ENVIRONMENTAL REMEDIATION EAT441/3 SEM I, 2014-2015 CHAPTER 7: ENV. REMEDIATION (PART 2) (Bioremediation Technique) S. Ragunathan AMPRIM, MIMM, AMESM Dip. (Public Health), B. Tech (Env), MSc. (Env. Eng), phD(Polymer Recycling) School of Environmental EngineeringUNIVERSITY MALAYSIA PERLIS
WHAT IS EXPECTED FROM YOU ? At the end of 2 hours lecture • Able to differentiate 4 most common bioremadiation techniques in Soil Remediation. • Know what is bio-venting and its initial/detail screening for employment? • Understand the Site & constituent characteristics for Bio-venting system efficiency. • Able to calculate no of extraction wells.
INTRODUCTION (Soil Remediation) Review from previous Lecture • Remediation techniques for contaminated soil: • Physical and chemical treatment • Biological treatment • Fixation/encapsulation • Thermal destruction • Physical and chemical treatment: • Soil vacuum extraction/soil vapor extraction (SVE) • Soil washing • Soil flushing • Neutralization • Oxidation • Photolysis • Precipitation • Reduction • Carbon adsorption • Ion exchange
INTRODUCTION (Soil Remediation) Review from previous Lecture • Biological treatment: • Aerobic bioremediation • Anaerobic bioremediation • Biological seeding • Composting • Enzyme addition • Remediation techniques for contaminated soil: • Physical and chemical treatment • Biological treatment • Fixation/encapsulation • Thermal destruction • Fixation/Encapsulation treatment: • Cement solidification • Glassification/vitrification • Lime solidification • Thermoplastis microencapsulation • Thermal treatment: • Pyrolysis • Soil thermal extraction • Thermal desorption
BIOREMEDIATION TECHNOLOGIES (Soil)
BIOREMEDIATION TECHNOLOGIES (Soil) 1. Bioventing – in situ aeration of soil 2.Composting – addition of moisture and nutrients, regular mixing for aeration 3. Biopiles – ex situ aeration of soil 4. Land farming/treatment – application of organic materials to natural soil followed by irrigation and tilling
BIOREMEDIATION (1. Bioventing-Component of Bioventing System) 1.Injection Wells 3. Treatment(Water/vapour) 2. Extraction/Monitoring Wells Vapor treatment Nutrient
BIOREMEDIATION TECHNOLOGIES (Soil) What does a typical extraction system look like?
BIOREMEDIATION (Basic’s) • Bioremediation refers to the use of microorganisms to remove undesirable compounds from soil, sludge, groundwater or surface water so that these sources will be returned to their "clean & natural" state. • It can be applied as in-situ treatment by using indigenous microorganisms to treat contaminated soil and ground water in place without moving the soil or ground water. • Bioremediation technology exploits various naturally occurring mitigation processes: natural attenuation, biostimulation, and bioaugmentation.
BIOREMEDIATION (Basic’s) • Bioremediation which occurs without human intervention other than monitoring is often called natural attenuation. This natural attenuation relies on natural conditions and behavior of soil microorganisms that are indigenous to soil. • Biostimulation also utilizes indigenous microbial populations to remediate contaminated soils. • Biostimulation consists of adding nutrients and other substances to soil to catalyze natural attenuation processes. • Bioaugmentationinvolves introduction of exogenic microorganisms (sourced from outside the soil environment) capable of detoxifying a particular contaminant, sometimes employing genetically altered microorganisms
BIOREMEDIATION (Basic’s) • Bioremediation can be implemented in a number of treatment modes: - aerobic (oxygen respiration) - anoxic (nitrate respiration) - anaerobic (non oxygen respiration) - co-metabolic • Three primary ingredients for bioremediation are: - presence of a contaminant, - an electron acceptor, - presence of microorganisms that are capable of degrading the specific contaminant. Microbes + Electron Donor (Energy & Carbon Source) + Nutrients + Electron Acceptor → More microbes + Oxidized End Products Electron donor : waste contaminants as energy source Electron acceptor: O2, NO3, SO4, CO2, organic carbon
BIOREMEDIATION (Basic’s) Aerobic and anaerobic bacteria can be identified by growing them in liquid culture:1:Obligate aerobic (oxygen-needing) bacteria gather at the top of the test tube in order to absorb maximal amount of oxygen.2:Obligate anaerobic bacteria gather at the bottom to avoid oxygen.3:Facultative bacteria gather mostly at the top, since aerobic respiration is the most beneficial one; but as lack of oxygen does not hurt them, they can be found all along the test tube.4:Microaerophiles gather at the upper part of the test tube but not at the top. They require oxygen but at a low concentration.5:Aerotolerant bacteria are not affected at all by oxygen, and they are evenly spread along the test tube.
