Environmental Engineering Environmental Engineering Management (EEM 690)Management (EEM 690)

Lecture 5. Lecture 5. - Water Quality and IWRM- Water Quality and IWRM- Soil and groundwater pollution and - Soil and groundwater pollution and

controlcontrol

FAISAL ANWAR

Water Quality Management: Rules Water Quality Management: Rules and Regulationsand Regulations

Drinking Water: Australian Drinking Water Drinking Water: Australian Drinking Water Quality Guideline or WHO guidelineQuality Guideline or WHO guideline

Water Pollution Control in Australia: Water Pollution Control in Australia: ANZECC Guidelines for Fresh and Marine Waters ANZECC Guidelines for Fresh and Marine Waters

(Australian and New Zealand Environment Conservation Council)(Australian and New Zealand Environment Conservation Council)

NHMRC recreational waters guidelinesNHMRC recreational waters guidelines

Around the world however is taking the USEPA’s Around the world however is taking the USEPA’s and WHO’s guideline as the basis to enact their and WHO’s guideline as the basis to enact their own guideline.own guideline.

Water Resources Management Water Resources Management SystemSystem

Water Supply SubsystemWater Supply Subsystem Wastewater Disposal SubsystemWastewater Disposal Subsystem River basin management systemRiver basin management system Groundwater and aquifer management systemGroundwater and aquifer management system Urban stormwater managementUrban stormwater management

Water Supply SubsystemWater Supply Subsystem

ComponentsComponents Raw water source – Treatment – Distribution – CustomerRaw water source – Treatment – Distribution – Customer

ObjectiveObjective Provide ample supply of water that meets the Provide ample supply of water that meets the

requirement of end uses of customersrequirement of end uses of customers

After using the waterAfter using the water

We dispose it to the sewer or other places We dispose it to the sewer or other places depending on the disposal methods.depending on the disposal methods.

Wastewater system starts from the users Wastewater system starts from the users (customers)(customers)

Wastewater disposal subsystemWastewater disposal subsystem

ComponentsComponents Customer – Wastewater Collection – Customer – Wastewater Collection –

Wastewater Treatment – DisposalWastewater Treatment – Disposal ObjectiveObjective

Safely collect and dispose so that health Safely collect and dispose so that health and aesthetics of public or any other and aesthetics of public or any other beneficial uses of water is not affected.beneficial uses of water is not affected.

Wastewater collection and disposal system

Deep water Ocean Outfall

Wastewater Treatment Plant

Industry

Sources of WWSources of WW

Characteristics are different for different origins Characteristics are different for different origins of wastewaterof wastewater Residence - kitchen sink, toilet, shower, bath, Residence - kitchen sink, toilet, shower, bath,

washing machine, storm water from roofwashing machine, storm water from roof Commercial establishmentsCommercial establishments Hospitals Hospitals IndustryIndustry AgricultureAgriculture Animal farmingAnimal farming AquacultureAquaculture

Disposal sitesDisposal sites

Depending on where it is disposed it has Depending on where it is disposed it has to be treated differentlyto be treated differently

Disposal sites: usually water bodies like Disposal sites: usually water bodies like river, lake, ocean and land fillsriver, lake, ocean and land fills

Water QualityWater Quality

Oxygen Demanding Material Oxygen Demanding Material

Anything that can be oxidized in the Anything that can be oxidized in the receiving water with the consumption of receiving water with the consumption of dissolved molecular oxygen is termed dissolved molecular oxygen is termed oxygen-demanding material. This material oxygen-demanding material. This material is usually biodegradable organic matter is usually biodegradable organic matter but also includes certain inorganic but also includes certain inorganic compounds. The consumption of dissolved compounds. The consumption of dissolved oxygen (DO) poses a threat to fish and oxygen (DO) poses a threat to fish and other aquatic species.other aquatic species.

