BIOREMEDIATION

• Bioremediation


  Using biological organisms to solve an environmental problem such as contaminated soil or groundwater
• How Bioremediation Works


  Uses naturally occurring microorganisms to break down hazardous substances into less toxic or nontoxic substances

  
• Types of Bioremediation


  • In situ bioremediation - material to be bioremediated doesn't leave the site
  • Ex situ bioremediation - material to be bioremediated is moved to another site to be treated
• In situ bioremediation of groundwater

  Almost invariably undergoes in situ bioremediation
• In situ bioremediation of soils

  • Don't require excavation of contaminated soils - less expensive, less chance of contaminating other sites
  • Possible to treat a large volume of soil at once

  
• In situ bioremediation of soils - Disadvantages

  • May be slow and difficult to manage
  • Require uncompacted soils

  
• Factors affecting successful bioremediation

  • Site Characterisation
  • Microbiological Characterisation
  • Environmental Factors
• Techniques of in situ bioremediation of soil

  • Bioventing
  • Injection of Hydrogen Peroxide
• Techniques of in situ bioremediation of groundwater

  • Activated Sludge Reactors
• Techniques of ex situ bioremediation of soil

  • Slurry Reactors
  • Landfarming
• Creosote


  A product mainly of coal tar but also of wood tar, characterized as a brown-black oily liquid having a significant fraction of mixed phenolics (10%) and heterocyclics (5%), along with the PAHs (85%)
• Uses of creosote


  • Wood treatment
  • Restricted-use pesticide
  • Animal and bird repellant
  • Insecticide
  • Fungicide
  • Animal dip

  
• Sources of creosote to the environment

  • Discarded products treated with creosote
  • Creosote spill sites

  
• Phenols


  Characterized by the presence of an aromatic ring and one or two hydroxyl groups

  
• Uses of phenolics


  • Phenolic disinfectants
  • Phenolic resins
• Chlorinated phenols


  There are 19 different chlorophenols depending upon the number and arrangement of chlorine atoms on the parent phenol ring

  
• Toxicity of chlorinated phenols


  • Generally, molecules with more chlorines are more toxic, due mainly to higher fat solubility as indicated by higher octanol/water coefficients (Kow)
• Sources of chlorophenols to the environment

  • Forest industry
  • Pulp bleacheries
  • Biocides
  • Industrial Waste streams
  • Chlorine treated water
  • Microbial breakdown herbicides
• Fate of chlorophenols in the environment


  • Physical and chemical degradative processes; photodegradation, oxidation, hydrolysis, evaporation/volatilization and sorption
  • Biological degradative processes such as uptake, breakdown and utilization
• Bioremediation


  The process where organic wastes are degraded biologically under controlled conditions to less toxic contaminants or to levels that do not constitute a threat to the environment
• Bioremediation reactions


  • Aerobic: Substitution of one or both of the oxygen atoms in the oxidation process
  • Anaerobic: Utilisation of alternative electron acceptors such as nitrate, iron, manganese, sulphate and carbon dioxide
• Bioremediation pathways of chlorinated phenols, phenolics and pentachlorophenol

  • Aerobic: Reaction initiated by action of oxygenase enzymes, insertion of hydroxyl substituents onto the aromatic ring, final end products of CO2 and water, cometabolism, insertion of methyl groups
  • Anaerobic: Alternative electron acceptors, reductive dechlorination, phenol as final end product or conversion to methane and CO2
• Microorganisms used for bioremediation

  • White rot fungi: Lignin peroxidases, manganese-dependent peroxidases and laccases, Phanerochaete chrysoporium, Phanerochaete sordida, Trametes versicolor
  • Bacteria and green algae for PAH degradation, non-ligninolytic fungi and prokaryotic algae

  
• Environmental factors affecting biodegradation

  • Oxygen
  • Nutrients
  • Moisture content
  • pH
  • Redox potential
  • Temperature
  • Bioavailability
• Advantages of bioremediation


  • Can be done on site
  • Keeps site disruption to a minimum
  • Eliminates risk of exposure to contaminants
  • Eliminates transportation costs and liabilities
  • Can be coupled with other treatment techniques
  • Lower costs than other systems
  • Minimal environmental impact
• Disadvantages of bioremediation


  • Not suitable for all situations, site specific
  • Slow process (several months)
  • Cannot degrade all hazardous wastes, especially metals
• Barriers to commercialization of bioremediation

  • Research barriers
  • Technical barriers
  • Economic barriers
  • Regulatory barriers
• Phytoremediation is using living plants for contaminant removal, degradation, or containment to clean up soil and/or groundwater

  
• Types of phytoremediation


  • Phytoextraction - Uptake by plants and accumulation in leaves or stem
  • Phytodegradation - Plants metabolize contaminants
  • Rhizodegradation - Plants promote microbial activity that breaks down contaminants
  • Phytovolatilization - Uptake and transpiration

  
• Other methods of contaminant removal include removal and landfilling of contaminated soil, incineration, and using surfactants to wash contaminants out of soil
• Pros of phytoremediation


  • Reduction in landfill volume
  • Low maintenance
  • Positive public opinion
  • Cost benefits
• Cons of phytoremediation


  • Slower to implement, seasonal process
  • Not as effective with very high concentrations
  • Limited by root depth
  • Toxicity of biodegradation products not always known
  • Possibility of contaminants entering food chain