Bioreactors and Bioremediation

Introduction to Bioremediation

• "Remediate" means to solve a problem, and "bioremediate" uses biological organisms to fix environmental issues like contaminated soil or water.
• Bioremediation is a cost-effective and permanent method for cleaning up xenobiotic compound-contaminated soil.
• Key aspects for considering a bioremediation approach include microbial systems, the type of contaminant, and the geological/chemical conditions of the contaminated site.

Definition of Bioremediation

• Bioremediation is the use of biological systems to destroy or reduce hazardous waste from contaminated areas.
• The American Academy of Microbiology defines bioremediation as using living organisms to reduce or remove environmental hazards caused by toxic chemicals and other harmful waste.
• It can also be defined as complete removal of pollutants and their toxicity through microbial metabolic reactions.
• Bioremediation involves manipulating living organisms to create the desired environmental changes in a controlled setting.

How Bioremediation Works

• The waste material is examined, and specific bacteria are isolated based on their ability to break down and convert the waste.
• These bacteria undergo testing to ensure safety and suitability for the specific waste.
• Selected bacteria are then introduced into the contaminated environment at high concentrations.
• Bacteria thrive and act as natural digestive agents converting waste into carbon dioxide and water.
• Finally, the bacteria naturally die off.

Basis of Bioremediation

• Bioremediation relies on microbial metabolism.
• Xenobiotics (foreign substances) can serve as substrates for microbial growth and energy if they are metabolized and broken down.
• If a xenobiotic is added to the soil, the microbial population grows.
• Specialized microorganisms that degrade the xenobiotic can be isolated via enrichment culture.

Advantages of Bioremediation

• Can be done on site, minimizing disruption to the environment.
• Often less expensive than other cleanup methods because it doesn't require extensive transportation of materials.
• No long-term liabilities for transportation or disposal of chemicals.
• Employs biological systems that are safer and less disruptive.
• Can be combined with other treatment methods.
• Can treat large volumes of soil.
• This method is viewed as natural, so it is often readily accepted by the public.

Disadvantages of Bioremediation

• Some chemical compounds are not biodegradable.
• Extensive monitoring is often required to observe changes and ensure the process effectiveness.
• Each contaminated site has unique requirements, necessitating site-specific analysis and consideration.
• Toxic byproducts may be formed during the degradation process, requiring further testing and assessment.
• Strong scientific support is often needed to ensure that the intended effect is achieved and properly monitored.
• Complex types of waste may inhibit the biological activity of the organisms.

Principles/Types of Bioremediation

• Bioremediation explores microbes' genetic diversity and metabolic abilities to break down contaminants into less harmful products.
• Selecting the correct bioremediation system depends on the contaminant and requires a multidisciplinary approach.
• Specialists in chemistry, microbiology, geology, and environmental engineering are needed.
• There are various treatment technologies for bioremediation.

Biodegradation

• Biodegradation is achieved using living organisms like bacteria or fungi. These organisms can be indigenous to the site or introduced.

Biostimulation

• Biostimulation involves enhancing the existing microbial population in the environment by adding nutrients.

Bioaugmentation

• Bioaugmentation involves introducing specific microbes to accelerate degradation of contaminants.

Biorestoration

• Biorestoration aims to restore the environment to its original or near original condition using living microbes.

Bioattenuation

• Bioattenuation is a method of monitoring environmental contaminant reduction over time.

Bioventing

• Bioventing involves introducing air to contaminated soil to stimulate aerobic microbial activity. This is used when air and oxygen are needed to encourage microbial growth.

Biomineralization

• This method uses microbial processes and interactions to precipitate heavy metals.

Bacteria Used in Bioremediation

• A number of bacteria types are listed. (See document for specifics)

Essential Characteristics of Microbes for Bioremediation

• Microbes with the ability to degrade target compounds are crucial.
• Accessible substrates in the environment as energy and carbon sources.
• Inducers that stimulate development of enzymes to break down specific compounds.
• Appropriate electron acceptor-doner systems.
• Optimal moisture and pH for microbial growth
• Adequate nutrients to support the microbes and their enzyme production.
• Optimal temperature and lack of toxic substances.
• Ideal conditions to reduce competing organisms.

Characterization of Essential Factors for Bioremediation

• Contaminated sites need assessment for chemical, geohydrochemical, and biodegradative factors to ensure successful bioremediation.

Site Characterization for Bioremediation

• Essential factors to assess site for effectiveness of bioremediation. Includes information on pollutants (composition, concentration, toxicity, bioavailability, solubility, sorption, and volatilization), hydrogeochemical properties (geological properties, hydraulic conductivity, heterogeneity, flow directions and rates, nutrients, electron acceptors, pH, and temperature), and microbial characterization of properties (specific catabolic population size and activities)

Bioremediation Mechanisms:

• Methods for accomplishing bioremediation include biosorption, bioaccumulation, precipitation, reduction, and solubilization.