NutrientsNutrients

Nitrogen and Phosphorous, two nutrients Nitrogen and Phosphorous, two nutrients of primary concern, are considered of primary concern, are considered pollutants. All living things require these pollutants. All living things require these nutrients to grow but problems arises nutrients to grow but problems arises when it is in excess amount. when it is in excess amount.

Pathogenic organismsPathogenic organisms

Microorganisms found in wastewater Microorganisms found in wastewater include bacteria, viruses, and protozoa include bacteria, viruses, and protozoa excreted by diseased persons or animals. excreted by diseased persons or animals. When discharged into surface waters, they When discharged into surface waters, they make the water polluted (non-drinkable). If make the water polluted (non-drinkable). If the pathogen concentration is high the pathogen concentration is high enough, the water may be unsafe for enough, the water may be unsafe for swimming and fishing.swimming and fishing.

Suspended solidSuspended solid

Organic and inorganic particles that are Organic and inorganic particles that are carried by the wastewater into a receiving carried by the wastewater into a receiving water are termed as Suspended solid (SS)water are termed as Suspended solid (SS)

SS usually settle in the bottom when the SS usually settle in the bottom when the flow velocity in reduced such as in Lake or flow velocity in reduced such as in Lake or pool.pool.

Colloidal particles that do not settle causes Colloidal particles that do not settle causes turbidity in the surface water bodies. turbidity in the surface water bodies.

SaltsSalts

Salt present in water are normally Salt present in water are normally measured by evaporation of a filtered measured by evaporation of a filtered water sample. The salts and other things water sample. The salts and other things that do not evaporate are called as total that do not evaporate are called as total dissolved solid (TDS). Problem arises dissolved solid (TDS). Problem arises when TDS is such that it is no longer when TDS is such that it is no longer usable for drinking and irrigation. High usable for drinking and irrigation. High concentration of TDS are discharged by concentration of TDS are discharged by many industries and urban storm runoff.many industries and urban storm runoff.

Toxic Metals and Toxic organic Toxic Metals and Toxic organic compoundscompounds

Agricultural runoff often contains Agricultural runoff often contains pesticides and herbicides. Urban runoff is pesticides and herbicides. Urban runoff is a source of zinc in many water bodies. a source of zinc in many water bodies. Other toxic metals and organic Other toxic metals and organic compounds are discharged by many compounds are discharged by many industries.industries.

Endocrine-Disrupting Chemicals Endocrine-Disrupting Chemicals (EDCs)(EDCs)

EDCs, a class of EDCs, a class of chemicals, can alter chemicals, can alter the normal the normal physiological function physiological function of endocrine system of endocrine system and can affect the and can affect the synthesis of synthesis of hormones. They can hormones. They can interfere with the interfere with the regulation of regulation of reproductive and reproductive and developmental developmental process in mammals, process in mammals, birds, reptiles and birds, reptiles and fish.fish.

Water Quality Management in Water Quality Management in RiversRivers

The objective of water quality management is to The objective of water quality management is to control the discharge of pollutants so that water control the discharge of pollutants so that water quality is not degraded to an unacceptable quality is not degraded to an unacceptable extent below the natural background level.extent below the natural background level.

We must be able to measure the pollutants, We must be able to measure the pollutants, predict the impact of the pollutant on water predict the impact of the pollutant on water quality, determine the background water quality quality, determine the background water quality (i.e without human intervention), and decide the (i.e without human intervention), and decide the levels acceptable for intended uses of the water.levels acceptable for intended uses of the water.

Water Quality Management in Water Quality Management in RiversRivers

The impact of pollution on a river depends on:The impact of pollution on a river depends on:- nature of the pollutant- nature of the pollutant- characteristics of the individual river (i.e. open - characteristics of the individual river (i.e. open

channel) – discharge capacity and flow velocity. Water channel) – discharge capacity and flow velocity. Water depth, bottom slope and sediment materials and depth, bottom slope and sediment materials and surrounding vegetation. surrounding vegetation.