BIOREMEDIATION (Basic’s) • In situ bioremediation causes minimal disturbance to the environment at the contamination site. In addition, it incurs less cost than conventional soil remediation or removal and replacement treatments because there is no transport of contaminated materials for off-site treatment. • in situ bioremediation has some limitations: • 1) it is not suitable for all soils, • 2) complete degradation is difficult to achieve, and 3) natural conditions (i.e. temperature) are hard to control for optimal biodegradation. Ex situ bioremediation, in which contaminated soil is excavated and treated elsewhere, is an alternative.
BIOREMEDIATION (Basic’s) • Ex situ bioremediation approaches include use of bioreactors, landfarming, and biopiles. In the use of a bioreactor, contaminated soil is mixed with water and nutrients and the mixture is agitated by a mechanical bioreactor to stimulate action of microorganisms. This method is better-suited to clay soils than other methods and is generally a quick process. • Microorganisms have limits of tolerance for particular environmental conditions, as well as optimal conditions for optimum performance. Factors that affect success and rate of microbial biodegradation are nutrient availability (N, P, trace metal), moisture content, pH, oxygen level and temperature of the soil matrix. Inorganic nutrients including, but not limited to, nitrogen, and phosphorus are necessary for microbial activity and cell growth
BIOREMEDIATION (Basic’s) Environmental factor affecting bioremediation • Microbial population • Oxygen • Soil moisture • pH • Temperature • Nutrients • Toxicant in Waste
BIOREMEDIATION (1. Bioventing) Bioventing
BIOREMEDIATION (1. Bioventing)
BIOREMEDIATION (1. Bioventing) • Bioventing is an in-situ remediation technology that uses indigenous microorganisms to biodegrade organic constituents adsorbed to soils in the unsaturated zone. • In bioventing, the activity of the indigenous bacteria is enhanced by inducing air (or oxygen) flow into the unsaturated zone (using extraction or injection wells) and, if necessary, by adding nutrients.
BIOREMEDIATION (1. Bioventing) Bioventing system combine with Vapor Extraction
BIOREMEDIATION (1. Bioventing-System) • Air delivery from atmosphere to the soil above water table through injecting well. Air blower may be used to push air into the soil through injection wells. • Air flow through the soil, and the oxygen present in the air is used by microorganism. • When extraction wells are used for bioventing, the process is similar to soil vapor extraction (SVE). However, while SVE removes constituents primarily through volatilization, bioventing systems promote biodegradation of constituents and minimize volatilization (generally by using lower air flow rates than for SVE). • In practice, some degree of volatilization and biodegradation occurs when either SVE or bioventing is used. • Applicable for BTEX, PAH, some chlorinated aliphatic compounds (TCE) • High molecular weight and less volatile hydrocarbons like diesel, kerosene are better treatment by bioventing than SVE
BIOREMEDIATION (1. Bioventing-Initial Screening) An initial screening of bioventing effectiveness, which will allow you to quickly gauge whether bioventing is likely to be effective, moderately effective, or ineffective. These factors are: (a) The permeability of the petroleum contaminated soils. This will determine the rate at which oxygen can be supplied to the hydrocarbon-degrading microorganisms found in the subsurface. (b) The biodegradability of the petroleum constituents. This will determine both the rate at which and the degree to which the constituents will be metabolized by microorganisms.
BIOREMEDIATION (1. Bioventing-Initial Screening) A screening tool that may use as an initial assessment of the potential effectiveness of bioventing.
BIOREMEDIATION (1. Bioventing-Initial Screening)
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Detailed Evaluation Of Bioventing Effectiveness
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Site Characteristics Intrinsic Permeability • Intrinsic permeability is a measure of the ability of soils to transmit air and is the single most important factor in determining the effectiveness of bio-venting because it determines how much oxygen can be delivered (via extraction or injection) to the subsurface bacteria. • To degrade large amounts of petroleum hydrocarbons, a substantial bacterial population is required which, in turn, requires oxygen for both the metabolic process and the growth of the bacterial mass itself. Approximately 3 to 3½ pounds of oxygen are needed to degrade one pound of petroleum product.
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Site Characteristics Intrinsic Permeability…….cont. • Coarse-grained soils (e.g., sands) have higher intrinsic permeability than fine-grained soils (e.g., clays, silts). The ability of a soil to transmit air, which is of prime importance to bioventing, is reduced by the presence of soil water, which can block the soil pore and reduce air flow.
