonite, montmorillonite, vermiculite, smectite and illite, where the basic

structure

of these minerals had a 2:1 lattice.

Organoclays

are

manufactured by modifying bento nite with quaternary amines. In groundwater, oil may be mechanically emulsified due to confining pressure. If time is of the essence, oil/water separator s and dissolved air flotation systems can be used, followed by polishing with organoclay and activated carbon. This

treatment is used after groundwater has been pumped out of the

aquifer . The contaminated water is passed through the organoclay and carbon unit where the organics are adsorbed and collected.

This is

the chemical substance onto a carbon matrix.

accomplished through the adsorption of A

combination of organoclay/activated

carbon can easily achieve non-detect levels of most organics.

The

effectiveness of this

process is related to the quality of the organoclay and the properties of the contaminants. Antifreeze

and aqueous cleaner s are filtered through organoclay beds to remove oils and

allow for reuse.


Fig4.1 Organoclay and carbon treatment

Organoclays

have found increased acceptance as pre-treatment for activated

carbon adsorption systems in both groundwater and wastewater cleanup. In this fashion organoclays can remove 50% or more of their dry weight in oil, diesel fuel, P NAH 's, PCBs and other chlorinated hydrocarbons. The main function of organoclays has been the prevention of fouling of activated carbon, ion exchange resins and membranes.

4.2 DIRECT PUSH GROUNDWATER CIRCULATION WELLS


Direct

push groundwater circulation wells (DP-GCW) are a promising

technology for remediation of groundwater contaminated with dissolved hydrocarbons and chlorinated solvents. In these wells, groundwater is withdrawn from the formation at the bottom of the well, aerated and vapor stripped and injected back into the formation at or above the water table. Previous field studies have shown that: (a) significant

volumes of groundwater; and (b)

GCWs

GCWs

can circulate

can effectively remove volatile

compounds and add oxygen. This induces a circulating flow field that carries clean water and oxygen throughout the contaminated regions of the aquifer

Fig4.2 Typical in-well aeration application (Hinchee, 1994)

BTEX -Contamination and Remediation The GCWs

were constructed with No. 20 slotted well screen (2.4

cm ID) and natural sand pack extending from 1.5 to

8.2

m below grade.

Air i s

introduced

at 7 .5 m below grade via 0.6 cm tubing. A pproximately 15% of the vertical length of the air supply tubing is wrapped in tangled mesh polypropylene geonet drainage fabric to provide surface area for biological growth and precipitation of oxidized iron. materials were selected to allow rapid installation of the Geoprobe

GCWs

using

3.8

T hese

cm direct push

rods, greatly reducing well installation cost.

The system

was tested in a petroleum contaminated aquifer .

The

contaminant plume there is approximately 10 m deep, 50 m wide and contains up to

4

mg/L total BTEX and 75 mg/L dissolved iron. An extensive pilot test was fir st performed to estimate the zone of influence for a single well.

At

this site an air injection rate of 1 .2

L/min resulted in a water flow rate of 1 to 2 L/min based on bromide dilution tests in the GCW. The GCW

increased the dissolved oxygen concentration in the discharge water to

between 6 and 8 mg/L and reduced contaminant concentrations to less than 20 g/L total BTEX.

Monitoring

results from a 73 day pilot test were then used to define the zone of

influence for a single DP-GCW and to design a full scale barrier system.

While a variety of types of groundwater circulation wells are available, the use of direct - push technology to install these wells enables a substantial reduction in the cost and complexity compared to other GCW types presently available. This

advantage comes with the limitation s of direct- push technology, including poor

utility in soils containing large amounts of rock or basalt. Direct push technology also ha s limitations on the depth that can be reached, but because BTEX contamination from motor fuels is typically found in the upper extent of an aquifer the hundred foot depth that direct push technology (in particular, sites.

Geoprobe)

can reach should be adequate for many

BTEX -Contamination and Remediation A serie s

of direct- push groundwater circulation wells (DP-GCW)

had to be arranged across the width of a BTEX plume to substantially remediate the plume.

The

wells used in this study were made of small diameter (0.8 inch inside

diameter) slotted PVC well screen. The

This

material is inexpensive and readily available.

use of such small wells achieved two goals: it allowed the use of the direct push

technology to install the wells, and it required only a small air flow rate to generate an acceptable liquid pumping rate in each well. For the field test, about 1.2 L/min of air wa s s

parged into each well, generating about 1 L/min of water circulation; this is low

compared to the circulation rates of other published GCWs.