- Climate of the region- Climate of the region- mineral heritage of the watershed- mineral heritage of the watershed- land use pattern- land use pattern- types of aquatic life in the river- types of aquatic life in the river

All of these factors should be considered for case by All of these factors should be considered for case by case. Some pollutants such as sediments, salt and heat case. Some pollutants such as sediments, salt and heat may by highly susceptible to some rivers, while some may by highly susceptible to some rivers, while some other may tolerate them without much damageother may tolerate them without much damage

Total Maximum Daily Load (TDML)Total Maximum Daily Load (TDML)

TDML specifies the maximum amount of pollutant that a water body can TDML specifies the maximum amount of pollutant that a water body can receive and still meet water quality standards.receive and still meet water quality standards.

TMDL allocates pollutant loadings that may be contributed among point and TMDL allocates pollutant loadings that may be contributed among point and non-point sources. non-point sources.

TMDL is computed by:TMDL is computed by:TMDL=TMDL=WLA + WLA + LA + MOSLA + MOS

WLA = waste load allocations, that is, portions of the TMDL assigned to WLA = waste load allocations, that is, portions of the TMDL assigned to existing and future point sources.existing and future point sources.

LA = load allocations, that is, portions of the TMDL assigned to existing and LA = load allocations, that is, portions of the TMDL assigned to existing and future non-point sources.future non-point sources.

MOS = margin of safety which is to account for uncertainty about relationships MOS = margin of safety which is to account for uncertainty about relationships between loads and water quality.between loads and water quality.

A software system called Better Assessment Science Integrating Point and A software system called Better Assessment Science Integrating Point and non-Point Sources (BASINS) that integrates a GIS, national watershed and non-Point Sources (BASINS) that integrates a GIS, national watershed and meteorological data, and state-of-the-art environmental assessment and meteorological data, and state-of-the-art environmental assessment and modeling tools is used to develop the TMDL (Ahmed 2002; US EPA 2005).modeling tools is used to develop the TMDL (Ahmed 2002; US EPA 2005).

Effect of Oxygen-Demanding Effect of Oxygen-Demanding Wastes on RiversWastes on Rivers

The introduction of oxygen demanding materials The introduction of oxygen demanding materials (organic or inorganic) into a river causes the (organic or inorganic) into a river causes the depletion of DO in water.depletion of DO in water.

This poses threat to fish and aquatic life if DO This poses threat to fish and aquatic life if DO concentration falls below a critical point.concentration falls below a critical point.

To predict the extent of oxygen depletion, it is To predict the extent of oxygen depletion, it is necessary to know how much waste is being necessary to know how much waste is being discharged and how much oxygen is required to discharged and how much oxygen is required to degrade the waste.degrade the waste.

Chemical Oxygen Demand (COD)Chemical Oxygen Demand (COD)

Chemical Oxygen Demand (COD): is a Chemical Oxygen Demand (COD): is a measured quantity that does not depend on measured quantity that does not depend on knowledge of the chemical compositions of the knowledge of the chemical compositions of the substances in water.substances in water.

A strong chemical oxidizing agent is (chromic A strong chemical oxidizing agent is (chromic acid) mixed with a water sample and then boiled. acid) mixed with a water sample and then boiled. The difference between the amount of oxidizing The difference between the amount of oxidizing agent at the beginning of the test and that agent at the beginning of the test and that remaining at the end of the test is used to remaining at the end of the test is used to calculate the COD.calculate the COD.

Biochemical Oxygen Demand (BOD)Biochemical Oxygen Demand (BOD)

If the oxidation of an organic compound is If the oxidation of an organic compound is carried out by microorganisms using the organic carried out by microorganisms using the organic matter as a food source, the oxygen consumed matter as a food source, the oxygen consumed is known as BOD.is known as BOD.

