Bioremediation Techniques Quiz

Environmental Biotechnology

• Bioremediation is a technology using living organisms to detoxify pollutants in soil and water.
• Bioremediation is preferably done in situ (in the contaminated environment), but can also be ex-situ.
• Bioremediation can involve processes such as biodegradation, biotransformation and mineralization.
• Traditional remediation techniques often are not cost-effective and require thorough understanding of microorganisms, their reaction to the environment, and proper implementation.

Terminology

• Depollution: the complete or partial elimination of a pollutant using physical, chemical or biological agents
• Biodegradation: the partial or complete breakdown of a substance by biological agents
• Biotransformation: transformation of a substance by biological agents (incomplete metabolism)
• Biostimulation: stimulation of native microflora by adding nutrients and controlling physico-chemical factors (pH, temperature, humidity, oxygen)
• Bioaugmentation: controlled addition of specific microorganisms to assist native microorganism
• Bioreduction: reduction of oxidized compounds (e.g., nitrates, metal oxides) through biological means
• Biolixiviation: extraction of metals from sludge, soil, sediment, mineral by solubilization induced by microorganisms
• Biofixation/biosorption: The fixation of pollutants (most commonly metals) found in a liquid effluent to microorganisms
• Xenobiotics: synthetic compounds created by humans, not naturally occurring
• Phytoremediation: The use of plants to decontaminate soil and water, extracting heavy metals or other contaminants
• Phytotransformation: Uptake of contaminants in soil/water and transformation by plants
• Phytostabilization: Preventing contaminant mobility via plant roots/structures
• Phytoextraction: Plants accumulating contaminants in their parts, harvestable material

Bioremediation Techniques

• Ex situ: Bioventing, land farming, biosparging, compositing, biopiles, bioaugmentation, bioreactors, phytoremediation
• In situ: Bioventing, land farming, biosparging, compost

Bioventing

• A common in situ treatment where air/nutrients are supplied via wells, stimulating the native bacteria to biodegrade
• Low air flow rates are employed
• Minimizes contaminants released into atmosphere

Biosparging

• Air is injected under pressure beneath the water table
• Enhances groundwater oxygen concentrations, encouraging biological degradation
• Promotes mixing in the saturated zone

Biostimulation

• Involves supplying oxygen and nutrients to stimulate naturally occurring bacteria
• Effective treatment for soil and groundwater environments

Bioaugmentation

• Utilizes the addition of microorganisms (indigenous or exogenous) to contaminated sites to enhance bioremediation
• Limitations: non-indigenous cultures may not compete well or create stable populations, most soils have indigenous microbes capable of effectively degrading waste.

Land Farming

• Contaminated soil is excavated, spread and tilled until the pollutants are degraded
• Aims to stimulate indigenous microorganisms to aerobically degrade contaminants

Composting

• Combines contaminated soil with non-hazardous organic amendments (like manure) to cultivate a rich microbial population, characterized by elevated temperatures.

Biopiles

• Hybrid of landfarming and composting
• Engineered cells for aerated and composted piles
• Effective treatment for soils contaminated by hydrocarbons (refined version of landfarming)

Bioreactors (Slurry Reactors)

• Ex-situ method
• Processes contaminated soil, sediments, sludge, or water in a controlled system.
• Creates a three-phase mixing environment (solid, liquid, gas) to accelerate rates of remediation
• Utilizes water slurry, indigenous microbes, to degrade pollutants

Phytoremediation

• Use of plants to remove or stabilize contaminants
• Plants grow in polluted soil, enabling them to extract contaminants from the soil or up into the stem/leaves
• Harvested plant material can be removed and disposed of or burned

Biolixiviation (Metal Recovery)

• Bacteria extract metallic elements from minerals by solubilizing them.
• Used for low-grade minerals
• Microorganisms are autotrophic (use CO2) or heterotrophic (use organic carbon)
• Examples of Used Microorganisms: Thiobacillus ferrooxidans, Leptospirillium ferrooxidans, Thiobacillus thiooxidans, Sulfobacillus thermosulfidooxidans

Biosorption

• General term for processes recovering metals using biomass
• Employs raw biomass material for sorption, performance depends on biomass type and solution chemistry
• Modifiable biosorbents can enhance sorption capacity

Types of Biosorbents

• Algae, bacteria, fungi, yeasts, and plants

Mechanisms of Biosorption

• Physical interactions like electrostatic attractions, complexation, precipitation, or covalent bonds
• Redox reactions by functional groups in the biomass (e.g., carboxyl, hydroxyl, phosphate)

Biosorption by Algae

• Algae contain high quantities of biopolymers with good metal adsorption capabilities
• Wide variety of algae types (red, brown, green)
• Contains polysaccharides (cellulose, xylan), uronic acids (alginate acids), sulfated polysaccharides (agarose, agaropectin, carrageenan), carboxyl, sulfonic, and hydroxyl groups
• Alginate comprises a significant portion of the dried algae and is important in metal adsorption

