INTRODUCTION TO ENVIRONMENTAL

REMEDIATION

Definition• Environmental remediation: providing a

remedy for an environmental problem

• This can include removing contaminants from groundwater or cleaning up after an oil spill

• Remediation is not always just subject to the will of the people, but is often a matter of government regulation or intervention

Purpose• One of the main purposes of environmental remediation

is to restore contaminated sites or resources to a level that is safe for humans and animals

• Depending on the type of damage that is done, this can be a complex and expensive process. There are companies that specialize in environmental remediation.

• Even with the help of these professionals and environmental experts, however, sometimes there is nothing that can be done to restore a contaminated site to a point where it is safe.

Classification

• Environmental remediation technologies are divided into groups called ex-situ and in-situ.

• Processes that involve excavation of soil are considered ex-situ

• In-situ procedures are those that attempt to treat contamination without removing soil

Remediation• Once a soil has to be remediated the key issue is ‘which is the most appropriate

technology to be used?’ • Nine possible criteria to select a remedy (The US National Contingency Plan (NCP) :

– the overall protection of human health and the environment;– compliance with applicable or relevant and appropriate requirements;– long-term effectiveness and permanence;– reduction of toxicity, mobility, and volume through treatment;– short-term effectiveness;– implementability;– cost;– state acceptance;– community acceptance.

• In the UK, three criteria that influence the choice of remediation techniques are considered (Beckett and Cairney 1993):– cost-effectiveness;– speed of reclamation;– flexibility.

Remediation Technologies

Classification/Categorization

• These processes can be classified according to Smith et al. (1995) as in situ and ex situ technologies

• Three Major categories or types of remedial actions:– Containment– Removal– Treatment

Classification/Categorization• Containment: Restriction of contaminants to a

specific domain to prevent further spreading• Removal: A contaminant is transferred from an

open to a controlled environment• Treatment: A contaminant is rendered

innocuous.– Since the inherent toxicity of a contaminant is

eliminated by treatment, this is the preferred approach of the three

Containment

• Accomplished by controlling the flow of the fluid that carries the contaminant OR by directly immobilizing the contaminant

• PHYSICAL BARRIERS: – Operation Principle: to control flow of water,

thus preventing the spread of contaminant– Usually, barrier installed downgradient of

contaminated site

Containment• Used in primarily unconsolidated materials e.g.

soil or sand• May be placed to a depth of 50m• Important Considerations:

– Presence of the zone of low permeability, into which the physical barriers can be seated/keyed (to prevent flow underneath the barrier]

– Permeability of the barrier itself (to be as low as practically possible

– Types of Physical Barriers (Chapter 11 Pollution Science Book)

Containment• HYDRAULIC BARRIERS:

– Similar Principle of Operation as Physical Barrier– Based on fluid potentials– Generated by the pressure differential arising from the extraction or

injection of water

• Key performance Factor– Capacity to capture the contaminant plume, in order to limit the spread of

the zone of contamination– Plum capture is a function of number, placement, and flow rate of the

wells or drains– Advantage of using well systems: tt is the only containment system that

can be used for deep systems, can be used on contaminant zones of any size (number of wells increased to handle large contaminant problems)

Containment

• Wells are the most widely used method for containment, albeit with disadvantages:

– Cost of long term operation and pump maintenance

– The need to store, treat and disposed of the large quantities of contaminated water pumped to the surface

Removal• Excavation (Dig and Dump):

– Excavation of the soil where contaminants reside

– Used at many sites and is highly successful

• Disadvantages:– Exposure of workers to hazardous compounds– Excavated soil require treatment and/or

disposal, which can be expensive– Limited to relatively small areas (shallow,

localized, highly contaminated source zones

Removal• Pump and Treat

– Currently the most widely used technology for contaminated groundwater

– Removes contaminated water from the sub surface by using one or more wells to pump it out

• Disadvantages:– Exposure of workers to hazardous compounds– Excavated soil require treatment and/or disposal,

which can be expensive– Limited to relatively small areas (shallow, localized,

highly contaminated source zones

Removal• Pump and Treat

– Currently the most widely used technology for contaminated groundwater

– Removes contaminated water from the sub surface by using one or more wells to pump it out

– Clean water brought into the contaminated region by the pumping action-removes/flushes additional contamination by inducing desorption from the solid phase

– The contaminated water pumped from the subsurface is directed to some type of treatment operation (e.g. air stripping, carbon adsorption, or biological treatment systems)

Removal• Pump and Treat

– Usually used for saturated subsurfaces, can also be used to remove contaminants from the vadose zone (Referred to as in situ soil washing)

• Performance Criteria– Contaminant Plume Capture– Effectiveness of contaminant removal