The BOD test is an indirect measurement of The BOD test is an indirect measurement of organic matter because we actually measure organic matter because we actually measure only the change in DO concentration caused by only the change in DO concentration caused by the microorganisms as they degrade the organic the microorganisms as they degrade the organic matter.matter.

DO SagDO Sag The concentration of DO in a river is an indicator of the The concentration of DO in a river is an indicator of the

general health of the river.general health of the river. All rivers have some capacity of self-purification. As long All rivers have some capacity of self-purification. As long

as the discharge of the oxygen-demanding wastes is as the discharge of the oxygen-demanding wastes is well within the self-purification capacity, DO level will well within the self-purification capacity, DO level will remain high to maintain the good quality of aquatic remain high to maintain the good quality of aquatic environment.environment.

As the amount wastes increase and DO level falls where As the amount wastes increase and DO level falls where aquatic environment is highly disturbed. After some time aquatic environment is highly disturbed. After some time it’s DO level again increase with aeration from it’s DO level again increase with aeration from atmosphere.atmosphere.

If DO=0, all the fish and other animals are killed and If DO=0, all the fish and other animals are killed and water becomes blackish and foul smelling as the sewage water becomes blackish and foul smelling as the sewage and dead animal life decompose under anaerobic and dead animal life decompose under anaerobic conditions.conditions.

DO Sag CurveDO Sag Curve

DO SagDO Sag

Effect on Nutrients on Water Effect on Nutrients on Water Quality in RiversQuality in Rivers

Effects of Nitrogen:Effects of Nitrogen:

- In high concentration, NH- In high concentration, NH33-N is toxic to fish-N is toxic to fish

- NH- NH33 in low concentration, and NO in low concentration, and NO33-- serve as nutrients for serve as nutrients for

excessive growth of algaeexcessive growth of algae

- The conversion of NH- The conversion of NH44++ to NO to NO33

-- consumes large quantities consumes large quantities of DOof DO

Effect of Phosphorus:Effect of Phosphorus: P enhance the growth of algae. When the P enhance the growth of algae. When the algae die, it becomes the oxygen-demanding material as bacteria algae die, it becomes the oxygen-demanding material as bacteria seek to degrade them. As a result DO level decreases.seek to degrade them. As a result DO level decreases.

Management StrategyManagement Strategy: Controlling the nutrient-caused water quality : Controlling the nutrient-caused water quality problems in streams is based on the removal of N or P from problems in streams is based on the removal of N or P from wastewater before it is discharged.wastewater before it is discharged.

Water Quality in lakes and Reservoir

Thermal Stratification in Lakes Thermal Stratification in Lakes and Reservoirsand Reservoirs

Thermal Stratification is driven by the relationship Thermal Stratification is driven by the relationship between temperature and densitybetween temperature and density

Dg

Nutrient and Trophic StateNutrient and Trophic State

Trophy is defined as the rate at which organic Trophy is defined as the rate at which organic matter is supplied to lakes, both from the matter is supplied to lakes, both from the watershed and through internal production.watershed and through internal production.

The growth of algae and macrophytes in lakes is The growth of algae and macrophytes in lakes is influenced by conditions of light and temperature influenced by conditions of light and temperature and the supply of nutrients.and the supply of nutrients.

As temperature and light is more or less As temperature and light is more or less constant in a region, trophy is mainly determined constant in a region, trophy is mainly determined by the availability of nutrients (mainly P and N)by the availability of nutrients (mainly P and N)

Lakes classification according to Lakes classification according to their trophic state:their trophic state:

EutrophicationEutrophication The process of nutrient enrichment of a The process of nutrient enrichment of a

body, with attendant increases in organic body, with attendant increases in organic matter, termed as Eutrophication. This is matter, termed as Eutrophication. This is considered to be a natural aging process considered to be a natural aging process in lakesin lakes

Addition of P by human activities and the Addition of P by human activities and the resulting aging of the lake is termed as resulting aging of the lake is termed as Cultural Eutrophication.Cultural Eutrophication.