Biosorption by Fungi and Yeasts

• Fungi and Yeasts contain chitin (essential component of cell walls)
• Utilizes chitin synthase activity

Biosorption with Bacteria

• Active Biosorption: Metal-bacteria interactions (living/active cells), includes precipitation, intracellular accumulation, oxidation-reduction, and methylation-demethylation processes
• Passive Biosorption: Physical interactions and reactions, includes complexation and sorption onto the bacterial cell wall

Bacteria

• Reactive surfaces with sorption sites
• Neutral pH, net negative charge
• Cell wall components (Gram (+): peptidoglycan, Gram (-): outer membrane rich in hydroxyls, carboxyls, phosphates, and amines)

Factors Influencing Biosorption

• Medium physicochemical properties (pH, temperature, ionic strength, dissolved oxygen, other metallic cations, ligands)
• The Metal: size to charge ratio, ionic radius, valence, metal speciation, concentration, solubility
• The Nature of Biosorbent: composition, concentration

Microbial Sulfate Reduction

• Primary process under anaerobic conditions, involving several bacteria like Desulfotomaculum
• Processes under strictly anaerobic conditions
• Neutrophillic, Optimal pH around 7
• Requires electron donors (e.g., lactate, formate, acetate, or H2)
• Performs complete or incomplete substrate oxidation
• Forms hydrogen sulfide, facilitating metal precipitation via insoluble solid production

Precipitation of Metals as Sulfides

• Metal precipitation depends on stability of formed solid
• FeS is generally more stable than MnS

Intracellular Accumulation

• Metals are initially combined with the cell wall
• Then transported inside the cell

Iron Oxidation-Reduction

• Alters the oxidation state
• Solubilizes Fe(II), oxidizes to Fe(III, more soluble form)
• Microbial reduction of Fe (III) contributes to the formation of Fe (II) phosphates

Phytoextraction

• Hyperaccumulators absorb contaminants through roots, concentrate in leaves, etc.
• Harvested material is removed from the environment

Phytotransformation

• The uptake of organic contaminants from soil, sediments, or water, and subsequent transformation to a more stable/less toxic/mobile form.
• Examples include reduction of chromium from hexavalent to trivalent.

Phytostabilization

• Plants reduce mobility and migration of contaminated soil
• Leachable constituents are adsorbed and bound into the plant structure
• Plants form a stable mass that prevents contaminants re-entering the environment

Phytodegradation

• Breakdown of contaminants within the rhizosphere
• Primarily due to proteins and enzymes from plants or soil organisms (e.g., bacteria, yeast, fungi)
• Plants provide nutrients to microbes for growth, microbes offer healthier soil environment.

Rhizofiltration

• Water remediation technique using plant roots to uptake contaminants.
• Used to reduce contamination in wetlands and estuary areas

Limitations of Bioremediation

• Contaminant type & concentration
• Environmental conditions (soil type, proximity of groundwater)
• Nature of organism
• Cost-benefit ratios (cost vs environmental impact)
• Applicability (not all surface areas are suitable)
• Length of time for the bioremediation process

Advantages of Bioremediation

• Minimal exposure to the contaminant for workers
• Long term benefit for preventing public health issues
• Cost effective compared to other methods
• Onsite process, no need to transport materials
• Uses natural processes
• Perform degradation in an acceptable time frame

Disadvantages of Bioremediation

• Cost overruns
• Failure to meet targets
• Poor management
• Environmental impact
• Release of contaminants
• Difficult to estimate completion times and varies by site.

Pollutants in Soil and Aquatic Bioremediation

• Organic compounds (hydrocarbons, pesticides, insecticides, herbicides, fungicides, organometallics, etc.)
• Metals (Essential: small amounts; non-essential: heavy metals in trace amounts in biosphere)

Biodegradation

• Complete oxidation or mineralization
• Complete biodegradation: decomposition, basic elements
• Partial biodegradation: formation of less complex intermediates
• Biotransformation: transformation into a stable molecule

Factors Affecting Biodegradation

• Biological factors (microorganism growth, metabolism, acclimatization, growth kinetics)
• Environmental factors (physical conditions, chemical factors, sorption, bioavailability)
• Chemical factors (structure, function, sorption, bioavailability, cometabolism, recalcitrance, toxicity)

Factors Affecting Bioremediation

• Factors governing microbial activity (redox potential, pH, temperature, water content, nutrients)
• Factors governing mobility (Macroscopic Heterogeneities: faults, fractures, stratification, soil structure, soil texture, Adsorption and desorption factors [including clay and organic matter])

Lack of Biodegradation

• Lack of nutrients
• Limiting environmental conditions (temperature, humidity, oxygen)
• Presence of toxic substances at high concentrations.
• Compounds present at low concentrations
• Non-bioavailable compounds
• Issues with bioavailability (sorption, presence in non-aqueous solution, pollutants' state, complexity, solubility)

Recalcitrant Pollutants

• Compounds slow or impossible to eliminate biologically
• Examples: polymers (PVC, Teflon), polychlorinated organic compounds (PCB, DDT), pentachlorophenol
• Resistance to microbial degradation, frequently encountered in natural substances like lignin, humic acids.