• Factors limiting the effectiveness of P&T– Presence of low permeability zones– Rate limited desorption– Presence of immiscible liquids

Enhancement of Removal

• Contaminant removal can be difficult due to such factors as:– Low solubility– High degree of sorption– Presence of immiscible liquid phases

• Which limit the amount of contaminant that can be flushed by a given volume of water

Enhancement of Removal• Approach: Enhancement of removal of low

solubility, high sorption contaminants

• One of the approaches: Inject a chemical into the aquifer (such as surfactant /detergent) that will promote dissolution and desorption of the contaminant, thus enhancing removal effectiveness

• (surfactants work like industrial and household detergents used to remove oily residues from machinery, clothing or dishes (details pg 159 pollution science book)

Soil Vapor Extraction• Aka soil venting: Similar to P&T

– The vadose (unsaturated) zone acts as a “buffer zone” for protecting the quality of the underlying ground water.

– When contaminated, however, it acts as a source zone for ground water pollutants and gaseous emissions

– A fluid is pumped though the contaminated domain to enhance removal

SVE

Tank

Vadose Zone

Capillary Fringe

Water Table

Saturated Zone

Ground Water Flow

Dissolved in Ground Water

Vapors

Separate Fluid Phase

Residual

SVE• Targets the removals of VOCs from

the vadose zone by volatilization• Shown to be effective at removing

NAPL, aqueous, and sorbed phases• Encourages aerobic biodegradation• Proven technology with some design

guidance (rule-of-thumb).

SVE

Groundwater

GWWell

SVEWell

Monit.Well

To GW Treatment

PressureGauge

FlowMeter

Vapor/LiquidSeparator

VacuumPump Treatment

Unit

airflowpaths

Air Sparging• Related to SVE:

– Involve injection of clean air into the saturated or aquifer

– Purpose: to volatilize contaminants from the soil into air bubles

– Air bubles make their way into the vadose zone where thay are captured using SVE system

– Can SERVE another purpose: for in situ bioremediation, air sparging can be used for oxygen supply

Bioremediation

• Aim: To exploit the naturally occuring biodegradative processes to clean up contaminated sites

• Types: In Situ, ex-situ and intrinsic bioremediation

• They all receive increasing attention as viable remediation alternatives for several reasons:– Good public acceptance/support, good success

rates to some application, low cost

Bioremediation

• Drawbacks:– Success can be unpredictable due to

complex nature of biological systems– Rarely restores the environment to its

original condition• Residual contamination is inherent, as a

source of future pollution (still little research in this aspect)

Bioremediation• Success: Domestic sewage waste treatment

• From this experience: Biodegradation = f(type of pollutant(s), type of microorganisms

• Outside sewage system: cleanup of oil spills using heterotrophic bacteria to degrade hydrocarbon

Bioremediation• Factors for the successful application:

– Environmental conditions– Contaminant/nutrient availability– Presence of degrading microorganisms– When bioremediation fails, isolate the “culprit”-

the limiting factor (not easy task)• Initial lab tests can help determine the

presence/absence of microorganisms, reveal an obvious environmental factor that limits biodegradation (extreme pH, bioavailability, toxicity)

Bioremediation

• Most developed bioremediation technologies based on two standard practices:– Addition of Oxygen– Addition of other nutrients

In Situ Bioremediation• Defn: Methods that allow in-place clean

up of contaminated field sites• Great interest on these technologies

because of cost effectiveness and less risk as a result of contacting the contaminants

• Two major types– Biological (in situ bioremediation)– Chemical

Bioventing• Technique used to add oxygen directly to a

site of contamination in the vadose zone (a combo of soil venting and bioremediation)– A series of wells constructed arnd the zone of

contamination– Vacuum introduced to force accelerated air movement– This will effectively increase oxygen supply, hence rate

of biodegradation– Volatile pollutants are removed as the air moves-

treated using biofilters

Air Sparging• Used to add oxygen to the saturated

zone• The injected air displaces water in the

soil matrix-create temp air-filled porosity

• Causes oxygen increase, enhancing biodegradation rates

• Volatile organics into the air stream, removed by vapor extraction

• Methane can also be used for sparging– To stimulate growth of methanotrophic activity and

comebotalic degradation of chlorinated solvents

Biodegradation and Metabolism• Biodegradation:

– involves chemical transformations mediated by microorganisms that satisfy nutritional requirements, satisfy energy requirements, detoxify the immediate environment, or occur fortuitously such that the organism receives no nutritional or energy benefit

• Mineralization: – complete biodegradation of organic materials to inorganic products, and often occurs

through the combined activities of microbial consortia rather than through a single microorganism

• Cometabolism:– is the partial biodegradation of organic compounds that occurs fortuitously and that does

not provide energy or cell biomass to the microorganism(s).– can result in partial transformation to an intermediate that can serve as a

carbon and energy substrate for microorganisms, as with some hydrocarbons, or can result in an intermediate that is toxic to the transforming microbial cell, as with trichloroethylene (TCE) and methanotrophs.

