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  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 Organic pollutants

Introduction  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 Pesticides

Introduction  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 Composting

Introduction Compost bioremediation - technology for treatment of organic pollutants Degradation Compost- compound interactions Organic pollutant in compost Mineralization Toxicity Mobility Organic matter Surface sorption- desorption Entrapment within humic complexes Increased mobility or toxicity 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 pesticide- contaminated soil

Methodology  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  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 Compost set-up Green wastes Mixing wastes and adjusting water Filling wastes in drums Herbicide application

Methodology Rotating drum (200L) Compost A (uncontaminated grass clipping) Compost B (atrazine- contaminated grass clipping) Compost C (2,4-D contaminated grass clipping) Compost D (tordon 101-contaminated grass clipping) Grass clippings (25 kg) + brown leaves (4.5 kg) + dry branches (5.5 kg) + finished compost (5 kg) Bulk density, pH, respiration test of final compost Other physico-chemical characteristics:  Moisture  Temperature Biodegradation study:  Volatile Solids  CO 2 evolution Mechanism of degradation: NMR and FTIR spectroscopy Monitoring

Results & Discussion Temperature profile A maximum temperature range of 55 o C for all the composts

Results & Discussion The moisture content of the composts: 55% to 73% Moisture content

Results & Discussion Volatile solids content Presence of herbicides was a limitation to organic matter degradation

Results & Discussion Respiration rate Same trend for CO 2 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-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

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

Results & Discussion 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 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 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

Thank you!