Transcript Biodegradation of organic pollutants in a composting

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
Overview
 Introduction
 Objectives
 Methodology
 Results
and Discussion
 Conclusion
 Future works
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
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
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
Introduction
Compost bioremediation - technology for treatment of organic pollutants
Organic pollutant
in compost
Mineralization
Compostcompound
interactions
Degradation
Mobility
Organic matter
Toxicity
Increased mobility
or toxicity
Surface sorptiondesorption
Entrapment within
humic complexes
Decreased mobility
or toxicity
Possible interactions between compost and organic pollutant to minimize pollution
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 pesticidecontaminated soil
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
Methodology
Herbicide application
Compost set-up
Green wastes
Mixing wastes
and adjusting water
Filling wastes
in drums
Methodology
Monitoring
Bulk density, pH, respiration
test of final compost
Grass clippings (25 kg) + brown
leaves (4.5 kg) + dry branches
(5.5 kg) + finished compost (5
kg)
Compost A
(uncontaminated
grass clipping)
Rotating
drum
(200L)
Compost D (tordon
101-contaminated
grass clipping)
Compost B (atrazinecontaminated grass
clipping)
Compost C (2,4-D
contaminated grass
clipping)
Biodegradation study:
Volatile Solids
CO2 evolution
Mechanism of
degradation:
NMR and FTIR
spectroscopy
Other physico-chemical
characteristics:
Moisture
Temperature
Results & Discussion
Temperature profile
60.0
Compost A
Compost B
Compost C
Compost D
Temperature ( C)
50.0
0
40.0
30.0
20.0
10.0
0.0
0
10
20
30
40
50
60
70
80
90
100
Time (Day)
A maximum temperature range of 55oC for all the composts
Results & Discussion
Moisture content
80.00
70.00
60.00
Moisture (%)
50.00
40.00
30.00
20.00
10.00
Compost A
Compost B
Compost C
Compost D
0.00
0
10
20
30
40
50
60
70
80
90
100
Time (Day)
The moisture content of the composts: 55% to 73%
Results & Discussion
Volatile solids content
100.00
95.00
% VS
90.00
85.00
80.00
75.00
Compost A
Compost C
Compost B
Compost D
70.00
3
10
17
24
31
38
45
89
Time (Day)
Presence of herbicides was a limitation to organic matter degradation
Results & Discussion
Respiration rate
Same trend for CO2 evolution for Composts A and C;
Acclimatization of microorganisms to herbicide degradates observed
Results & Discussion



Degradation occurred faster, within 10
days, in the case of the 2,4-Dcontaminated 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
Results & Discussion
Mechanistic pathways of degradation of the herbicides
CH3
O
O
CH2
C
O
+
OH
NH2
Cl
Cl
CH3
Cl
Cl
2,4-DCP
2,4-D amine salt
oxidation
OH
OH
Cl
COOH
COOH
products
Cl
Cl
Cl
2,4-dichloromuconate
3,5-dichlorocatechol
Mechanism of degradation of 2,4-D during composting
Results & Discussion
H
O
H
OH
Cl
N
N
Chemical hydrolysis
HN
HN
N
N
Biological hydrolytic dechlorination
N
N
HN
HN
Hydroxyatrazine
Atrazine
Humic acid
O
OH or Cl
e
N
transfer
HA-Atrazine
or
HA-Hydroxyatrazine
complexes
HN
HA
N
N
HN
O
Quinone-like units of HA
desorption
OH
OH
N
N
HN
N
HO
N
N-dealkylation
N
N
HN
HN
N-ethylammelide
Hydroxyatrazine
N-dealkylation
OH
N
HO
Route 1
N
N
Route 2
OH
Cyanuric acid
Mechanism of degradation of atrazine during composting
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
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
Future works

Investigate on the treatment of pesticidecontaminated 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
strategy
for
the
contaminated soil
compost bioremediation
treatment
of
atrazine-
Thank you!