Biodegradation and Metabolism

• Two classes of biodegradation reactions are aerobic and anaerobic– Aerobic biodegradation: involves the use of molecular oxygen,

where (the "terminal electron acceptor") receives electrons transferred from an organic contaminant:

Biodegradation and Metabolism• Thus, the organic substrate is oxidized (addition of

oxygen), and the is reduced (addition of 2 electrons and hydrogen) to water (H2O)

• In this case, the organic substrate serves as the sources 2 of energy (electrons) and the source of cell carbon used to build microbial cells (biomass).

• Some microorganisms (chemoautotrophic aerobes or lithotrophic aerobes) oxidize reduced inorganic compounds (NH3 , Fe2+ , or H2S) to gain energy and fix CO2 to build cell carbon:

Environmental Factors Affecting Biodegradation

Site Characterization• A contaminated site is a system generally consisting of four

phases:– solid, which has an organic matter component and an inorganic mineral

component composed of sand, silt, and clay, – oil (commonly referred to as nonaqueous phase liquid, or NAPL), – gas, and – aqueous (leachate or ground water).

• These phases and compartments need to be characterized with regard to extent and distribution of contamination as well as potential exposure to human and environmental receptors.

• Each phase affects bioavailability, i.e., interactions with microorganisms and exposure to human health and environmental receptors.

Site Characterization• Evaluating the extent and distribution of contamination at a

site will provide important information that can be used as a basis to select specific bioremediation technologies, or to select a treatment train that represents a combination of physical/chemical and biological technologies.

• If contamination is widespread and low in concentration, then in situ treatment or natural attenuation may be feasible

• Conversely, with high concentrations of contaminants, soil excavation and placement in a confined treatment facility (CTF) or a land treatment prepared-bed reactor may be advisable.

Site Characterization• Distribution of contaminants at a site is determined by the

physical and chemical properties of the contaminants and the properties of the site.

• Contaminant properties will affect whether contaminants are leachable, volatile, and/or adsorbable, and therefore will indicate which subsurface phases contain the contaminant(s).

• Physical phases containing the contaminants require evaluation of bioremediation potential. – When the physical and chemical properties are evaluated within the

context of site characteristics, a site-based waste characterization can be used to identify the phases/compartments at the site and the chemicals associated with each phase.

Concept of Treatability Studies

• Treatability studies are conducted in laboratory microcosms, at pilot scale, or in the field.

• Treatability studies that examine the bioavailability of contaminants in waste matrices, potential for toxic effects of intermediate metabolites during the degradation process, and interactions between waste chemicals and organisms are desired.

• The overall goal: to develop a better understanding of factors that threaten ecosystems and human health and of chemicals and their degradation products during bioremediation so that the regulatory community can take into consideration the possibility of alternatives to complete mineralization.

Bioremediation

Bioremediation

Bioremediation

Bioremediation

Breakdown of Sites by Type of Contaminant

Percentage of Sites Treating Each Medium

Groundwater32%

Soil59% Sediment

6%

Sludge2%

Surface Water1%

Breakdown of Process by Treatment Technology

(includes laboratory-, pilot-, and full-scale)

In situ68%

Ex-situ (with reactor)

15%

Ex-situ (without reactor)

17%

Top 9 BIOREMEDIATION METHODS

Solid Phase, prepared bed

11%

Soil Bioremediation

14%

Ground Water Bioremediation

14%

Bioventing25%

All Other Method11%

Attached Growth5%

Air Sparging6%

Fixed Film4% Solid Phase, pile

treatment4%

Natural Attenuation

6%

Why Bioremediation? III

• Frequency of Contaminant Subgroups (US EPA TIO, 1992)

• US. EPA/540/N-93/001

Major Waste Types Applicable to Bioremediation

WHY BIOREMEDIATION? IV

WHY BIOREMEDIATION

Cost Effectiveness of Bioremediation ($)

Method Year 1 Year 2 Year 3Incineration 5301 None None Solidification 115 None None Landfill 670 None None Thermal Desorption 200 None None Bioremediation 175 27 20

1 - costs are per cubic yard

Adapted from Cookson, 1995

WHY BIOREMEDIATION? VI

• Some Other Advantages of Bioremediation• Can be done on site • Permanent elimination of waste (limiting liability) • Positive public acceptance • Minimum site disruption • Eliminates transportation cost and liability • Can be couple with other treatment techniques

Adapted from Cookson, 1995

Advantages of Using Bioremediation Processes

Compared With Other Remediation Technologies

(1) biologically-based remediation detoxifies hazardous substances instead of merely transferring contaminants from one environmental medium to another;

(2) bioremediation is generally less disruptive to the environment than excavation-based processes; and

(3) the cost of treating a hazardous waste site using bioremediation technologies can be considerably lower than that for conventional treatment methods: vacuuming, absorbing, burning, dispersing, or moving the material .