Wetland Management Wetland Management

Wetland functions:

(1) Water storage and flood mitigation (2) Filtration of water and removal of suspended solids, bacteria, nutrients and toxic substances (3) Wildlife habitat (4) biogeochemical cycling of materials.

Created/Constructed WetlandCreated/Constructed Wetland If damage to wetland is deemed unavoidable, new or If damage to wetland is deemed unavoidable, new or

improved wetlands must be created to offset the improved wetlands must be created to offset the functions lost in the damaged wetlands. The creation or functions lost in the damaged wetlands. The creation or restoration of wetlands to compensate for damage to restoration of wetlands to compensate for damage to other wetlands is termed as compensatory mitigation.other wetlands is termed as compensatory mitigation.

Compensatory mitigation is intended to offset the loss of Compensatory mitigation is intended to offset the loss of wetland functions by creating, restoring, or enhancing wetland functions by creating, restoring, or enhancing wetlands that will play a similar role before damage.wetlands that will play a similar role before damage.

Created wetlandCreated wetland refers to a wetland built for mitigation refers to a wetland built for mitigation purposes, and purposes, and constructed wetlandconstructed wetland denotes a wetland denotes a wetland designed for pollutant removal from wastewater, urban designed for pollutant removal from wastewater, urban and agricultural runoff, stormwater and mining wastes.and agricultural runoff, stormwater and mining wastes.

Low-Impact DevelopmentLow-Impact Development

Bio-retention cellBio-retention cell

Shallow depressions in the soil to which Shallow depressions in the soil to which stormwater is directed for storage and to stormwater is directed for storage and to maximize infiltration. They are sometimes maximize infiltration. They are sometimes referred to as bio-infiltration cells, referred to as bio-infiltration cells, vegetated bio-filters, and rain gardens.vegetated bio-filters, and rain gardens.

They are often mulched (for aesthetic They are often mulched (for aesthetic values and water treatment) planted with values and water treatment) planted with native vegetation that promotes native vegetation that promotes evapotranspiration.evapotranspiration.

Bio-retention cellBio-retention cell

Integrated Water Resources Integrated Water Resources Management (IWRM)Management (IWRM)

Water is Already a Global Issue

More than 2 billion people in 40 countries live in river basins under “water stress”

Decreasing per-capita water availability - global population increased by a factor of 3 in 20th century, while water withdrawals increased by a factor of 7

As global population is expected to increase from 6 billion to 10 billion in 50 some years, demand on water will increase further

Failure with Past Approaches

Sectoral, limited coordination, fragmented,uncoordinated development – inadequate to meetglobal challenges !

Supply-driven augmentation, top-down management, lack ofdemand management, subsidies led to inefficient investment, waste of water

Restrictions on water transfers have prevented waterfrom being allocated to the most beneficial use

New Approach is Needed…..

What is IWRM ?What is IWRM ?IWRM:

IWRM is a process which promotes the co-ordinated development and management of water, land and related resources in order to maximise the resultant economic and social welfare in an equitable manner without compromising the sustainability of vital ecosystem.

IWRM (as defined by global water partnership, GWP);

“A participatory planning and implementation process, based on sound science, which brings together stakeholders, to determine how to meet society’s long-term needs for water and coastal resources while maintaining essential ecological services and economic benefits.”

What is IWRM ?What is IWRM ?

The Three Pillars of IWRM The Three Pillars of IWRM

The Three Pillars of IWRM The Three Pillars of IWRM

Implementing an IWRM process is in fact, a question of getting the “three pillars” right:

(1)Moving towards an enabling environment of appropriate policies, strategies and legislation for sustainable water resources development and management

(2)Putting in place the institutional framework through which the policies, strategies and legislation can be implemented, and

(3)setting up the management instruments required by these institutions to do their job.

What do we mean by Integrated Approach?

