1、Biodegradation of organic pollutants in a composting environment in Mauritius,Vijayalaxmi Jumnoodoo PhD CandidateDepartment of Chemical and Environmental EngineeringUniversity of Mauritius,February 2010,Overview,Introduction Objectives Methodology Results and Discussion Conclusion Future works,Intro
2、duction,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 hazardou
3、s 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
4、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
5、 includes the application of composts allows farmers to be less dependent on synthetic fertilizers and pesticides and hence minimize pollution due to these compoundsHowever, the detection of clopyralid and picloram in finished composts has aroused concern for the use of pesticide-contaminated compos
6、ts 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,Possible interactions between compost and organic pollut
7、ant to minimize pollution,Aims,Study the biodegradation of 3 chlorinated herbicides of different degrees of persistency during compostingDevelop theoretical mechanistic pathways of degradation of the herbicidesApplication of compost bioremediation technology for treatment of pesticide-contaminated s
8、oil,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 clippingsIn-vessel composting system set-up: rotary dru
9、ms 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 compostGrass clippings were contaminated with respective herbicide emulsions: Compos
10、t A: uncontaminated grass Compost B: atrazine-contaminated grass Compost C: 2,4-D-contaminated grass clippings Compost D: Tordon 101-contaminated grass clippingsIn-vessel composting system: rotary drums of 200L capacity,Methodology,Compost set-up,Herbicide application,Methodology,Monitoring,Results
11、& Discussion,Temperature profile,A maximum temperature range of 55oC 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
12、& 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-D-contaminated compost due to its low persistencyCompost B was
13、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
14、 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 intermedia
15、te occurred through oxidation. Atrazine degradation occurred mainly due to the interaction of the herbicide with compost humusBiologically mediated hydrolytic dechlorination of atrazine has been observed,Conclusion,The in-vessel composting system was effective in the degradation of pesticides of low
16、 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 so
17、il 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 contaminantDetermination of the optimum environmental conditions and nutrient amendments for the degradation of atrazineStudy 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!,