Effective Bioremediation, Utilizing Microbial Inoculation,

Basic and Absolutely Essential Requirements

1. Oxygen at a residual level of 1 ppm. or more 2. Essential inorganic nutrients 3. Microbes and substrate must be in contact 4. Water - either salt or fresh Other conditions must be taken into account, such as

pH, temperature, salinity, type of contaminant,

POLLUTANTS

– Bio-degradable petroleum products (gas, diesel, fuel oil) •crude oil compounds (benzene, toluene, xylene, naphthalene) •some pesticides (malathion) •some industrial solvents •coal compounds (phenols, cyanide in coal tars and coke waste)

– Partially degradable / PersistentTCE (trichlorethylene) threat to ground water •PCE (perchlorethlene) dry cleaning solvent •PCB’s (have been degraded in labs, but not in field work) •Arsenic, Chromium, Selenium

– Not degradable / Recalcitrant Uranium •Mercury •DDT

PAH structures

Adapted from “A Citizen’s Guide to Bioremediation”, United Nation Environmental Agencies, Office of Solid Waste and Emergency Response, EPA 542-F-01-001

Remediation Options for Organic Pollutants

in Soils– Containment/landfill– Thermal desorption– Advanced organic stabilisation– Mobile catalytic chemical oxidation– Bioremediation

• Landfarm• Biopile• Composting• Slurry reactors

COMPARISON OF BIOREMEDIATION AND OTHER TECHNIQUES

• Soil Gas Extraction: A process by which petroleum vapors are removed from the soil using wells and vacuum pumps. Volatile compounds are extracted from the area between soil particles by applying negative pressure to screened wells in the vadose zone.

• Low Temperature Thermal Stripping: A process by which soil is excavated and fed into a mobile unit designed to heat the soil and drive off contaminates.

• Excavation: A process which involves the digging up of contaminated soils and hauling them away.

TYPES OF TREATMENT TECHNOLOGY

Bioaugumentation

• the addition of naturally occuring microbes to sites

• sites can be treated with high concentrations of specific microbes

• costs little money, time and disruption• simple testing done for

biocompatibility and biodegradation efficiency

TYPES OF TREATMENT TECHNOLOGY

Biostimulation

• The use of indigenous microbes • the modification of the site to promote

the growth of native microbes already present

• depends on necessary native microbial and organic material to be present

• costs little time and money • testing appropriate microbes can be

difficult and complex

TECHNOLOGY-OTHER OPTIONS

Bioventing – treating soil by drawing oxygen though it to

stimulate microbe growth

Composting – contaminated soils mixed with a bulking agent and

exposed to air

Landfarming – adaptation of traditional farming techniques

(aerating, ploughing) to contaminated areas to increase microbes activity

Treatment Options for Contaminated Soils

from Natusch, 1997.•Remediation Method•Excavation-landfill•Containment on-site•Landfarming/Bio•Co-burning•Stabilisation•Thermal desorption•Soil washing•Vapour extraction•Dechlorination

•% Use in Australia•60-90•10-30•15-20•<5•5-10•<5•<5•<5•<1

Limitations to Bioremediation

– Timescale– Residual Contaminants Levels– Inconsistency– Recalcitrant Pollutants eg DDT, PAHs

• Bioavailability• Degrading microorganisms• Aqueous solubility• Toxicity

ConclusionBIOREMEDIATION:

• Is a process which uses naturally occurring microorganisms to enhance normal biological breakdown.

• It is an effective method for treating many hazardous materials.

• Of all the different processes available for clean-up of sites, Bioremediation is the best and most cost effective method for remediation, with respect to environmental liability.

• The nature and location of the contamination, the type of soils and geological conditions, determine which method of remediation is best for each individual clean-up site.

“Plan the Work, and Work the Plan” An Engineering Perspective

•Planning the Work •what is to be done •when is it to be done •how much is the scheduled cost •who will do it •Working the Plan •budgeting & scheduling control •coordinating activities across the team •How to Evaluate & Recommend the Technology •must provide a net improvement over conventional

technologies •goals must be achieved: •faster, cheaper, safer, better, etc.

Cookson, 1995

END OF INTRODUCTION TO BIOREMEDIATION