IWRM is a Rolling Process

Soil and Groundwater Pollution and Soil and Groundwater Pollution and ControlControl

Sources of Groundwater Pollution

Industrialwaste

Sewer leakageAgricultural land Oil

Chloro-hydrocarbons

Pollutedriver

S e e p a g e

Flow

Watertable

Dissolvedpollutant

DissolvedcontaminantLNAPL

(< water)DNAPL

( > water)Impermeable layer

Rainfall Rainfall Rainfall

Domestic waste

Agricultural IndustrialMunicipal & DomesticSurface water

Saturated zone

Unsaturatedzone

Contaminantvapor

Sources of Groundwater Pollution

Industrialwaste

Sewer leakageAgricultural land Oil

Chloro-hydrocarbons

Pollutedriver

S e e p a g e

Flow

Watertable

Dissolvedpollutant

DissolvedcontaminantLNAPL

(< water)DNAPL

( > water)Impermeable layer

Rainfall Rainfall Rainfall

Domestic waste

Agricultural IndustrialIndustrialMunicipal & DomesticSurface water

Saturated zone

Unsaturatedzone

Contaminantvapor

Subsurface system

Subsurface System composed of:

1. Soil2. Water3. Air and4. Chemicals

(pollutants/contaminants)

Table 2.2 Common contaminants found in groundwater and their properties

NAPL

Common Contaminants

Densitya (gm/cm3)

Solubilitya (mg/l)

Dynamic viscositya

(cp)

Max contaminant level (MCL)b (mg/l)

Toluene 0.867 515 0.59 1 Benzene 0.876 1780 0.65 0.005

LNAPL

Xylene (total) 0.88 152 0.81 10 Dichloroetylene

(DCE) 1.22 400 0.33 0.007

Trichloroethylene (TCE)

1.46 1100 0.58 0.005

DNAPL

Tetrachloroethylene

(PCE) 1.62 149 0.89 0.005

avalue taken from the CRC Handbook (Weast et al., 1998) bFetter (1993)

Table 2.3 Toxic effects of the selected groundwater contaminants Source: Watson and Burnett (1993)

Toluene

Benzene

Xylene

Dichloroethylene (DCE)

Trichloroethylene (TCE)

Tetrachloroethylene (PCE)

Soil and GroundwaterContaminants

Schematic representation of LNAPL movement through the unsaturated and into the saturated zone

Contaminant atresidual saturation

VaporUnsaturated zone

Volatilization ofcontaminants

Capillaryfringe

Watertable

Saturated Zone

Source

Ground Surface

LNAPL

Dissolved contaminant

Schematic representation of DNAPL movement through the unsaturated and saturated zone

DNAPL Pool

Ground surface

Capillary Fringe

Water Table

VaporResidualNAPL saturation

Dissolved contaminant

Impermeable layer

Source

Unsaturated Zone

Saturated Zone

Flow

Interfacial Tension and Wettability

- By convention, is measured through the denser fluid. - In general, one or the other of the fluids will preferentially spread over, or wet, the entire solid surface. If <900, then liquid, L will preferentially wet the surface. If >900, then the liquid G will preferentially wet the surface.

That is, if there are two liquids competing for a surface, one dominates and coats the solid surface and hence it is called wetting fluid and other is called nonwetting fluid.

In NAPL-water systems, water tends to preferentially wet the surface and the water is called wetting fluid and NAPL is nonwetting fluid. However, if the surfaces are dry and coated with NAPL first, then NAPL is wetting fluid. In two phase NAPL-gas system in porous media, NAPL is the wetting fluid and air is the nonwetting fluid.