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Site Characteristics SoiI Structure And Stratification • Soil structure and stratification are important to bioventing because they affect how and where soil vapors will flow within the soil matrix when extracted or injected. • Structural characteristics such as microfracturing can result in higher permeabilities than expected for certain soils (e.g., clays). Increased flow will occur in the fractured but not in the unfractured media. • Stratification of soils with different permeabilities can dramatically increase the lateral flow of soil vapors in more permeable strata while reducing the soil vapor flow through less permeable strata. This preferential flow behavior can lead to ineffective or extended remedial times for less-permeable strata or to the possible spreading of contamination if injection wells are used.
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Site Characteristics Microbial Presence • Soil normally contains large numbers of diverse microorganisms including bacteria, algae, fungi and protozoa. In well aerated soils, which are most appropriate for bioventing, these organisms are generally aerobic. • Bacteria require a carbon source for cell growth and an energy source to sustain metabolic functions required for growth. • Microbes are classified by the carbon and TEA sources they use to carry out metabolic processes. Bacteria that use organic compounds (such as petroleum constituents and other naturally occurring organics) as their source of carbon are called heterotrophic; those that use inorganic carbon compounds such as carbon dioxide are called autotrophic.
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Site Characteristics Microbial Presence…….Cont. • For bioventing applications directed at petroleum products, bacteria that are both aerobic (or facultative) and heterotrophic are most important in the degradation process.
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Site Characteristics Soil pH • The optimum pH for bacterial growth is approximately 7; the acceptable range for soil pH in bioventing is between 6 and 8. Soils with pH values outside this range prior to bioventing will require pH adjustments during bioventing operations.
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Moisture Content • Bacteria require moist soil conditions for proper growth. Excessive soil moisture, however, reduces the availability of oxygen, which is also necessary for bacterial metabolic processes, by restricting the flow of air through soil pores. • The ideal range for soil moisture is between 40 and 85 percent of the water-holding capacity of the soil. • The capillary fringe usually extends from one to several feet above the elevation of the groundwater table. Moisture content of soils within the capillary fringe may be too high for effective bioventing. • Depression of the water table by groundwater pumping may be necessary to biovent soils within the capillary fringe.
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Soil Temperature • Bacterial growth rate is a function of temperature. Soil microbial activity has been shown to decrease significantly at temperatures below 10 °C and essentially to cease at 5 C. • Microbial activity of most bacteria important to petroleum hydrocarbon biodegradation also diminishes at temperatures greater than 45 °C. Nutrient Concentrations • Bacteria require inorganic nutrients such as ammonium and phosphate to support cell growth and sustain biodegradation processes. Nutrients may be available in sufficient quantities in the site soils but, more frequently, nutrients need to be added to soils to maintain bacterial populations.
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Nutrient Concentrations……..Cont. • A rough approximation of minimum nutrient requirements can be based on the stoichiometry of the overall biodegradation process: C-source + N-source + O2 + Minerals + Nutrients ---> Cell mass + CO2 + H2O + products • Different empirical formulas of bacterial cell mass have been proposed; the most widely accepted are C5H7O2N and C60H87O32N12P. • Using the empirical formulas for cell biomass and other assumptions, the carbon:nitrogen:phosphorus ratios necessary to enhance biodegradation fall in the range of 100:10:l to 100:1:0.5, depending on the constituents and bacteria involved in the biodegradation process.
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Depth To Groundwater • Bioventing is not appropriate for sites with groundwater tables located less than 3 feet below the land surface. Special considerations must be taken for sites with a groundwater table located less than 10 feet below the land surface because groundwater upwelling can occur within bioventing wells under vacuum pressures, potentially reducing or eliminating vacuum-induced soil vapor flow. • This potential problem is not encountered if injection wells are used instead of extraction wells to induce air flow.
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Constituent Characteristics Chemical Structure • The chemical structures of the constituents present in the soils proposed for treatment by bioventing are important for determining the rate at which biodegradation will occur. • Although nearly all constituents in petroleum products typically found at UST sites are biodegradable, the more complex the molecular structure of the constituent, the more difficult and less rapid is biological treatment. • Most low-molecular weight (nine carbon atoms or less) aliphatic and mono aromatic constituents are more easily biodegraded than higher-molecular-weight aliphatic or polyaromatic organic constituents.
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) • Evaluation of the chemical structure of the constituents proposed for reduction by bioventing at the site will allow you to determine which constituents will be the most difficult to degrade.
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Vapor Pressure • Vapor pressure is important in evaluating the extent to which constituents will be volatilized rather than biodegraded. • Constituents with vapor pressures higher than 0.5 mm Hg will likely be volatilized by the induced air stream before they biodegrade. • Constituents with vapor pressures lower than 0.5 mm Hg will not volatilize to a significant degree and can instead undergo in situ biodegradation by bacteria.
