Biodegradation of organic pollutants in a composting environment in Mauritius

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Biodegradation of organic pollutants in a
composting environment in Mauritius

• Vijayalaxmi Jumnoodoo
• PhD Candidate
• Department of Chemical and Environmental
  Engineering
• University of Mauritius

February 2010
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Overview

• Introduction
• Objectives
• Methodology
• Results and Discussion
• Conclusion
• Future works

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Introduction
Organic pollutants

• Extensive production and use of synthetic organic
  compounds for domestic, municipal, agricultural,
  industrial and military activities has led to a
  wide distribution of these compounds in the
  environment
• Contamination of soils, groundwater, sediments,
  surface water and air with these hazardous
  compounds is one of the major problems that the
  world is facing today
• Polyaromatic hydrocarbons (PAHs), polychlorinated
  biphenyls (PCBs), pesticides and other endocrine
  disruptors remain the main pollutants of concern
  today

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Introduction
Pesticides

• Environmental pollution due to pesticides is a
  global consideration
• Herbicides consumption in 2005 in Mauritius
  amounted to about 57 of the average annual
  consumption (2141 tons) of pesticides
• Atrazine, hexazinone, 2,4-D and ioxynil are
  commonly used by the planters in Mauritius

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Introduction
Composting

• The practice of organic farming which includes
  the application of composts allows farmers to be
  less dependent on synthetic fertilizers and
  pesticides and hence minimize pollution due to
  these compounds
• However, the detection of clopyralid and picloram
  in finished composts has aroused concern for the
  use of pesticide-contaminated composts made from
  yard trimmings and agricultural residues
• The application of the contaminated composts has
  been found to be detrimental to plant growth

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Introduction
Compost bioremediation - technology for treatment
of organic pollutants
Possible interactions between compost and organic
pollutant to minimize pollution
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Aims

• Study the biodegradation of 3 chlorinated
  herbicides of different degrees of persistency
  during composting
• Develop theoretical mechanistic pathways of
  degradation of the herbicides
• Application of compost bioremediation technology
  for treatment of pesticide-contaminated soil

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Methodology

• Herbicides used Atrazine (moderately
  persistent), 2,4-D (low degree of persistency)
  and Tordon 101 (persistent)
• Composting materials Grass clippings, shredded
  branches, brown leaves and finished compost
• Grass clippings were contaminated with respective
  herbicide emulsions
• Compost A uncontaminated grass
• Compost B atrazine-contaminated grass
• Compost C 2,4-D-contaminated grass clippings
• Compost D Tordon 101-contaminated grass
  clippings
• In-vessel composting system rotary drums of 200L
  capacity

• Grass clippings were contaminated with respective
  herbicide emulsions
• Compost A uncontaminated grass
• Compost B atrazine-contaminated grass
• Compost C 2,4-D-contaminated grass clippings
• Compost D Tordon 101-contaminated grass
  clippings
• In-vessel composting system set-up rotary drums
  of 200L capacity

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Methodology
Herbicide application
Compost set-up
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Methodology
Monitoring
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Results Discussion
Temperature profile
A maximum temperature range of 55oC for all the
composts
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Results Discussion
Moisture content
The moisture content of the composts 55 to 73
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Results Discussion
Volatile solids content
Presence of herbicides was a limitation to
organic matter degradation
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Results Discussion
Respiration rate
Same trend for CO2 evolution for Composts A and
C Acclimatization of microorganisms to
herbicide degradates observed
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Results Discussion

• Degradation occurred faster, within 10 days, in
  the case of the 2,4-D-contaminated compost due to
  its low persistency
• Compost B was associated with a lag phase and
  degradation could only be observed on Day 24
  onwards (cooling/maturation stage)
• Tordon 101/picloram was still persistent at the
  end of composting process

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Results Discussion
Mechanistic pathways of degradation of the
herbicides
Mechanism of degradation of 2,4-D during
composting
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Results Discussion
Mechanism of degradation of atrazine during
composting
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Results Discussion

• The microbial metabolism of 2,4-D during the
  composting process ? soil systems
• Initial side chain cleavage resulted in the
  formation of 2,4-Dichlorophenol. Further
  degradation of the intermediate occurred through
  oxidation.
• Atrazine degradation occurred mainly due to the
  interaction of the herbicide with compost humus
• Biologically mediated hydrolytic dechlorination
  of atrazine has been observed

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Conclusion

• The in-vessel composting system was effective in
  the degradation of pesticides of low to moderate
  persistency
• Degradation of 2,4-D occurred within 10-17 days
  of composting while that of atrazine was
  associated with lag phases of 24 days
  respectively. Tordon 101/picloram was still
  persistent at the end of composting
• The microbial metabolism of 2,4-D was similar to
  that observed in soil systems.
• In the case of atrazine, there was a
  predomination of adsorption mechanism over
  microbial metabolism

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Future works

• Investigate on the treatment of
  pesticide-contaminated soil through composting
  atrazine would be the target contaminant
• Determination of the optimum environmental
  conditions and nutrient amendments for the
  degradation of atrazine
• Study the degradation of atrazine during
  composting of both contaminated soil with
  finished composts and primary composting
  ingredients
• Devise a suitable compost bioremediation strategy
  for the treatment of atrazine-contaminated soil

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Thank you!