TWO-PHASE LIQUID-GAS SYSTEM IN POROUS MEDIA

(a) (b)

(c)

NAPL

Air

Solid grain

Different states of fluid saturation in Subsurface system

Different fluid saturation states in NAPL wet porous medium

Ground surface

NAPL

Level

Vadosezone

Pendular zone

Funicular zone or Variable zone

Residual saturation(negative pressureor suction head)

Bubblingpressure

Percent saturation 1000

Capillary fringe

Residual nonwetting saturation

Soil and Groundwater RemediationSoil and Groundwater Remediation

Soil and Groundwater Remediation Techniques

Based on two removal principles: (i) convective transport and (ii) biological degradation

Convective transport takes place in the mobile phases of the soil (the gas phase and the liquid phase).

- the soil must be sufficiently permeable and - the contaminants must be volatile or soluble

Biological Degradation:- Many of the contaminants are biologically degraded by microorganisms. - In most cases, sufficient microorganisms capable of degrading the contamination are present in the soil (Otten et al., 1997).

Volatility and solubility of the most common contaminants

Contaminants Volatility Solubility

+ - - -

Mineral oil petrol diesel domestic fuel oil kerosene + - Aromatic compounds + + PAHs

+ +

Chlorinated hydrocarbon (CHC) aliphatic CHC mono-, dichlorobenzene tri-, tetra-, hexachlorobenzene - - Source: Otten et al. (1997); + = good; = moderate; - = poor

NAPL Remediation Technologies

1. Pump and Treat2. Soil Vapour Extraction

-Soil venting-Air Sparging

3. Flushing Techniques4. Bioremediation5. Reactive Permeable Barrier

1. Pump and Treat

- Very common method for cleaning up groundwater- Relatively slow process (at least 5 to 10 years, sometimes decades)- Time needed depends on

- type and amount of harmful chemicals present- size and depth of polluted groundwater- type of soil and rock in the area

2. Soil Vapor Extraction (SVE) Technique

For Unsaturated zone: Soil Venting- Soil venting is usually used to remove the VOCs from the unsaturated soil. - As the name suggests, SVE extracts contaminants from the soil in vapor form.

For Saturated Zone: Air Sparging- Soil venting alone cannot remove the contaminants from the saturated zone, where the water-soaked soil that lies below the water table. - At sites where contamination is in the saturated zone, a process called air sparging may be used or may used along with the soil venting as shown in Fig.

A typical SVE system: combination of soil venting and air sparging

Water

Table

Air vent

Air Sparging Well

VOC GasesVacuum Pump Treatment

System

Vapor Extraction Well

Unsaturated Zone

SaturatedZone

3. Flushing Technique

- Those contaminants are nonvolatile or semi-volatile that cannot be extracted by SVE technique; soil-flushing technique is used for them.

- In situ soil flushing is an innovative treatment technology that floods contaminated soils with a solution that moves the contaminants to an area where they are removed

- Surfactant (surface active agents), a detergent or emulsifier, can be used as a flushing solution in order to remove the contaminants.

- Sometimes alcohol is solely used as the flushing solution or can be used as the combination of surfactant and alcohol.

- The interfacial tension is lowered sufficiently, and physical mobilization of NAPL can occur

Flushing technique

SeperatorContaminantTreatment

ConcentratedNAPLs

AirEmissions Control

TreatedEmission

Flushing Solution

Flushing Solution

Flushing Solution

Injection Well

ExtractionWell

Flushing solution/Contaminant mixture

Treated water (either recycled foe use in flushing solution or discharged in another acceptable manner

Contamination

Characteristics of the Surfactant

- Surfactants are surface active because they have the criteria to concentrate at the interfacial regions. -Surfactant molecules called monomers having hydrophilic head and hydrophobic tail

Hydrophilic (carry charge; anionic surfactant (-) cationic surfactant (+) nonionic surfactant (no charge)

Hydrophobic

• The major characteristic feature of a surfactant is that the monomers should accumulate at different interfaces, such as air-water, NAPL-water or solid-liquid interfaces in an oriented fashion

NAPL

Water

Air

Water

Liquid

Interface

(I) (II)

(III)