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Product Composition And Boiling Point • Boiling point is another measure of constituent volatility. • Nearly all petroleum-derived organic compounds are capable of biological degradation, although constituents of higher molecular weights and higher boiling points require longer periods of time to be degraded. • Products with boiling points of less than about 250 C to 300 C will volatilize to some extent and can be removed by a combination of volatilization and biodegradation in a bioventing system.
BIOREMEDIATION (1. Bioventing-Detail Evaluation ) Henry*s Law Constant • Another method of measuring the volatility of a constituent is by noting its Henry*s law constant. • Henry*s law constants for several common constituents found in petroleum products are shown in table. Constituents with Henry*s law constants of greater than100 atmospheres are generally considered volatile and are more likely to be volatilized rather than biodegraded.
BIOREMEDIATION (1. Bioventing-Component of Bioventing System) Necessary component of a Bio-venting System • Extraction Wells • Air Injection Wells • Vapor Pretreatment • Vapor Treatment • Nutrient Delivery System • Surface seals • Groundwater Pumps
BIOREMEDIATION (1. Bioventing-Component of Bioventing System) 1) Extraction Wells Vapor treatment Nutrient
BIOREMEDIATION (1. Bioventing-Component of Bioventing System) 1) Extraction Wells i) Well Orientation • A bio-venting system can use either vertical or horizontal extraction wells. Orientation of the wells should be based on site-specific needs and conditions.
BIOREMEDIATION (1. Bioventing-Component of Bioventing System) ii) Well Placement and Number of Wells • The number and location of extraction wells can be determined by using several methods. a) In the first method, divide the area of the site requiring treatment by the area corresponding to the design ROI of a single well to obtain the total number of wells needed. Then space the wells evenly within the treatment area to provide areal coverage so that the areas of influence cover the entire area of contamination. Π (ROI)2 Area of influence for single extraction well = Treatment area (m2) Number of wells needed = Area of influence for single extraction well (m2/well)
BIOREMEDIATION (1. Bioventing-Component of Bioventing System) Extraction Walls-ROI of Bioventing system • The ROI is the radial distance from an extraction well that has adequate air flow for effective removal of contaminants when a vacuum is applied to the extraction well.
BIOREMEDIATION (1. Bioventing-Component of Bioventing System) Question 1 • area of 1000 ft x 100 ft area of paddy field was contaminated. The expert evaluation shows a maximum 10 ft depth was affected. Assuming radius of influence (ROI) as 50 ft. Calculate no of wells required Π (ROI)2 Area of influence for single extraction well = Treatment area (m2) Number of wells needed = Area of influence for single extraction well (m2/well)
BIOREMEDIATION (1. Bioventing-Component of Bioventing System) b) In the second method, determine the total extraction flow rate needed to exchange the soil pore volume within the treatment area in a reasonable amount of time (3 to 7 days). Determine the number of wells required by dividing the total extraction flow rate needed by the flow rate achievable with a single well. (µV/t)/q Number of well needed = µ = soil porosity (m3 vapor/m3 soil) V = volume of soil in treatment area (m3 soil) q = vapor extraction rate from single extraction well t = time for exchange pore volume (hr) In the example below, an 7 d exchange time is used, Number of well needed = m3 vapor m3 soil m3 soil 168 h m3 vapor h
BIOREMEDIATION (1. Bioventing-Component of Bioventing System) Question 2 Reasonable amount of time (3 to 7 days). Determine the number of wells required ? (µV/t)/q Number of well needed = µ = soil porosity (52 m3 vapor/m3 soil) V = volume of soil in treatment area (1,000,000m3 soil) q = 7853.53m3 /well -Vapor extraction rate from single extraction well t = time for exchange pore volume (168hr) In the example below, an 7 d exchange time is used, Number of well needed = m3 vapor m3 soil m3 soil 168 h m3 vapor h
BIOREMEDIATION (1. Bioventing-Component of Bioventing System) • Consider the following additional factor in determining well spacing: - use closer spacing in areas of high contaminant concentration to increase oxygen flow and accelerate biodegradation rate - at sites with stratified soils, wells that are screened in strata with low intrinsic permeabilites should be spaced more closely than wells that screened in strata with higher intrinsic permeabilities - if surface seal exists or is planned for the design, space the well slightly farther apart. A surface seal increase the ROI by forcing air to be drawn from a greater distance by preventing short-circuiting from land surface. However, passive vent wells or injecting wells may be required to supplement flow of air in the subsurface