BIOREMEDIATION ENGINEERING STRATEGIES FOR BIOREMEDIATION

DR. N. BANUASSOCIATE PROFESSORVELS UNIVERSITYBIOREMEDIATION

BIOREMEDIATIONENGINEERING STRATEGIES FOR BIOREMEDIATIONSite characterization:The chemical nature of contaminationThe geohydrochemical properties andThe biodegradation potential for the site.Pollutant characterization:composition, conc., toxicity, bioavailability, solubility, sorption and volatilization.Geohydrochemical characterization:Physical and chemical properties of the geological material.geohydrological conditions of the siteDirection and velocity direction of the underground flow.

ENGINEERING STRATEGIES FOR BIOREMEDIATIONMIROBIOLOGICAL CHARACTERIZATIONDegradative capacity of microbial flora and native flora.SUITABILITY OF THE SITE FOR BIOTREATABILITY TESTS:To know its specific requirements.Biotreatability:performed at mesocosm level, trying to maintain the environmental conditions that will prevail during treatment in the field.

BIOTREATABILITYShallow strata: Large trays or jars to hold several pounds of soil could be used.Maintenance of humidity and homogenity.Uniform micribial activity throughout the soil volume.Watertable: columns packed with contaminated soil.Necessary to determine the ground water flow rate to define the operating mechanism of the columns.

ENGINEERING STRATEGIES FOR BIOREMEDIATIONBioaugmentation:When the microbial population will degradative potential is limited or practically zero, the addition of exogenous microorganisms is necessary.Alternative methods:1. addition of commercial compound lease success.2. isolation of few degradative microbe during site characterizatin and promote its growth to obtain pure culture and used as inoculum. Require longer time to increase the microbial biomass.

ENGINEERING STRATEGIES FOR BIOREMEDIATIONPurpose of biotreatability:To predict the behaviour of the processTo determine the nutritional requirement for the microorganisms to perform biodegradation.Measures:1. Oxygen consumption2. CO2 generated3. Exhaustion of added nutrients (N and P)4. Contaminant removal.

From laboratory to fieldBioavailabilityThe concept of bioreactorThe supply of oxygenMass transfer

BioavailabilityFor biotransformation, the contaminants to be made ready for attack by microorganisms.Enzymatic reactions occur in water.But pollutans are insoluble in water e.g. HydrocarbonSurfactant are incorporated to the medium and improve the bioavailability.Surfactant act by solubilizing organic contaminants in the aqueous medium thus making accessible to the enzymes of microbe.

The concept of bioreactorPollutant present in shallow soil layersBiopile The contaminated materials is piled on the ground surfaceBiocell excavation in a clean site to deposit the material for further treatment.If the contaminants reached water table:The bioreactor built through bore-holes

Oxygen supplyMany Degradative process anaerobic.Aerobic complete mineralization.Sources of carbon lack of oxygen oxygen demand for their degradation are higher.

Mass transferHomogeneity of the system. The same microenvironmental conditions exist to promote microbial activity.Nutrient conc., humidity, pH and conc. of oxygen.

Types of bioremediationIn situ bioremediation:Microbes are responsible for the stabilization and treatment of waste products containing organic matter.Limiting factors:They require min. oxygen and Available nutrients.

Intrinsic In situ bioremediationRelies on naturally occurring supplies of e- acceptors, nutrients and other necessary materials to develop a biologically active zone (BAZ) and prevent the migration of contaminants away from the source.It doesnot accelerate the rate of cleanup.No engineering principles involved.Long term monitoring of site is necessary.Well suited for ground water with high e- acceptors and adequate conc. of nutrients.

Engineered in situ bioremediationUsed to speed up the process of contaminant removal from the solid phase.Increased inputs of stimulating materials.The ideal site :1. the hydraulic conductivity is relatively homogenous, isotrophic and large.2. residual conc. are not excessive.3. contamination is in shallow, thus minimize the cost of drilling and sampling.

Engineered in situ bioremediationTypes:BioventingBiosparging/ Air spargingBioaugmentation/ stimulation

BioventingIncreased oxygen supply with vapour extraction.A vacuum is applied at some depth in the contaminated soil.This draws any volatile organic compound.Supplementation with nutrients.Increased o2 favours aerobes and faster the reaction.Effective for volatitle compounds.

Biosparging/ Air spargingTo increase the biological activity of soil by increasing the supply of oxygen by sparging air or oxygen into the soil.Supply of Hydrogen Peroxide toxic at low conc. to microbe.Success depends on the structure of the soil.

Bioaugmentation/ stimulationStimulation of the degradative activities of endogenous microbes by the provision of nutrients or external electrons or by the introduction of competent, exogenous microbes with or without nutritional enrichment.Bioaugmentation failures:Limited population of microbes.Conc. of contaminant is not sufficient to support growth.Environment may contain substances that inhibit growth.Predation by protozoa.Microbe use some other substrate in the environment.Microbe my not be able to penetrate the soil and get the contaminant.

Bioaugmentation/ stimulationExamples:Bacteria Methlosinus trichosporium (degrades TCE)Fungi Absidia cylindrospora degrade fluorene.Cladophialophora sp. degrades BTEX.

Ex-situ bioremediation techniquesContaminated soils can be excavated and treated in above ground or ex situ.Solid phase systemLand FarmingCompost heapsEngineered biopilesSlurry phase systemAerated lagoonslow-shear airlift reactorfluidized bed soil reactor

Ex-situ bioremediation techniquesSolid phase systems:It includes organic wastes(leaves, animal manures and agricultural wastes)and problematic wastes (domestic and industrial wastes, sewage sludge and municipal solid wastes)Land farming:Simplest processMixing of the soil by ploughing or mechanical tilling.This increases the o2 level in the soil and distributes the contaminants more evenly, which increases the rate of degradation.Well suited for shallow soil surface contamination.Average half-life for degradation of diesel fuel and heavy oil is 54 days.

Ex-situ bioremediation techniquesCompost heap:Compost materials like straw, bark and wood chips are mixed with the contaminated soil. Piled into heap to maintain the water, air holding capacity.This process increases temp. to 60C and favours thermophiles.Useful for highly contaminated sites.E.g. TNT Phanerochate chrysosporium.RDX Pseudomonas fluorescnes, P. aeruginosa.

Ex-situ bioremediation techniquesEngineered biopiles:Piling up of contaminated soil within a lined area to prevent leaching.The piles are covered with polythene and liquid nutrients applied to surface.Aeration is supplied via network of pipes inserted in the piles.Leachate collected by pipes at the base.Useful for limited space.

Slurry phase bioremediationContaminated solid material, microbe and water formulated into slurry and brought to a bioractor.It is a triphasic system:Water; suspended paniuculate matter; air.Aerated lagoons; low-shear airlift ractor and fluidized bed soil reactor.Best for pesticides, petroleum hydrocarbons, pcp, polychlorophenol, pcbs, coal tars, wood preserving wastes and so on.

Factors affecting slurry phase bioremediationpH opt. 5.5 8.5Moisture contentTemp. 20 30 cO2AgingMixing (mechanical and air mixing)Nutrients (N, P and micro)Microbial populationsReactor operation.