Biosorption

• Biosorption involves sequestration of chemicals (often heavy metals) by materials of biological origin (e.g., certain microbes and seaweed).
• Biomaterials act as "magic granules" to concentrate and remove heavy metals, especially from industrial waste.
• Some examples of biomass types are waste byproducts of large-scale, industrial fermentations (e.g., Rhizopus, Bacillus subtiliss) as well as brown seaweeds (e.g., Sargassum, Ecklonia).

Threat from the Environment

• Dissolved metals, especially heavy metals escaping into the environment, pose a serious health risk.
• They build up in living tissues within the food chain.
• Control of metal emissions into the environment is necessary to prevent issues from potentially toxic metals.

Ranking of Risks

• Metals by risk level are included in a table.

Physical Adsorption

• Physical adsorption of contaminants is achieved by electrostatic forces between microbes and the contaminant.
• Microbes can utilize physical adsorption to remove metal ions from the surrounding environment, holding them to the cell surface.

Ion Exchange

• Various mechanisms for biosorption, including ion exchange, are involved.

Chelation

• Chelation is a molecular process where metal ions bind with organic molecules to protect the mineral from unfavorable chemical reactions in the environment.
• Certain organic molecules (ligands) form ring structures that prevent the metal ions from participating in unwanted reactions.
• Examples of chelating agents in the natural environment include carbonate and oxalate ions.

Coordination (Complex Formation)

• Metals may be removed from a solution by complex formation with organic molecules on a microbial cell surface, removing the threat of toxicity from the solution.
• Chelation of metal compounds occurs, reducing the toxicity and mobility of contaminants in solution.
• Organic acids such as citric, oxalic, gluonic, fumaric, lactic and malic acids participate in chelating metals, supporting solubilization of these compounds and increasing the release of metals from the surfaces.

Organisms for Biosorption of Toxic Metals

• Numerous microorganisms absorb toxic heavy metals. The types of specific microorganisms and metal types are listed in a table.

Advantages of Biosorption

• The advantage of biosorption for bioremediation is highlighted. This technology competes effectively with existing technologies, its performance is competitive, it is selective for specific heavy metals, is cost-effective, and leaves no sludge.

Bioaccumulation

• Bioaccumulation is the buildup of foreign substances in an organism at a rate that exceeds the rate of loss of the substance from the organism.
• Substances bioaccumulate more readily by increasing duration of exposure, rising substance uptake rates, and reducing the rate of substance removal.
• Lipid-soluble compounds are more likely to accumulate in organisms since they can more readily build up in fatty tissues

Bioaccumulation Examples

• Tetraethyl lead (found in leaded petrol) and DDT are examples of lipid-soluble substances in the environment that bioaccumulate.
• The accumulation of the chemical is stored in fatty tissues and released when those tissues are used for energy. This may result in acute poisoning.

Precipitation

• Precipitation involves contaminants reacting with microbial metabolic products to yield insoluble derivatives (precipitates).
• Sulphides and phosphates are common precipitating agents in microbes.
• This is often important for the remediation of acidic metals.

Reduction

• Microbes can perform reduction of inorganic anions, such as the reduction of nitrate (NO3), sulfate (SO4) and carbonation (CO3) to achieve a lower oxidation state of the element (e.g., Mn(IV) to Mn(II))
• The reduction of the metal element commonly results in a lowering of toxicity, increased water solubility, and increased mobility of the element.

Metabolic Process in Bioremediation

• Microorganisms are essential components of bioremediation, functioning as catalysts and producing energy for further microbial synthesis.
• Bioremediation metabolic steps are categorized based on the type of electron acceptor.

Respiration

• Respiration can be aerobic or anaerobic, depending on whether oxygen is present.
• Inorganic electron acceptors such as oxygen, nitrate or sulfate can be present during this process.

Fermentations

• Fermentation utilizes organic electron acceptors when the environment lacks an inorganic electron acceptor.

Strategies for Improvement of Bioremediation Techniques

• Supplemental oxygen, using pumps and treatments, or alternative electron acceptors such as nitrates or sulfates help improve microbial bioactivity and improve the process rates.
• The composition of microbial communities can influence the process.
• Organisms sensitive to water content are utilized for specific applications to maximize activity rates.

Biomass Immobilization and Bioremediation

• Immobilizing microbes enhances their utilization in waste water treatments.
• Immobilization involves confining, or sequestering, whole cells in a solid phase, which allows for controlled movement of solutes (nutrients) to and from the microbes, controlling the reaction but not isolating the cells.

Substances for Immobilization

• A variety of materials including polyacrylamide, alginate and silica, as well as natural materials (agar, agarose, carrageenan, and diatomaceous earth) are used for immobilization.
• Synthetic materials (e.g., polyurethane, polyvinyl foams, polyacrylamide, ceramics, epoxy resin, and glass beads) are a wide variety of options.