Charged solid surface

-

-

++++++

-

-

-

-

-

-

-

-

-

-Interface

Liquid

Uncharged solid surface

• As surfactant added to aqueous solution, surfactant molecules will tend to accumulate at fluid-fluid and fluid-solid interfaces while some other will exist in free solution. • Once a sufficient amount of surfactant has been added to aqueous solution, however, aggregation of surfactant monomers referred to as micelles will form. • Micelles are often spherical in shape and can contain several hundred surfactant monomers. Formation of micelles increases the aqueous solubility of the contaminants• the threshold concentration at which micelles begin to form is termed as the critical micelle concentration (CMC).

Water Phase

NAPL phase

Contaminant molecule

Surfactant Micelle

Surfactant monomerwith hydrophilic head and hydrophobic tail

Surfactant Concentration

Mon

omer

Con

cent

rati

onCritical Micelle Concentration (CMC)

• Bioremediation is a treatment process that uses naturally occurring microorganisms (yeast, fungi, or bacteria) to break down, or degrade the hazardous substances into less toxic or nontoxic substances. • Microorganisms, eat and digest organic substances for nutrients and energy. • Organic compounds are usually composed of carbon and hydrogen atoms. • Certain microorganisms can digest organic substances such as fuels or solvents • The microorganisms break down the organic contaminants into harmless products – mainly carbon dioxide and water

4. Bioremediation Technique

Oil OilOil

Microorganism eat oilor other organic contaminant

Microorganisms digest oil andconvert it to carbon dioxide

(CO2) and water (H2O)

Microorganisms give off CO2 and

H2O

Remediation Techniques LNAPLs DNAPLs Unsaturated Saturated

SVE:Soil venting (volatile compounds)Air sparging(to strip volatile compounds)(add oxygen for biodegradation)

Flushing by surfactant/alcohol(non-volatile and semi volatile compounds)

Bioremediation(volatile, semi-volatile and non-volatile compounds)

Summary of commonly used NAPL remediation techniques

Other Method: Permeable Reactive Barrier (PRB)A permeable reactive subsurface barrier can be defined as:an emplacement of reactive materials in the subsurface designed to intercept a contaminant plume, provide a preferential flow path through the reactive media, and transform the contaminant (s) into environmentally acceptable forms to attain remediation concentration goals at the discharge of the barrier.

Permeable reactive barriers are currently being used for the treatment of plumes of chlorinated hydrocarbons.

Research in both the laboratory and in the field is being carried out on a variety of reactive materials and contaminants.

Acid Sulphate Soil

Actual acid sulphate materials (i.e. sulfuric horizon) are sedimentary materials that once contained pyrites and may still contain some, but which havebeen exposed to the atmosphere by drainage or disturbance so that the pyrite has oxidized to form sulfuric acid, thereby decreasing the pH to less than 3.5.

Potential acid sulphate materials (i.e. sulfidic materials) are coastal sedimentary materials that contain iron pyrites that has not been oxidized.

Oxidation of Sulfidic Compounds

The overall equation for pyrite oxidation is:

FeS2 + 15/4 O2 + 7/2 H2O → Fe(OH)3 + 2SO42-+ 4H+

With each mole of pyrite yielding 4 moles of acidity.

PRB for the Remediation of Acid Sulphate soil

Though Permeable reactive barriers (PRB) are mainly used for the treatment of chlorinated hydrocarbons but research for the treatment of ASS has been started in Australia.

Alkaline materials are used as PRB to neutralize the solution.

Golab et al (2006) has performed experiments on several alkaline materials to select the most suitable material for PRB:

-recycled concrete-limestone, -calcite-bearing-zeolitic breccia, - blast furnace slag, -lime and-fly ash etc.

Found most suitable because it is:(i) a waste material;(ii) capable of neutralizing the acidity (iii) coarse grained to encourage flow through the barrier; and(iv) Does not release toxins into theenvironment.

But still research is going on……..