4.3 REMEDIATION OF CONTAMINATED USING IN SITU CHEMICAL OXIDATION One

GROUNDWATER

of the most well developed and widely used in sit u remediation

technologies for soil and groundwater contaminated with organic compounds is in sit u chemical oxidation (ISCO). Various chemical oxidants are commercially available.

The

four major oxidants used for soil and groundwater remediation are: permanganate, per sulfate, peroxide, and ozone.

Additional

differences between the oxidants include the

required oxidant dosage (mass and volume); location, number, and type of required injection points; logistics involved in mixing and delivering the oxidants to the subsurface;

and health and safety considerations.


Fig4.3 Typical ISCO Injection

ISCO involves the delivery of chemical oxidants directly to the subsurface contamination source

zones and down gradient groundwater contamination plumes.

This is

commonly

achieved by either temporary injection points or permanent injection wells. Upon direct contact with organic contaminants, a chemical oxidation reaction occur s, which mineralizes the contaminant compound and produces non-toxic end products such as carbon dioxide (CO2) and water .

The

contaminants susceptible to chemical oxidation

include total petroleum hydrocarbons (TPH) (i.e., fuels), polycyclic aromatic hydrocarbons (P AHs), oxygenates (e.g., pesticides.

MTBE),

chlorinated

solvents,

phenols, and

BTEX -Contamination and Remediation 4.3.2 Treatment of ground water

The

apparatus consist of mixing tank, air compressor, pipes and pumps.

Fig 4.4 Injection System Process Flow Diagram A

pilot study was conducted. The purpose of the study was to evaluate the

efficiency of ISCO using per sulfate for treating groundwater contaminated with free- and dissolved- phase petroleum hydrocarbons and chlorinated solvents. Per sulfate was chosen due to its reactivity with a wide range of organic contaminants including the COCs. Groundwater

occur s at approximately 15 meter s below ground surface.

The study

was

performed in two phases. During fir st phase, batches of per sulfate were hydrated, mixed, and injected into the injection well.

During

Phase II of the study, air was continuously

injected below the contaminated zone (i.e., air s parging) for the purpose of enhancing the distribution of per sulfate in groundwater . A total of 3,800 kilograms of sodium per sulfate were hydrated with 26,000 liter s of water and injected into groundwater via the injection well.


4.3.3 ADVANTAGES AND DISADVANTAGES

Advantages

relatively short

 Non-toxic

remediation period

byproducts.

 minimized minimized

waste generation.

 minimized site

disturbance.

Disadvantages

Effectivene ss

dependant upon ability to dis per se oxidant in aquifer .

health

and safety risk to worker s handling oxidants.

Temporary

mobilization of metal s.

 potential secondary

drinking water

impact (taste, odor).

Cost effective for source area s and highconcentration plumes.

Cost ineffective for low-concentration plumes.


5. CONCLUSION

BTEX contamination is a threat to the mankind as well as to animals and plants. Prolonged exposure to the compounds even in small quantiti quant itiees is highly fatal. The reason why the BTEX entering our soil and groundwater system, are considered such a serious problem si that they all have some acute and long term toxic effects. Benzene is carcinogenic to humans. So the detection of these compounds is of utmost importance.

There

nowadays.

are a lot of advanced methods of detection BTEX contamination emerging

Three

advanced techniques are

studied

in this paper .

Among

the three,

detection using laser induced fluorescence (LIF) is found to be more effective. LIF is a very compact background.

system. This

This

time consuming.

method detects contaminants relative to a baseline or

method of detection is quick compared to the other methods which are Since

it is possible to detect, identify and quantify the BTX

contamination, it is easy to select the type and extent of treatment to be given.

Though

this method is a bit costly, it provides a powerful, accurate and reliable means to detect the contaminants in both water and soil.

Various treatment techniques are also implemented nowadays. Three remediation methods are

studied

in this paper .

Among

the three, remediation of contaminated

groundwater using in sit u chemical oxidation (ISCO) is found to be safer . ISCO is one of the most well developed and widely used.

This

method needs only relatively short

remediation period compared to other methods. In this method chemical oxidation reaction produces non-toxic end products such as carbon dioxide (CO2) and water . This method is cost effective for high-concentration plumes. The inert final product provides a safe

means of treatment of contaminants in both soil and water .


REFERENCES

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