Cell Immobilization Methods and Techniques

• Immobilization methods for cells are primarily physical or chemical, depending on binding method.

Cell Immobilization Techniques

• Some techniques include physical immobilization, chemical immobilization, gelation, polymerization, and insolubilization methods.

Applications of Immobilized Cells

• Immobilized cells are applied in multiple ways, including the pharmaceutical, food and dairy industries, waste water treatment, and for synthesis of various chemicals.

List of Immobilized Microbes

• A list of microbial organisms are used in bioremediation processes and types of substrate used for immobilization are shown.

Bioremediation Techniques (Methods)

• Bioremediation methods encompass in situ (on-site) and ex situ (off-site).

Techniques in Bioremediation

• Bioremediation methods include in situ methods such as bioventing, biostimulation and bioaugmentation and ex situ methods including land farming, composting, and biopiles

In situ Treatment

• Bioremediation occurring at the same location is an on-site treatment, involving the direct contact of microbes with contaminants for decomposition.
• This method is highlighted as a valuable technique for various environmental contaminant degradation projects

Bioventing

• Uses air injection to introduce oxygen into the subsurface, enhancing aerobic biodegradation of soil and groundwater contaminants such as VOCs and SVOCs.

Biostimulation

• Adds nutrients to stimulate the growth of existing microbes and improve contaminant degradation. The nutrients involved include nitrogen and phosphorus.
• Microbes existing at the contaminated site can be encouraged to breakdown contaminants with nutrient additions.

Bioaugmentation

• Adds microbes to the targeted area to improve degradation effectiveness if indigenous microbes are insufficient or ineffective.

Air Sparging

• A method to increase volatilization and gas phase removal of contaminants by injecting air. This process is a phase transfer process of hydrocarbons that converts contaminants from the liquid phase into a gas or vapor phase.

Advantages In Situ Bioremediation:

• Minimal disruption to the site (less environmental harm).
• Minimizes exposure to the public.
• Typically lower cost than other remediation methods.
• Disadvantages of in situ Bioremediation:
• It is a time-consuming method.
• Conditions change constantly, which impacts effectiveness.
• Problematic to distribute/apply additives such as nutrients, surfactants or supplemental oxygen.
• Effective only when waste materials provide energy and nutrients to support existing microorganisms properly.

Ex situ Bioremediation

• The process of removing a contaminated medium and treating it elsewhere.

Solid-Phase Systems

• Methods such as land farming, composting and biopiling can be used for bioremediation, particularly for contaminated solid materials.

Composting

• Mixing contaminated soil with other organic materials and introducing microorganisms to enhance microbial activity to digest the waste, improving the situation within the pile.

Biopiles

• An advancement in techniques. Contaminated soil is layered in a pile, creating oxygen conditions for microbial growth and enhancing a decomposition process. This method helps reduce the spread of contaminants.

Slurry Phase System

• Mixing the contaminated materials (soil, degraded sediments) with water and microbes in a bioreactor (fermenter)

Bioreactor

• A vessel in which microbial processes can occur; can be monitored (and adjusted as needed) and modelled to optimize degradation rates.
• This application provides control over elements like temperature, pH, nutrients, oxygen to help maximize efficacy and efficiency

Aerated Lagoons

• Used for treating municipal wastewater.
• Provides nutrients, and oxygen via surface aerators, promotes microbial growth effectively and treats the contaminated slurry.

Low Shear Airlift Reactors (LSARs)

• Useful for treating wastewater that includes volatile components.
• Constructed in cylindrical designs, often containing stainless steel.
• Process conditions (pH, temperature, nutrient additions) can be monitored and adjusted.
• Includes a shaft system that helps facilitate mixing and prevent settling of larger solids.
• Air diffusers can be placed on the side of the shaft to aid in treatment and distribute air more evenly.

Fluidized Bed Reactor (FBRs)

• Utilizes small particles (such as sand, carbon, fly ash) to support microbial growth within the treatment and decomposition process, ensuring the microorganisms are in suspension for optimal treatment.
• Upward movement of fluids keeps the substrate in suspension throughout the process, facilitating complete mixing and maximizing the contact between microorganisms and the substances to be treated.
• Perforated plates are used within the bed to evenly distribute liquids, air and nutrients during the reaction to optimize conditions for microbial activity and ensure thorough treatment.

Advantages of Bioremediation

• Some key benefits of bioremediation are simple design, low-maintenance equipment, less space required and comparatively low startup cost.

Explore the functions of bioreactor components like rake arms and baffles, the unique aspects of fluidized bed reactors, and bioremediation processes. Learn about the role of microbial metabolism and xenobiotics in bioremediation efforts.