Classification of Recalcitrant Compounds

• Compounds resistant to microbial attack, metabolized very slowly or not at all
• Compounds rapidly degraded in dense cultures of specific microbes.

Conditions for Biodegradation

• Enzyme for substrate degradation must exist
• Microbes capable of using/producing the enzyme must be present in the same environment
• Molecule to be degraded must be available to the microbes
• Substrate must penetrate the microbes cell membrane
• Enzyme induction conditions (sufficient substrate concentration or presence of another substrate allowing cometabolism) must be met.
• Favorable environmental conditions for microbial growth

Half-Life and Persistence of Pollutants

• Time required for the biodegradation of 50% of the pollutant
• Depends on pollutant properties, environmental conditions (aerobic/anaerobic conditions, microbial activity, temperature, pH)

Microbial Depollution Mechanisms: Degradation

• Degradation: Breakdown of substrate, e.g., H2O, CO2, CH4, H2, chloride, acetate.
• Mineralization: Assimilation of substrate, e.g., CO2

Microbial Depollution Mechanisms: Cometabolism

• Unexpected conversions due to low enzyme specificity.
• Substrate may not trigger enzyme synthesis unless present in sufficient quantities to activate the appropriate enzymes
• Substrate conversion may lead to unusable compounds
• Degradation of a xenobiotic may require reduction reactions, where electrons must come from another substrate.

Detoxifying Transformations

• Modifications to molecules to make them inactive, may be minor or significant
• Examples provided (e.g., hydrolysis, hydroxylation, dehalogenation, demethylation, methylation, reduction of a NO2 function, etc., to remove halogen, converting nitrile to amide, opening benzene rings)

Metabolism of Decomposers

• Food particles transported to surface and adsorbed onto cell membrane via diffusion.
• Pre-digestion of food particles facilitated by exoenzymes or surface enzymes.
• Molecules’ dimensions reduced.
• Permeation of food molecules across the cell membrane.
• Degradation of molecules

Cometabolism of TCE (Trichloroethylene)

• Breakdown of TCE through a multi-step process, facilitated by a specific methane mono-oxygenase in the presence of methane.

Aromatic Hydrocarbons

• BTEX: Benzene, Toluene, Ethylbenzene, and Xylenes.
• PAHs: Polycyclic aromatic hydrocarbons (more than two fused aromatic rings).
• Biodegradation of aromatic compounds (2 main steps): Hydroxylation (incorporation of hydroxyl ion, reaction catalyzed by monooxygenase/dioxygenase), and cleavage of aromatic ring (catechol is cleaved by dioxygenase).
• The hydroxylations are initial reactions in metabolism, with oxygenases.

Oxygenases

• Involved in initial hydroxylations of aromatic rings
• Divided into 2 groups
• 1-Hydroxylation group: these enzymes add one oxygen atom to the substrate while reducing a second oxygen atom to water
• 2-Dioxygenase group: these oxygenases add two oxygen atoms without reduction to water.
• Examples include the hydroxylation of benzoic acid and to catechol

Ortho and Meta Cleavage

• Important reactions in the degradation of catechol and protocatechuic acid.
• Lead to the formation of other necessary molecules, eventually breaking down and releasing carbon elements to be used in the Krebs cycle.

Aromatic Compound Biodegration of Benzene

• Benzene's hydroxylation to catechol and subsequent cleavage are important steps in aerobic degradation.

Dehalogenation mechanisms of Haloaromatic Compounds

• Oxidative, Hydroxylating, Reductive dehalogenation

Polyaromatic Hydrocarbons (PAHs)

• Multiple associated rings, often resistant to biodegradation, significant environmental issues
• Produced through combustion of fossil fuels or natural processes (e.g., decomposition of lignin)

Factors Affecting PAH Degradation

• Number of rings
• Number/position of Substituents
• Degree of Saturation

Insecticides

• Example: DDT and analogues
• DDT analogues result from degradation
• A major reaction involves intermediates like DDE

Organophosphorus Compounds

• These compounds include common insecticides (malathion, parathion) that are less persistent compared to organochlorines.
• Metabolized by bacteria like Pseudomonas, Arthrobacter, Streptomyces, Thiobacillus and fungi (Trichoderma).
• Several degradation products.

Test your knowledge on bioremediation techniques, including the role of biopiles, types of reactors, and the processes involved in phytoremediation. This quiz covers essential concepts related to the degradation of aromatic compounds and the effectiveness of biotechnological solutions. Challenge yourself and see how well you understand these critical environmental processes.